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plants that hold soil in place between growing seasons

(A) contour cropping (B) strip cropping (C) cover crop (D) windbreak (E) no-till planting (F) plowing (G) terracing

C

There are many ways to protect soil. We can add organic material like manure or compost. This increases the soils fertility. Increased fertility improves the soils ability to hold water and nutrients. Inorganic fertilizers also increase fertility. These fertilizers are less expensive than natural fertilizers, but they do not provide the same long term benefits. Careful farming helps to keep up soil quality each season. One way is to plant different crops each year. Another is to alternate the crops planted in each row of the field. These techniques preserve and replenish soil nutrients. Planting nutrient rich cover crops helps the soil. Planting trees as windbreaks, plowing along contours of a field, or building terraces into steeper slopes all help to hold soil in place (Figure 9.14). No-till or low-till farming disturbs the ground as little as possible during planting. Stems are organs that hold plants upright. They allow plants to get the sunlight and air they need. Stems also bear leaves, flowers, cones, and smaller stems. These structures grow at points called nodes. The stem between nodes is called an internode. (See Figure 10.5.) Stems are needed for transport and storage. Their vascular tissue carries water and minerals from roots to leaves. It carries dissolved sugar from the leaves to the rest of the plant. Without this connection between roots and leaves, plants could not survive high above the ground in the air. In many plants, ground tissue in stems also stores food or water during cold or dry seasons. Its very important to control wind erosion of soil. Good soil is a precious resource that takes a long time to form. Covering soil with plants is one way to reduce wind erosion. Plants and their roots help hold the soil in place. They also help the soil retain water so it is less likely to blow away. Planting rows of trees around fields is another way to reduce wind erosion. The trees slow down the wind, so it doesnt cause as much erosion. Fences like the one in Figure 10.26 serve the same purpose. The fence in the figure is preventing erosion and migration of sand dunes on a beach.

planting fields without plowing them first

(A) contour cropping (B) strip cropping (C) cover crop (D) windbreak (E) no-till planting (F) plowing (G) terracing

E

The photos in Figure 19.2 show how farming practices can increase soil erosion. Plant roots penetrate the soil and keep it from eroding. Plowing turns over bare soil and cuts through plant roots. Bare soil is exposed to wind and water. In the past, farmers always plowed fields before planting. Some farmers now use no-till farming, which does not disturb the soil as much. The problem doesnt stop with plowing. Crops are usually planted in rows, with bare soil in between the rows. In places where crops grow only during part of the year, the land may be bare for a few months. Asking a question is one really good way to begin to learn about the natural world. You might have seen something that makes you curious. You might want to know what to change to produce a better result. Lets say a farmer is having an erosion problem. She wants to keep more soil on her farm. The farmer learns that a farming method called no-till farming allows farmers to plant seeds without plowing the land. She wonders if planting seeds without plowing will reduce the erosion problem and help keep more soil on her farmland. Her question is this: Will using the no-till method of farming help me to lose less soil on my farm? (Figure 1.2). The Dust Bowl taught people that soil could be lost by plowing and growing crops. This led to the development of new ways of farming that help protect the soil. Some of the methods are described in Figure 19.6.

row of trees planted between fields

(A) contour cropping (B) strip cropping (C) cover crop (D) windbreak (E) no-till planting (F) plowing (G) terracing

D

Its very important to control wind erosion of soil. Good soil is a precious resource that takes a long time to form. Covering soil with plants is one way to reduce wind erosion. Plants and their roots help hold the soil in place. They also help the soil retain water so it is less likely to blow away. Planting rows of trees around fields is another way to reduce wind erosion. The trees slow down the wind, so it doesnt cause as much erosion. Fences like the one in Figure 10.26 serve the same purpose. The fence in the figure is preventing erosion and migration of sand dunes on a beach. The photos in Figure 19.2 show how farming practices can increase soil erosion. Plant roots penetrate the soil and keep it from eroding. Plowing turns over bare soil and cuts through plant roots. Bare soil is exposed to wind and water. In the past, farmers always plowed fields before planting. Some farmers now use no-till farming, which does not disturb the soil as much. The problem doesnt stop with plowing. Crops are usually planted in rows, with bare soil in between the rows. In places where crops grow only during part of the year, the land may be bare for a few months. Secondary succession occurs in a formerly inhabited area that was disturbed.

building broad steps on steep slopes before planting

(A) contour cropping (B) strip cropping (C) cover crop (D) windbreak (E) no-till planting (F) plowing (G) terracing

G

If people dig into the base of a slope to create a road or a homesite, the slope may become unstable and move downhill. This is particularly dangerous when the underlying rock layers slope towards the area. When construction workers cut into slopes for homes or roads, they must stabilize the slope to help prevent a landslide (Figure 1.6). Tree roots or even grasses can bind soil together. It is also a good idea to provide drainage so that the slope does not become saturated with water. The steeper the slope, the less likely material will be able to stay in place to form soil. Material on a steep slope is likely to go downhill. Materials will accumulate and soil will form where land areas are flat or gently undulating. New construction can be made safer in many ways: Skyscrapers and other large structures built on soft ground must be anchored to bedrock, even if it lies hundreds of meters below the ground surface. The correct building materials must be used. Houses should bend and sway. Wood and steel are better than brick, stone, and adobe, which are brittle and will break. Larger buildings must sway, but not so much that they touch nearby buildings. Counterweights and diagonal steel beams are used to hold down sway. Large buildings can be placed on rollers so that they move with the ground. Buildings may be placed on layers of steel and rubber to absorb the shock of the waves. Connections, such as where the walls meet the foundation, must be made strong. In a multi-story building, the first story must be well supported (Figure 1.1). The first floor of this San Francisco build- ing is collapsing after the 1989 Loma Pri- eta earthquake.

planting crops in curved rows to follow the contour of hills

(A) contour cropping (B) strip cropping (C) cover crop (D) windbreak (E) no-till planting (F) plowing (G) terracing

A

The photos in Figure 19.2 show how farming practices can increase soil erosion. Plant roots penetrate the soil and keep it from eroding. Plowing turns over bare soil and cuts through plant roots. Bare soil is exposed to wind and water. In the past, farmers always plowed fields before planting. Some farmers now use no-till farming, which does not disturb the soil as much. The problem doesnt stop with plowing. Crops are usually planted in rows, with bare soil in between the rows. In places where crops grow only during part of the year, the land may be bare for a few months. Soil is a natural resource that is vitally important for sustaining natural habitats and for growing food. Although soil is a renewable resource, it is renewed slowly, taking hundreds or thousands of years for a good fertile soil to develop. Organic material can be added to soil to help increase its fertility. Most of the best land for farming is already being cultivated. With human populations continuing to grow, it is extremely important to protect our soil resources. Agricultural practices such as rotating crops, alternating the types of crops planted in each row, and planting nutrient-rich cover crops all help to keep soil more fertile as it is used season after season. Planting trees as windbreaks, plowing along contours of the field, or building terraces into steeper slopes will all help to hold soil in place (Figure 1.3). No-till or low-tillage farming helps to keep soil in place by disturbing the ground as little as possible when planting. Steep slopes can be terraced to make level planting areas and decrease surface water runoff and erosion. The rate of topsoil loss in the United States and other developed countries has decreased recently as better farming practices have been adopted. Unfortunately, in developing nations, soil is often not protected. Table 1.1 shows some steps that we can take to prevent erosion. Some are things that can be done by farmers or developers. Others are things that individual homeowners or community members can implement locally. Source of Erosion Strategies for Prevention Leave leaf litter on the ground in the winter. Grow cover crops, special crops grown in the winter to cover the soil. Plant tall trees around fields to buffer the effects of wind. Drive tractors as little as possible. Use drip irrigation that puts small amounts of water in the ground frequently. Avoid watering crops with sprinklers that make big water drops on the ground. Keep fields as flat as possible to avoid soil erod- ing down hill. Grazing Animals Move animals throughout the year, so they dont consume all the vegetation in one spot. Keep animals away from stream banks, where hills are especially prone to erosion. Logging and Mining Reduce the amount of land that is logged and mined. Reduce the number of roads that are built to access logging areas. Avoid logging and mining on steep lands. Cut only small areas at one time and quickly replant logged areas with new seedlings. Development Reduce the amount of land area that is developed into urban areas, parking lots, etc. Keep as much green space in cities as possible, such as parks or strips where plants can grow. Invest in and use new technologies for parking lots that make them permeable to water in order to reduce runoff of water. Recreational Activities Avoid using off-road vehicles on hilly lands. Stay on designated trails. Avoid building on steep hills. Grade surrounding land to distribute water rather than collecting it in one place. Where water collects, drain to creeks and rivers. Landscape with plants that minimize erosion. Click image to the left or use the URL below. URL: There are several other ways to help prevent soil loss. Some of them are shown in Figure 19.7. Prevent overgrazing. Frequently move animals from field to field. This gives the grass a chance to recover. Avoid logging steep hillsides. Cut only a few trees in any given place. Plant new trees to replace those that are cut down. Reclaim mine lands. Save the stripped topsoil and return it to the land. Once the soil is in place, plant trees and other plants to protect the bare soil. Use barriers to prevent runoff and soil erosion at construction sites. Plant grass to hold the soil in place. Develop paving materials that absorb water and reduce runoff. Restrict the use of off-road vehicles, especially in hilly areas.

cutting through plant roots and turning over soil before planting

(A) contour cropping (B) strip cropping (C) cover crop (D) windbreak (E) no-till planting (F) plowing (G) terracing

F

The photos in Figure 19.2 show how farming practices can increase soil erosion. Plant roots penetrate the soil and keep it from eroding. Plowing turns over bare soil and cuts through plant roots. Bare soil is exposed to wind and water. In the past, farmers always plowed fields before planting. Some farmers now use no-till farming, which does not disturb the soil as much. The problem doesnt stop with plowing. Crops are usually planted in rows, with bare soil in between the rows. In places where crops grow only during part of the year, the land may be bare for a few months. If people dig into the base of a slope to create a road or a homesite, the slope may become unstable and move downhill. This is particularly dangerous when the underlying rock layers slope towards the area. When construction workers cut into slopes for homes or roads, they must stabilize the slope to help prevent a landslide (Figure 1.6). Tree roots or even grasses can bind soil together. It is also a good idea to provide drainage so that the slope does not become saturated with water. Grazing animals (Figure 1.2) wander over large areas of pasture or natural grasslands eating grasses and shrubs. Grazers expose soil by removing the plant cover for an area. They also churn up the ground with their hooves. If too many animals graze the same land area, the animals hooves pull plants out by their roots. A land is overgrazed if too many animals are living there. Grazing animals can cause erosion if they are allowed to overgraze and remove too much or all of the vegetation in a pasture.

planting strips of groundcover plants between fields of crops

(A) contour cropping (B) strip cropping (C) cover crop (D) windbreak (E) no-till planting (F) plowing (G) terracing

B

There are several other ways to help prevent soil loss. Some of them are shown in Figure 19.7. Prevent overgrazing. Frequently move animals from field to field. This gives the grass a chance to recover. Avoid logging steep hillsides. Cut only a few trees in any given place. Plant new trees to replace those that are cut down. Reclaim mine lands. Save the stripped topsoil and return it to the land. Once the soil is in place, plant trees and other plants to protect the bare soil. Use barriers to prevent runoff and soil erosion at construction sites. Plant grass to hold the soil in place. Develop paving materials that absorb water and reduce runoff. Restrict the use of off-road vehicles, especially in hilly areas. The photos in Figure 19.2 show how farming practices can increase soil erosion. Plant roots penetrate the soil and keep it from eroding. Plowing turns over bare soil and cuts through plant roots. Bare soil is exposed to wind and water. In the past, farmers always plowed fields before planting. Some farmers now use no-till farming, which does not disturb the soil as much. The problem doesnt stop with plowing. Crops are usually planted in rows, with bare soil in between the rows. In places where crops grow only during part of the year, the land may be bare for a few months. Its very important to control wind erosion of soil. Good soil is a precious resource that takes a long time to form. Covering soil with plants is one way to reduce wind erosion. Plants and their roots help hold the soil in place. They also help the soil retain water so it is less likely to blow away. Planting rows of trees around fields is another way to reduce wind erosion. The trees slow down the wind, so it doesnt cause as much erosion. Fences like the one in Figure 10.26 serve the same purpose. The fence in the figure is preventing erosion and migration of sand dunes on a beach.

Factors that contributed to the Dust Bowl included

(A) plowing the land (B) lack of rain (C) high winds (D) all of the above

D

The Dust Bowl taught people that soil could be lost by plowing and growing crops. This led to the development of new ways of farming that help protect the soil. Some of the methods are described in Figure 19.6. Bad farming practices and a return to normal rainfall levels after an unusually wet period led to the Dust Bowl. In some regions more than 75% of the topsoil blew away. This is the most extreme example of soil erosion the United States has ever seen. Still, in many areas of the world, the rate of soil erosion is many times greater than the rate at which it is forming. Drought, insect plagues, or outbreaks of disease are natural cycles of events that can negatively impact ecosystems and the soil, but there are also many ways in which humans neglect or abuse this important resource. Soils can also be contaminated if too much salt accumulates in the soil or where pollutants sink into the ground. One harmful practice is removing the vegetation that helps to hold soil in place. Sometimes just walking or riding your bike over the same place will kill the grass that normally grows there. Land is also deliberately cleared or deforested for wood. The loose soils then may be carried away by wind or running water. A farmer and his sons walk through a dust storm in Cimarron County, Oklahoma in 1936. Click image to the left or use the URL below. URL: Droughts also depend on what is normal for a region. When a region gets significantly less precipitation than normal for an extended period of time, it is in drought. The Southern United States is experiencing an ongoing and prolonged drought. Drought has many consequences. When soil loses moisture it may blow away, as happened during the Dust Bowl in the United States in the 1930s. Forests may be lost, dust storms may become common, and wildlife are disturbed. Wildfires become much more common during times of drought.

Plants need soil to

(A) obtain carbon dioxide (B) anchor their roots (C) prevent runoff (D) all of the above

B

Life as we know it would not be possible without plants. Why are plants so important? Plants supply food to nearly all land organisms, including people. We mainly eat either plants or other living things that eat plants. Plants produce oxygen during photosynthesis. Oxygen is needed by all aerobic organisms. Plants absorb carbon dioxide during photosynthesis. This helps control the greenhouse effect and global warming. Plants recycle matter in ecosystems. For example, they are an important part of the water cycle. They take up liquid water from the soil through their roots. They release water vapor to the air from their leaves. This is called transpiration. Plants provide many products for human use. They include timber, medicines, dyes, oils, and rubber. Plants provide homes for many other living things. For example, a single tree may provide food and shelter to many species of animals, like the birds in Figure 10.2. Plants are somewhat limited by temperature in terms of where they can grow. They need temperatures above freezing while they are actively growing. They also need light, carbon dioxide, and water. These substances are required for photosynthesis. Like most other living things, plants need oxygen. Oxygen is required for cellular respiration. In addition, plants need minerals. The minerals are required to make proteins and other organic molecules. Plants live just about everywhere on Earth. To live in so many different habitats, they have evolved adaptations that allow them to survive and reproduce under a diversity of conditions. Some plants have evolved special adaptations that let them live in extreme environments.

The main cause of soil erosion is

(A) wind (B) abrasion (C) ice wedging (D) running water

D

The agents of soil erosion are the same as the agents of all types of erosion: water, wind, ice, or gravity. Running water is the leading cause of soil erosion, because water is abundant and has a lot of power. Wind is also a leading cause of soil erosion because wind can pick up soil and blow it far away. Activities that remove vegetation, disturb the ground, or allow the ground to dry are activities that increase erosion. What are some human activities that increase the likelihood that soil will be eroded? Agriculture is probably the most significant activity that accelerates soil erosion because of the amount of land that is farmed and how much farming practices disturb the ground (Figure 1.1). Farmers remove native vegetation and then plow the land to plant new seeds. Because most crops grow only in spring and summer, the land lies fallow during the winter. Of course, winter is also the stormy season in many locations, so wind and rain are available to wash soil away. Tractor tires make deep grooves, which are natural pathways for water. Fine soil is blown away by wind. The soil that is most likely to erode is the nutrient-rich topsoil, which degrades the farmland. (a) The bare areas of farmland are especially vulnerable to erosion. (b) Slash-and-burn agriculture leaves land open for soil erosion and is one of the leading causes of soil erosion in the world. Runoff carved channels in the soil in Figure 19.1. Running water causes most soil erosion, but wind can carry soil away too. What humans do to soil makes it more or less likely to be eroded by wind or water. Human actions that can increase soil erosion are described below.

Farming practices that increase soil erosion include

(A) tilling (B) strip cropping (C) contour cropping (D) two of the above

A

The photos in Figure 19.2 show how farming practices can increase soil erosion. Plant roots penetrate the soil and keep it from eroding. Plowing turns over bare soil and cuts through plant roots. Bare soil is exposed to wind and water. In the past, farmers always plowed fields before planting. Some farmers now use no-till farming, which does not disturb the soil as much. The problem doesnt stop with plowing. Crops are usually planted in rows, with bare soil in between the rows. In places where crops grow only during part of the year, the land may be bare for a few months. Agriculture is probably the most significant activity that accelerates soil erosion because of the amount of land that is farmed and how much farming practices disturb the ground (Figure 1.1). Farmers remove native vegetation and then plow the land to plant new seeds. Because most crops grow only in spring and summer, the land lies fallow during the winter. Of course, winter is also the stormy season in many locations, so wind and rain are available to wash soil away. Tractor tires make deep grooves, which are natural pathways for water. Fine soil is blown away by wind. The soil that is most likely to erode is the nutrient-rich topsoil, which degrades the farmland. (a) The bare areas of farmland are especially vulnerable to erosion. (b) Slash-and-burn agriculture leaves land open for soil erosion and is one of the leading causes of soil erosion in the world. Bad farming practices and a return to normal rainfall levels after an unusually wet period led to the Dust Bowl. In some regions more than 75% of the topsoil blew away. This is the most extreme example of soil erosion the United States has ever seen. Still, in many areas of the world, the rate of soil erosion is many times greater than the rate at which it is forming. Drought, insect plagues, or outbreaks of disease are natural cycles of events that can negatively impact ecosystems and the soil, but there are also many ways in which humans neglect or abuse this important resource. Soils can also be contaminated if too much salt accumulates in the soil or where pollutants sink into the ground. One harmful practice is removing the vegetation that helps to hold soil in place. Sometimes just walking or riding your bike over the same place will kill the grass that normally grows there. Land is also deliberately cleared or deforested for wood. The loose soils then may be carried away by wind or running water. A farmer and his sons walk through a dust storm in Cimarron County, Oklahoma in 1936. Click image to the left or use the URL below. URL:

Grazing animals that are likely to leave the soil bare include

(A) cattle (B) sheep (C) goats (D) two of the above

D

As you can see in Figure 19.3, some grazing animals, especially sheep and goats, eat grass right down to the roots. They may even pull the grass entirely out of the ground. Grazing animals can kill the grass or thin it out so much that it offers little protection to the soil. If animals are kept in the same place too long, the soil may become completely bare. The bare soil is easily eroded by wind and water. Grazing animals (Figure 1.2) wander over large areas of pasture or natural grasslands eating grasses and shrubs. Grazers expose soil by removing the plant cover for an area. They also churn up the ground with their hooves. If too many animals graze the same land area, the animals hooves pull plants out by their roots. A land is overgrazed if too many animals are living there. Grazing animals can cause erosion if they are allowed to overgraze and remove too much or all of the vegetation in a pasture. There are several other ways to help prevent soil loss. Some of them are shown in Figure 19.7. Prevent overgrazing. Frequently move animals from field to field. This gives the grass a chance to recover. Avoid logging steep hillsides. Cut only a few trees in any given place. Plant new trees to replace those that are cut down. Reclaim mine lands. Save the stripped topsoil and return it to the land. Once the soil is in place, plant trees and other plants to protect the bare soil. Use barriers to prevent runoff and soil erosion at construction sites. Plant grass to hold the soil in place. Develop paving materials that absorb water and reduce runoff. Restrict the use of off-road vehicles, especially in hilly areas.

