Earth science

eruption is the release of stored energy from below the surface of Earth. The heat comes mostly from radioactive decay, and convection, in the Earth's core and mantle.]]

**Earth science** is an all-covering term for the sciences related to the planet Earth. Earth science may also be called **geoscience**. Geoscience is the study of the architecture of the Earth.

It is a broader term than geology because it includes aspects of planetary science, which is part of astronomy. The Earth sciences include the study of the atmosphere, oceans and biosphere, as well as the solid earth. Typically Earth scientists use ideas from physics, chemistry, biology, chronology and mathematics to understand the Earth, and how it evolved to its current state.

If there is one fact which underlies all Earth science it is this: the Earth is an ancient planet which has been changing the whole time since its formation. The extent of the changes is much greater than people used to think.

## Main Branches of Earth Science
'', Apollo 17, December 1972]]
Earth science is the study of the Earth, how it works, what it is made of, and how its systems interact. It includes many different types of science that work together to explain everything from rocks beneath our feet to the space around our planet. Earth science helps us understand natural events like earthquakes and weather patterns, and it also helps us solve problems like pollution or climate change. These areas of science often overlap. For example, to fully understand a volcanic eruption, scientists might use knowledge from geology, atmospheric science, geophysics, and geochemistry. There are several major branches of Earth science. These include Geology (the study of Earth's solid parts), Oceanography (the study of oceans), Meteorology or Atmospheric science (the study of the atmosphere and weather), Astronomy (especially how space affects Earth), Environmental science (how humans interact with Earth), Physical geography (how natural landscapes form and change), Geophysics (the physics of Earth’s interior and surface), and Geochemistry (the chemistry of Earth’s materials). Even though these are separate fields, they often work together to help us understand Earth as one large, connected system.

Geology is the main branch of Earth science and focuses on Earth’s solid parts. Geologists study things like rocks, minerals, and mountains, as well as processes such as volcanoes, earthquakes, and landslides. They use tools like maps, satellite images, and underground exploration methods to learn about what’s happening below the surface. Geologists also look at fossils to learn about life in the past and use the geologic time scale to organize Earth’s long history. There are different areas within geology. Petrology focuses on rocks, stratigraphy studies layers of rock, and paleontology looks at ancient life through fossils. Geologists also help us prepare for natural hazards by studying where earthquakes are likely to happen or when a volcano might erupt. For example, the Himalayas are still rising today because of plate tectonics, the movement of Earth’s outer shell. Areas around the Pacific Ocean, known as the Ring of Fire, have many earthquakes and volcanoes for the same reason. Another important part of geology is economic geology, which focuses on finding useful resources like coal, oil, metals, and rare earth elements. These are important for things like building technology and producing energy.

Oceanography is the science that studies Earth’s oceans, which cover more than 70% of the planet’s surface. Oceans are very important because they affect climate, weather, and life on Earth. Oceanographers learn about the oceans in four main areas: physical, chemical, biological, and geological oceanography. Each area looks at different parts of how the ocean works and how it connects with the rest of the Earth. Physical oceanographers study how water moves through the ocean. They look at waves, currents, and how the ocean and atmosphere affect each other. One example is El Niño, which is a change in ocean temperatures that affects weather all over the world. Another important topic is thermohaline circulation, a system of ocean currents that moves heat around the planet and helps control global climate. Chemical oceanographers focus on what the ocean is made of. They study things like salinity (how salty the water is), nutrient cycles, and how gases like carbon dioxide (CO₂) affect the ocean. One major issue is ocean acidification, which happens when too much CO₂ is absorbed by the ocean, making the water more acidic. This can harm animals like corals and shellfish that rely on calcium carbonate to build their shells. Biological oceanographers study the plants and animals that live in the ocean, from tiny plankton to huge whales. They explore all kinds of environments, like coral reefs and the deep sea, to learn how marine life survives and interacts. This helps us protect biodiversity and understand the ocean’s role in the food chain. Geological oceanographers look at the shape and structure of the ocean floor. They study underwater features like mid-ocean ridges, hydrothermal vents, and submarine canyons. These features tell us how the Earth’s crust moves and how new seafloor is formed through a process called seafloor spreading. Scientists use high-tech tools like underwater robots (AUVs), satellites, and deep-sea drilling platforms to explore these areas.

Meteorology, also known as atmospheric science, is the study of the Earth’s atmosphere and how it controls weather and climate. Meteorologists collect data on things like temperature, humidity, air pressure, and wind to understand how weather works and to make forecasts. Tools like weather balloons, Doppler radar, and computer models help scientists predict weather days in advance. Meteorology is especially important for understanding extreme weather events, such as hurricanes, tornadoes, droughts, and heat waves. These events can cause a lot of damage to people, animals, and the environment, so being able to predict them can help keep communities safe. A special part of meteorology is climate science, which studies long-term weather patterns and how they are changing. Scientists look at how greenhouse gases, like carbon dioxide, and aerosols in the atmosphere are causing global warming and melting polar ice. Another branch, called paleoclimatology, uses clues from ice cores, tree rings, and sediment layers to learn about climates from thousands of years ago. This information helps us understand what might happen to Earth’s climate in the future. One interesting area of research is how the jet stream, a fast-moving ribbon of air high above Earth, affects weather. Scientists are also studying how changes in the polar vortex, a group of cold winds near the poles, might lead to unusual cold weather in places like North America and Europe. This helps us better understand the connection between global climate and local weather.

