Introduction to the Atmosphere: Background Material Introduction to the Atmosphere This section provides a brief overview of the properties associated with the atmosphere. The general concepts found in this section are: The earth's atmosphere is a very thin layer wrapped around a very large planet. Two gases make up the bulk of the earth's atmosphere: nitrogen ( ), which comprises 78% of the atmosphere, and oxygen ( ), which accounts for 21%. Various trace gases make up the remainder. Based on temperature, the atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere. Energy is transferred between the earth's surface and the atmosphere via conduction, convection, and radiation. Ocean currents play a significant role in transferring this heat poleward. Major currents, such as the northward flowing Gulf Stream, transport tremendous amounts of heat poleward and contribute to the development of many types of weather phenomena. This section includes seven classroom activities. Atmospheric Properties The thin envelope of air that surrounds our planet is a mixture of gases, each with its own physical properties. The mixture is far from evenly divided. Two elements, nitrogen and oxygen, make up 99% of the volume of air.

The other 1% is composed of "trace" gases, the most prevalent of which is the inert gaseous element argon. The rest of the trace gases, although present in only minute amounts, are very important to life on earth. Two in particular, carbon dioxide and ozone, can have a large impact on atmospheric processes. Another gas, water vapor, also exists in small amounts. It varies in concentration from being almost non-existent over desert regions to about 4% over the oceans. Water vapor is important to weather production since it exists in gaseous, liquid, and solid phases and absorbs radiant energy from the earth. Structure of the Atmosphere The atmosphere is divided vertically into four layers based on temperature: the troposphere, stratosphere, mesosphere, and thermosphere. Throughout the Cycles unit, we'll focus primarily on the layer in which we live - the troposphere. Troposphere The word troposphere comes from tropein, meaning to turn or change. All of the earth's weather occurs in the troposphere. The troposphere has the following characteristics. It extends from the earth's surface to an average of 12 km (7 miles).

The pressure ranges from 1000 to 200 millibars (29.92 in. to 5.92 in.). The temperature generally decreases with increasing height up to the tropopause (top of the troposphere); this is near 200 millibars or 36,000 ft. The temperature averages 15°C (59°F) near the surface and -57°C (-71°F) at the tropopause. The layer ends at the point where temperature no longer varies with height. This area, known as the tropopause, marks the transition to the stratosphere. Winds increase with height up to the jet stream. The moisture concentration decreases with height up to the tropopause. The air is much drier above the tropopause, in the stratosphere. The sun's heat that warms the earth's surface is transported upwards largely by convection and is mixed by updrafts and downdrafts. The troposphere is 70% Atmospheric Processes Interactions - Atmosphere and Ocean In the Cycles overview, we learned that water is an essential part of the earth's system.

The oceans cover nearly three-quarters of the earth's surface and play an important role in exchanging and transporting heat and moisture in the atmosphere. Most of the water vapor in the atmosphere comes from the oceans. Most of the precipitation falling over land finds its way back to oceans. About two-thirds returns to the atmosphere via the water cycle. You may have figured out by now that the oceans and atmosphere interact extensively. Oceans not only act as an abundant moisture source for the atmosphere but also as a heat source and sink (storage). The exchange of heat and moisture has profound effects on atmospheric processes near and over the oceans. Ocean currents play a significant role in transferring this heat poleward. Major currents, such as the northward flowing Gulf Stream, transport tremendous amounts of heat poleward and contribute to the development of many types of weather phenomena. They also warm the climate of nearby locations. Conversely, cold southward flowing currents, such as the California current, cool the climate of nearby locations. Energy Heat Transfer Practically all of the energy that reaches the earth comes from the sun. Intercepted first by the atmosphere, a small part is directly absorbed, particularly by certain gases such as ozone and water vapor.

Some energy is also reflected back to space by clouds and the earth's surface. Energy is transferred between the earth's surface and the atmosphere via conduction, convection, and radiation. Conduction is the process by which heat energy is transmitted through contact with neighboring molecules. Some solids, such as metals, are good conductors of heat while others, such as wood, are poor conductors. Air and water are relatively poor conductors. Since air is a poor conductor, most energy transfer by conduction occurs right at the earth's surface. At night, the ground cools and the cold ground conducts heat away from the adjacent air. During the day, solar radiation heats the ground, which heats the air next to it by conduction. Convection transmits heat by transporting groups of molecules from place to place within a substance. Convection occurs in fluids such as water and air, which move freely. In the atmosphere, convection includes large- and small-scale rising and sinking of air masses and smaller air parcels. These vertical motions effectively distribute heat and moisture throughout the atmospheric column and contribute to cloud and storm development (where rising motion occurs) and dissipation (where sinking motion occurs).