Human actions that increase the risk of soil loss include

(A) logging (B) terracing (C) tree planting (D) no till planting

A

Other human actions that put soil at risk include logging, mining, and construction. You can see examples of each in Figure 19.4. When forests are cut down, the soil is suddenly exposed to wind and rain. Without trees, there is no leaf litter to cover the ground and protect the soil. When leaf litter decays, it adds humus and nutrients to the soil. Mining and construction strip soil off the ground and leave the land bare. Paved roads and parking lots prevent rainwater from soaking into the ground. This increases runoff and the potential for soil erosion. Bad farming practices and a return to normal rainfall levels after an unusually wet period led to the Dust Bowl. In some regions more than 75% of the topsoil blew away. This is the most extreme example of soil erosion the United States has ever seen. Still, in many areas of the world, the rate of soil erosion is many times greater than the rate at which it is forming. Drought, insect plagues, or outbreaks of disease are natural cycles of events that can negatively impact ecosystems and the soil, but there are also many ways in which humans neglect or abuse this important resource. Soils can also be contaminated if too much salt accumulates in the soil or where pollutants sink into the ground. One harmful practice is removing the vegetation that helps to hold soil in place. Sometimes just walking or riding your bike over the same place will kill the grass that normally grows there. Land is also deliberately cleared or deforested for wood. The loose soils then may be carried away by wind or running water. A farmer and his sons walk through a dust storm in Cimarron County, Oklahoma in 1936. Click image to the left or use the URL below. URL: Even things that people do for fun can expose soil to erosion. For example, overuse of hiking trails can leave bare patches of soil. Off-road vehicles cause even more damage. You can see examples of this in Figure 19.5.

Soil erosion can be reduced by

(A) paving the land (B) planting cover crops (C) planting crops in rows (D) riding off-road vehicles in hilly areas

B

There are several other ways to help prevent soil loss. Some of them are shown in Figure 19.7. Prevent overgrazing. Frequently move animals from field to field. This gives the grass a chance to recover. Avoid logging steep hillsides. Cut only a few trees in any given place. Plant new trees to replace those that are cut down. Reclaim mine lands. Save the stripped topsoil and return it to the land. Once the soil is in place, plant trees and other plants to protect the bare soil. Use barriers to prevent runoff and soil erosion at construction sites. Plant grass to hold the soil in place. Develop paving materials that absorb water and reduce runoff. Restrict the use of off-road vehicles, especially in hilly areas. Soil is a natural resource that is vitally important for sustaining natural habitats and for growing food. Although soil is a renewable resource, it is renewed slowly, taking hundreds or thousands of years for a good fertile soil to develop. Organic material can be added to soil to help increase its fertility. Most of the best land for farming is already being cultivated. With human populations continuing to grow, it is extremely important to protect our soil resources. Agricultural practices such as rotating crops, alternating the types of crops planted in each row, and planting nutrient-rich cover crops all help to keep soil more fertile as it is used season after season. Planting trees as windbreaks, plowing along contours of the field, or building terraces into steeper slopes will all help to hold soil in place (Figure 1.3). No-till or low-tillage farming helps to keep soil in place by disturbing the ground as little as possible when planting. Steep slopes can be terraced to make level planting areas and decrease surface water runoff and erosion. The rate of topsoil loss in the United States and other developed countries has decreased recently as better farming practices have been adopted. Unfortunately, in developing nations, soil is often not protected. Table 1.1 shows some steps that we can take to prevent erosion. Some are things that can be done by farmers or developers. Others are things that individual homeowners or community members can implement locally. Source of Erosion Strategies for Prevention Leave leaf litter on the ground in the winter. Grow cover crops, special crops grown in the winter to cover the soil. Plant tall trees around fields to buffer the effects of wind. Drive tractors as little as possible. Use drip irrigation that puts small amounts of water in the ground frequently. Avoid watering crops with sprinklers that make big water drops on the ground. Keep fields as flat as possible to avoid soil erod- ing down hill. Grazing Animals Move animals throughout the year, so they dont consume all the vegetation in one spot. Keep animals away from stream banks, where hills are especially prone to erosion. Logging and Mining Reduce the amount of land that is logged and mined. Reduce the number of roads that are built to access logging areas. Avoid logging and mining on steep lands. Cut only small areas at one time and quickly replant logged areas with new seedlings. Development Reduce the amount of land area that is developed into urban areas, parking lots, etc. Keep as much green space in cities as possible, such as parks or strips where plants can grow. Invest in and use new technologies for parking lots that make them permeable to water in order to reduce runoff of water. Recreational Activities Avoid using off-road vehicles on hilly lands. Stay on designated trails. Avoid building on steep hills. Grade surrounding land to distribute water rather than collecting it in one place. Where water collects, drain to creeks and rivers. Landscape with plants that minimize erosion. Click image to the left or use the URL below. URL: Its very important to control wind erosion of soil. Good soil is a precious resource that takes a long time to form. Covering soil with plants is one way to reduce wind erosion. Plants and their roots help hold the soil in place. They also help the soil retain water so it is less likely to blow away. Planting rows of trees around fields is another way to reduce wind erosion. The trees slow down the wind, so it doesnt cause as much erosion. Fences like the one in Figure 10.26 serve the same purpose. The fence in the figure is preventing erosion and migration of sand dunes on a beach.

most tsunami are caused by

(A) Earthquakes (B) Meteorites (C) Volcanic eruptions (D) Collisions of ships at sea

A

Tsunami are deadly ocean waves from the sharp jolt of an undersea earthquake. Less frequently, these waves can be generated by other shocks to the sea, like a meteorite impact. Fortunately, few undersea earthquakes, and even fewer meteorite impacts, generate tsunami. Earthquakes can cause tsunami. These deadly ocean waves may result from any shock to ocean water. A shock could be a meteorite impact, landslide, or a nuclear explosion. An underwater earthquake creates a tsunami this way: The movement of the crust displaces water. The displacement forms a set of waves. The waves travel at jet speed through the ocean. Since the waves have low amplitudes and long wavelengths, they are unnoticed in deep water. As the waves reach shore they compress. They are also pushed upward by the shore. For these reasons, tsunami can grow to enormous wave heights. Tsunami waves can cause tremendous destruction and loss of life. Fortunately, few undersea earthquakes generate tsunami. Not all waves are caused by winds. A shock to the ocean can also send waves through water. A tsunami is a wave or set of waves that is usually caused by an earthquake. As we have seen in recent years, the waves can be enormous and extremely destructive. Usually tsunami waves travel through the ocean unnoticed. But when they reach the shore they become enormous. Tsunami waves can flood entire regions. They destroy property and cause many deaths. Figure 14.11 shows the damage caused by a tsunami in the Indian Ocean in 2004.

the 2004 boxing day tsunami killed people all around this ocean basin

(A) Pacific Ocean (B) Atlantic Ocean (C) Indian Ocean (D) Arctic Ocean

C

The Boxing Day Tsunami struck on December 26, 2004. This tsunami was by far the deadliest of all time (Figure registered magnitude 9.1. The quake struck near Sumatra, Indonesia, where the Indian plate is subducting beneath the Burma plate. It released about 550 million times the energy of the atomic bomb dropped on Hiroshima. Several tsunami waves were created. The tsunami struck eight countries around the Indian Ocean (Figure 7.31). About 230,000 people died. More than 1.2 million people lost their homes. Many more lost their way of making a living. Fishermen lost their boats, and businesspeople lost their restaurants and shops. Many marine animals washed onshore, including dolphins, turtles, and sharks. Not everyone had the same warning the people on Tillys beach had. The Boxing Day Tsunami of December 26, 2004 was by far the deadliest of all time (Figure 1.1). The tsunami was caused by the 2004 Indian Ocean Earthquake. With a magnitude of 9.2, it was the second largest earthquake ever recorded. The extreme movement of the crust displaced trillions of tons of water along the entire length of the rupture. Several tsunami waves were created with about 30 minutes between the peaks of each one. The waves that struck nearby Sumatra 15 minutes after the quake reached more than 10 meters (33 feet) in height. The size of the waves decreased with distance from the earthquake and were about 4 meters (13 feet) high in Somalia. The tsunami did so much damage because it traveled throughout the Indian Ocean. About 230,000 people died in eight countries. There were fatalities even as far away as South Africa, nearly 8,000 kilometers (5,000 miles) from the earthquake epicenter. More than 1.2 million people lost their homes and many more lost their ways of making a living. The countries that were most affected by the 2004 Boxing Day tsunami. As a result of the 2004 tsunami, an Indian Ocean warning system was put into operation in June 2006. Prior to 2004, no one had thought a large tsunami was possible in the Indian Ocean. In comparison, a warning system has been in effect around the Pacific Ocean for more than 50 years. The system was used to warn of possible tsunami waves after the Tohoku earthquake, but most were too close to the quake to get to high ground in time. Further away, people were evacuated along many Pacific coastlines, but the waves were not that large.

the tsunami went around the indian ocean over the course of about one hour.

(A) True (B) False

B

As a result of the 2004 tsunami, an Indian Ocean warning system was put into operation in June 2006. Prior to 2004, no one had thought a large tsunami was possible in the Indian Ocean. In comparison, a warning system has been in effect around the Pacific Ocean for more than 50 years. The system was used to warn of possible tsunami waves after the Tohoku earthquake, but most were too close to the quake to get to high ground in time. Further away, people were evacuated along many Pacific coastlines, but the waves were not that large. Not everyone had the same warning the people on Tillys beach had. The Boxing Day Tsunami of December 26, 2004 was by far the deadliest of all time (Figure 1.1). The tsunami was caused by the 2004 Indian Ocean Earthquake. With a magnitude of 9.2, it was the second largest earthquake ever recorded. The extreme movement of the crust displaced trillions of tons of water along the entire length of the rupture. Several tsunami waves were created with about 30 minutes between the peaks of each one. The waves that struck nearby Sumatra 15 minutes after the quake reached more than 10 meters (33 feet) in height. The size of the waves decreased with distance from the earthquake and were about 4 meters (13 feet) high in Somalia. The tsunami did so much damage because it traveled throughout the Indian Ocean. About 230,000 people died in eight countries. There were fatalities even as far away as South Africa, nearly 8,000 kilometers (5,000 miles) from the earthquake epicenter. More than 1.2 million people lost their homes and many more lost their ways of making a living. The countries that were most affected by the 2004 Boxing Day tsunami. Since tsunami are long-wavelength waves, a long time can pass between crests or troughs. Any part of the wave can make landfall first. In 1755 in Lisbon, Portugal, a tsunami trough hit land first. A large offshore earthquake did a great deal of damage on land. People rushed out to the open space of the shore. Once there, they discovered that the water was flowing seaward fast and some of them went out to observe. What do you think happened next? The people on the open beach drowned when the crest of the wave came up the beach. Large tsunami in the Indian Ocean and more recently Japan have killed hundreds of thousands of people in recent years. The west coast is vulnerable to tsunami since it sits on the Pacific Ring of Fire. Scientists are trying to learn everything they can about predicting tsunamis before a massive one strikes a little closer to home. Although most places around the Indian Ocean did not have warning systems in 2005, there is a tsunami warning system in that region now. Tsunami warning systems have been placed in most locations where tsunami are possible. Click image to the left or use the URL below. URL:

the boxing day tsunami was so huge because the earthquake displaced trillions of tons of water.

(A) True (B) False

A

Not everyone had the same warning the people on Tillys beach had. The Boxing Day Tsunami of December 26, 2004 was by far the deadliest of all time (Figure 1.1). The tsunami was caused by the 2004 Indian Ocean Earthquake. With a magnitude of 9.2, it was the second largest earthquake ever recorded. The extreme movement of the crust displaced trillions of tons of water along the entire length of the rupture. Several tsunami waves were created with about 30 minutes between the peaks of each one. The waves that struck nearby Sumatra 15 minutes after the quake reached more than 10 meters (33 feet) in height. The size of the waves decreased with distance from the earthquake and were about 4 meters (13 feet) high in Somalia. The tsunami did so much damage because it traveled throughout the Indian Ocean. About 230,000 people died in eight countries. There were fatalities even as far away as South Africa, nearly 8,000 kilometers (5,000 miles) from the earthquake epicenter. More than 1.2 million people lost their homes and many more lost their ways of making a living. The countries that were most affected by the 2004 Boxing Day tsunami. The Boxing Day Tsunami struck on December 26, 2004. This tsunami was by far the deadliest of all time (Figure registered magnitude 9.1. The quake struck near Sumatra, Indonesia, where the Indian plate is subducting beneath the Burma plate. It released about 550 million times the energy of the atomic bomb dropped on Hiroshima. Several tsunami waves were created. The tsunami struck eight countries around the Indian Ocean (Figure 7.31). About 230,000 people died. More than 1.2 million people lost their homes. Many more lost their way of making a living. Fishermen lost their boats, and businesspeople lost their restaurants and shops. Many marine animals washed onshore, including dolphins, turtles, and sharks. The Japanese received a one-two punch in March 2011. The 2011 Tohoku earthquake offshore was a magnitude 9.0 and damage from the quake was extensive. People didnt have time to recover before massive tsunami waves hit the island nation. As seen in Figure 1.2, waves in some regions topped 9 meters (27 feet). The tsunami did much more damage than the massive earthquake (Figure 1.3). Worst was the damage done to nuclear power plants along the northeastern coast. Eleven reactors were automatically shut down. Power and backup power were lost at the Fukushima plant, leading to equipment failures, meltdowns, and the release of radioactive materials. Control and cleanup of the disabled plants will go on for many years.

the magnitude of the earthquake that caused the boxing day tsunami of 2004 was

(A) 72 (B) 82 (C) 92 (D) 102

C

Not everyone had the same warning the people on Tillys beach had. The Boxing Day Tsunami of December 26, 2004 was by far the deadliest of all time (Figure 1.1). The tsunami was caused by the 2004 Indian Ocean Earthquake. With a magnitude of 9.2, it was the second largest earthquake ever recorded. The extreme movement of the crust displaced trillions of tons of water along the entire length of the rupture. Several tsunami waves were created with about 30 minutes between the peaks of each one. The waves that struck nearby Sumatra 15 minutes after the quake reached more than 10 meters (33 feet) in height. The size of the waves decreased with distance from the earthquake and were about 4 meters (13 feet) high in Somalia. The tsunami did so much damage because it traveled throughout the Indian Ocean. About 230,000 people died in eight countries. There were fatalities even as far away as South Africa, nearly 8,000 kilometers (5,000 miles) from the earthquake epicenter. More than 1.2 million people lost their homes and many more lost their ways of making a living. The countries that were most affected by the 2004 Boxing Day tsunami. The Boxing Day Tsunami struck on December 26, 2004. This tsunami was by far the deadliest of all time (Figure registered magnitude 9.1. The quake struck near Sumatra, Indonesia, where the Indian plate is subducting beneath the Burma plate. It released about 550 million times the energy of the atomic bomb dropped on Hiroshima. Several tsunami waves were created. The tsunami struck eight countries around the Indian Ocean (Figure 7.31). About 230,000 people died. More than 1.2 million people lost their homes. Many more lost their way of making a living. Fishermen lost their boats, and businesspeople lost their restaurants and shops. Many marine animals washed onshore, including dolphins, turtles, and sharks. The Japanese received a one-two punch in March 2011. The 2011 Tohoku earthquake offshore was a magnitude 9.0 and damage from the quake was extensive. People didnt have time to recover before massive tsunami waves hit the island nation. As seen in Figure 1.2, waves in some regions topped 9 meters (27 feet). The tsunami did much more damage than the massive earthquake (Figure 1.3). Worst was the damage done to nuclear power plants along the northeastern coast. Eleven reactors were automatically shut down. Power and backup power were lost at the Fukushima plant, leading to equipment failures, meltdowns, and the release of radioactive materials. Control and cleanup of the disabled plants will go on for many years.

tilly smith saved about 100 people on a beach in thailand because she

(A) Saw the tsunami coming and screamed (B) Noticed the bubbling sea and thought it was like a tsunami video she’d seen in a class (C) Fainted and they all rushed uphill to help her (D) getting out of the path of the wave (E) d All of these

B

Like other waves, a tsunami wave has a crest and a trough. When the wave hits the beach, the crest or the trough may come ashore first. When the trough comes in first, water is sucked out to sea. The seafloor just offshore from the beach is exposed. Curious people often walk out onto the beach to see the unusual sight. They drown when the wave crest hits. One amazing story from the Indian Ocean tsunami is that of Tilly Smith. Tilly was a 10-year-old British girl who was visiting Maikhao Beach in Thailand with her parents. Tilly had learned about tsunami in school two weeks before the earthquake. She knew that the receding water and the frothy bubbles at the sea surface meant a tsunami was coming. Tilly told her parents, who told other tourists and the staff at their hotel. The beach was evacuated and no one on Maikhao Beach died. Tilly is credited with saving nearly 100 people! Not everyone had the same warning the people on Tillys beach had. The Boxing Day Tsunami of December 26, 2004 was by far the deadliest of all time (Figure 1.1). The tsunami was caused by the 2004 Indian Ocean Earthquake. With a magnitude of 9.2, it was the second largest earthquake ever recorded. The extreme movement of the crust displaced trillions of tons of water along the entire length of the rupture. Several tsunami waves were created with about 30 minutes between the peaks of each one. The waves that struck nearby Sumatra 15 minutes after the quake reached more than 10 meters (33 feet) in height. The size of the waves decreased with distance from the earthquake and were about 4 meters (13 feet) high in Somalia. The tsunami did so much damage because it traveled throughout the Indian Ocean. About 230,000 people died in eight countries. There were fatalities even as far away as South Africa, nearly 8,000 kilometers (5,000 miles) from the earthquake epicenter. More than 1.2 million people lost their homes and many more lost their ways of making a living. The countries that were most affected by the 2004 Boxing Day tsunami. Most of the Indian Ocean tragedy could have been avoided if a warning system had been in place(Figure 7.32). As of June 2006, the Indian Ocean now has a warning system. Since tsunami are much more common in the Pacific, communities around the Pacific have had a tsunami warning system since 1948. Warning systems arent always helpful. People in communities very close to the earthquake do not have enough time to move inland or uphill. Farther away from the quake, evacuation of low-lying areas saves lives.

in japan in 2011, a tsunami in that followed an offshore earthquake

(A) Severely damaged nuclear power plants (B) Killed thousands of people (C) Kept rescuers from being able to put out fires and get to people who needed help (D) All of these

D

The Japanese received a one-two punch in March 2011. The 2011 Tohoku earthquake offshore was a magnitude 9.0 and damage from the quake was extensive. People didnt have time to recover before massive tsunami waves hit the island nation. As seen in Figure 1.2, waves in some regions topped 9 meters (27 feet). The tsunami did much more damage than the massive earthquake (Figure 1.3). Worst was the damage done to nuclear power plants along the northeastern coast. Eleven reactors were automatically shut down. Power and backup power were lost at the Fukushima plant, leading to equipment failures, meltdowns, and the release of radioactive materials. Control and cleanup of the disabled plants will go on for many years. Earthquakes in Japan are caused by ocean-ocean convergence. The Philippine Plate and the Pacific Plate subduct beneath oceanic crust on the North American or Eurasian plates. This complex plate tectonics situation creates a chain of volcanoes, the Japanese islands, and as many as 1,500 earthquakes annually. In March 2011 an enormous 9.0 earthquake struck off of Sendai in northeastern Japan. This quake, called the 2011 Tohoku earthquake, was the most powerful ever to strike Japan and one of the top five known in the world. Damage from the earthquake was nearly overshadowed by the tsunami it generated, which wiped out coastal cities and towns This cross section of earthquake epicen- ters with depth outlines the subducting plate with shallow, intermediate, and deep earthquakes. (Figure 1.2). Several months after the earthquake, about 22,000 people were dead or missing, and 190,000 buildings had been damaged or destroyed. Aftershocks, some as large as major earthquakes, have continued to rock the region. Destruction in Ofunato, Japan, from the 2011 Tohoku Earthquake. As a result of the 2004 tsunami, an Indian Ocean warning system was put into operation in June 2006. Prior to 2004, no one had thought a large tsunami was possible in the Indian Ocean. In comparison, a warning system has been in effect around the Pacific Ocean for more than 50 years. The system was used to warn of possible tsunami waves after the Tohoku earthquake, but most were too close to the quake to get to high ground in time. Further away, people were evacuated along many Pacific coastlines, but the waves were not that large.

nearly all of japan experienced the tsunami to some degree.

(A) True (B) False

A

The Japanese received a one-two punch in March 2011. The 2011 Tohoku earthquake offshore was a magnitude 9.0 and damage from the quake was extensive. People didnt have time to recover before massive tsunami waves hit the island nation. As seen in Figure 1.2, waves in some regions topped 9 meters (27 feet). The tsunami did much more damage than the massive earthquake (Figure 1.3). Worst was the damage done to nuclear power plants along the northeastern coast. Eleven reactors were automatically shut down. Power and backup power were lost at the Fukushima plant, leading to equipment failures, meltdowns, and the release of radioactive materials. Control and cleanup of the disabled plants will go on for many years. Not everyone had the same warning the people on Tillys beach had. The Boxing Day Tsunami of December 26, 2004 was by far the deadliest of all time (Figure 1.1). The tsunami was caused by the 2004 Indian Ocean Earthquake. With a magnitude of 9.2, it was the second largest earthquake ever recorded. The extreme movement of the crust displaced trillions of tons of water along the entire length of the rupture. Several tsunami waves were created with about 30 minutes between the peaks of each one. The waves that struck nearby Sumatra 15 minutes after the quake reached more than 10 meters (33 feet) in height. The size of the waves decreased with distance from the earthquake and were about 4 meters (13 feet) high in Somalia. The tsunami did so much damage because it traveled throughout the Indian Ocean. About 230,000 people died in eight countries. There were fatalities even as far away as South Africa, nearly 8,000 kilometers (5,000 miles) from the earthquake epicenter. More than 1.2 million people lost their homes and many more lost their ways of making a living. The countries that were most affected by the 2004 Boxing Day tsunami. The Boxing Day Tsunami struck on December 26, 2004. This tsunami was by far the deadliest of all time (Figure registered magnitude 9.1. The quake struck near Sumatra, Indonesia, where the Indian plate is subducting beneath the Burma plate. It released about 550 million times the energy of the atomic bomb dropped on Hiroshima. Several tsunami waves were created. The tsunami struck eight countries around the Indian Ocean (Figure 7.31). About 230,000 people died. More than 1.2 million people lost their homes. Many more lost their way of making a living. Fishermen lost their boats, and businesspeople lost their restaurants and shops. Many marine animals washed onshore, including dolphins, turtles, and sharks.

why wasnt there a tsunami warning system in the indian ocean in 2004?