Astronomy, when studied as part of Earth science, looks at how things in space affect our planet. This includes the Sun, the Moon, and other objects in the solar system. For example, Earth’s orbit, tilt, and a slow wobble called precession help create the seasons and affect climate patterns over thousands of years. These long-term changes are called the Milankovitch cycles, and they help explain ice ages in Earth's history. The Sun’s activity can also affect life on Earth. Events like sunspots and solar flares can change the amount of energy Earth receives. Strong solar flares can disturb Earth's magnetic field, which may damage satellites, affect GPS signals, and even cause problems with electric power grids. Astronomers also study meteoroids and asteroids, especially because impacts from space rocks have caused major events in Earth’s past, such as the asteroid that likely led to the extinction of the dinosaurs 66 million years ago. A special field called planetary geology compares Earth to other planets and moons. This helps scientists understand how volcanoes, earthquakes, and surface changes work not just on Earth, but also on places like Mars or the Moon. The Moon also plays a big role in our daily lives. Its gravity causes ocean tides, and its steady pull helps keep Earth’s axial tilt stable, which is important for long-term climate balance.

Environmental science is the study of how humans interact with the natural world. It brings together different sciences like biology, chemistry, and geology, as well as social science, to understand and solve environmental problems. Environmental scientists look at how human activities affect air, water, soil, and ecosystems. Some of the big issues they study include pollution, climate change, and how to manage natural resources wisely. For example, when harmful substances like mercury build up in fish, it can affect the entire food chain. Another problem is eutrophication, which happens when too many nutrients like fertilizer enter lakes and rivers. This causes too much algae to grow, which uses up oxygen and harms fish and other animals. Environmental scientists use tools like satellites, maps, and computer models to track changes and predict future problems. They also study the life cycle of pollutants, how they move through air, water, and soil. They also try to find ways to reduce or clean them up. Their work helps governments create rules and policies to protect the environment, like the Clean Air Act, the Kyoto Protocol, and the Paris Agreement, which aim to reduce pollution and fight global warming.

Physical geography is the study of the natural features and physical processes on Earth’s surface. This branch of science looks at landforms (like mountains, valleys, and rivers), climate zones (such as tropical or polar areas), ecosystems, soils, and water systems. Physical geographers want to understand how these features form, change over time, and interact with each other. They use special tools like GIS (Geographic Information Systems) and remote sensing (satellite images) to map and study patterns on Earth. For example, they might track deforestation in the Amazon rainforest or desertification (land turning to desert) in areas like the Sahel region in Africa. There are several subfields in physical geography. Geomorphology focuses on how landforms are created and shaped by forces like wind, water, and ice. Hydrology studies how water moves through the environment, including rivers, lakes, and underground water. Climatology looks at weather patterns and climate zones in different places. Physical geographers also study how human activities affect nature. For instance, cities often become urban heat islands, where temperatures are higher because of buildings and roads. River management, such as building dams or levees, can change how floodplains work and affect local plants and animals. Another key idea is ecotones, which are areas where different ecosystems meet. These zones usually have rich biodiversity. Physical geography helps in planning for natural disasters and protecting the environment.

Geophysics is the science that uses physics to study Earth’s inside and its physical properties. Geophysicists try to understand what is going on below Earth’s surface without digging deep holes. One major area is seismology, which uses vibrations from earthquakes (called seismic waves) to learn about Earth’s internal layers like the crust, mantle, and core. Another area is gravimetry, which measures small changes in Earth’s gravity to find things underground, such as oil, minerals, or caves. Magnetometry maps changes in Earth’s magnetic field and can be used to find mineral deposits or learn about past movement of tectonic plates. Geophysicists also study Earth’s heat flow, magnetic field changes over time, and how the crust bends or flexes (called lithospheric flexure). They use different tools and techniques, like electrical resistivity tomography (ERT) and ground-penetrating radar (GPR). These are used in looking for natural resources, studying buried ruins in archaeology, or checking for pollution underground. In oil and gas exploration, a method called reflection seismology helps create pictures of underground rock layers to find places where oil or gas may be trapped. Geophysics is not just for Earth, it also helps scientists study other planets. For example, NASA’s InSight mission to Mars placed seismometers on the planet to find marsquakes and learn about the Martian interior.

Geochemistry is the study of the chemicals and elements that make up the Earth and how they move and change over time. Geochemists look at how elements like carbon, oxygen, iron, and others are found in rocks, water, air, and living things. They also study how these elements move through different parts of the Earth, such as from the crust to the atmosphere or from soil into plants. One important part of this field is isotope geochemistry, which uses different forms of elements (called isotopes) to trace where things like groundwater or carbon come from. Another area is trace element analysis, which helps find valuable ore deposits like gold or copper. Radiogenic isotopes, isotopes that break down over time, are used in radiometric dating to figure out how old rocks and fossils are. Geochemists also study how elements move between solid rocks and melted magma, which helps them understand how volcanoes form and what the mantle (the layer below Earth’s crust) is made of. This information is important not just for science, but also for protecting the environment. For example, geochemists test soils for toxic metals or check for problems like acid mine drainage, which happens when mining releases harmful chemicals into nearby water. A related field called biogeochemistry looks at how living things and Earth’s systems work together. For example, it studies how bacteria help form minerals or how nutrients move through ecosystems. Geochemical fingerprints, unique chemical patterns, can be used to find out where sediments came from or to learn what past environments were like.