To understand the convection cells that distribute heat over the whole earth, let's consider a simplified, smooth earth with no land/sea interactions and a slow rotation. Under these conditions, the equator is warmed by the sun more than the poles. The warm, light air at the equator rises and spreads northward and southward, and the cool dense air at the poles sinks and spreads toward the equator. As a result, two convection cells are formed. Meanwhile, the slow rotation of the earth toward the east causes the air to be deflected toward the right in the northern hemisphere and toward the left in the southern hemisphere. This deflection of the wind by the earth's rotation is known as the Coriolis effect. Radiation is the transfer of heat energy without the involvement of a physical substance in the transmission. Radiation can transmit heat through a vacuum. Energy travels from the sun to the earth by means of electromagnetic waves. The shorter the wavelength, the higher the energy associated with it. This is demonstrated in the animation below. As the drill's revolutions per minute (RPMs) increase, the number of waves generated on the string increases, as does the oscillation rate.

The same principle applies to electromagnetic waves from the sun, where shorter wavelength radiation has higher energy than longer wavelength radiation. Most of the sun's radiant energy is concentrated in the visible and near-visible portions of the spectrum. Shorter-than-visible wavelengths account for a small percentage of the total but are extremely important because they have much higher energy. These are known as ultraviolet wavelengths. Concluding Thoughts The physical and chemical structure of the atmosphere, the way that the gases interact with solar energy, and the physical and chemical interactions between the atmosphere, land, and oceans all combine to make the atmosphere an integral part of the global biosphere. For students to truly understand the nature and importance of the atmosphere, they should understand the answers to these questions: What is the structure and composition of the atmosphere? How does solar energy influence the atmosphere? How does the atmosphere interact with land and oceans? How is heat transferred throughout the earth system? Activities Spheres of Influence Spheres of Influence: The Earth's Differentiation Into Solid, Liquid, and Gas Layers by Neil Sitron and Dan Goldstein Introduction Any person examining their surroundings immediately realizes the vastness of what envelopes him. However, the visible objects of the Earth pale in comparison to what is going on, unseen and unnoticed.

The Earth around us is divided into three layers, the gas layer (atmosphere), liquid layer (hydrosphere), and solid layer (land). These layers developed and evolved over the course of billions of years and are still changing today. More importantly, these layers perform constant mutations of the planet and interact with each other. The three layers, solid, liquid, and gas form the basis of what we call Planet Earth. History of the Earth's Layers The Earth, as we know it today, consists of three separate states of matter: solid, liquid, and gas. They are better known as land, sea, and air. Initially though, during its infancy, the Earth was a part-molten planet with very primitive and less clearly defined forms of each layer. The differentiation that occurred to bring about the modern day Earth took billions of years and involved several complex processes. One must first examine the formation of land. At first, Earth was a large melt, from which a nickel and iron core developed. Eventually, a solid silicate mantle evolved. The mantle became the foundation from which the crust, or modern day land, was formed. To explain the crust's evolution, it was proposed that the crust of the continents originated from a particular mantle.

The average continental crust has properties quite similar to those of granite, but the mantle has properties closer to ocean-floor basalt and chondritic meteorites. Through a process called "chemical fractionation", a concentration of relatively light elements distilled from the basalt mantle to form a granitic residue. This residue comprised approximately 7-8% of the original mantle. As the mantle underwent this process, numerous amounts of light elements including silicon, oxygen, potassium, sodium, aluminum, carbon, nitrogen, hydrogen, helium, and calcium rose to the surface to form a primitive crust. Through these elements, the most familiar rock-producing minerals of today were formed including alkali feldspar (KAlSi3O8 and NaAlSi3O8), quartz (SiO2), and pyroxenes (Ca [Mg, Fe] Si2O6). A complete list of these minerals can be found in Table 1. Table 1 (Batten & Dott, 126) This original continental crust did not become stable until nearly 1 billion years after the separation of the mantle from the core. During its period of instability, Earth was much hotter and saw several times more radioactive decay than today.

As a result, some crust would form, melt, and re-form again. As the Earth cooled down, however, this process ceased, and the current crust has been stable for roughly 3.5 billion years. The evolution of the Earth's atmosphere poses more of a mystery than that of the crust. In an effort to develop an accurate explanation, geologists have decided to compare our present atmosphere with that of large planets, such as Jupiter and the meteorites. Planetologists believe that the larger planets, Jupiter especially, retained the greatest percentage of original gases from the initial atmospheres of the planets. Table 2 lists the components of Earth's atmosphere and compares them to Jupiter's and the gases found on meteorites. The meteorites are widely believed to resemble the early protoplanets, so studying their various gases provides important clues to the Earth's past. Table 2 (Batten & Dott, 128) In analyzing the atmosphere's evolution, two popular hypotheses exist, both assuming that considerable free hydrogen and helium have drifted into space over time because of their small atomic masses. The great mystery that both of these hypotheses attempt to explain is the emergence of free oxygen, something that has not occurred on either Jupiter or the meteorites.