(A) The region is too poor to afford one (B) No one thought such a large tsunami would happen there (C) The technology didn’t exist yet (D) The people didn’t want one

B

As a result of the 2004 tsunami, an Indian Ocean warning system was put into operation in June 2006. Prior to 2004, no one had thought a large tsunami was possible in the Indian Ocean. In comparison, a warning system has been in effect around the Pacific Ocean for more than 50 years. The system was used to warn of possible tsunami waves after the Tohoku earthquake, but most were too close to the quake to get to high ground in time. Further away, people were evacuated along many Pacific coastlines, but the waves were not that large. Most of the Indian Ocean tragedy could have been avoided if a warning system had been in place(Figure 7.32). As of June 2006, the Indian Ocean now has a warning system. Since tsunami are much more common in the Pacific, communities around the Pacific have had a tsunami warning system since 1948. Warning systems arent always helpful. People in communities very close to the earthquake do not have enough time to move inland or uphill. Farther away from the quake, evacuation of low-lying areas saves lives. Since tsunami are long-wavelength waves, a long time can pass between crests or troughs. Any part of the wave can make landfall first. In 1755 in Lisbon, Portugal, a tsunami trough hit land first. A large offshore earthquake did a great deal of damage on land. People rushed out to the open space of the shore. Once there, they discovered that the water was flowing seaward fast and some of them went out to observe. What do you think happened next? The people on the open beach drowned when the crest of the wave came up the beach. Large tsunami in the Indian Ocean and more recently Japan have killed hundreds of thousands of people in recent years. The west coast is vulnerable to tsunami since it sits on the Pacific Ring of Fire. Scientists are trying to learn everything they can about predicting tsunamis before a massive one strikes a little closer to home. Although most places around the Indian Ocean did not have warning systems in 2005, there is a tsunami warning system in that region now. Tsunami warning systems have been placed in most locations where tsunami are possible. Click image to the left or use the URL below. URL:

why didnt the tsunami warning system in the pacific ocean save more lives in the japan tsunami of 2011?

(A) The people heard the warning but thought it was a false alarm (B) There was nowhere to go once the people heard the warning (C) The quake was so close that there wasn’t time to get to high ground once the warning (D) The quake was too small to activate the warning system and so the tsunami was unexpected

C

Most of the Indian Ocean tragedy could have been avoided if a warning system had been in place(Figure 7.32). As of June 2006, the Indian Ocean now has a warning system. Since tsunami are much more common in the Pacific, communities around the Pacific have had a tsunami warning system since 1948. Warning systems arent always helpful. People in communities very close to the earthquake do not have enough time to move inland or uphill. Farther away from the quake, evacuation of low-lying areas saves lives. As a result of the 2004 tsunami, an Indian Ocean warning system was put into operation in June 2006. Prior to 2004, no one had thought a large tsunami was possible in the Indian Ocean. In comparison, a warning system has been in effect around the Pacific Ocean for more than 50 years. The system was used to warn of possible tsunami waves after the Tohoku earthquake, but most were too close to the quake to get to high ground in time. Further away, people were evacuated along many Pacific coastlines, but the waves were not that large. Since tsunami are long-wavelength waves, a long time can pass between crests or troughs. Any part of the wave can make landfall first. In 1755 in Lisbon, Portugal, a tsunami trough hit land first. A large offshore earthquake did a great deal of damage on land. People rushed out to the open space of the shore. Once there, they discovered that the water was flowing seaward fast and some of them went out to observe. What do you think happened next? The people on the open beach drowned when the crest of the wave came up the beach. Large tsunami in the Indian Ocean and more recently Japan have killed hundreds of thousands of people in recent years. The west coast is vulnerable to tsunami since it sits on the Pacific Ring of Fire. Scientists are trying to learn everything they can about predicting tsunamis before a massive one strikes a little closer to home. Although most places around the Indian Ocean did not have warning systems in 2005, there is a tsunami warning system in that region now. Tsunami warning systems have been placed in most locations where tsunami are possible. Click image to the left or use the URL below. URL:

What explains the phenomenon that Hubble discovered?

(A) the universe is becoming warmer (B) the universe is becoming cooler (C) the universe is expanding (D) the universe is collapsing

C

Hubble measured the distances to galaxies. He also studied the motions of galaxies. In doing these things, Hubble noticed a relationship. This is now called Hubbles Law: The farther away a galaxy is, the faster it is moving away from us. There was only one conclusion he could draw from this. The universe is expanding! Figure 26.15 shows a simple diagram of the expanding universe. Imagine a balloon covered with tiny dots. When you blow up the balloon, the rubber stretches. The dots slowly move away from each other as the space between them increases. In an expanding universe, the space between galaxies is expanding. We see this as the other galaxies moving away from us. We also see that galaxies farther away from us move away faster than nearby galaxies. After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing, and would even yield clues as to how the universe formed. Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of redshift. From this data, he noticed a relationship, which is now called Hubbles Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding. Figure 1.2 shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies. When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them. If you were standing on one of the dots, you would see the other dots moving away from you. Also, the dots farther away from you on the balloon would move away faster than dots nearby. In this diagram of the expansion of the universe over time, the distance between galaxies gets bigger over time, although the size of each galaxy stays the same. An inflating balloon is only a rough analogy to the expanding universe for several reasons. One important reason is that the surface of a balloon has only two dimensions, while space has three dimensions. But space itself is stretching out between galaxies, just as the rubber stretches when a balloon is inflated. This stretching of space, which increases the distance between galaxies, is what causes the expansion of the universe. One other difference between the universe and a balloon involves the actual size of the galaxies. On a balloon, the dots will become larger in size as you inflate it. In the universe, the galaxies stay the same size; only the space between the galaxies increases.

Scientists believe dark energy can explain what phenomenon?

(A) the creation of the universe (B) the increasing rate of expansion of the universe (C) the collapse of the universe (D) the shape of the universe

B

The things we observe in space are objects that emit some type of electromagnetic radiation. However, scientists think that matter that emits light makes up only a small part of the matter in the universe. The rest of the matter, about 80%, is dark matter. Dark matter emits no electromagnetic radiation, so we cant observe it directly. However, astronomers know that dark matter exists because its gravity affects the motion of objects around it. When astronomers measure how spiral galaxies rotate, they find that the outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than they can see. Gravitational lensing occurs when light is bent from a very distant bright source around a super-massive object (Figure 1.1). To explain strong gravitational lensing, more matter than is observed must be present. With so little to go on, astronomers dont really know much about the nature of dark matter. One possibility is that it could just be ordinary matter that does not emit radiation in objects such as black holes, neutron stars, and brown dwarfs objects larger than Jupiter but smaller than the smallest stars. But astronomers cannot find enough of these types of objects, which they have named MACHOs (massive astrophyiscal compact halo object), to account for all the dark matter, so they are thought to be only a small part of the total. Another possibility is that the dark matter is very different from the ordinary matter we see. Some appear to be particles that have gravity, but dont otherwise appear to interact with other particles. Scientists call these theoretical particles WIMPs, which stands for Weakly Interactive Massive Particles. Most scientists who study dark matter think that the dark matter in the universe is a combination of MACHOs and some type of exotic matter, such as WIMPs. Researching dark matter is an active area of scientific research, and astronomers knowledge about dark matter is changing rapidly. We know that the universe is expanding. Astronomers have wondered if it is expanding fast enough to escape the pull of gravity. Would the universe just expand forever? If it could not escape the pull of gravity, would it someday start to contract? This means it would eventually get squeezed together in a big crunch. This is the opposite of the Big Bang. Scientists may now have an answer. Recently, astronomers have discovered that the universe is expanding even faster than before. What is causing the expansion to accelerate? One hypothesis is that there is energy out in the universe that we cant see. Astronomers call this dark energy. We know even less about dark energy than we know about dark matter. Some scientists think that dark energy makes up more than half of the universe. Meet one of the three winners of the 2011 Nobel Prize in Physics, Lawrence Berkeley Lab astrophysicist Saul Perlmutter. He explains how dark energy, which makes up 70 percent of the universe, is causing our universe to expand. Click image to the left or use the URL below. URL:

The farther away a galaxy is

(A) the faster it is moving away from us (B) the slower it is moving away from us (C) the faster it is coming toward us (D) the slower it is coming toward us

A

Hubble measured the distances to galaxies. He also studied the motions of galaxies. In doing these things, Hubble noticed a relationship. This is now called Hubbles Law: The farther away a galaxy is, the faster it is moving away from us. There was only one conclusion he could draw from this. The universe is expanding! Figure 26.15 shows a simple diagram of the expanding universe. Imagine a balloon covered with tiny dots. When you blow up the balloon, the rubber stretches. The dots slowly move away from each other as the space between them increases. In an expanding universe, the space between galaxies is expanding. We see this as the other galaxies moving away from us. We also see that galaxies farther away from us move away faster than nearby galaxies. When we look at stars and galaxies, we are seeing over great distances. More importantly, we are also seeing back in time. When we see a distant galaxy, we are actually seeing how the galaxy used to look. For example, the Andromeda Galaxy, shown in Figure 23.1, is about 2.5 million light-years from Earth. When you see an image of the galaxy what are you seeing? You are seeing the galaxy as it was 2.5 million years ago! Since scientists can look back in time they can better understand the Universes history. Check out http://science.n Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of redshift. From this data, he noticed a relationship, which is now called Hubbles Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding. Figure 1.2 shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies. When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them. If you were standing on one of the dots, you would see the other dots moving away from you. Also, the dots farther away from you on the balloon would move away faster than dots nearby. In this diagram of the expansion of the universe over time, the distance between galaxies gets bigger over time, although the size of each galaxy stays the same. An inflating balloon is only a rough analogy to the expanding universe for several reasons. One important reason is that the surface of a balloon has only two dimensions, while space has three dimensions. But space itself is stretching out between galaxies, just as the rubber stretches when a balloon is inflated. This stretching of space, which increases the distance between galaxies, is what causes the expansion of the universe. One other difference between the universe and a balloon involves the actual size of the galaxies. On a balloon, the dots will become larger in size as you inflate it. In the universe, the galaxies stay the same size; only the space between the galaxies increases.

What does it mean if light is red shifted?

(A) The object is moving away from the observer (B) The object is moving towards the observer (C) The object is slowing down (D) The object is moving perpendicular to the observer

A

If you look at a star through a prism, you will see a spectrum, or a range of colors through the rainbow. The spectrum will have specific dark bands where elements in the star absorb light of certain energies. By examining the arrangement of these dark absorption lines, astronomers can determine the composition of elements that make up a distant star. In fact, the element helium was first discovered in our Sun not on Earth by analyzing the absorption lines in the spectrum of the Sun. While studying the spectrum of light from distant galaxies, astronomers noticed something strange. The dark lines in the spectrum were in the patterns they expected, but they were shifted toward the red end of the spectrum, as shown in Figure 1.1. This shift of absorption bands toward the red end of the spectrum is known as redshift. Redshift is a shift in absorption bands toward the red end of the spectrum. What could make the absorption bands of a star shift toward the red? Redshift occurs when the light source is moving away from the observer or when the space between the observer and the source is stretched. What does it mean that stars and galaxies are redshifted? When astronomers see redshift in the light from a galaxy, they know that the galaxy is moving away from Earth. If galaxies were moving randomly, would some be redshifted but others be blueshifted? Of course. Since almost every galaxy in the universe has a redshift, almost every galaxy is moving away from Earth. Click image to the left or use the URL below. URL: Transmission of light occurs when light passes through matter. As light is transmitted, it may pass straight through matter or it may be refracted or scattered as it passes through. When light is refracted, it changes direction as it passes into a new medium and changes speed. The straw in the Figure 1.2 looks bent where light travels from water to air. Light travels more quickly in air than in water and changes direction. Scattering occurs when light bumps into tiny particles of matter and spreads out in all directions. In the Figure air, giving the headlights a halo appearance. Q: What might be another example of light scattering? A: When light passes through smoky air, it is scattered by tiny particles of soot. When light passes from one medium (or type of matter) to another, it changes speed. You can actually see this happen. If light strikes a new substance at an angle, the light appears to bend. This is what explains the straw looking broken in the picture above. So, does light always bend as it travels into a new medium? If light travels straight into a new substance it is not bent. You may know this angle as perpendicular. The light still slows down, just does not appear to bend. Any angle other than perpendicular the light will bend as it slows down. The bending of light is called refraction. Figure 1.1 shows how refraction occurs. Notice that the angle of light changes again as it passes from the glass back to the air. In this case, the speed increases, and the ray of light resumes its initial direction. For a more detailed explanation of refraction, watch this video: Click image to the left or use the URL below. URL:

The outside edges and interior of a galaxy rotate at the same speed. This is evidence for the existence of

(A) gravitational lensing (B) the Big Bang (C) dark energy (D) dark matter

D

Although it is difficult to know what the shape of the Milky Way Galaxy is because we are inside of it, astronomers have identified it as a typical spiral galaxy containing about 200 billion to 400 billion stars (Figure 1.1). An artists rendition of what astronomers think the Milky Way Galaxy would look like seen from above. The Sun is located approximately where the arrow points. Like other spiral galaxies, our galaxy has a disk, a central bulge, and spiral arms. The disk is about 100,000 light- years across and 3,000 light-years thick. Most of the Galaxys gas, dust, young stars, and open clusters are in the disk. What evidence do astronomers find that lets them know that the Milky Way is a spiral galaxy? 1. The shape of the galaxy as we see it (Figure 1.2). 2. The velocities of stars and gas in the galaxy show a rotational motion. 3. The gases, color, and dust are typical of spiral galaxies. The central bulge is about 12,000 to 16,000 light-years wide and 6,000 to 10,000 light-years thick. The central bulge contains mostly older stars and globular clusters. Some recent evidence suggests the bulge might not be spherical, but is instead shaped like a bar. The bar might be as long as 27,000 light-years long. The disk and bulge are surrounded by a faint, spherical halo, which also contains old stars and globular clusters. Astronomers have discovered that there is a gigantic black hole at the center of the galaxy. The Milky Way Galaxy is a big place. If our solar system were the size of your fist, the Galaxys disk would still be An infrared image of the Milky Way shows the long thin line of stars and the central bulge typical of spiral galaxies. wider than the entire United States! The Milky Way Galaxy is a spiral galaxy that contains about 400 billion stars. Like other spiral galaxies, it has a disk, a central bulge, and spiral arms. The disk is about 100,000 light-years across. It is about 3,000 light years thick. Most of the galaxys gas, dust, young stars, and open clusters are in the disk. Some astronomers think that there is a gigantic black hole at the center of the galaxy. Figure 26.13 shows what the Milky Way probably looks like from the outside. Our solar system is within one of the spiral arms. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are a little more than halfway out from the center of the Galaxy to the edge, as shown in Figure 26.13. Our solar system orbits the center of the galaxy as the galaxy spins. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. Spiral galaxies spin, so they appear as a rotating disk of stars and dust, with a bulge in the middle, like the Sombrero Galaxy shown in Figure 1.2. Several arms spiral outward in the Pinwheel Galaxy (seen in Figure 1.2) and are appropriately called spiral arms. Spiral galaxies have lots of gas and dust and lots of young stars. The Andromeda Galaxy is a large spiral galaxy similar to the Milky Way. (a) The Sombrero Galaxy is a spiral galaxy that we see from the side so the disk and central bulge are visible. (b) The Pinwheel Galaxy is a spiral galaxy that we see face-on so we can see the spiral arms. Because they contain lots of young stars, spiral arms tend to be blue.

Edwin Hubble used powerful telescopes to discover other galaxies.

(A) true (B) false

A

After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing, and would even yield clues as to how the universe formed. Hubble measured the distances to galaxies. He also studied the motions of galaxies. In doing these things, Hubble noticed a relationship. This is now called Hubbles Law: The farther away a galaxy is, the faster it is moving away from us. There was only one conclusion he could draw from this. The universe is expanding! Figure 26.15 shows a simple diagram of the expanding universe. Imagine a balloon covered with tiny dots. When you blow up the balloon, the rubber stretches. The dots slowly move away from each other as the space between them increases. In an expanding universe, the space between galaxies is expanding. We see this as the other galaxies moving away from us. We also see that galaxies farther away from us move away faster than nearby galaxies. What did the ancient Greeks recognize as the universe? In their model, the universe contained Earth at the center, the Sun, the Moon, five planets, and a sphere to which all the stars were attached. This idea held for many centuries until Galileos telescope helped people recognize that Earth is not the center of the universe. They also found out that there are many more stars than were visible to the naked eye. All of those stars were in the Milky Way Galaxy. In the early 20th century, an astronomer named Edwin Hubble (Figure 1.1) discovered that what scientists called the Andromeda Nebula was actually over 2 million light years away many times farther than the farthest distances that had ever been measured. Hubble realized that many of the objects that astronomers called nebulas were not actually clouds of gas, but were collections of millions or billions of stars what we now call galaxies. Hubble showed that the universe was much larger than our own galaxy. Today, we know that the universe contains about a hundred billion galaxies about the same number of galaxies as there are stars in the Milky Way Galaxy. (a) Edwin Hubble used the 100-inch reflecting telescope at the Mount Wilson Observatory in California to show that some distant specks of light were galaxies. (b) Hubbles namesake space telescope spotted this six galaxy group. Edwin Hubble demonstrated the existence of galaxies. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL:

As the distance between galaxies grows, the size of each galaxy shrinks.

(A) true (B) false

B

Hubble measured the distances to galaxies. He also studied the motions of galaxies. In doing these things, Hubble noticed a relationship. This is now called Hubbles Law: The farther away a galaxy is, the faster it is moving away from us. There was only one conclusion he could draw from this. The universe is expanding! Figure 26.15 shows a simple diagram of the expanding universe. Imagine a balloon covered with tiny dots. When you blow up the balloon, the rubber stretches. The dots slowly move away from each other as the space between them increases. In an expanding universe, the space between galaxies is expanding. We see this as the other galaxies moving away from us. We also see that galaxies farther away from us move away faster than nearby galaxies. Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of redshift. From this data, he noticed a relationship, which is now called Hubbles Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding. Figure 1.2 shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies. When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them. If you were standing on one of the dots, you would see the other dots moving away from you. Also, the dots farther away from you on the balloon would move away faster than dots nearby. In this diagram of the expansion of the universe over time, the distance between galaxies gets bigger over time, although the size of each galaxy stays the same. An inflating balloon is only a rough analogy to the expanding universe for several reasons. One important reason is that the surface of a balloon has only two dimensions, while space has three dimensions. But space itself is stretching out between galaxies, just as the rubber stretches when a balloon is inflated. This stretching of space, which increases the distance between galaxies, is what causes the expansion of the universe. One other difference between the universe and a balloon involves the actual size of the galaxies. On a balloon, the dots will become larger in size as you inflate it. In the universe, the galaxies stay the same size; only the space between the galaxies increases. After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing, and would even yield clues as to how the universe formed.

When the universe began, it was much larger than it is today.

(A) true (B) false

B

About 13.7 billion years ago, the entire universe was packed together. Everything was squeezed into a tiny volume. Then there was an enormous explosion. After this big bang, the universe expanded rapidly (Figure 26.16). All of the matter and energy in the universe has been expanding ever since. Scientists have evidence this is how the universe formed. One piece of evidence is that we see galaxies moving away from us. If they are moving apart, they must once have been together. Also, there is energy left over from this explosion throughout the universe. The theory for the origin of the universe is called the Big Bang Theory. Timeline of the Big Bang and the expan- sion of the Universe. The Big Bang theory is the most widely accepted cosmological explanation of how the universe formed. If we start at the present and go back into the past, the universe is contracting getting smaller and smaller. What is the end result of a contracting universe? According to the Big Bang theory, the universe began about 13.7 billion years ago. Everything that is now in the universe was squeezed into a very small volume. Imagine all of the known universe in a single, hot, chaotic mass. An enormous explosion a big bang caused the universe to start expanding rapidly. All the matter and energy in the universe, and even space itself, came out of this explosion. What came before the Big Bang? There is no way for scientists to know since there is no remaining evidence. In the first few moments after the Big Bang, the universe was extremely hot and dense. As the universe expanded, it became less dense. It began to cool. First protons, neutrons, and electrons formed. From these particles came hydrogen. Nuclear fusion created helium atoms. Some parts of the universe had matter that was densely packed. Enormous clumps of matter were held together by gravity. Eventually this material became the gas clouds, stars, galaxies, and other structures that we see in the universe today.