## Geology: Study of the Solid Earth
### Structure of the Earth
The Earth is made up of different layers, and learning about these layers is very important in geology, the science that studies the Earth. These layers affect how the surface of our planet changes and how it has developed over time. There are three main layers inside the Earth: the crust, the mantle, and the core. Each layer is different in what it is made of, how hot it is, and whether it is solid or liquid. The crust is the thin, solid outer layer of the Earth, and it is the part we live on. There are two kinds of crust. The continental crust is found under land. It is thicker (up to 70 kilometers) and made mostly of a rock called granite, which is not very dense. The oceanic crust is found under the oceans. It is thinner (about 5 to 10 kilometers) and made mostly of basalt, which is heavier and denser than granite. Underneath the crust is the mantle, which reaches about 2,900 kilometers deep. It is made mostly of a rock called peridotite. Although the mantle is solid, it can slowly flow like thick syrup because it is very hot. This slow movement, called convection, is caused by heat from inside the Earth and helps move the outer layers of the Earth.

The lithosphere is made up of the crust and the uppermost part of the mantle. It is hard and broken into large pieces called tectonic plates. These plates float on top of the asthenosphere, a softer and slightly melted part of the upper mantle. The asthenosphere can flow slowly, which allows the tectonic plates above it to move. At the center of the Earth is the core, which has two parts. The outer core is liquid and made mostly of iron and nickel. As it moves, it creates Earth's magnetic field through a process called the dynamo effect. The inner core is solid and also made mostly of iron and nickel. It stays solid because the pressure at the center of the Earth is extremely high. The way the Earth is built on the inside helps explain the theory of plate tectonics. This theory says that the plates of the lithosphere move over time, and this movement shapes the Earth’s surface. For example, at the Mid-Atlantic Ridge, new ocean floor is made as plates move apart. At the San Andreas Fault in California, two plates slide past each other, which causes earthquakes.

### Rocks and minerals
, a cut through layers of sedimentary rocks.]]
Geologists, who are scientists that study the Earth, group all Earth materials into two main categories: rocks and minerals. Rocks are made up of one or more minerals, and they can change from one type to another over time through a process called the rock cycle. There are three main types of rocks: igneous, sedimentary, and metamorphic. Igneous rocks form when melted rock, known as magma (if it is underground) or lava (if it's on the surface), cools and hardens. If the magma cools slowly underground, it forms rocks like granite, which have large, visible crystals. These are called intrusive igneous rocks. If the lava cools quickly at the surface, it forms rocks like basalt, which have small or no visible crystals. These are called extrusive igneous rocks. Over time, rocks on the Earth’s surface are broken down into small pieces by wind, water, and other natural forces. This process is called weathering. The small pieces, called sediments, can build up in layers. As more layers pile on top, the weight presses them together. Over time, these layers stick together to form sedimentary rocks like limestone or sandstone. These rocks often contain fossils and can give clues about what the Earth was like in the past. When rocks are buried deep underground, they are exposed to a lot of heat and pressure. This can change the rocks into a new type called metamorphic rocks. This transformation does not melt the rock, but it changes its structure and mineral makeup. Examples of metamorphic rocks include schist and marble.

Minerals are the tiny building blocks that make up rocks. A mineral is a natural, solid substance with a special crystal shape and a chemical formula. Minerals have different properties that help scientists identify them. These include hardness (how easily it can be scratched), cleavage (how it breaks), luster (how shiny it is), density (how heavy it feels), and crystal structure (the shape of the crystals it forms). For example, the mineral quartz is quite hard and has a Mohs hardness of 7. It breaks in a curved way called conchoidal fracture. Another mineral, calcite, is softer and reacts by fizzing when it touches weak acid because it contains carbonate. Minerals are sorted into groups based on the main elements they contain. Some examples are silicates (like feldspar and mica), carbonates (like calcite), oxides (like hematite), and sulfides (like pyrite). Knowing about minerals is important in many jobs, like finding and using natural resources (mining), studying rocks (petrology), and protecting the Earth (environmental geology).

### Geological processes
, Earth's highest mountain]]
Geological processes are natural actions that change the Earth's surface. These processes are important for understanding how our planet has changed in the past and how it continues to change today. They include events like volcanic eruptions, earthquakes, mountain formation, and the breaking down and movement of rocks and soil. Volcanism happens when magma (hot, melted rock from inside the Earth) comes to the surface. When it reaches the surface, it is called lava, and it may also explode as ash and other materials called pyroclastics. Volcanoes often form along the edges of tectonic plates or above hot spots deep in the Earth. There are different types of volcanoes. For example, stratovolcanoes like Mount Fuji are tall and steep because their magma is thick and sticky, leading to explosive eruptions. Shield volcanoes like Mauna Loa have gentle, broad slopes because their magma is thinner and flows more easily, causing less violent eruptions.

Earthquakes happen when stress builds up along faults (cracks in the Earth's crust) and is suddenly released, causing the ground to shake. Scientists who study earthquakes are called seismologists, and they use tools called seismographs to measure how strong the shaking is and where it starts. The point where the earthquake begins is called the epicenter, and the strength is measured using the Moment Magnitude Scale. Some of the most earthquake-prone areas are subduction zones, where one tectonic plate slides underneath another. A well-known example is the Ring of Fire, which circles much of the Pacific Ocean. These areas often have both earthquakes and volcanoes.