In the first few moments after the Big Bang, the universe was very hot and dense.

(A) true (B) false

A

In the first few moments after the Big Bang, the universe was extremely hot and dense. As the universe expanded, it became less dense. It began to cool. First protons, neutrons, and electrons formed. From these particles came hydrogen. Nuclear fusion created helium atoms. Some parts of the universe had matter that was densely packed. Enormous clumps of matter were held together by gravity. Eventually this material became the gas clouds, stars, galaxies, and other structures that we see in the universe today. In the first few moments after the Big Bang, the universe was unimaginably hot and dense. As the universe expanded, it became less dense and began to cool. After only a few seconds, protons, neutrons, and electrons could form. After a few minutes, those subatomic particles came together to create hydrogen. Energy in the universe was great enough to initiate nuclear fusion, and hydrogen nuclei were fused into helium nuclei. The first neutral atoms that included electrons did not form until about 380,000 years later. The matter in the early universe was not smoothly distributed across space. Dense clumps of matter held close together by gravity were spread around. Eventually, these clumps formed countless trillions of stars, billions of galaxies, and other structures that now form most of the visible mass of the universe. If you look at an image of galaxies at the far edge of what we can see, you are looking at great distances. But you are also looking across a different type of distance. What do those far away galaxies represent? Because it takes so long for light from so far away to reach us, you are also looking back in time (Figure 1.2). About 13.7 billion years ago, the entire universe was packed together. Everything was squeezed into a tiny volume. Then there was an enormous explosion. After this big bang, the universe expanded rapidly (Figure 26.16). All of the matter and energy in the universe has been expanding ever since. Scientists have evidence this is how the universe formed. One piece of evidence is that we see galaxies moving away from us. If they are moving apart, they must once have been together. Also, there is energy left over from this explosion throughout the universe. The theory for the origin of the universe is called the Big Bang Theory.

The first matter to form in the universe consisted of protons, neutrons, and electrons.

(A) true (B) false

A

In the first few moments after the Big Bang, the universe was extremely hot and dense. As the universe expanded, it became less dense. It began to cool. First protons, neutrons, and electrons formed. From these particles came hydrogen. Nuclear fusion created helium atoms. Some parts of the universe had matter that was densely packed. Enormous clumps of matter were held together by gravity. Eventually this material became the gas clouds, stars, galaxies, and other structures that we see in the universe today. In the first few moments after the Big Bang, the universe was unimaginably hot and dense. As the universe expanded, it became less dense and began to cool. After only a few seconds, protons, neutrons, and electrons could form. After a few minutes, those subatomic particles came together to create hydrogen. Energy in the universe was great enough to initiate nuclear fusion, and hydrogen nuclei were fused into helium nuclei. The first neutral atoms that included electrons did not form until about 380,000 years later. The matter in the early universe was not smoothly distributed across space. Dense clumps of matter held close together by gravity were spread around. Eventually, these clumps formed countless trillions of stars, billions of galaxies, and other structures that now form most of the visible mass of the universe. If you look at an image of galaxies at the far edge of what we can see, you are looking at great distances. But you are also looking across a different type of distance. What do those far away galaxies represent? Because it takes so long for light from so far away to reach us, you are also looking back in time (Figure 1.2). Although atoms are very tiny, they consist of even smaller particles. Atoms are made of protons, neutrons, and electrons: Protons have a positive charge. Electrons have a negative charge. Neutrons are neutral in charge.

Redshift is the shift of absorption bands toward the red end of the spectrum.

(A) true (B) false

A

If you look at a star through a prism, you will see a spectrum, or a range of colors through the rainbow. The spectrum will have specific dark bands where elements in the star absorb light of certain energies. By examining the arrangement of these dark absorption lines, astronomers can determine the composition of elements that make up a distant star. In fact, the element helium was first discovered in our Sun not on Earth by analyzing the absorption lines in the spectrum of the Sun. While studying the spectrum of light from distant galaxies, astronomers noticed something strange. The dark lines in the spectrum were in the patterns they expected, but they were shifted toward the red end of the spectrum, as shown in Figure 1.1. This shift of absorption bands toward the red end of the spectrum is known as redshift. Redshift is a shift in absorption bands toward the red end of the spectrum. What could make the absorption bands of a star shift toward the red? Redshift occurs when the light source is moving away from the observer or when the space between the observer and the source is stretched. What does it mean that stars and galaxies are redshifted? When astronomers see redshift in the light from a galaxy, they know that the galaxy is moving away from Earth. If galaxies were moving randomly, would some be redshifted but others be blueshifted? Of course. Since almost every galaxy in the universe has a redshift, almost every galaxy is moving away from Earth. Click image to the left or use the URL below. URL: Stars shine in many different colors. The color relates to a stars temperature and often its size. Visible light is the part of the electromagnetic spectrum (Figure 23.3) that humans can see. Visible light includes all the colors of the rainbow. Each color is determined by its wavelength. Visible light ranges from violet wavelengths of 400 nanometers (nm) through red at 700 nm. There are parts of the electromagnetic spectrum that humans cannot see. This radiation exists all around you. You just cant see it! Every star, including our Sun, emits radiation of many wavelengths. Astronomers can learn a lot from studying the details of the spectrum of radiation from a star. Many extremely interesting objects cant be seen with the unaided eye. Astronomers use telescopes to see objects at wavelengths all across the electromagnetic spectrum. Some very hot stars emit light primarily at ultraviolet wavelengths. There are extremely hot objects that emit X-rays and even gamma rays. Some very cool stars shine mostly in the infrared light wavelengths. Radio waves come from the faintest, most distant objects. To learn more about stars spectra, visit

Hubbles Law states, the farther away a galaxy is, the faster it is moving away from us.

(A) true (B) false

A

Hubble measured the distances to galaxies. He also studied the motions of galaxies. In doing these things, Hubble noticed a relationship. This is now called Hubbles Law: The farther away a galaxy is, the faster it is moving away from us. There was only one conclusion he could draw from this. The universe is expanding! Figure 26.15 shows a simple diagram of the expanding universe. Imagine a balloon covered with tiny dots. When you blow up the balloon, the rubber stretches. The dots slowly move away from each other as the space between them increases. In an expanding universe, the space between galaxies is expanding. We see this as the other galaxies moving away from us. We also see that galaxies farther away from us move away faster than nearby galaxies. Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of redshift. From this data, he noticed a relationship, which is now called Hubbles Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding. Figure 1.2 shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies. When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them. If you were standing on one of the dots, you would see the other dots moving away from you. Also, the dots farther away from you on the balloon would move away faster than dots nearby. In this diagram of the expansion of the universe over time, the distance between galaxies gets bigger over time, although the size of each galaxy stays the same. An inflating balloon is only a rough analogy to the expanding universe for several reasons. One important reason is that the surface of a balloon has only two dimensions, while space has three dimensions. But space itself is stretching out between galaxies, just as the rubber stretches when a balloon is inflated. This stretching of space, which increases the distance between galaxies, is what causes the expansion of the universe. One other difference between the universe and a balloon involves the actual size of the galaxies. On a balloon, the dots will become larger in size as you inflate it. In the universe, the galaxies stay the same size; only the space between the galaxies increases. After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing, and would even yield clues as to how the universe formed.

Scientists think that stars and galaxies make up only a small part of the matter in the universe.

(A) true (B) false

A

We see many objects out in space that emit light. This matter is contained in stars, and the stars are contained in galaxies. Scientists think that stars and galaxies make up only a small part of the matter in the universe. The rest of the matter is called dark matter. Dark matter doesnt emit light, so we cant see it. We know it is there because it affects the motion of objects around it. For example, astronomers measure how spiral galaxies rotate. The outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than we can see. What is dark matter? Actually, we dont really know. Dark matter could just be ordinary matter, like what makes up Earth. The universe could contain lots of objects that dont have enough mass to glow on their own. There might just be a lot of black holes. Another possibility is that the universe contains a lot of matter that is different from anything we know. If it doesnt interact much with ordinary matter, it would be very difficult or impossible to detect directly. Most scientists who study dark matter think it is a combination. Ordinary matter is part of it. That is mixed with some kind of matter that we havent discovered yet. Most scientists think that ordinary matter is less than half of the total matter in the universe. Earth is just a tiny speck in the universe. Our planet is surrounded by lots of space. Light travels across empty space. Astronomers can study light from stars to learn about the universe. Light is the visible part of the electromagnetic spectrum. Astronomers use the light that comes to us to gather information about the universe. The biggest groups of stars are called galaxies. A few million to many billions of stars may make up a galaxy. With the unaided eye, every star you can see is part of the Milky Way Galaxy. All the other galaxies are extremely far away. The closest spiral galaxy, the Andromeda Galaxy, shown in Figure 26.8, is 2,500,000 light years away and contains one trillion stars!

Scientists have proven conclusively that dark matter and dark energy exist.

(A) true (B) false

B

We see many objects out in space that emit light. This matter is contained in stars, and the stars are contained in galaxies. Scientists think that stars and galaxies make up only a small part of the matter in the universe. The rest of the matter is called dark matter. Dark matter doesnt emit light, so we cant see it. We know it is there because it affects the motion of objects around it. For example, astronomers measure how spiral galaxies rotate. The outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than we can see. What is dark matter? Actually, we dont really know. Dark matter could just be ordinary matter, like what makes up Earth. The universe could contain lots of objects that dont have enough mass to glow on their own. There might just be a lot of black holes. Another possibility is that the universe contains a lot of matter that is different from anything we know. If it doesnt interact much with ordinary matter, it would be very difficult or impossible to detect directly. Most scientists who study dark matter think it is a combination. Ordinary matter is part of it. That is mixed with some kind of matter that we havent discovered yet. Most scientists think that ordinary matter is less than half of the total matter in the universe. The things we observe in space are objects that emit some type of electromagnetic radiation. However, scientists think that matter that emits light makes up only a small part of the matter in the universe. The rest of the matter, about 80%, is dark matter. Dark matter emits no electromagnetic radiation, so we cant observe it directly. However, astronomers know that dark matter exists because its gravity affects the motion of objects around it. When astronomers measure how spiral galaxies rotate, they find that the outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than they can see. Gravitational lensing occurs when light is bent from a very distant bright source around a super-massive object (Figure 1.1). To explain strong gravitational lensing, more matter than is observed must be present. With so little to go on, astronomers dont really know much about the nature of dark matter. One possibility is that it could just be ordinary matter that does not emit radiation in objects such as black holes, neutron stars, and brown dwarfs objects larger than Jupiter but smaller than the smallest stars. But astronomers cannot find enough of these types of objects, which they have named MACHOs (massive astrophyiscal compact halo object), to account for all the dark matter, so they are thought to be only a small part of the total. Another possibility is that the dark matter is very different from the ordinary matter we see. Some appear to be particles that have gravity, but dont otherwise appear to interact with other particles. Scientists call these theoretical particles WIMPs, which stands for Weakly Interactive Massive Particles. Most scientists who study dark matter think that the dark matter in the universe is a combination of MACHOs and some type of exotic matter, such as WIMPs. Researching dark matter is an active area of scientific research, and astronomers knowledge about dark matter is changing rapidly. Meet one of the three winners of the 2011 Nobel Prize in Physics, Lawrence Berkeley Lab astrophysicist Saul Perlmutter. He explains how dark energy, which makes up 70 percent of the universe, is causing our universe to expand. Click image to the left or use the URL below. URL:

Redshift was discovered by Edwin Hubble.

(A) true (B) false

A

After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing, and would even yield clues as to how the universe formed. What did the ancient Greeks recognize as the universe? In their model, the universe contained Earth at the center, the Sun, the Moon, five planets, and a sphere to which all the stars were attached. This idea held for many centuries until Galileos telescope helped people recognize that Earth is not the center of the universe. They also found out that there are many more stars than were visible to the naked eye. All of those stars were in the Milky Way Galaxy. In the early 20th century, an astronomer named Edwin Hubble (Figure 1.1) discovered that what scientists called the Andromeda Nebula was actually over 2 million light years away many times farther than the farthest distances that had ever been measured. Hubble realized that many of the objects that astronomers called nebulas were not actually clouds of gas, but were collections of millions or billions of stars what we now call galaxies. Hubble showed that the universe was much larger than our own galaxy. Today, we know that the universe contains about a hundred billion galaxies about the same number of galaxies as there are stars in the Milky Way Galaxy. (a) Edwin Hubble used the 100-inch reflecting telescope at the Mount Wilson Observatory in California to show that some distant specks of light were galaxies. (b) Hubbles namesake space telescope spotted this six galaxy group. Edwin Hubble demonstrated the existence of galaxies. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: Incredible images have come from the Hubble Space Telescope (HST). Even more incredible scientific discoveries have come from HST. The Hubble was the first telescope in space. It was put into orbit by the space shuttle Discovery in 1990. Since then, four shuttle missions have gone to the Hubble to make repairs and upgrades. The last repair mission to the Hubble happened in 2009. An example of a HST image is in Figure 23.28,

The nature of dark matter is unknown.

(A) true (B) false

A

We see many objects out in space that emit light. This matter is contained in stars, and the stars are contained in galaxies. Scientists think that stars and galaxies make up only a small part of the matter in the universe. The rest of the matter is called dark matter. Dark matter doesnt emit light, so we cant see it. We know it is there because it affects the motion of objects around it. For example, astronomers measure how spiral galaxies rotate. The outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than we can see. What is dark matter? Actually, we dont really know. Dark matter could just be ordinary matter, like what makes up Earth. The universe could contain lots of objects that dont have enough mass to glow on their own. There might just be a lot of black holes. Another possibility is that the universe contains a lot of matter that is different from anything we know. If it doesnt interact much with ordinary matter, it would be very difficult or impossible to detect directly. Most scientists who study dark matter think it is a combination. Ordinary matter is part of it. That is mixed with some kind of matter that we havent discovered yet. Most scientists think that ordinary matter is less than half of the total matter in the universe. The things we observe in space are objects that emit some type of electromagnetic radiation. However, scientists think that matter that emits light makes up only a small part of the matter in the universe. The rest of the matter, about 80%, is dark matter. Dark matter emits no electromagnetic radiation, so we cant observe it directly. However, astronomers know that dark matter exists because its gravity affects the motion of objects around it. When astronomers measure how spiral galaxies rotate, they find that the outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than they can see. Gravitational lensing occurs when light is bent from a very distant bright source around a super-massive object (Figure 1.1). To explain strong gravitational lensing, more matter than is observed must be present. With so little to go on, astronomers dont really know much about the nature of dark matter. One possibility is that it could just be ordinary matter that does not emit radiation in objects such as black holes, neutron stars, and brown dwarfs objects larger than Jupiter but smaller than the smallest stars. But astronomers cannot find enough of these types of objects, which they have named MACHOs (massive astrophyiscal compact halo object), to account for all the dark matter, so they are thought to be only a small part of the total. Another possibility is that the dark matter is very different from the ordinary matter we see. Some appear to be particles that have gravity, but dont otherwise appear to interact with other particles. Scientists call these theoretical particles WIMPs, which stands for Weakly Interactive Massive Particles. Most scientists who study dark matter think that the dark matter in the universe is a combination of MACHOs and some type of exotic matter, such as WIMPs. Researching dark matter is an active area of scientific research, and astronomers knowledge about dark matter is changing rapidly. We know that the universe is expanding. Astronomers have wondered if it is expanding fast enough to escape the pull of gravity. Would the universe just expand forever? If it could not escape the pull of gravity, would it someday start to contract? This means it would eventually get squeezed together in a big crunch. This is the opposite of the Big Bang. Scientists may now have an answer. Recently, astronomers have discovered that the universe is expanding even faster than before. What is causing the expansion to accelerate? One hypothesis is that there is energy out in the universe that we cant see. Astronomers call this dark energy. We know even less about dark energy than we know about dark matter. Some scientists think that dark energy makes up more than half of the universe.

idea that explains how the universe formed

(A) universe (B) Big Bang theory (C) ordinary matter (D) dark matter (E) Hubbles law

B

Timeline of the Big Bang and the expan- sion of the Universe. The Big Bang theory is the most widely accepted cosmological explanation of how the universe formed. If we start at the present and go back into the past, the universe is contracting getting smaller and smaller. What is the end result of a contracting universe? According to the Big Bang theory, the universe began about 13.7 billion years ago. Everything that is now in the universe was squeezed into a very small volume. Imagine all of the known universe in a single, hot, chaotic mass. An enormous explosion a big bang caused the universe to start expanding rapidly. All the matter and energy in the universe, and even space itself, came out of this explosion. What came before the Big Bang? There is no way for scientists to know since there is no remaining evidence. About 13.7 billion years ago, the entire universe was packed together. Everything was squeezed into a tiny volume. Then there was an enormous explosion. After this big bang, the universe expanded rapidly (Figure 26.16). All of the matter and energy in the universe has been expanding ever since. Scientists have evidence this is how the universe formed. One piece of evidence is that we see galaxies moving away from us. If they are moving apart, they must once have been together. Also, there is energy left over from this explosion throughout the universe. The theory for the origin of the universe is called the Big Bang Theory. The Big Bang Theory is the dominant and highly supported theory of the origin of the universe. It states that the universe began from an initial point which has expanded over billions of years to form the universe as we now know it. In 1922, Alexander Friedman found that the solutions to Einsteins general relativity equations resulted in an expanding universe. Einstein, at that time, believed in a static, eternal universe so he added a constant to his equations to eliminate the expansion. Einstein would later call this the biggest blunder of his life. In 1924, Edwin Hubble was able to measure the distance to observed celestial objects that were thought to be nebula and discovered that they were so far away they were not actually part of the Milky Way (the galaxy containing our sun). He discovered that the Milky Way was only one of many galaxies. In 1927, Georges Lemaitre, a physicist, suggested that the universe must be expanding. Lemaitres theory was supported by Hubble in 1929 when he found that the galaxies most distant from us also had the greatest red shift (were moving away from us with the greatest speed). The idea that the most distance galaxies were moving away from us at the greatest speed was exactly what was predicted by Lemaitre. In 1931, Lemaitre went further with his predictions and by extrapolating backwards, found that the matter of the universe would reach an infinite density and temperature at a finite time in the past (around 15 billion years). This meant that the universe must have begun as a small, extremely dense point of matter. At the time, the only other theory that competed with Lemaitres theory was the Steady State Theory of Fred Hoyle. The steady state theory predicted that new matter was created which made it appear that the universe was expanding but that the universe was constant. It was Hoyle who coined the term Big Bang Theory which he used as a derisive name for Lemaitres theory. George Gamow (1904 - 1968) was the major advocate of the Big Bang theory. He predicted that cosmic microwave background radiation should exist throughout the universe as a remnant of the Big Bang. As atoms formed from sub-atomic particles shortly after the Big Bang, electromagnetic radiation would be emitted and this radiation would still be observable today. Gamow predicted that the expansion of the universe would cool the original radiation so that now the radiation would be in the microwave range. The debate continued until 1965 when two Bell Telephone scientists stumbled upon the microwave radiation with their radio telescope.

The universe contains about a hundred million galaxies.

(A) true (B) false

B

The Milky Way Galaxy, which is our galaxy. The Milky Way is made of millions of stars along with a lot of gas and dust. It looks different from other galaxies because we are looking at the main disk from within the galaxy. Astronomers estimate that the Milky Way contains 200 to 400 billion stars. The Milky Way Galaxy is a spiral galaxy that contains about 400 billion stars. Like other spiral galaxies, it has a disk, a central bulge, and spiral arms. The disk is about 100,000 light-years across. It is about 3,000 light years thick. Most of the galaxys gas, dust, young stars, and open clusters are in the disk. Some astronomers think that there is a gigantic black hole at the center of the galaxy. Figure 26.13 shows what the Milky Way probably looks like from the outside. Our solar system is within one of the spiral arms. Most of the stars we see in the sky are relatively nearby stars that are also in this spiral arm. We are a little more than halfway out from the center of the Galaxy to the edge, as shown in Figure 26.13. Our solar system orbits the center of the galaxy as the galaxy spins. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. Galaxies are the biggest groups of stars and can contain anywhere from a few million stars to many billions of stars. Every star that is visible in the night sky is part of the Milky Way Galaxy. To the naked eye, the closest major galaxy the Andromeda Galaxy, shown in Figure 1.1 looks like only a dim, fuzzy spot. But that fuzzy spot contains one trillion 1,000,000,000,000 stars! Galaxies are divided into three types according to shape: spiral galaxies, elliptical galaxies, and irregular galaxies.

matter that can be detected only by its effects on the motion of objects around it

(A) universe (B) Big Bang theory (C) ordinary matter (D) dark matter (E) Hubbles law

D

We usually cant sense the air around us unless it is moving. But air has the same basic properties as other matter. For example, air has mass, volume and, of course, density. Regardless of what gravity is a force between masses or the result of curves in space and time the effects of gravity on motion are well known. You already know that gravity causes objects to fall down to the ground. Gravity affects the motion of objects in other ways as well. Here is a riddle for you to ponder: What do you and a tiny speck of dust in outer space have in common? Think you know the answer? Both you and the speck of dust consist of matter. So does the ground beneath your feet. In fact, everything you can see and touch is made of matter. The only things that are not matter are forms of energy. This would include things such as light and sound. Although forms of energy are not matter, the air and other substances they travel through are. So what is matter? Matter is defined as anything that has mass and volume. You may recall that atoms are the building blocks of matter. Even things as small as atoms have mass and volume. The more atoms, or matter, the more mass and volume are present. Different types of atoms have different amounts of mass and volume. So, its not enough to know the count of atoms to determine the mass. You must also know the type of atoms an item is made of. Mass and volume are just two ways to describe the physical property of a substance. Physical properties are all determined by the amounts and type of atoms that compose items.

observation that the farther away a galaxy is, the faster it is moving away from us

(A) universe (B) Big Bang theory (C) ordinary matter (D) dark matter (E) Hubbles law

E

Hubble measured the distances to galaxies. He also studied the motions of galaxies. In doing these things, Hubble noticed a relationship. This is now called Hubbles Law: The farther away a galaxy is, the faster it is moving away from us. There was only one conclusion he could draw from this. The universe is expanding! Figure 26.15 shows a simple diagram of the expanding universe. Imagine a balloon covered with tiny dots. When you blow up the balloon, the rubber stretches. The dots slowly move away from each other as the space between them increases. In an expanding universe, the space between galaxies is expanding. We see this as the other galaxies moving away from us. We also see that galaxies farther away from us move away faster than nearby galaxies. Edwin Hubble combined his measurements of the distances to galaxies with other astronomers measurements of redshift. From this data, he noticed a relationship, which is now called Hubbles Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding. Figure 1.2 shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies. When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them. If you were standing on one of the dots, you would see the other dots moving away from you. Also, the dots farther away from you on the balloon would move away faster than dots nearby. In this diagram of the expansion of the universe over time, the distance between galaxies gets bigger over time, although the size of each galaxy stays the same. An inflating balloon is only a rough analogy to the expanding universe for several reasons. One important reason is that the surface of a balloon has only two dimensions, while space has three dimensions. But space itself is stretching out between galaxies, just as the rubber stretches when a balloon is inflated. This stretching of space, which increases the distance between galaxies, is what causes the expansion of the universe. One other difference between the universe and a balloon involves the actual size of the galaxies. On a balloon, the dots will become larger in size as you inflate it. In the universe, the galaxies stay the same size; only the space between the galaxies increases. When we look at stars and galaxies, we are seeing over great distances. More importantly, we are also seeing back in time. When we see a distant galaxy, we are actually seeing how the galaxy used to look. For example, the Andromeda Galaxy, shown in Figure 23.1, is about 2.5 million light-years from Earth. When you see an image of the galaxy what are you seeing? You are seeing the galaxy as it was 2.5 million years ago! Since scientists can look back in time they can better understand the Universes history. Check out http://science.n

less than half of the total matter in the universe

(A) universe (B) Big Bang theory (C) ordinary matter (D) dark matter (E) Hubbles law

C

All known matter can be divided into a little more than 100 different substances called elements. We see many objects out in space that emit light. This matter is contained in stars, and the stars are contained in galaxies. Scientists think that stars and galaxies make up only a small part of the matter in the universe. The rest of the matter is called dark matter. Dark matter doesnt emit light, so we cant see it. We know it is there because it affects the motion of objects around it. For example, astronomers measure how spiral galaxies rotate. The outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than we can see. What is dark matter? Actually, we dont really know. Dark matter could just be ordinary matter, like what makes up Earth. The universe could contain lots of objects that dont have enough mass to glow on their own. There might just be a lot of black holes. Another possibility is that the universe contains a lot of matter that is different from anything we know. If it doesnt interact much with ordinary matter, it would be very difficult or impossible to detect directly. Most scientists who study dark matter think it is a combination. Ordinary matter is part of it. That is mixed with some kind of matter that we havent discovered yet. Most scientists think that ordinary matter is less than half of the total matter in the universe. In the first few moments after the Big Bang, the universe was unimaginably hot and dense. As the universe expanded, it became less dense and began to cool. After only a few seconds, protons, neutrons, and electrons could form. After a few minutes, those subatomic particles came together to create hydrogen. Energy in the universe was great enough to initiate nuclear fusion, and hydrogen nuclei were fused into helium nuclei. The first neutral atoms that included electrons did not form until about 380,000 years later. The matter in the early universe was not smoothly distributed across space. Dense clumps of matter held close together by gravity were spread around. Eventually, these clumps formed countless trillions of stars, billions of galaxies, and other structures that now form most of the visible mass of the universe. If you look at an image of galaxies at the far edge of what we can see, you are looking at great distances. But you are also looking across a different type of distance. What do those far away galaxies represent? Because it takes so long for light from so far away to reach us, you are also looking back in time (Figure 1.2).

all the matter and energy that exists and all of space and time

(A) universe (B) Big Bang theory (C) ordinary matter (D) dark matter (E) Hubbles law

A

Matter is all the stuff that exists in the universe. Everything you can see and touch is made of matter, including you! The only things that arent matter are forms of energy, such as light and sound. In science, matter is defined as anything that has mass and volume. Mass and volume measure different aspects of matter. Both you and the speck of dust consist of atoms of matter. So does the ground beneath your feet. In fact, everything you can see and touch is made of matter. The only things that arent matter are forms of energy, such as light and sound. Although forms of energy are not matter, the air and other substances they travel through are. So what is matter? Matter is defined as anything that has mass and volume. Physical science is the study of matter and energy. That covers a lot of territory because matter refers to all the stuff that exists in the universe. It includes everything you can see and many things that you cannot see, including the air around you. Energy is also universal. Its what gives matter the ability to move and change. Electricity, heat, and light are some of the forms that energy can take.

According to the Big Bang theory

(A) dark matter is changing to ordinary matter throughout the universe (B) dark energy is pulling the universe into black holes (C) the universe will someday end because of a big bang (D) the universe began with an enormous explosion

D

The Big Bang Theory is the dominant and highly supported theory of the origin of the universe. It states that the universe began from an initial point which has expanded over billions of years to form the universe as we now know it. In 1922, Alexander Friedman found that the solutions to Einsteins general relativity equations resulted in an expanding universe. Einstein, at that time, believed in a static, eternal universe so he added a constant to his equations to eliminate the expansion. Einstein would later call this the biggest blunder of his life. In 1924, Edwin Hubble was able to measure the distance to observed celestial objects that were thought to be nebula and discovered that they were so far away they were not actually part of the Milky Way (the galaxy containing our sun). He discovered that the Milky Way was only one of many galaxies. In 1927, Georges Lemaitre, a physicist, suggested that the universe must be expanding. Lemaitres theory was supported by Hubble in 1929 when he found that the galaxies most distant from us also had the greatest red shift (were moving away from us with the greatest speed). The idea that the most distance galaxies were moving away from us at the greatest speed was exactly what was predicted by Lemaitre. In 1931, Lemaitre went further with his predictions and by extrapolating backwards, found that the matter of the universe would reach an infinite density and temperature at a finite time in the past (around 15 billion years). This meant that the universe must have begun as a small, extremely dense point of matter. At the time, the only other theory that competed with Lemaitres theory was the Steady State Theory of Fred Hoyle. The steady state theory predicted that new matter was created which made it appear that the universe was expanding but that the universe was constant. It was Hoyle who coined the term Big Bang Theory which he used as a derisive name for Lemaitres theory. George Gamow (1904 - 1968) was the major advocate of the Big Bang theory. He predicted that cosmic microwave background radiation should exist throughout the universe as a remnant of the Big Bang. As atoms formed from sub-atomic particles shortly after the Big Bang, electromagnetic radiation would be emitted and this radiation would still be observable today. Gamow predicted that the expansion of the universe would cool the original radiation so that now the radiation would be in the microwave range. The debate continued until 1965 when two Bell Telephone scientists stumbled upon the microwave radiation with their radio telescope. Timeline of the Big Bang and the expan- sion of the Universe. The Big Bang theory is the most widely accepted cosmological explanation of how the universe formed. If we start at the present and go back into the past, the universe is contracting getting smaller and smaller. What is the end result of a contracting universe? According to the Big Bang theory, the universe began about 13.7 billion years ago. Everything that is now in the universe was squeezed into a very small volume. Imagine all of the known universe in a single, hot, chaotic mass. An enormous explosion a big bang caused the universe to start expanding rapidly. All the matter and energy in the universe, and even space itself, came out of this explosion. What came before the Big Bang? There is no way for scientists to know since there is no remaining evidence. About 13.7 billion years ago, the entire universe was packed together. Everything was squeezed into a tiny volume. Then there was an enormous explosion. After this big bang, the universe expanded rapidly (Figure 26.16). All of the matter and energy in the universe has been expanding ever since. Scientists have evidence this is how the universe formed. One piece of evidence is that we see galaxies moving away from us. If they are moving apart, they must once have been together. Also, there is energy left over from this explosion throughout the universe. The theory for the origin of the universe is called the Big Bang Theory.

From our point of view in the Milky Way Galaxy, all other galaxies in the universe appear to be

(A) crowding closer together (B) moving away from us (C) getting dimmer (D) growing larger

B

The Milky Way Galaxy, which is our galaxy. The Milky Way is made of millions of stars along with a lot of gas and dust. It looks different from other galaxies because we are looking at the main disk from within the galaxy. Astronomers estimate that the Milky Way contains 200 to 400 billion stars. If you get away from city lights and look up in the sky on a very clear night, you will see something spectacular. A band of milky light stretches across the sky, as in Figure 26.12. This band is the disk of the Milky Way Galaxy. This is the galaxy where we all live. The Milky Way Galaxy looks different to us than other galaxies because our view is from inside of it! When we look at stars and galaxies, we are seeing over great distances. More importantly, we are also seeing back in time. When we see a distant galaxy, we are actually seeing how the galaxy used to look. For example, the Andromeda Galaxy, shown in Figure 23.1, is about 2.5 million light-years from Earth. When you see an image of the galaxy what are you seeing? You are seeing the galaxy as it was 2.5 million years ago! Since scientists can look back in time they can better understand the Universes history. Check out http://science.n

After the big bang occurred, the universe

(A) shrank in size (B) became denser (C) became hotter (D) began to cool

D

About 13.7 billion years ago, the entire universe was packed together. Everything was squeezed into a tiny volume. Then there was an enormous explosion. After this big bang, the universe expanded rapidly (Figure 26.16). All of the matter and energy in the universe has been expanding ever since. Scientists have evidence this is how the universe formed. One piece of evidence is that we see galaxies moving away from us. If they are moving apart, they must once have been together. Also, there is energy left over from this explosion throughout the universe. The theory for the origin of the universe is called the Big Bang Theory. In the first few moments after the Big Bang, the universe was extremely hot and dense. As the universe expanded, it became less dense. It began to cool. First protons, neutrons, and electrons formed. From these particles came hydrogen. Nuclear fusion created helium atoms. Some parts of the universe had matter that was densely packed. Enormous clumps of matter were held together by gravity. Eventually this material became the gas clouds, stars, galaxies, and other structures that we see in the universe today. Timeline of the Big Bang and the expan- sion of the Universe. The Big Bang theory is the most widely accepted cosmological explanation of how the universe formed. If we start at the present and go back into the past, the universe is contracting getting smaller and smaller. What is the end result of a contracting universe? According to the Big Bang theory, the universe began about 13.7 billion years ago. Everything that is now in the universe was squeezed into a very small volume. Imagine all of the known universe in a single, hot, chaotic mass. An enormous explosion a big bang caused the universe to start expanding rapidly. All the matter and energy in the universe, and even space itself, came out of this explosion. What came before the Big Bang? There is no way for scientists to know since there is no remaining evidence.

Most scientists who study dark matter think that it is

(A) a mix of ordinary matter and matter we havent yet discovered (B) matter that makes up black holes (C) just a tiny fraction of all the matter that exists in the universe (D) none of the above

A

We see many objects out in space that emit light. This matter is contained in stars, and the stars are contained in galaxies. Scientists think that stars and galaxies make up only a small part of the matter in the universe. The rest of the matter is called dark matter. Dark matter doesnt emit light, so we cant see it. We know it is there because it affects the motion of objects around it. For example, astronomers measure how spiral galaxies rotate. The outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than we can see. What is dark matter? Actually, we dont really know. Dark matter could just be ordinary matter, like what makes up Earth. The universe could contain lots of objects that dont have enough mass to glow on their own. There might just be a lot of black holes. Another possibility is that the universe contains a lot of matter that is different from anything we know. If it doesnt interact much with ordinary matter, it would be very difficult or impossible to detect directly. Most scientists who study dark matter think it is a combination. Ordinary matter is part of it. That is mixed with some kind of matter that we havent discovered yet. Most scientists think that ordinary matter is less than half of the total matter in the universe. The things we observe in space are objects that emit some type of electromagnetic radiation. However, scientists think that matter that emits light makes up only a small part of the matter in the universe. The rest of the matter, about 80%, is dark matter. Dark matter emits no electromagnetic radiation, so we cant observe it directly. However, astronomers know that dark matter exists because its gravity affects the motion of objects around it. When astronomers measure how spiral galaxies rotate, they find that the outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than they can see. Gravitational lensing occurs when light is bent from a very distant bright source around a super-massive object (Figure 1.1). To explain strong gravitational lensing, more matter than is observed must be present. With so little to go on, astronomers dont really know much about the nature of dark matter. One possibility is that it could just be ordinary matter that does not emit radiation in objects such as black holes, neutron stars, and brown dwarfs objects larger than Jupiter but smaller than the smallest stars. But astronomers cannot find enough of these types of objects, which they have named MACHOs (massive astrophyiscal compact halo object), to account for all the dark matter, so they are thought to be only a small part of the total. Another possibility is that the dark matter is very different from the ordinary matter we see. Some appear to be particles that have gravity, but dont otherwise appear to interact with other particles. Scientists call these theoretical particles WIMPs, which stands for Weakly Interactive Massive Particles. Most scientists who study dark matter think that the dark matter in the universe is a combination of MACHOs and some type of exotic matter, such as WIMPs. Researching dark matter is an active area of scientific research, and astronomers knowledge about dark matter is changing rapidly. Meet one of the three winners of the 2011 Nobel Prize in Physics, Lawrence Berkeley Lab astrophysicist Saul Perlmutter. He explains how dark energy, which makes up 70 percent of the universe, is causing our universe to expand. Click image to the left or use the URL below. URL:

Scientists recently discovered that the universe

(A) has started to contract in size (B) is expanding even faster than before (C) is no longer expanding or contracting (D) will soon go through another big bang

B

About 13.7 billion years ago, the entire universe was packed together. Everything was squeezed into a tiny volume. Then there was an enormous explosion. After this big bang, the universe expanded rapidly (Figure 26.16). All of the matter and energy in the universe has been expanding ever since. Scientists have evidence this is how the universe formed. One piece of evidence is that we see galaxies moving away from us. If they are moving apart, they must once have been together. Also, there is energy left over from this explosion throughout the universe. The theory for the origin of the universe is called the Big Bang Theory. We know that the universe is expanding. Astronomers have wondered if it is expanding fast enough to escape the pull of gravity. Would the universe just expand forever? If it could not escape the pull of gravity, would it someday start to contract? This means it would eventually get squeezed together in a big crunch. This is the opposite of the Big Bang. Scientists may now have an answer. Recently, astronomers have discovered that the universe is expanding even faster than before. What is causing the expansion to accelerate? One hypothesis is that there is energy out in the universe that we cant see. Astronomers call this dark energy. We know even less about dark energy than we know about dark matter. Some scientists think that dark energy makes up more than half of the universe. What did the ancient Greeks recognize as the universe? In their model, the universe contained Earth at the center, the Sun, the Moon, five planets, and a sphere to which all the stars were attached. This idea held for many centuries until Galileos telescope helped people recognize that Earth is not the center of the universe. They also found out that there are many more stars than were visible to the naked eye. All of those stars were in the Milky Way Galaxy. In the early 20th century, an astronomer named Edwin Hubble (Figure 1.1) discovered that what scientists called the Andromeda Nebula was actually over 2 million light years away many times farther than the farthest distances that had ever been measured. Hubble realized that many of the objects that astronomers called nebulas were not actually clouds of gas, but were collections of millions or billions of stars what we now call galaxies. Hubble showed that the universe was much larger than our own galaxy. Today, we know that the universe contains about a hundred billion galaxies about the same number of galaxies as there are stars in the Milky Way Galaxy. (a) Edwin Hubble used the 100-inch reflecting telescope at the Mount Wilson Observatory in California to show that some distant specks of light were galaxies. (b) Hubbles namesake space telescope spotted this six galaxy group. Edwin Hubble demonstrated the existence of galaxies. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL:

Scientists have introduced the concept of dark energy to explain the

(A) rate of growth of the universe (B) contraction of the universe (C) origin of dark matter (D) all of the above

A

We know that the universe is expanding. Astronomers have wondered if it is expanding fast enough to escape the pull of gravity. Would the universe just expand forever? If it could not escape the pull of gravity, would it someday start to contract? This means it would eventually get squeezed together in a big crunch. This is the opposite of the Big Bang. Scientists may now have an answer. Recently, astronomers have discovered that the universe is expanding even faster than before. What is causing the expansion to accelerate? One hypothesis is that there is energy out in the universe that we cant see. Astronomers call this dark energy. We know even less about dark energy than we know about dark matter. Some scientists think that dark energy makes up more than half of the universe. Astronomers who study the expansion of the universe are interested in knowing the rate of that expansion. Is the rate fast enough to overcome the attractive pull of gravity? If yes, then the universe will expand forever, although the expansion will slow down over time. If no, then the universe would someday start to contract, and eventually get squeezed together in a big crunch, the opposite of the Big Bang. Recently, astronomers have made a discovery that answers that question: the rate at which the universe is expanding is actually increasing. In other words, the universe is expanding faster now than ever before, and in the future it will expand even faster. So now astronomers think that the universe will keep expanding forever. But it also proposes a perplexing new question: what is causing the expansion of the universe to accelerate? One possible hypothesis involves a new, hypothetical form of energy called dark energy (Figure 1.2). Some scientists think that dark energy makes up as much as 71% of the total energy content of the universe. Today matter makes up a small percentage of the universe, but at the start of the universe it made up much more. Where did dark energy, if it even exists, come from? Other scientists have other hypotheses about why the universe is continuing to expand; the causes of the universes expansion is another unanswered question that scientists are researching. Click image to the left or use the URL below. URL: Meet one of the three winners of the 2011 Nobel Prize in Physics, Lawrence Berkeley Lab astrophysicist Saul Perlmutter. He explains how dark energy, which makes up 70 percent of the universe, is causing our universe to expand. Click image to the left or use the URL below. URL:

Which of the following is the basic unit of matter?

(A) molecule (B) chemical compound (C) atom (D) nucleus

C

Compare and contrast the basic properties of matter, such as mass and volume. Here is a riddle for you to ponder: What do you and a tiny speck of dust in outer space have in common? Think you know the answer? Both you and the speck of dust consist of matter. So does the ground beneath your feet. In fact, everything you can see and touch is made of matter. The only things that are not matter are forms of energy. This would include things such as light and sound. Although forms of energy are not matter, the air and other substances they travel through are. So what is matter? Matter is defined as anything that has mass and volume. You may recall that atoms are the building blocks of matter. Even things as small as atoms have mass and volume. The more atoms, or matter, the more mass and volume are present. Different types of atoms have different amounts of mass and volume. So, its not enough to know the count of atoms to determine the mass. You must also know the type of atoms an item is made of. Mass and volume are just two ways to describe the physical property of a substance. Physical properties are all determined by the amounts and type of atoms that compose items. Both you and the speck of dust consist of atoms of matter. So does the ground beneath your feet. In fact, everything you can see and touch is made of matter. The only things that arent matter are forms of energy, such as light and sound. Although forms of energy are not matter, the air and other substances they travel through are. So what is matter? Matter is defined as anything that has mass and volume.