Other important geological processes include weathering, erosion, and deposition. Weathering is the breaking down of rocks. It can happen physically, like when water freezes in cracks and breaks the rock apart (called frost wedging), or chemically, like when acid rain dissolves certain rocks like limestone. Once rocks are broken down, the pieces can be moved by wind, water, or ice in a process called erosion. These materials are eventually dropped off in new places in a process called deposition, where they may build up into layers over time. Mountains are created through a process called orogeny, which happens when tectonic plates collide. When one plate pushes against another, the land can be pushed upward to form mountains. The Andes Mountains formed when an ocean plate was pushed under a continent (a process called subduction), while the Alps formed from two continental plates crashing into each other. Mountain building involves things like uplift (land rising), folding (bending of rock layers), and faulting (breaking and movement along faults). These events often bring heat and pressure, which can change rocks into metamorphic rocks and lead to magma forming underground.

### Geologic time
 to scale. Ma means "million years ago".]]
Geologists study geologic time to understand the history of the Earth, which is about 4.54 billion years old. This helps them figure out when certain events happened and how the Earth’s surface and life forms have changed over time. Because Earth’s history is so long, scientists divide it into different parts to make it easier to study and understand. To tell the order of events, geologists use something called relative dating. This does not give the exact age of a rock or fossil, but it tells which ones are older or younger. One rule is superposition, which means that in a stack of rock layers, the younger layers are on top, and the older layers are on the bottom. Another rule is cross-cutting relationships, which means that if a fault or igneous rock cuts through other rocks, it is younger than the rocks it cuts through.

To find out the actual age of rocks, scientists use radiometric dating. This method uses the natural breakdown of radioactive elements into other elements over time. For example, uranium-238 slowly changes into lead-206, and potassium-40 changes into argon-40. Because this decay happens at a constant rate, scientists can measure how much of each element is present and calculate the rock's age. Using these methods, the oldest minerals ever found on Earth, tiny crystals called zircons in Australia, have been dated to about 4.4 billion years old. To organize Earth’s history, scientists created the Geologic Time Scale. It breaks time into eons, eras, periods, and epochs. These time divisions are based on major changes in Earth’s systems or in the life forms living at the time. For example, the boundary between the Palaeozoic and Mesozoic eras, about 252 million years ago, marks the Permian–Triassic mass extinction. This was the largest extinction in Earth’s history and wiped out over 90% of marine species. Another famous event is the Cretaceous-Paleogene extinction event, about 66 million years ago, likely caused by an asteroid. This event brought the age of dinosaurs to an end.

## Oceanography: Study of Earth’s Oceans
 of Earth seen from space in 1969]]
Oceanography is the science that studies Earth’s oceans. Since oceans cover more than 70% of Earth’s surface, they are a huge part of how our planet works. Oceans affect climate, help control weather, support a wide variety of living things, and shape parts of the Earth’s surface. Oceanography helps scientists understand not just the ocean itself, but also how it connects to things like the carbon cycle, global warming, and even the movement of the Earth’s tectonic plates.

Oceanography is made up of different branches, each studying a special part of the ocean. Physical oceanography looks at how water moves, like currents, waves, and how oceans and the atmosphere interact. Marine geology studies the ocean floor, including underwater mountains, volcanoes, and trenches. Chemical oceanography focuses on what the ocean is made of, like salt, gases, and nutrients. Biological oceanography studies ocean life, from tiny plankton to whales, and how these living things survive in different parts of the ocean.

### Physical oceanography
Physical oceanography is the branch of ocean science that studies how ocean water moves and what its physical properties are, like temperature and density. One important part of this is understanding ocean currents. There are two main types of currents: surface currents and deep currents. Surface currents are mostly driven by winds and the Coriolis effect, which is caused by Earth’s rotation. Famous surface currents include the Gulf Stream in the Atlantic Ocean and the Kuroshio Current in the Pacific Ocean. These currents move warm water from the equator toward the poles, helping to warm places like Europe by bringing heat from tropical regions. Deep ocean currents, on the other hand, are powered by differences in water density. These differences happen because of changes in temperature and salinity (how salty the water is). This system of deep-water movement is called thermohaline circulation. It is also known as the global conveyor belt because it slowly moves water all around the world. These deep currents bring cold, nutrient-rich water from the poles into the deeper parts of the ocean, which helps store carbon and support the nutrient cycle that feeds marine life.

Ocean waves are mostly formed by the wind blowing across the surface of the water. The size and strength of a wave depend on how fast and long the wind blows, and how much open water (called the fetch) it travels across. Waves crash onto beaches, shape coastlines, and can even carry energy across entire oceans. Tides are another important ocean movement. They are the regular rise and fall of sea levels, mostly caused by the gravitational pull of the Moon and the Sun. When the Moon and Sun line up, we get spring tides, which are especially high and low. When they are at right angles, we get neap tides, which are more moderate. Tides affect sea life and the way people use coastlines. There are also internal waves, which happen under the surface of the ocean where different layers of water meet. These waves cannot be seen from above, but they are very important because they help mix ocean layers and move nutrients around. Another key process is upwelling. This happens when deep, cold water rises up to the surface, bringing nutrients with it. These areas, like those near Peru and California, are some of the most productive places in the ocean. They support large numbers of fish and other marine animals because there is so much food available.