Water is an example of a(n)

(A) atom (B) molecule (C) ion (D) native element

B

Water vapor is an example of a gas. A gas is matter that has neither a fixed volume nor a fixed shape. Instead, a gas takes both the volume and the shape of its container. It spreads out to take up all available space. You can see an example in Figure 4.6. Water (H2 O) is an example of a chemical compound. Water molecules always consist of two atoms of hydrogen and one atom of oxygen. Like water, all other chemical compounds consist of a fixed ratio of elements. It doesnt matter how much or how little of a compound there is. It always has the same composition. Ocean water is an example of a liquid. A liquid is matter that has a fixed volume but not a fixed shape. Instead, a liquid takes the shape of its container. If the volume of a liquid is less than the volume of its container, the top surface will be exposed to the air, like the oil in the bottles in Figure 4.4. Two interesting properties of liquids are surface tension and viscosity. Surface tension is a force that pulls particles at the exposed surface of a liquid toward other liquid particles. Surface tension explains why water forms droplets, like those in Figure 4.5. Viscosity is a liquids resistance to flowing. Thicker liquids are more viscous than thinner liquids. For example, the honey in Figure 4.5 is more viscous than the vinegar. You can learn more about surface tension and viscosity at these URLs: http://io9.com/5668221/an-experiment-with-soap-water-pepper-and-surface-tension http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Viscosity-840.html (1:40) MEDIA Click image to the left or use the URL below. URL:

An atom is only an ion if it has more or less

(A) neutrons than electrons (B) protons than neutrons (C) neutrons than protons (D) electrons than protons

D

Atoms cannot only gain extra electrons. They can also lose electrons. In either case, they become ions. Ions are atoms that have a positive or negative charge because they have unequal numbers of protons and electrons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine (see Figure 1.1). A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with an electric charge of -1. Sometimes atoms lose or gain electrons. Then they become ions. Ions have a positive or negative charge. Thats because they do not have the same number of electrons as protons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine in Figure 5.5. A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with a negative charge of minus one. Electrons are extremely small. The mass of an electron is only about 1/2000 the mass of a proton or neutron, so electrons contribute virtually nothing to the total mass of an atom. Electrons have an electric charge of -1, which is equal but opposite to the charge of proton, which is +1. All atoms have the same number of electrons as protons, so the positive and negative charges cancel out, making atoms electrically neutral.

An example of a pure element is

(A) table salt (B) silicon dioxide (C) sulfur (D) calcium carbonate

C

A pure substance is called an element. An element is a pure substance because it cannot be separated into any other substances. Currently, 92 different elements are known to exist in nature, although additional elements have been formed in labs. All matter consists of one or more of these elements. Some elements are very common; others are relatively rare. The most common element in the universe is hydrogen, which is part of Earths atmosphere and a component of water. The most common element in Earths atmosphere is nitrogen, and the most common element in Earths crust is oxygen. Click image to the left or use the URL below. URL: An element is a pure substance. It cannot be separated into any other substances. There are more than 90 different elements that occur in nature. Some are much more common than others. Hydrogen is the most common element in the universe. Oxygen is the most common element in Earths crust. Figure 3.7 shows other examples of elements. Still others are described in the video below. MEDIA Click image to the left or use the URL below. URL: Native elements contain only atoms of one type of element. They are not combined with other elements. There are very few examples of these types of minerals. Some native elements are rare and valuable. Gold, silver, sulfur, and diamond are examples.

The crystal shape of a mineral

(A) shows how the atoms are arranged (B) will always be the same if it is made from the same atoms (C) can usually only be seen under a microscope (D) can help account for how hard or brittle a mineral is

C

Minerals are "crystalline" solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. Notice that in Figure 1.1 the green and purple spheres, representing sodium and chlorine, form a repeating pattern. In this case, they alternate in all directions. Sodium ions (purple balls) bond with chlo- ride ions (green balls) to make table salt (halite). All of the grains of salt that are in a salt shaker have this crystalline structure. The patterns of atoms that make a mineral affect its physical properties. A minerals crystal shape is determined by the way the atoms are arranged. For example, you can see how atoms are arranged in halite in Figure 3.3. You can see how salt crystals look under a microscope in Figure 3.5. Salt crystals are all cubes whether theyre small or large. Other physical properties help scientists identify different minerals. They include: Color: the color of the mineral. Streak: the color of the minerals powder. Luster: the way light reflects off the minerals surface. Specific gravity: how heavy the mineral is relative to the same volume of water. Cleavage: the minerals tendency to break along flat surfaces. Fracture: the pattern in which a mineral breaks. Hardness: what minerals it can scratch and what minerals can scratch it. Cleavage is the tendency of a mineral to break along certain planes. When a mineral breaks along a plane it makes a smooth surface. Minerals with different crystal structures will break or cleave in different ways, as in Figure 3.14. Halite tends to form cubes with smooth surfaces. Mica tends to form sheets. Fluorite can form octahedrons. Minerals can form various shapes. Polygons are shown in Figure 3.15. The shapes form as the minerals are broken along their cleavage planes. Cleavage planes determine how the crystals can be cut to make smooth surfaces. People who cut gemstones follow cleavage planes. Diamonds and emeralds can be cut to make beautiful gemstones.

Some minerals are chemical compounds.

(A) true (B) false

A

All minerals have a definite chemical makeup. A few minerals are made of only one kind of element. Silver is a mineral made only of silver atoms. Diamond and graphite are both made only of the element carbon. Minerals that are not pure elements are made of chemical compounds. For example, the mineral quartz is made of the compound silicon dioxide, or SiO2 . This compound has one atom of the element silicon for every two atoms of the element oxygen. Each mineral has its own unique chemical formula. For example, the mineral hematite has two iron atoms for every three oxygen atoms. The mineral magnetite has three iron atoms for every four oxygen atoms. Many minerals have very complex chemical formulas that include several elements. However, even in more complicated compounds, the elements occur in definite ratios. Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups. A mineral is a solid material that forms by a natural process. A mineral can be made of an element or a compound. It has a specific chemical composition that is different from other minerals. One minerals physical properties differ from others. These properties include crystal structure, hardness, density and color. Each is made of different elements. Each has different physical properties. For example, silver is a soft, shiny metal. Salt is a white, cube- shaped crystal. Diamond is an extremely hard, translucent crystal.

Each mineral has a specific chemical composition.

(A) true (B) false

A

All minerals have a definite chemical makeup. A few minerals are made of only one kind of element. Silver is a mineral made only of silver atoms. Diamond and graphite are both made only of the element carbon. Minerals that are not pure elements are made of chemical compounds. For example, the mineral quartz is made of the compound silicon dioxide, or SiO2 . This compound has one atom of the element silicon for every two atoms of the element oxygen. Each mineral has its own unique chemical formula. For example, the mineral hematite has two iron atoms for every three oxygen atoms. The mineral magnetite has three iron atoms for every four oxygen atoms. Many minerals have very complex chemical formulas that include several elements. However, even in more complicated compounds, the elements occur in definite ratios. Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups. A mineral is a solid material that forms by a natural process. A mineral can be made of an element or a compound. It has a specific chemical composition that is different from other minerals. One minerals physical properties differ from others. These properties include crystal structure, hardness, density and color. Each is made of different elements. Each has different physical properties. For example, silver is a soft, shiny metal. Salt is a white, cube- shaped crystal. Diamond is an extremely hard, translucent crystal.

Minerals are inorganic substances.

(A) true (B) false

A

A mineral is an inorganic substance. It was not made by living organisms. Organic substances contain carbon. Some organic substances are proteins, carbohydrates, and oils. Everything else is inorganic. In a few cases, living organisms make inorganic materials. The calcium carbonate shells made by marine animals are inorganic. To understand minerals, we must first understand matter. Matter is the substance that physical objects are made of. Organic substances are the carbon-based compounds made by living creatures and include proteins, carbohydrates, and oils. Inorganic substances have a structure that is not characteristic of living bodies. Coal is made of plant and animal remains. Is it a mineral? Coal is a classified as a sedimentary rock, but is not a mineral.

A molecule is the smallest unit of an element.

(A) true (B) false

B

The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7. A molecule is the smallest unit of a chemical compound. A compound is a substance made of two or more elements. The elements in a chemical compound are always present in a certain ratio. Water is probably one of the simplest compounds that you know. A water molecule is made of two hydrogen atoms and one oxygen atom (Figure 3.2). All water molecules have the same ratio: two hydrogen atoms to one oxygen atom. The smallest particle of a compound that still has the compounds properties is a molecule. A molecule consists of two or more atoms that are joined together. For example, a molecule of water consists of two hydrogen atoms joined to one oxygen atom (see Figure 3.10). You can learn more about molecules at this link: Some compounds form crystals instead of molecules. A crystal is a rigid, lattice-like framework of many atoms bonded together. Table salt is an example of a compound that forms crystals (see Figure 3.11). Its crystals are made up of many sodium and chloride ions. Ions are electrically charged forms of atoms. You can actually watch crystals forming in this video: .

Table salt is an example of a sulfide mineral.

(A) true (B) false

B

Sulfate minerals contain sulfur atoms bonded to four oxygen atoms, just like silicates and phosphates. Like halides, they form where salt water evaporates. The most common sulfate mineral is probably gypsum (CaSO4 (OH)2 ) (Figure 1.9). Some gigantic 11-meter gypsum crystals have been found (See opening image). That is about as long as a school bus! Gypsum. Sulfate minerals contain sulfur atoms bonded to oxygen atoms. Like halides, they can form in places where salt water evaporates. Many minerals belong in the sulfate group, but there are only a few common sulfate minerals. Gypsum is a common sulfate mineral that contains calcium, sulfate, and water. Gypsum is found in various forms. For example, it can be pink and look like it has flower petals. However, it can also grow into very large white crystals. Gypsum crystals that are 11 meters long have been found. That is about as long as a school bus! Gypsum also forms at the Mammoth Hot Springs in Yellowstone National Park, shown in Figure 3.9. Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt (see Figure bond with various metallic atoms to make halide minerals. All halides are ionic minerals, which means that they are typically soluble in water. Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite. Azurite and malachite are carbonates that contain copper instead of calcium. Beautiful halite crystal.

Protons and electrons are found in the nucleus of an atom.

(A) true (B) false

B

The nucleus (plural, nuclei) is a positively charged region at the center of the atom. It consists of two types of subatomic particles packed tightly together. The particles are protons, which have a positive electric charge, and neutrons, which are neutral in electric charge. Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons whizzing through it. The Figure 1.1 shows these parts of the atom. Unlike protons and neutrons, which are located inside the nucleus at the center of the atom, electrons are found outside the nucleus. Because opposite electric charges attract each other, negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving through the otherwise empty space around the nucleus. The Figure shown 1.1 is a common way to represent the structure of an atom. It shows the electron as a particle orbiting the nucleus, similar to the way that planets orbit the sun. The basic unit of matter is an atom. At the center of an atom is its nucleus. Protons are positively charged particles in the nucleus. Also in the nucleus are neutrons with no electrical charge. Orbiting the nucleus are tiny electrons. Electrons are negatively charged. An atom with the same number of protons and electrons is electrically neutral. If the atom has more or less electrons to protons it is called an ion. An ion will have positive charge if it has more protons than electrons. It will have negative charge if it has more electrons than protons. An atom is the smallest unit of a chemical element. That is, an atom has all the properties of that element. All atoms of the same element have the same number of protons.

Fracture is the tendency of a mineral to break along flat surfaces

(A) true (B) false

B

Fracture describes how a mineral breaks without any pattern. A fracture is uneven. The surface is not smooth and flat. You can learn about a mineral from the way it fractures. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, fracture to form smooth, curved surfaces. A mineral that broke forming a smooth, curved surface is shown in Figure 3.16. Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways. Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite (Figure 1.3) breaks between layers of sodium and chlorine to form cubes with smooth surfaces. Mica has cleavage in one direction and forms sheets (Figure 1.4). Minerals can cleave into polygons. Magnetite forms octahedrons (Figure 1.5). One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral. Minerals may have characteristic fractures (Figure 1.6). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. Sheets of mica. Cleavage is the tendency of a mineral to break along certain planes. When a mineral breaks along a plane it makes a smooth surface. Minerals with different crystal structures will break or cleave in different ways, as in Figure 3.14. Halite tends to form cubes with smooth surfaces. Mica tends to form sheets. Fluorite can form octahedrons. Minerals can form various shapes. Polygons are shown in Figure 3.15. The shapes form as the minerals are broken along their cleavage planes. Cleavage planes determine how the crystals can be cut to make smooth surfaces. People who cut gemstones follow cleavage planes. Diamonds and emeralds can be cut to make beautiful gemstones.

Minerals are classified in groups based on their physical properties.

(A) true (B) false

B

Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups. A mineral is a solid material that forms by a natural process. A mineral can be made of an element or a compound. It has a specific chemical composition that is different from other minerals. One minerals physical properties differ from others. These properties include crystal structure, hardness, density and color. Each is made of different elements. Each has different physical properties. For example, silver is a soft, shiny metal. Salt is a white, cube- shaped crystal. Diamond is an extremely hard, translucent crystal. Minerals are everywhere! Scientists have identified more than 4,000 minerals in Earths crust, although the bulk of the planet is composed of just a few. A mineral possesses the following qualities: It must be solid. It must be crystalline, meaning it has a repeating arrangement of atoms. It must be naturally occurring. It must be inorganic. It must have a specific chemical composition. Minerals can be identified by their physical properties, such as hardness, color, luster (shininess), and odor. The most common laboratory technique used to identify a mineral is X-ray diffraction (XRD), a technique that involves shining an X-ray light on a sample, and observing how the light exiting the sample is bent. XRD is not useful in the field, however. The definition of a mineral is more restricted than you might think at first. For example, glass is made of sand, which is rich in the mineral quartz. But glass is not a mineral, because it is not crystalline. Instead, glass has a random assemblage of molecules. What about steel? Steel is made by mixing different metal minerals like iron, cobalt, chromium, vanadium, and molybdenum, but steel is not a mineral because it is made by humans and therefore is not naturally occurring. However, almost any rock you pick up is composed of minerals. Below we explore the qualities of minerals in more detail.

Halides (salts) make up the largest group of minerals on Earth.

(A) true (B) false

B

Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt (see Figure bond with various metallic atoms to make halide minerals. All halides are ionic minerals, which means that they are typically soluble in water. Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite. Azurite and malachite are carbonates that contain copper instead of calcium. Beautiful halite crystal. Halide minerals are salts. They form when salt water evaporates. This mineral class includes more than just table salt. Halide minerals may contain the elements fluorine, chlorine, bromine, or iodine. Some will combine with metal elements. Common table salt is a halide mineral that contains the elements chlorine and sodium. Fluorite is a type of halide that contains fluorine and calcium. Fluorite can be found in many colors. If you shine an ultraviolet light on fluorite, it will glow! Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups.

Scientists use the physical properties of minerals to identify them.

(A) true (B) false

A

There are a multitude of laboratory and field techniques for identifying minerals. While a mineralogist might use a high-powered microscope to identify some minerals, or even techniques like x-ray diffraction, most are recognizable using physical properties. The most common field techniques put the observer in the shoes of a detective, whose goal it is to determine, by process of elimination, what the mineral in question is. The process of elimination usually includes observing things like color, hardness, smell, solubility in acid, streak, striations and/or cleavage. Check out the mineral in the opening image. What is the minerals color? What is its shape? Are the individual crystals shiny or dull? Are there lines (striations) running across the minerals? In this concept, the properties used to identify minerals are described in more detail. Some minerals can be identified with little more than the naked eye. We do this by examining the physical properties of the mineral in question, which include: Color: the color of the mineral. Streak: the color of the minerals powder (this is often different from the color of the whole mineral). Luster: shininess. Density: mass per volume, typically reported in "specific gravity," which is the density relative to water. Cleavage: the minerals tendency to break along planes of weakness. Fracture: the pattern in which a mineral breaks. Hardness: which minerals it can scratch and which minerals can scratch it. How physical properties are used to identify minerals is described in the concept "Mineral Identification." Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: Minerals have other properties that can be used for identification. For example, a minerals shape may indicate its crystal structure. Sometimes crystals are too small to see. Then a mineralogist may use a special instrument to find the crystal structure. Some minerals have unique properties. These can be used to the minerals. Some of these properties are listed in Table 3.3. An example of a mineral that has each property is also listed. Property Fluorescence Magnetism Radioactivity Reactivity Smell Description Mineral glows under ultraviolet light Mineral is attracted to a magnet Mineral gives off radiation that can be measured with Geiger counter Bubbles form when mineral is ex- posed to a weak acid Some minerals have a distinctive smell Example of Mineral Fluorite Magnetite Uraninite Calcite Sulfur (smells like rotten eggs)

Coal and diamonds are different minerals because they have different structure.

(A) true (B) false

A

Minerals must be solid. For example, ice and water have the same chemical composition. Ice is a solid, so it is a mineral. Water is a liquid, so it is not a mineral. Some solids are not crystals. Glass, or the rock obsidian, are solid but not crystals. In a crystal, the atoms are arranged in a pattern. This pattern is regular and it repeats. Figure 3.3 shows how the atoms are arranged in halite (table salt). Halite contains atoms of sodium and chlorine in a pattern. Notice that the pattern goes in all three dimensions. The pattern of atoms in all halite is the same. Think about all of the grains of salt that are in a salt shaker. The atoms are arranged in the same way in every piece of salt. Sometimes two different minerals have the same chemical composition. But they are different minerals because they have different crystal structures. Diamonds are beautiful gemstones because they are very pretty and very hard. Graphite is the lead in pencils. Its not hard at all! Amazingly, both are made just of carbon. Compare the diamond with the pencil lead in Figure 3.4. Why are they so different? The carbon atoms in graphite bond to form layers. The bonds between each layer are weak. The carbon sheets can just slip past each other. The carbon atoms in diamonds bond together in all three directions. This strong network makes diamonds very hard. Diamonds have many valuable properties. Diamonds are extremely hard and are used for industrial purposes. The most valuable diamonds are large, well-shaped and sparkly. Turquoise is another mineral that is used in jewelry because of its striking greenish-blue color. Many minerals have interesting appearances. Specific terms are used to describe the appearance of minerals. Minerals are made by natural processes, those that occur in or on Earth. A diamond created deep in Earths crust is a mineral, but a diamond made in a laboratory by humans is not. Be careful about buying a laboratory-made diamond for jewelry. It may look pretty, but its not a diamond and is not technically a mineral.

In a crystal, the atoms are arranged in a pattern.

(A) true (B) false

A

Minerals are "crystalline" solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. Notice that in Figure 1.1 the green and purple spheres, representing sodium and chlorine, form a repeating pattern. In this case, they alternate in all directions. Sodium ions (purple balls) bond with chlo- ride ions (green balls) to make table salt (halite). All of the grains of salt that are in a salt shaker have this crystalline structure. Minerals must be solid. For example, ice and water have the same chemical composition. Ice is a solid, so it is a mineral. Water is a liquid, so it is not a mineral. Some solids are not crystals. Glass, or the rock obsidian, are solid but not crystals. In a crystal, the atoms are arranged in a pattern. This pattern is regular and it repeats. Figure 3.3 shows how the atoms are arranged in halite (table salt). Halite contains atoms of sodium and chlorine in a pattern. Notice that the pattern goes in all three dimensions. The pattern of atoms in all halite is the same. Think about all of the grains of salt that are in a salt shaker. The atoms are arranged in the same way in every piece of salt. Sometimes two different minerals have the same chemical composition. But they are different minerals because they have different crystal structures. Diamonds are beautiful gemstones because they are very pretty and very hard. Graphite is the lead in pencils. Its not hard at all! Amazingly, both are made just of carbon. Compare the diamond with the pencil lead in Figure 3.4. Why are they so different? The carbon atoms in graphite bond to form layers. The bonds between each layer are weak. The carbon sheets can just slip past each other. The carbon atoms in diamonds bond together in all three directions. This strong network makes diamonds very hard. Different types of minerals break apart in their own way. Remember that all minerals are crystals. This means that the atoms in a mineral are arranged in a repeating pattern. This pattern determines how a mineral will break. When you break a mineral, you break chemical bonds. Because of the way the atoms are arranged, some bonds are weaker than other bonds. A mineral is more likely to break where the bonds between the atoms are weaker.

There are only 40 known minerals.

(A) true (B) false

B

Native elements contain only atoms of one type of element. They are not combined with other elements. There are very few examples of these types of minerals. Some native elements are rare and valuable. Gold, silver, sulfur, and diamond are examples. All known matter can be divided into a little more than 100 different substances called elements. Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups.

The largest mineral group is called the native elements.

(A) true (B) false

B

Native elements contain atoms of only one type of element. Only a small number of minerals are found in this category. Some of the minerals in this group are rare and valuable. Gold (Figure 1.3), silver, sulfur, and diamond are examples of native elements. Native elements contain only atoms of one type of element. They are not combined with other elements. There are very few examples of these types of minerals. Some native elements are rare and valuable. Gold, silver, sulfur, and diamond are examples. Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups.