### Marine geology
Marine geology is the study of the ocean floor, what it is made of, how it changes, and how it has developed over time. The bottom of the ocean, also called the seafloor, has many interesting features. These include continental margins (edges of continents underwater), abyssal plains (flat, deep ocean areas), mid-ocean ridges (underwater mountain chains), ocean trenches (deep valleys), and submarine volcanoes (volcanoes under the sea). At mid-ocean ridges, like the Mid-Atlantic Ridge, two tectonic plates move away from each other. When they do, magma from below the Earth's surface rises up and hardens to form new oceanic crust. This process is called seafloor spreading. It is one of the main ways scientists know that plate tectonics, the idea that Earth’s outer shell is made of moving plates, is true. Another interesting discovery is the pattern of magnetic stripes on either side of these ridges. These stripes show that Earth's magnetic field has reversed many times in the past. The magnetic pattern is the same on both sides of the ridge, which means the seafloor has been spreading evenly for millions of years.

Submarine volcanoes form in several places. They can be found in volcanic arcs (chains of volcanoes near trenches) or over hotspots, like the one that created the Hawaiian Islands. As lava from these volcanoes piles up, it can build underwater mountains or even islands that rise above the sea. On the other hand, oceanic trenches are the deepest parts of the ocean. The Mariana Trench is the deepest of them all. Trenches form where one tectonic plate goes under another in a process called subduction. These zones are very active. They are often the site of powerful earthquakes, volcanic eruptions, and even tsunamis. Scientists also study marine sediments, tiny particles that settle on the seafloor over time. These layers help us understand the Earth's past climate, ocean life, and tectonic activity. For example, shells of tiny sea creatures called foraminifera can be found in deep-sea cores. The chemical makeup of their shells helps scientists understand what the ocean temperatures were like and whether there was ice thousands or even millions of years ago.

### Chemical oceanography
Chemical oceanography is the study of what seawater is made of and how chemicals move and change in the ocean. One important thing chemical oceanographers look at is salinity, which means how much salt is dissolved in ocean water. On average, seawater has about 35 parts of salt for every 1,000 parts of water, but this can change depending on the location. For example, salinity is higher in places where lots of water evaporates, like in hot, dry areas, and lower where there is lots of rainfall or fresh water from rivers. The two most common parts, or ions, in seawater are sodium (Na⁺) and chloride (Cl⁻), which together make table salt. But seawater also contains other important elements like magnesium, calcium, sulfate, and bicarbonate. There are also tiny amounts of trace metals, like iron and zinc, which are very important for marine life even though there is not much of them.

The ocean and the atmosphere are constantly exchanging gases, which helps drive Earth’s carbon cycle and oxygen cycle. Oceans absorb about 25 to 30 percent of the carbon dioxide (CO₂) that humans release into the air. When the ocean takes in too much CO₂, it affects the carbonate buffering system, which keeps the pH (how acidic or basic) of seawater balanced. Too much CO₂ makes the ocean more acidic, a problem known as ocean acidification. This makes it harder for sea creatures like corals, shellfish, and mollusks to build their calcium carbonate shells. Oceans are also the largest source of dissolved oxygen, which comes from two main sources. It comes from the air into the water. It is also made by phytoplankton, tiny ocean plants that do photosynthesis. Just like land plants, they produce oxygen as they turn sunlight into energy. Another key part of chemical oceanography is studying how nutrients move through the ocean. Important nutrients include nitrogen, phosphorus, and silica. These are used by marine organisms to grow and survive. Nutrients are taken up by living things, released when organisms decompose, and moved around by the mixing of ocean water. In places called upwelling zones, deep water full of nutrients rises to the surface, helping tiny organisms like phytoplankton grow. This leads to primary production, which supports the entire ocean food chain.

### Biological oceanography
Biological oceanography is the study of marine life, the animals, plants, and tiny organisms that live in the ocean. It also studies how they interact with each other and with their environment. The ocean is divided into different layers or zones, from the sunlit surface to the dark, deep trenches. Each zone has its own types of life, adapted to different levels of light, pressure, and temperature. At the very bottom of the ocean food web are tiny organisms called phytoplankton. These are microscopic algae, like diatoms and dinoflagellates, that use sunlight to make their own food through photosynthesis, just like land plants. In fact, phytoplankton produce about half of the oxygen on Earth. They are eaten by zooplankton, which are small animals like copepods and krill, and these are then eaten by larger animals, such as fish and whales.

One of the most famous marine ecosystems is the coral reef. Found in shallow, warm tropical waters, coral reefs are full of life and support more than 25% of all ocean species, even though they cover less than 1% of the ocean floor. Corals themselves are tiny animals that live in groups and build hard skeletons. They have a special partnership with algae called zooxanthellae, which live inside their tissues and help provide them with food. But if the water gets too warm, this relationship can break down, causing the corals to lose their color, a problem called coral bleaching.

Marine life includes a wide variety of organisms. Nektonic animals, like fish, squid, and whales, can swim freely through the water. Benthic animals, such as crabs, sea stars, and worms, live on or near the ocean floor. In the deep ocean, where there is no sunlight, some animals live near hydrothermal vents or cold seeps. These areas are powered not by sunlight, but by chemosynthesis, where bacteria use chemicals like hydrogen sulfide or methane to make food. Creatures like giant tube worms, vent crabs, and the fuzzy-looking Yeti crab live in these dark, extreme environments. Biological oceanography is important because it helps us learn how to protect marine animals, manage fisheries, and understand how ocean life is affected by things like pollution, climate change, and overfishing. It helps scientists find ways to keep ocean ecosystems healthy and balanced for the future.