Minerals with similar crystal structures are grouped together.

(A) true (B) false

A

Minerals are divided into groups based on chemical composition. Most minerals fit into one of eight mineral groups. Minerals are "crystalline" solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. Notice that in Figure 1.1 the green and purple spheres, representing sodium and chlorine, form a repeating pattern. In this case, they alternate in all directions. Sodium ions (purple balls) bond with chlo- ride ions (green balls) to make table salt (halite). All of the grains of salt that are in a salt shaker have this crystalline structure. Imagine you are in charge of organizing more than 100 minerals for a museum exhibit. People can learn a lot more if they see the minerals together in groups. How would you group the minerals together in your exhibit? Mineralogists are scientists who study minerals. They divide minerals into groups based on chemical composition. Even though there are over 4,000 minerals, most minerals fit into one of eight mineral groups. Minerals with similar crystal structures are grouped together.

atom that has become electrically charged by gaining or losing electron(s)

(A) atom (B) electron (C) ion (D) molecule (E) neutron (F) nucleus (G) proton

C

Atoms cannot only gain extra electrons. They can also lose electrons. In either case, they become ions. Ions are atoms that have a positive or negative charge because they have unequal numbers of protons and electrons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine (see Figure 1.1). A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with an electric charge of -1. The girl pictured above became negatively charged because electrons flowed from the van de Graaff generator to her. Whenever electrons are transferred between objects, neutral matter becomes charged. This occurs even with individual atoms. Atoms are neutral in electric charge because they have the same number of negative electrons as positive protons. However, if atoms lose or gain electrons, they become charged particles called ions. You can see how this happens in the Figure 1.1. When an atom loses electrons, it becomes a positively charged ion, or cation. When an atom gains electrons, it becomes a negative charged ion, or anion. Sometimes atoms lose or gain electrons. Then they become ions. Ions have a positive or negative charge. Thats because they do not have the same number of electrons as protons. If atoms lose electrons, they become positive ions, or cations. If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine in Figure 5.5. A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with a negative charge of minus one.

positively charged particle in the nucleus of an atom

(A) atom (B) electron (C) ion (D) molecule (E) neutron (F) nucleus (G) proton

G

The nucleus (plural, nuclei) is a positively charged region at the center of the atom. It consists of two types of subatomic particles packed tightly together. The particles are protons, which have a positive electric charge, and neutrons, which are neutral in electric charge. Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons whizzing through it. The Figure 1.1 shows these parts of the atom. An electron is a particle outside the nucleus of an atom that has a negative electric charge. The charge of an electron is opposite but equal to the charge of a proton. Atoms have the same number of electrons as protons. As a result, the negative and positive charges "cancel out." This makes atoms electrically neutral. For example, a carbon atom has six electrons that "cancel out" its six protons. A neutron is a particle inside the nucleus of an atom. It has no electric charge. Atoms of an element often have the same number of neutrons as protons. For example, most carbon atoms have six neutrons as well as six protons. This is also shown in Figure below .

smallest particle of an element that has all the elements properties

(A) atom (B) electron (C) ion (D) molecule (E) neutron (F) nucleus (G) proton

A

The smallest particle of an element that still has the elements properties is an atom. All the atoms of an element are alike, and they are different from the atoms of all other elements. For example, atoms of gold are the same whether they are found in a gold nugget or a gold ring (see Figure 3.8). All gold atoms have the same structure and properties. The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7. The smallest particle of a compound that still has the compounds properties is a molecule. A molecule consists of two or more atoms that are joined together. For example, a molecule of water consists of two hydrogen atoms joined to one oxygen atom (see Figure 3.10). You can learn more about molecules at this link: Some compounds form crystals instead of molecules. A crystal is a rigid, lattice-like framework of many atoms bonded together. Table salt is an example of a compound that forms crystals (see Figure 3.11). Its crystals are made up of many sodium and chloride ions. Ions are electrically charged forms of atoms. You can actually watch crystals forming in this video: .

center of an atom consisting of protons and neutrons

(A) atom (B) electron (C) ion (D) molecule (E) neutron (F) nucleus (G) proton

F

The nucleus (plural, nuclei) is a positively charged region at the center of the atom. It consists of two types of subatomic particles packed tightly together. The particles are protons, which have a positive electric charge, and neutrons, which are neutral in electric charge. Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons whizzing through it. The Figure 1.1 shows these parts of the atom. At the center of an atom is the nucleus (plural, nuclei). The nucleus contains most of the atoms mass. However, in size, its just a tiny part of the atom. The model in Figure 5.1 is not to scale. If an atom were the size of a football stadium, the nucleus would be only about the size of a pea. The nucleus, in turn, consists of two types of particles, called protons and neutrons. These particles are tightly packed inside the nucleus. Constantly moving about the nucleus are other particles called electrons. You can see a video about all three types of atomic particles at this URL: (1:57). At the center of an atom is the nucleus (plural, nuclei). The nucleus contains most of the atoms mass. However, in size, its just a tiny part of the atom. The model in Figure above is not to scale. If an atom were the size of a football stadium, the nucleus would be only about the size of a pea. The nucleus, in turn, consists of two types of particles, called protons and neutrons. These particles are tightly packed inside the nucleus. Constantly moving about the nucleus are other particles called electrons.

negatively charged particle that orbits the nucleus of an atom

(A) atom (B) electron (C) ion (D) molecule (E) neutron (F) nucleus (G) proton

B

An electron is a particle outside the nucleus of an atom that has a negative electric charge. The charge of an electron is opposite but equal to the charge of a proton. Atoms have the same number of electrons as protons. As a result, the negative and positive charges "cancel out." This makes atoms electrically neutral. For example, a carbon atom has six electrons that "cancel out" its six protons. An electron is a particle outside the nucleus of an atom. It has a negative electric charge. The charge of an electron is opposite but equal to the charge of a proton. Atoms have the same number of electrons as protons. As a result, the negative and positive charges "cancel out." This makes atoms electrically neutral. For example, a carbon atom has six electrons that "cancel out" its six protons. The nucleus (plural, nuclei) is a positively charged region at the center of the atom. It consists of two types of subatomic particles packed tightly together. The particles are protons, which have a positive electric charge, and neutrons, which are neutral in electric charge. Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons whizzing through it. The Figure 1.1 shows these parts of the atom.

smallest possible particle of a chemical compound

(A) atom (B) electron (C) ion (D) molecule (E) neutron (F) nucleus (G) proton

D

The smallest particle of an element that still has the properties of that element is an atom. Atoms are extremely tiny. They can be observed only with an electron microscope. They are commonly represented by models, like the one Figure 2.6. An atom has a central nucleus that is positive in charge. The nucleus is surrounded by negatively charged particles called electrons. The smallest particle of a compound that still has the properties of that compound is a molecule. A molecule consists of two or more atoms. For example, a molecule of water consists of two atoms of hydrogen and one atom of oxygen. Thats why the chemical formula for water is H2 O. You can see a simple model of a water molecule in Figure 2.7. The smallest particle of a compound that still has the compounds properties is a molecule. A molecule consists of two or more atoms that are joined together. For example, a molecule of water consists of two hydrogen atoms joined to one oxygen atom (see Figure 3.10). You can learn more about molecules at this link: Some compounds form crystals instead of molecules. A crystal is a rigid, lattice-like framework of many atoms bonded together. Table salt is an example of a compound that forms crystals (see Figure 3.11). Its crystals are made up of many sodium and chloride ions. Ions are electrically charged forms of atoms. You can actually watch crystals forming in this video: . The smallest particle of an element that still has the elements properties is an atom. All the atoms of an element are alike, and they are different from the atoms of all other elements. For example, atoms of gold are the same whether they are found in a gold nugget or a gold ring (see Figure 3.8). All gold atoms have the same structure and properties.

uncharged particle in the nucleus of an atom

(A) atom (B) electron (C) ion (D) molecule (E) neutron (F) nucleus (G) proton

E

A neutron is a particle in the nucleus of an atom that has no electric charge. Atoms of an element often have the same number of neutrons as protons. For example, most carbon atoms have six neutrons as well as six protons. This is also shown in Figure 5.2. A neutron is a particle inside the nucleus of an atom. It has no electric charge. Atoms of an element often have the same number of neutrons as protons. For example, most carbon atoms have six neutrons as well as six protons. This is also shown in Figure below . The nucleus (plural, nuclei) is a positively charged region at the center of the atom. It consists of two types of subatomic particles packed tightly together. The particles are protons, which have a positive electric charge, and neutrons, which are neutral in electric charge. Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons whizzing through it. The Figure 1.1 shows these parts of the atom.

Examples of minerals include

(A) silver (B) table salt (C) quartz (D) all of the above

D

Metals and gemstones are often shiny, so they catch your eye. Many minerals that we use everyday are not so noticeable. For example, the buildings on your block could not have been built without minerals. The walls in your home might use the mineral gypsum for the sheetrock. The glass in your windows is made from sand, which is mostly the mineral quartz. Talc was once commonly used to make baby powder. The mineral halite is mined for rock salt. Diamond is commonly used in drill bits and saw blades to improve their cutting ability. Copper is used in electrical wiring, and the ore bauxite is the source for the aluminum in your soda can. Native elements contain only atoms of one type of element. They are not combined with other elements. There are very few examples of these types of minerals. Some native elements are rare and valuable. Gold, silver, sulfur, and diamond are examples. Native elements contain atoms of only one type of element. Only a small number of minerals are found in this category. Some of the minerals in this group are rare and valuable. Gold (Figure 1.3), silver, sulfur, and diamond are examples of native elements.

All minerals

(A) have a definite chemical makeup (B) are pure elements (C) form crystals (D) contain carbon

A

All minerals have a definite chemical makeup. A few minerals are made of only one kind of element. Silver is a mineral made only of silver atoms. Diamond and graphite are both made only of the element carbon. Minerals that are not pure elements are made of chemical compounds. For example, the mineral quartz is made of the compound silicon dioxide, or SiO2 . This compound has one atom of the element silicon for every two atoms of the element oxygen. Each mineral has its own unique chemical formula. For example, the mineral hematite has two iron atoms for every three oxygen atoms. The mineral magnetite has three iron atoms for every four oxygen atoms. Many minerals have very complex chemical formulas that include several elements. However, even in more complicated compounds, the elements occur in definite ratios. Metals and gemstones are often shiny, so they catch your eye. Many minerals that we use everyday are not so noticeable. For example, the buildings on your block could not have been built without minerals. The walls in your home might use the mineral gypsum for the sheetrock. The glass in your windows is made from sand, which is mostly the mineral quartz. Talc was once commonly used to make baby powder. The mineral halite is mined for rock salt. Diamond is commonly used in drill bits and saw blades to improve their cutting ability. Copper is used in electrical wiring, and the ore bauxite is the source for the aluminum in your soda can. Nearly all (98.5%) of Earths crust is made up of only eight elements - oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium - and these are the elements that make up most minerals. All minerals have a specific chemical composition. The mineral silver is made up of only silver atoms and diamond is made only of carbon atoms, but most minerals are made up of chemical compounds. Each mineral has its own chemical formula. Table salt (also known as halite), pictured in Figure 1.1, is NaCl (sodium chloride). Quartz is always made of two oxygen atoms (red) bonded to a silicon atom (grey), represented by the chemical formula SiO2 (Figure 1.2). Quartz is made of two oxygen atoms (red) bonded to a silicon atom (grey). In nature, things are rarely as simple as in the lab, and so it should not come as a surprise that some minerals have a range of chemical compositions. One important example in Earth science is olivine, which always has silicon and oxygen as well as some iron and magnesium, (Mg, Fe)2 SiO4 .

Minerals may form when

(A) rocks are heated to high temperatures (B) rocks are exposed to high pressure (C) lava cools and hardens (D) all of the above

D

Minerals form in a variety of ways: crystallization from magma precipitation from ions in solution biological activity a change to a more stable state as in metamorphism precipitation from vapor Most minerals form at high pressure or high temperatures deep in the crust, or sometimes in the mantle. When these rocks are uplifed onto Earths surface, they are at very low temperatures and pressures. This is a very different environment from the one in which they formed and the minerals are no longer stable. In chemical weathering, minerals that were stable inside the crust must change to minerals that are stable at Earths surface. Magma heats nearby underground water, which reacts with the rocks around it to pick up dissolved particles. As the water flows through open spaces in the rock and cools, it deposits solid minerals. The mineral deposits that form when a mineral fills cracks in rocks are called veins (Figure 1.4). Quartz veins formed in this rock. When minerals are deposited in open spaces, large crystals form (Figure 1.5). Amethyst formed when large crystals grew in open spaces inside the rock. These special rocks are called geodes.

The color of a minerals powder is its

(A) streak (B) luster (C) color (D) cleavage

A

Color is probably the easiest property to observe. Unfortunately, you can rarely identify a mineral only by its color. Sometimes, different minerals are the same color. For example, you might find a mineral that is a gold color, and so think it is gold. But it might actually be pyrite, or fools gold, which is made of iron and sulfide. It contains no gold atoms. A certain mineral may form in different colors. Figure 3.11 shows four samples of quartz, including one that is colorless and one that is purple. The purple color comes from a tiny amount of iron. The iron in quartz is a chemical impurity. Iron is not normally found in quartz. Many minerals are colored by chemical impurities. Other factors can also affect a minerals color. Weathering changes the surface of a mineral. Because color alone is unreliable, geologists rarely identify a mineral just on its color. To identify most minerals, they use several properties. Streak is the color of a minerals powder, which often is not the same color as the mineral itself. Many minerals, such as the quartz in the Figure 1.1, do not have streak. Hematite is an example of a mineral that displays a certain color in hand sample (typically black to steel gray, sometimes reddish), and a different streak color (red/brown). Color may be the first feature you notice about a mineral, but color is not often important for mineral identification. For example, quartz can be colorless, purple (amethyst), or a variety of other colors depending on chemical impurities Figure 1.1.

The mineral gypsum is a common

(A) sulfide (B) sulfate (C) carbonate (D) silicate

B

Sulfate minerals contain sulfur atoms bonded to oxygen atoms. Like halides, they can form in places where salt water evaporates. Many minerals belong in the sulfate group, but there are only a few common sulfate minerals. Gypsum is a common sulfate mineral that contains calcium, sulfate, and water. Gypsum is found in various forms. For example, it can be pink and look like it has flower petals. However, it can also grow into very large white crystals. Gypsum crystals that are 11 meters long have been found. That is about as long as a school bus! Gypsum also forms at the Mammoth Hot Springs in Yellowstone National Park, shown in Figure 3.9. Sulfate minerals contain sulfur atoms bonded to four oxygen atoms, just like silicates and phosphates. Like halides, they form where salt water evaporates. The most common sulfate mineral is probably gypsum (CaSO4 (OH)2 ) (Figure 1.9). Some gigantic 11-meter gypsum crystals have been found (See opening image). That is about as long as a school bus! Gypsum. Metals and gemstones are often shiny, so they catch your eye. Many minerals that we use everyday are not so noticeable. For example, the buildings on your block could not have been built without minerals. The walls in your home might use the mineral gypsum for the sheetrock. The glass in your windows is made from sand, which is mostly the mineral quartz. Talc was once commonly used to make baby powder. The mineral halite is mined for rock salt. Diamond is commonly used in drill bits and saw blades to improve their cutting ability. Copper is used in electrical wiring, and the ore bauxite is the source for the aluminum in your soda can.

Minerals known as salts are classified as

(A) oxides (B) phosphates (C) halides (D) silicates

C

Minerals are "crystalline" solids. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. Notice that in Figure 1.1 the green and purple spheres, representing sodium and chlorine, form a repeating pattern. In this case, they alternate in all directions. Sodium ions (purple balls) bond with chlo- ride ions (green balls) to make table salt (halite). All of the grains of salt that are in a salt shaker have this crystalline structure. Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral, but table salt (see Figure bond with various metallic atoms to make halide minerals. All halides are ionic minerals, which means that they are typically soluble in water. Two carbonate minerals: (a) deep blue azurite and (b) opaque green malachite. Azurite and malachite are carbonates that contain copper instead of calcium. Beautiful halite crystal. Halide minerals are salts. They form when salt water evaporates. This mineral class includes more than just table salt. Halide minerals may contain the elements fluorine, chlorine, bromine, or iodine. Some will combine with metal elements. Common table salt is a halide mineral that contains the elements chlorine and sodium. Fluorite is a type of halide that contains fluorine and calcium. Fluorite can be found in many colors. If you shine an ultraviolet light on fluorite, it will glow!

Oxides include

(A) hematite (B) feldspar (C) calcite (D) none of the above

A

Oxides contain one or two metal elements combined with oxygen. Many important metal ores are oxides. Hematite (Fe2 O3 ), with two iron atoms to three oxygen atoms, and magnetite (Fe3 O4 ) (Figure 1.7), with three iron atoms to four oxygen atoms, are both iron oxides. Magnetite is one of the most distinctive oxides since it is magnetic. Earths crust contains a lot of oxygen. The oxygen combines with many other elements to create oxide minerals. Oxides contain one or two metal elements combined with oxygen. Oxides are different from silicates because they do not contain silicon. Many important metals are found as oxides. For example, hematite and magnetite are both oxides that contain iron. Hematite (Fe2 O3 ) has a ratio of two iron atoms to three oxygen atoms. Magnetite (Fe3 O4 ) has a ratio of three iron atoms to four oxygen atoms. Notice that the word magnetite contains the word magnet. Magnetite is a magnetic mineral. Oxidation is a chemical reaction that takes place when oxygen reacts with another element. Oxygen is very strongly chemically reactive. The most familiar type of oxidation is when iron reacts with oxygen to create rust (Figure 1.4). Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide produces the red color in soils.

amount of mass per unit volume of a substance

(A) cleavage (B) fluorescence (C) density (D) fracture (E) hardness (F) luster (G) streak

C

Mass is the amount of matter in a substance or object. Mass is commonly measured with a balance. A simple mechanical balance is shown in Figure 3.1. It allows an object to be matched with other objects of known mass. SI units for mass are the kilogram, but for smaller masses grams are often used instead. Density is an important physical property of matter. It reflects how closely packed the particles of matter are. Density is calculated from the amount of mass in a given volume of matter, using the formula: Density (D) = Mass (M) Volume (V ) Problem Solving Problem: What is the density of a substance that has a mass of 20 g and a volume of 10 mL? Solution: D = 20 g/10 mL = 2.0 g/mL You Try It! Problem: An object has a mass of 180 kg and a volume of 90 m3 . What is its density? To better understand density, think about a bowling ball and a volleyball. The bowling ball feels heavy. It is solid all the way through. It contains a lot of tightly packed particles of matter. In contrast, the volleyball feels light. It is full of air. It contains fewer, more widely spaced particles of matter. Both balls have about the same volume, but the bowling ball has a much greater mass. Its matter is denser. The density of matter is actually the amount of matter in a given space. The amount of matter is measured by its mass. The space matter takes up is measured by its volume. Therefore, the density of matter can be calculated with this formula: Density = mass volume Assume, for example, that a book has a mass of 500 g and a volume of 1000 cm3 . Then the density of the book is: Density = 500 g = 0.5 g/cm3 1000 cm3 Q: What is the density of a liquid that has a volume of 30 mL and a mass of 300 g? A: The density of the liquid is: Density = 300 g = 10 g/mL 30 mL

If the volume of a mineral is 6 and the mass is 3, what is its density?