## Meteorology: Study of the Atmosphere
 with a polar low seen at the top of the image]]
Meteorology is the science that studies the atmosphere, the thin layer of gases that surrounds the Earth. Even though the atmosphere is thin, it is very important for life. It helps keep Earth’s temperature just right, moves water around the planet through rain and snow, and protects us from the Sun’s harmful rays. Meteorologists are scientists who study the atmosphere to understand weather and climate. They look at things like temperature, air pressure, humidity (how much moisture is in the air), and wind. To do this, they use special tools such as weather balloons that rise high into the sky, satellites that watch the Earth from space, and radar systems that track rain and storms. They also use computer models to predict how weather patterns might change in the future.

Meteorology helps us in many ways. It helps predict the weather so people can prepare for storms, heatwaves, or cold fronts. It is also important for airplane safety, planning farming activities, and creating climate models to understand long-term changes in Earth’s climate. This science combines ideas from physics, chemistry, and the study of fluids to explain how the atmosphere works. By learning how energy and moisture move through the atmosphere, meteorologists can better understand both daily weather and big climate changes over time. This knowledge is important for helping communities prepare for natural disasters, make smart environmental decisions, and stay safe during extreme weather events.

### Composition and structure
 when seen from space on board the ISS at an altitude of  (the Moon is visible as a crescent in the far background).]]
The atmosphere is made up of different gases that are very important for life on Earth and for creating weather. Most of the atmosphere is nitrogen (78%) and oxygen (21%). The last 1% includes gases like argon, carbon dioxide, methane, ozone, and a few others. Even though these other gases are only present in small amounts, they have big effects. For example, carbon dioxide and methane trap heat, helping to warm the Earth, while ozone helps block harmful ultraviolet (UV) rays from the Sun. Water vapor, which can range from 0 to 4% of the atmosphere, is also very important because it forms clouds, causes rain, and plays a big role in the greenhouse effect. The atmosphere has five main layers, which are separated by how the temperature changes as you go higher up. The lowest layer is the troposphere. It goes from the ground up to about 8 to 15 kilometers, depending on where you are and what season it is. This is where all weather happens, and it contains about 75% of the atmosphere’s total mass. As you go higher in the troposphere, the air gets colder. The top of this layer is called the tropopause, where the temperature stops dropping.

Above that is the stratosphere, where the ozone layer is found. This layer warms up as you go higher because ozone absorbs UV radiation from the Sun. Next is the mesosphere, which is the coldest layer. In this layer, the temperature drops again with altitude, and it is where meteors usually burn up when they enter Earth’s atmosphere. Then comes the thermosphere, where temperatures go way up because of solar activity. This layer contains the ionosphere, which is important because it reflects radio waves, making long-distance radio communication possible. The last layer is the exosphere, which is the outermost layer and slowly fades into outer space. In this layer, some gases can even escape into space. Even very tiny amounts of certain chemicals, like CFCs (chlorofluorocarbons), can have huge effects. In the past, CFCs caused major damage to the ozone layer, which made it easier for harmful UV rays to reach Earth. Scientists and governments worked together to stop using these chemicals, helping to protect the ozone and the environment.

### Weather
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Weather happens because of the way energy moves through the atmosphere, especially through heat and water. One of the most important weather processes is cloud formation. This happens when warm, moist air rises and cools down. As it cools to its dew point, the water vapor in the air condenses (turns into tiny droplets) around tiny particles in the air, like dust or sea salt. These tiny droplets form clouds. Clouds come in different shapes and heights. The main types are cirrus (thin and wispy, high up), cumulus (fluffy and white), and stratus (flat and gray). Sometimes clouds are a mix of types. Precipitation, like rain, snow, or hail, happens when the droplets or ice crystals in a cloud get big and heavy enough to fall to the ground. There are different ways this happens depending on the temperature inside the cloud. For example, in cold clouds, ice crystals grow as water vapor sticks to them (called the Bergeron process). In warm clouds, droplets collide and join together until they fall (called collision-coalescence).

Large bodies of air called air masses can also affect the weather. These air masses have the same temperature and humidity throughout and form over large areas like oceans or continents. When two air masses meet, they form a front, which is the boundary between them. Fronts are where we get most of our active weather. A cold front pushes under warm air and can cause thunderstorms. A warm front brings lighter rain and gentle warming. Occluded fronts and stationary fronts can lead to long-lasting or complicated weather patterns with lots of rain or clouds.

Some weather systems are very powerful. One type is called an extratropical cyclone, which forms along fronts in mid-latitudes. These storms are shaped by the jet stream (fast-moving air high in the sky) and changes in air temperature. Another type is a thunderstorm, which starts when warm, moist air rises and releases energy as it cools. Some thunderstorms become supercells, which are strong enough to produce hail, strong winds, and even tornadoes. A tornado is a spinning column of air that reaches from a thunderstorm down to the ground. Tornadoes are measured using the Enhanced Fujita (EF) Scale, from EF0 (weakest) to EF5 (most destructive). Another major type of storm is a tropical cyclone, also called a hurricane or typhoon depending on where it forms. These storms get their energy from warm ocean water and have a calm center called the eye, surrounded by spiral bands of rain and wind. The strength of a hurricane is measured using the Saffir–Simpson Scale, which ranks them by their wind speed. Their path depends on things like ocean temperatures, the Coriolis effect (caused by Earth’s rotation), and winds high in the atmosphere.

### Climate science
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Climate science is the study of long-term weather patterns and what causes them. Unlike weather, which can change daily, climate looks at how temperature and rainfall behave over many years. Scientists use systems like the Köppen classification to group different parts of the world into climate zones. These include tropical, dry (arid), temperate, continental, and polar climates. Each zone has its own average temperatures and types of precipitation, like rain or snow. Climate zones are shaped by how air moves around the Earth. These air movements are called global circulation patterns, and they are driven by the Sun's heat and the Earth's spinning motion. There are three main circulation cells in each hemisphere: the Hadley, Ferrel, and Polar cells. These help move warm air from the equator toward the poles. Winds like the trade winds, westerlies, and polar easterlies form because of these air movements and affect weather in different regions. Jet streams, which are strong winds high in the sky, also influence how storms move.

Scientists use computer models, called Global Circulation Models (GCMs), to predict how the climate might change in the future. These models include information about the atmosphere, oceans, land, and ice. They also use satellite data, historical records, and data about how the Earth reacts to sunlight and greenhouse gases. These tools help scientists understand how human actions and natural changes affect the climate. One of the biggest topics in climate science is climate change caused by human activity. Since the Industrial Revolution, people have burned more fossil fuels (like coal, oil, and gas), cut down forests, and used farming methods that release gases like carbon dioxide, methane, and nitrous oxide. These gases trap heat in the atmosphere, a process called the greenhouse effect, which is causing global warming.

The Earth's average temperature has gone up by more than 1.1°C since the late 1800s. This warming has led to melting ice, rising sea levels, and stronger storms and heatwaves. Scientists also worry about feedback loops, changes that make warming even worse. For example, when ice melts, it reflects less sunlight, causing the Earth to heat up faster (this is called the ice–albedo feedback). Also, frozen ground (permafrost) can release methane as it thaws, adding more greenhouse gases to the air. Climate change affects different places in different ways. In Africa, droughts may get worse. In the Atlantic Ocean, hurricanes may become stronger. Changing rainfall patterns may harm farming and water supplies. Scientists study past climates, using ice cores, tree rings, and ocean sediments to learn how Earth’s climate has changed before. The Intergovernmental Panel on Climate Change (IPCC) brings together scientists from all over the world to study climate change and give advice to governments. Understanding how Earth’s atmosphere works helps us find solutions, such as cutting greenhouse gas emissions, planting more trees to absorb carbon, or using new technologies to cool the planet.

## Astronomy: Earth in Space
 of European Southern Observatory shooting a laser guide star to the Galactic Center]]
Astronomy, when connected to Earth science, helps us understand how Earth fits into the larger universe. It looks at how objects in space, like the Sun, the Moon, and the planets, affect life on Earth. These celestial events play a big role in shaping things like our climate, seasons, tides, and even some geological processes such as how the Earth’s crust behaves over time. For example, Earth’s orbit around the Sun and its tilted axis are what cause the seasons. The Moon’s gravity pulls on Earth’s oceans and creates tides, which rise and fall regularly. Even biological rhythms, like how animals migrate or plants grow, are often linked to daylight cycles caused by Earth’s rotation. Events like solar flares and geomagnetic storms from the Sun can also affect Earth’s magnetic field and even interfere with satellites and communication systems.

Over the centuries, people have watched the skies to learn more about these effects. Today, scientists use powerful tools like space telescopes, radio antennas, and satellites to observe the universe in much more detail. These instruments help track the movement of planets, predict eclipses, monitor solar activity, and study asteroids that might come close to Earth.

### The Earth-Sun-Moon System
The tilt of Earth’s axis, which is about 23.5 degrees, and its oval-shaped (elliptical) orbit around the Sun are what cause the seasons. When Earth tilts toward the Sun, that part of the world gets more sunlight and experiences summer. When it tilts away, it is winter. A solstice happens when the tilt is most extreme. Around June 21, the summer solstice in the Northern Hemisphere brings the longest day of the year. Around December 21, the winter solstice brings the shortest. The equinoxes, which happen around March 21 and September 23, are times when day and night are nearly equal all over the world. That’s because the Sun is shining directly on the equator.

The Moon’s phases, like the new moon, half moon, and full moon, happen because of how the Moon orbits Earth and how sunlight shines on it from different angles. A new moon occurs when the Moon is between Earth and the Sun, so we cannot see the lit side. A full moon happens when Earth is between the Sun and the Moon, so we see the entire lit side. Sometimes, the Sun, Earth, and Moon line up perfectly, causing an eclipse. In a solar eclipse, the Moon blocks the Sun’s light and casts a shadow on Earth. In a lunar eclipse, Earth’s shadow falls on the Moon, making it look dark or red. Eclipses do not happen every month because the Moon’s orbit is tilted, and it only crosses Earth’s orbital path at certain times called eclipse seasons.

The Moon’s gravity also pulls on Earth’s oceans and causes tides. When the Sun and Moon line up, during new and full moons, they create spring tides, which have higher high tides and lower low tides. During quarter moons, the Sun and Moon are at right angles, and they create neap tides, which are not as strong. In some places, like the Bay of Fundy in Canada, the shape of the coastline can make tides even more extreme due to a special effect called tidal resonance.

### Influence of the Sun
The Sun affects Earth in many important ways, not just by giving us light and heat, but also by sending out energy and particles. Most of the energy we get from the Sun comes as visible light, ultraviolet (UV) radiation, and infrared (IR) energy. This energy powers Earth’s climate and helps plants perform photosynthesis, which is how they make food. The amount of sunlight, also called insolation, depends on how Earth is tilted and how far it is from the Sun. Even small changes in the Sun’s energy output, such as those during the 11-year sunspot cycle, can slightly affect Earth’s weather and climate.