(A) 6 (B) 3 (C) 2 (D) 5

D

The density of matter is actually the amount of matter in a given space. The amount of matter is measured by its mass. The space matter takes up is measured by its volume. Therefore, the density of matter can be calculated with this formula: Density = mass volume Assume, for example, that a book has a mass of 500 g and a volume of 1000 cm3 . Then the density of the book is: Density = 500 g = 0.5 g/cm3 1000 cm3 Q: What is the density of a liquid that has a volume of 30 mL and a mass of 300 g? A: The density of the liquid is: Density = 300 g = 10 g/mL 30 mL The density of matter is actually the amount of matter in a given space. The amount of matter is measured by its mass, and the space matter takes up is measured by its volume. Therefore, the density of matter can be calculated with this formula: Density = mass volume Assume, for example, that a book has a mass of 500 g and a volume of 1000 cm3 . Then the density of the book is: Density = 500 g = 0.5 g/cm3 1000 cm3 Q: What is the density of a liquid that has a volume of 30 mL and a mass of 300 g? A: The density of the liquid is: Density = 300 g = 10 g/mL 30 mL Density is an important physical property of matter. It reflects how closely packed the particles of matter are. Density is calculated from the amount of mass in a given volume of matter, using the formula: Density (D) = Mass (M) Volume (V ) Problem Solving Problem: What is the density of a substance that has a mass of 20 g and a volume of 10 mL? Solution: D = 20 g/10 mL = 2.0 g/mL You Try It! Problem: An object has a mass of 180 kg and a volume of 90 m3 . What is its density? To better understand density, think about a bowling ball and a volleyball. The bowling ball feels heavy. It is solid all the way through. It contains a lot of tightly packed particles of matter. In contrast, the volleyball feels light. It is full of air. It contains fewer, more widely spaced particles of matter. Both balls have about the same volume, but the bowling ball has a much greater mass. Its matter is denser.

how a mineral breaks when it does not break along a plane

(A) cleavage (B) fluorescence (C) density (D) fracture (E) hardness (F) luster (G) streak

D

Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways. Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite (Figure 1.3) breaks between layers of sodium and chlorine to form cubes with smooth surfaces. Mica has cleavage in one direction and forms sheets (Figure 1.4). Minerals can cleave into polygons. Magnetite forms octahedrons (Figure 1.5). One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral. Minerals may have characteristic fractures (Figure 1.6). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. Sheets of mica. Fracture describes how a mineral breaks without any pattern. A fracture is uneven. The surface is not smooth and flat. You can learn about a mineral from the way it fractures. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, fracture to form smooth, curved surfaces. A mineral that broke forming a smooth, curved surface is shown in Figure 3.16. Cleavage is the tendency of a mineral to break along certain planes. When a mineral breaks along a plane it makes a smooth surface. Minerals with different crystal structures will break or cleave in different ways, as in Figure 3.14. Halite tends to form cubes with smooth surfaces. Mica tends to form sheets. Fluorite can form octahedrons. Minerals can form various shapes. Polygons are shown in Figure 3.15. The shapes form as the minerals are broken along their cleavage planes. Cleavage planes determine how the crystals can be cut to make smooth surfaces. People who cut gemstones follow cleavage planes. Diamonds and emeralds can be cut to make beautiful gemstones.

The streak of a mineral is

(A) the same as the color of the mineral (B) never the same color of the mineral (C) the same even when the same mineral is found in various colors (D) either black or white

C

Streak is the color of the powder of a mineral. To do a streak test, you scrape the mineral across an unglazed porcelain plate. The plate is harder than many minerals, causing the minerals to leave a streak of powder on the plate. The color of the streak often differs from the color of the larger mineral sample, as Figure 3.12 shows. Streak is more reliable than color to identify minerals. The color of a mineral may vary. Streak does not vary. Also, different minerals may be the same color, but they may have a different color streak. For example, samples of hematite and galena can both be dark gray. They can be told apart because hematite has a red streak and galena has a gray streak. Streak is the color of a minerals powder, which often is not the same color as the mineral itself. Many minerals, such as the quartz in the Figure 1.1, do not have streak. Hematite is an example of a mineral that displays a certain color in hand sample (typically black to steel gray, sometimes reddish), and a different streak color (red/brown). Luster describes the reflection of light off a minerals surface. Mineralogists have special terms to describe luster. One simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such as pyrite, have a metallic luster. Minerals such as quartz have a non-metallic luster. Different types of non-metallic luster are described in Table 1.1. Luster Adamantine Earthy Pearly Resinous Silky Vitreous Appearance Sparkly Dull, clay-like Pearl-like Like resins, such as tree sap Soft-looking with long fibers Glassy The streak of hematite across an unglazed porcelain plate is red-brown.

color of the powder of a mineral

(A) cleavage (B) fluorescence (C) density (D) fracture (E) hardness (F) luster (G) streak

G

Streak is the color of the powder of a mineral. To do a streak test, you scrape the mineral across an unglazed porcelain plate. The plate is harder than many minerals, causing the minerals to leave a streak of powder on the plate. The color of the streak often differs from the color of the larger mineral sample, as Figure 3.12 shows. Streak is more reliable than color to identify minerals. The color of a mineral may vary. Streak does not vary. Also, different minerals may be the same color, but they may have a different color streak. For example, samples of hematite and galena can both be dark gray. They can be told apart because hematite has a red streak and galena has a gray streak. Streak is the color of a minerals powder, which often is not the same color as the mineral itself. Many minerals, such as the quartz in the Figure 1.1, do not have streak. Hematite is an example of a mineral that displays a certain color in hand sample (typically black to steel gray, sometimes reddish), and a different streak color (red/brown). Color may be the first feature you notice about a mineral, but color is not often important for mineral identification. For example, quartz can be colorless, purple (amethyst), or a variety of other colors depending on chemical impurities Figure 1.1.

Which of the following is NOT a property used to identify a mineral?

(A) radioactivity (B) cleavage (C) reactivity (D) number of electrons

D

Minerals have other properties that can be used for identification. For example, a minerals shape may indicate its crystal structure. Sometimes crystals are too small to see. Then a mineralogist may use a special instrument to find the crystal structure. Some minerals have unique properties. These can be used to the minerals. Some of these properties are listed in Table 3.3. An example of a mineral that has each property is also listed. Property Fluorescence Magnetism Radioactivity Reactivity Smell Description Mineral glows under ultraviolet light Mineral is attracted to a magnet Mineral gives off radiation that can be measured with Geiger counter Bubbles form when mineral is ex- posed to a weak acid Some minerals have a distinctive smell Example of Mineral Fluorite Magnetite Uraninite Calcite Sulfur (smells like rotten eggs) Some minerals can be identified with little more than the naked eye. We do this by examining the physical properties of the mineral in question, which include: Color: the color of the mineral. Streak: the color of the minerals powder (this is often different from the color of the whole mineral). Luster: shininess. Density: mass per volume, typically reported in "specific gravity," which is the density relative to water. Cleavage: the minerals tendency to break along planes of weakness. Fracture: the pattern in which a mineral breaks. Hardness: which minerals it can scratch and which minerals can scratch it. How physical properties are used to identify minerals is described in the concept "Mineral Identification." Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: There are a multitude of laboratory and field techniques for identifying minerals. While a mineralogist might use a high-powered microscope to identify some minerals, or even techniques like x-ray diffraction, most are recognizable using physical properties. The most common field techniques put the observer in the shoes of a detective, whose goal it is to determine, by process of elimination, what the mineral in question is. The process of elimination usually includes observing things like color, hardness, smell, solubility in acid, streak, striations and/or cleavage. Check out the mineral in the opening image. What is the minerals color? What is its shape? Are the individual crystals shiny or dull? Are there lines (striations) running across the minerals? In this concept, the properties used to identify minerals are described in more detail.

Mass is

(A) how much space an object takes up (B) the amount of matter in an object (C) how much matter takes up a certain amount of space (D) the weight of an object

B

Mass is the amount of matter in a substance or object. Mass is commonly measured with a balance. A simple mechanical balance is shown in Figure 3.1. It allows an object to be matched with other objects of known mass. SI units for mass are the kilogram, but for smaller masses grams are often used instead. Mass is often confused with weight. The two are closely related, but they are not the same. Mass is the amount of matter. Weight is a measure of the force of gravity acting on the mass. On Earth, the force of gravity is constant. If we are comparing objects on Earth, objects with a greater mass also have a greater weight. Weight is measured with a device called a scale. Remember, mass is measured with a balance. You might find an example of a scale in your kitchen or bathroom. Scales detect how forcefully objects are being pulled downward by gravity. The SI unit for weight is the newton (N). A mass of 10 kg has a weight of 100 newtons (N). Mass is a measure of the amount of matter in a substance or an object. The basic SI unit for mass is the kilogram (kg), but smaller masses may be measured in grams (g). To measure mass, you would use a balance. In the lab, mass may be measured with a triple beam balance or an electronic balance, but the old-fashioned balance pictured below may give you a better idea of what mass is. If both sides of this balance were at the same level, it would mean that the fruit in the left pan has the same mass as the iron object in the right pan. In that case, the fruit would have a mass of 1 kg, the same as the iron. As you can see, however, the fruit is at a higher level than the iron. This means that the fruit has less mass than the iron, that is, the fruits mass is less than 1 kg. Q: If the fruit were at a lower level than the iron object, what would be the mass of the fruit? A: The mass of the fruit would be greater than 1 kg. Mass is commonly confused with weight. The two are closely related, but they measure different things. Whereas mass measures the amount of matter in an object, weight measures the force of gravity acting on an object. The force of gravity on an object depends on its mass but also on the strength of gravity. If the strength of gravity is held constant (as it is all over Earth), then an object with a greater mass also has a greater weight. Q: With Earths gravity, an object with a mass of 1 kg has a weight of 2.2 lb. How much does a 10 kg object weigh on Earth? A: A 10 kg object weighs ten times as much as a 1 kg object: 10 2.2 lb = 22 lb

tendency of a mineral to break along certain planes

(A) cleavage (B) fluorescence (C) density (D) fracture (E) hardness (F) luster (G) streak

A

Cleavage is the tendency of a mineral to break along certain planes. When a mineral breaks along a plane it makes a smooth surface. Minerals with different crystal structures will break or cleave in different ways, as in Figure 3.14. Halite tends to form cubes with smooth surfaces. Mica tends to form sheets. Fluorite can form octahedrons. Minerals can form various shapes. Polygons are shown in Figure 3.15. The shapes form as the minerals are broken along their cleavage planes. Cleavage planes determine how the crystals can be cut to make smooth surfaces. People who cut gemstones follow cleavage planes. Diamonds and emeralds can be cut to make beautiful gemstones. Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals break apart in characteristic ways. Cleavage is the tendency of a mineral to break along certain planes to make smooth surfaces. Halite (Figure 1.3) breaks between layers of sodium and chlorine to form cubes with smooth surfaces. Mica has cleavage in one direction and forms sheets (Figure 1.4). Minerals can cleave into polygons. Magnetite forms octahedrons (Figure 1.5). One reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with smooth faces. Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral. Minerals may have characteristic fractures (Figure 1.6). Metals usually fracture into jagged edges. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, form smooth curved surfaces when they fracture. Sheets of mica. Fracture describes how a mineral breaks without any pattern. A fracture is uneven. The surface is not smooth and flat. You can learn about a mineral from the way it fractures. If a mineral splinters like wood, it may be fibrous. Some minerals, such as quartz, fracture to form smooth, curved surfaces. A mineral that broke forming a smooth, curved surface is shown in Figure 3.16.

ability of a mineral to resist being scratched

(A) cleavage (B) fluorescence (C) density (D) fracture (E) hardness (F) luster (G) streak

E

Hardness is a minerals ability to resist being scratched. Minerals that are not easily scratched are hard. You test the hardness of a mineral by scratching its surface with a mineral of a known hardness. Mineralogists use the Mohs Hardness Scale, shown in Table 3.2, as a reference for mineral hardness. The scale lists common minerals in order of their relative hardness. You can use the minerals in the scale to test the hardness of an unknown mineral. Hardness is a measure of whether a mineral will scratch or be scratched. Mohs Hardness Scale, shown in Table Hardness 1 2 3 4 5 6 7 8 Mineral Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Hardness 9 10 Mineral Corundum Diamond With a Mohs scale, anyone can test an unknown mineral for its hardness. Imagine you have an unknown mineral. You find that it can scratch fluorite or even apatite, but feldspar scratches it. You know then that the minerals hardness is between 5 and 6. Note that no other mineral can scratch diamond. As you can see, diamond is a 10 on the Mohs Hardness Scale. Diamond is the hardest mineral; no other mineral can scratch a diamond. Quartz is a 7. It can be scratched by topaz, corundum, and diamond. Quartz will scratch minerals that have a lower number on the scale. Fluorite is one. Suppose you had a piece of pure gold. You find that calcite scratches the gold. Gypsum does not. Gypsum has a hardness of 2 and calcite is a 3. That means the hardness of gold is between gypsum and calcite. So the hardness of gold is about 2.5 on the scale. A hardness of 2.5 means that gold is a relatively soft mineral. It is only about as hard as your fingernail. Hardness 1 Mineral Talc

What mineral is number 1 on the Mohs Scale?

(A) talc (B) diamond (C) topaz (D) calcite

A

Hardness is a measure of whether a mineral will scratch or be scratched. Mohs Hardness Scale, shown in Table Hardness 1 2 3 4 5 6 7 8 Mineral Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Hardness 9 10 Mineral Corundum Diamond With a Mohs scale, anyone can test an unknown mineral for its hardness. Imagine you have an unknown mineral. You find that it can scratch fluorite or even apatite, but feldspar scratches it. You know then that the minerals hardness is between 5 and 6. Note that no other mineral can scratch diamond. As you can see, diamond is a 10 on the Mohs Hardness Scale. Diamond is the hardest mineral; no other mineral can scratch a diamond. Quartz is a 7. It can be scratched by topaz, corundum, and diamond. Quartz will scratch minerals that have a lower number on the scale. Fluorite is one. Suppose you had a piece of pure gold. You find that calcite scratches the gold. Gypsum does not. Gypsum has a hardness of 2 and calcite is a 3. That means the hardness of gold is between gypsum and calcite. So the hardness of gold is about 2.5 on the scale. A hardness of 2.5 means that gold is a relatively soft mineral. It is only about as hard as your fingernail. Hardness 1 Mineral Talc Hardness is a minerals ability to resist being scratched. Minerals that are not easily scratched are hard. You test the hardness of a mineral by scratching its surface with a mineral of a known hardness. Mineralogists use the Mohs Hardness Scale, shown in Table 3.2, as a reference for mineral hardness. The scale lists common minerals in order of their relative hardness. You can use the minerals in the scale to test the hardness of an unknown mineral.

ability of a mineral to glow under ultraviolet light

(A) cleavage (B) fluorescence (C) density (D) fracture (E) hardness (F) luster (G) streak

B

Some minerals have other unique properties, some of which are listed in Table 1.3. Can you name a unique property that would allow you to instantly identify a mineral thats been described quite a bit in this concept? (Hint: It is most likely found on your dinner table.) Chrysotile has splintery fracture. Property Fluorescence Magnetism Radioactivity Reactivity Smell Taste Description Mineral glows under ultraviolet light Mineral is attracted to a magnet Mineral gives off radiation that can be measured with Geiger counter Bubbles form when mineral is ex- posed to a weak acid Some minerals have a distinctive smell Some minerals taste salty Example of Mineral Fluorite Magnetite Uraninite Calcite Sulfur (smells like rotten eggs) Halite Some objects produce light without becoming very hot. They generate light through chemical reactions or other processes. Producing light without heat is called luminescence. Luminescence, in turn, can occur in several different ways: One type of luminescence is called fluorescence. In this process, a substance absorbs shorter-wavelength ultraviolet light and then gives off light in the visible range of wavelengths. Certain minerals produce light in this way, including gemstones such as amethyst, diamond, and emerald. Another type of luminescence is called electroluminescence. In this process, a substance gives off light when an electric current passes through it. Gases such as neon, argon, and krypton produce light by this means. The car dash lights in the Figure 1.2 are produced by electroluminescence. A third type of luminescence is called bioluminescence. This is the production of light by living things as a result of chemical reactions. The jellyfish in the opening photo above produces light by bioluminescence. So does the firefly in the Figure 1.3. Fireflies give off visible light to attract mates. Minerals have other properties that can be used for identification. For example, a minerals shape may indicate its crystal structure. Sometimes crystals are too small to see. Then a mineralogist may use a special instrument to find the crystal structure. Some minerals have unique properties. These can be used to the minerals. Some of these properties are listed in Table 3.3. An example of a mineral that has each property is also listed. Property Fluorescence Magnetism Radioactivity Reactivity Smell Description Mineral glows under ultraviolet light Mineral is attracted to a magnet Mineral gives off radiation that can be measured with Geiger counter Bubbles form when mineral is ex- posed to a weak acid Some minerals have a distinctive smell Example of Mineral Fluorite Magnetite Uraninite Calcite Sulfur (smells like rotten eggs)

how light reflects off the surface of a mineral

(A) cleavage (B) fluorescence (C) density (D) fracture (E) hardness (F) luster (G) streak

F

Luster describes the reflection of light off a minerals surface. Mineralogists have special terms to describe luster. One simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such as pyrite, have a metallic luster. Minerals such as quartz have a non-metallic luster. Different types of non-metallic luster are described in Table 1.1. Luster Adamantine Earthy Pearly Resinous Silky Vitreous Appearance Sparkly Dull, clay-like Pearl-like Like resins, such as tree sap Soft-looking with long fibers Glassy The streak of hematite across an unglazed porcelain plate is red-brown. Luster describes the way light reflects off of the surface of the mineral. You might describe diamonds as sparkly or pyrite as shiny. But mineralogists have special terms to describe luster. They first divide minerals into metallic and non-metallic luster. Minerals that are opaque and shiny, like pyrite, are said to have a metallic luster. Minerals with a non-metallic luster do not look like metals. There are many types of non-metallic luster. Six are described in Table 3.1. Non-Metallic Luster Adamantine Earthy Pearly Resinous Silky Vitreous Appearance Sparkly Dull, clay-like Pearl-like Like resins, such as tree sap Soft-looking with long fibers Glassy Can you match the minerals in Figure 3.13 with the correct luster from Table 3.1 without looking at the caption? Reflection of light occurs when light bounces back from a surface that it cannot pass through. Reflection may be regular or diffuse. If the surface is very smooth, like a mirror, the reflected light forms a very clear image. This is called regular, or specular, reflection. In the Figure 1.1, the smooth surface of the still water in the pond on the left reflects light in this way. When light is reflected from a rough surface, the waves of light are reflected in many different directions, so a clear image does not form. This is called diffuse reflection. In the Figure 1.1, the ripples in the water in the picture on the right cause diffuse reflection of the blooming trees.

A minerals physical properties are determined by its

(A) vitreous luster (B) crystal structure (C) chemical composition (D) two of the above

D

The patterns of atoms that make a mineral affect its physical properties. A minerals crystal shape is determined by the way the atoms are arranged. For example, you can see how atoms are arranged in halite in Figure 3.3. You can see how salt crystals look under a microscope in Figure 3.5. Salt crystals are all cubes whether theyre small or large. Other physical properties help scientists identify different minerals. They include: Color: the color of the mineral. Streak: the color of the minerals powder. Luster: the way light reflects off the minerals surface. Specific gravity: how heavy the mineral is relative to the same volume of water. Cleavage: the minerals tendency to break along flat surfaces. Fracture: the pattern in which a mineral breaks. Hardness: what minerals it can scratch and what minerals can scratch it. Some minerals can be identified with little more than the naked eye. We do this by examining the physical properties of the mineral in question, which include: Color: the color of the mineral. Streak: the color of the minerals powder (this is often different from the color of the whole mineral). Luster: shininess. Density: mass per volume, typically reported in "specific gravity," which is the density relative to water. Cleavage: the minerals tendency to break along planes of weakness. Fracture: the pattern in which a mineral breaks. Hardness: which minerals it can scratch and which minerals can scratch it. How physical properties are used to identify minerals is described in the concept "Mineral Identification." Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: Imagine you were given a mineral sample similar to the one shown in Figure 3.10. How would you try to identify your mineral? You can observe some properties by looking at the mineral. For example, you can see that its color is beige. The mineral has a rose-like structure. But you cant see all mineral properties. You need to do simple tests to determine some properties. One common one is how hard the mineral is. You can use a minerals properties to identify it. The minerals physical properties are determined by its chemical composition and crystal structure.

Factors that may affect a minerals color include

(A) mass (B) streak (C) cleavage (D) weathering

D

Color is probably the easiest property to observe. Unfortunately, you can rarely identify a mineral only by its color. Sometimes, different minerals are the same color. For example, you might find a mineral that is a gold color, and so think it is gold. But it might actually be pyrite, or fools gold, which is made of iron and sulfide. It contains no gold atoms. A certain mineral may form in different colors. Figure 3.11 shows four samples of quartz, including one that is colorless and one that is purple. The purple color comes from a tiny amount of iron. The iron in quartz is a chemical impurity. Iron is not normally found in quartz. Many minerals are colored by chemical impurities. Other factors can also affect a minerals color. Weathering changes the surface of a mineral. Because color alone is unreliable, geologists rarely identify a mineral just on its color. To identify most minerals, they use several properties. Color may be the first feature you notice about a mineral, but color is not often important for mineral identification. For example, quartz can be colorless, purple (amethyst), or a variety of other colors depending on chemical impurities Figure 1.1. The patterns of atoms that make a mineral affect its physical properties. A minerals crystal shape is determined by the way the atoms are arranged. For example, you can see how atoms are arranged in halite in Figure 3.3. You can see how salt crystals look under a microscope in Figure 3.5. Salt crystals are all cubes whether theyre small or large. Other physical properties help scientists identify different minerals. They include: Color: the color of the mineral. Streak: the color of the minerals powder. Luster: the way light reflects off the minerals surface. Specific gravity: how heavy the mineral is relative to the same volume of water. Cleavage: the minerals tendency to break along flat surfaces. Fracture: the pattern in which a mineral breaks. Hardness: what minerals it can scratch and what minerals can scratch it.