Besides light, the Sun also sends out a steady flow of tiny charged particles called the solar wind. These particles, mostly protons and electrons, travel very fast through space and reach Earth all the time. Earth is protected by a powerful magnetic field, called the magnetosphere, which is created by movement in Earth’s liquid outer core. This magnetic shield stops most of the solar wind. But during strong solar events like solar storms or coronal mass ejections (CMEs), the flow of particles becomes much stronger and can compress the magnetosphere. When this happens, it can disturb satellites, GPS signals, and even electrical power grids on Earth.

When the solar wind hits the upper part of Earth’s atmosphere near the North and South Poles, it creates beautiful displays called auroras. In the Northern Hemisphere, it's called the aurora borealis (Northern Lights), and in the Southern Hemisphere, it is called the aurora australis (Southern Lights). These colorful lights appear when solar particles excite atoms like oxygen and nitrogen in the thermosphere, causing them to glow. Different gases and heights produce different colors: green light comes from oxygen around 100 kilometers high, red from oxygen even higher up, and blue or purple from nitrogen. Auroras are most visible during times of high solar activity and are often seen in places like Scandinavia, Alaska, and Antarctica.

### Earth’s Place in the Universe
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Earth travels around the Sun in a slightly oval-shaped path called an elliptical orbit. It takes about 365.25 days to complete one full trip around the Sun, which is why we have a leap day every four years to keep our calendar in sync. Earth also spins on its axis once every 23 hours and 56 minutes, which is called a sidereal day. However, because Earth is also moving around the Sun, our normal solar day, from one noon to the next, is exactly 24 hours. Earth’s orbit follows rules discovered by the scientist Johannes Kepler. According to Kepler’s laws, Earth moves faster in its orbit when it is closer to the Sun (called perihelion) and slower when it is farther away (called aphelion). Over thousands of years, the gravity from the Sun, Moon, and other planets can slightly change Earth’s orbit. These slow changes, called Milankovitch cycles, include shifts in Earth’s shape of orbit (eccentricity), its tilt (axial tilt), and the wobble of its axis (precession). These cycles are connected to long-term climate patterns like ice ages.

Earth formed about 4.54 billion years ago from a cloud of gas and dust called the solar nebula, which was left over from exploded stars. Small pieces called planetesimals stuck together through accretion, slowly building up into planets. As Earth grew, its heavier materials sank to the center, forming a metal core, while lighter rocks rose to become the mantle and crust. A big event called the giant impact hypothesis suggests that a Mars-sized object named Theia hit Earth early on. The debris from this crash likely formed the Moon, and the impact also tilted Earth’s axis, giving us seasons. Earth is located in a special part of the solar system called the habitable zone, where temperatures allow liquid water, a key ingredient for life, to exist. Our planet moves through the Milky Way galaxy in a spiral region known as the Orion Arm, taking about 225 to 250 million years to orbit the galaxy’s center once.

## Fields of study
–Silurian boundary, an example of marine transgression as exposed on the Southern tip of the Hovedøya island, Norway. Due to the folding of the Caledonian mountain range, the layers have been inverted, leaving Ordovician granular limestone on top of the later Silurian brownish mudstone.]]
The following disciplines are generally recognised as being within the geosciences:
* Geology describes the rocky parts of the Earth's crust (or lithosphere) and its historic development. Major subdisciplines are mineralogy and petrology, geochemistry, geomorphology, paleontology, Mineralogy, petrophysics, stratigraphy, structural geology, engineering geology and sedimentology.
* Geophysics and Geodesy investigate the shape of the Earth, its reaction to forces and its magnetic and gravity fields. Geophysicists explore the Earth's core and mantle as well as the tectonic and seismic activity of the lithosphere.
* Soil science covers the outermost layer of the Earth's crust that is subject to soil formation processes (or pedosphere).
* Oceanography and hydrology (includes limnology) describe the marine and freshwater domains of the watery parts of the Earth (or hydrosphere). Includes Marine biology.
* Glaciology covers the icy parts of the Earth (or cryosphere).
* Atmospheric sciences cover the gaseous parts of the Earth (or atmosphere) between the surface and the exosphere (about 1000&nbsp;km). Major subdisciplines are meteorology, climatology, atmospheric chemistry and physics.
* Astronomy includes the study of distant stars and galaxies to the examination of the 4.6 billion years old Earth from an astronomical point of view. It is also closely related with the study of the solar system and its planets, a subdiscipline called planetology. A more distant relative of astronomy is physical cosmology, which aims to study the Universe as a whole.
* Closely related to the earth sciences are physical geography and biology.

## List of Earth science topics 
### Atmosphere 
* Atmospheric chemistry
* Climatology
* Meteorology
* Paleoclimatology

### Biosphere 
* Biogeography
* Paleontology
** Micropaleontology

### Hydrosphere 
* Hydrology
** Limnology
* Hydrogeology
* Oceanography
** Marine biology
** Paleoceanography
** Physical oceanography

### Lithosphere or geosphere 
* Geology
** Environmental geology
** Historical geology
** Planetary geology
** Sedimentology
** Stratigraphy
** Structural geology
* Geography
** Physical geography
* Geochemistry
* Geomorphology
* Geophysics
** Geodynamics (see also Tectonics)
** Geomagnetics
** Seismology
* Glaciology
* Mineralogy
** Crystallography
* Petrology
* Volcanology

### Pedosphere 
* Soil science

### Systems 
* Environmental science
* Geography
* Gaia hypothesis

### Others 
* Engineering Geology
* Geostatistics
* Geodesy

## References