The first hypothesis is called the Photochemical Dissociation Hypothesis. Based on studies of Jupiter, it assumes that the original atmosphere contained the same primary gases that Jupiter does- ammonia, methane and water vapor. The original atmosphere contained no free oxygen nor did it contain ozone. As a result, high-energy, ultraviolet radiation could easily penetrate the atmosphere at will. One property of such intense radiation is its ability to trigger photochemical, or light-induced, reactions. The Photochemical Dissociation Hypothesis states that these reactions caused the evolution of the atmosphere through the following four step process: Step 1: The ultraviolet lights combined with the water vapor to set the hydrogen off into space and free the oxygen. 2H2O + uv light energy ----> 2H2 (freed into space) + O2 Step 2: The newly freed oxygen reacted with methane, forming carbon dioxide and additional water vapor. CH4 + 2O2 ----> CO2 + 2H2O Step 3: The oxygen also reacted with ammonia, producing nitrogen and water.

4NH3 + 3O2 ----> 2N2 + 6H2O Step 4: After converting the ammonia and methane to carbon dioxide and nitrogen, free oxygen began to accumulate as further dissociation of water vapor continued. This hypothesis states that once the water vapor reacted with the intense radiation, oxygen was freed, allowing the creation of nitrogen and carbon dioxide. Together, these three elements form the main consituents of the modern day atmosphere. The Outgassing Hypothesis presents an alternative to the Photochemical Dissociation Hypothesis. It states that most of the atmospheric gases arose from the interior by a process called "outgassing". Through outgassing, a gaseous transfer occurred between the Earth's interior and its surface, mainly through igneous activity. A perfect example of outgassing today comes from volcanoes. When volcanoes erupt, they expel steam, carbon dioxide, nitrogen, hydrogen and carbon monoxide into the air. So, according to the hypothesis, before volcanoes even existed, some other process occurred which launched gases such as nitrogen, carbon dioxide and water vapor into the atmosphere.

In contrast to the Photochemical Dissociation Hypothesis, the Outgassing Hypothesis argues that the free oxygen came from the photosynthesis of primitive organisms which existed 1.5 - 3.5 billion years ago. The oxygen took approximately 2 billion years to become free, but when it did, it formed the ozone layer, eliminating the dangerous radiation and setting up the foundation for a habitable planet. In either example, the formation of the atmosphere no doubt included the presence of water vapor. This water vapor, in turn, accumulated and liquefied to form the seas and oceans that today comprise over two thirds of the Earth's surface. Geologists do not concern themselves so much with how the water vapor liquefied; instead, they tend to focus on the rate at which the water accumulated over time. Initially, it was assumed that the water grew at a constant rate over time. Others believed that the rate of accumulation of sea water would depend exclusively on atmospheric production. The atmospheric production, in turn, depended on chemical fractionation, based on the hypothesis' link between the Earth's interior and atmospheric gases of nitrogen, carbon dioxide and water vapor.

Thus, it was reasoned that the rate of accumulation grew (and still does grow) in direct proportion to an inferred increase of the volume of the continental crust over time. Geologists have compared estimates analyzing the rate of releases of helium and argon from the interior into the atmosphere. It is believed that if water was released at a comparable rate, then the water would accumulate over a long period of time, but not at a constant rate. Most likely, crustal growth and outgassing were far more rapid earlier in the Earth's history as a result of the immense radioactivity that existed. Table 3 shows a graph of the water accumulating at a constant rate and plots it against the proposed accumulation rate. As a result, the water accumulated at a faster rate as well and has gradually increased at a decreasing rate over the past 2 billion years. SOLID LAYER A computer-generated model isolating the Geosphere, picturing the world as if the Hydrosphere did not exist ( The exterior of the Earth represents the planet's solid layer. Its base is formed by the uppermost part of the mantle, known as the lithosphere which contains the rigid material of the outer portion of the Earth.

The lithosphere possesses a thin, rocky outer layer called the crust. The crust ranges in thickness, from 30-60 kilometers thick beneath the continents to only 5-10 kilometers thick beneath the oceans. Bedrock of the crust is covered by loose rock particles called the regolith that forms when bedrock reacts with the atmosphere and hydrosphere. When nature transports regolith to a different location, the regolith is re-named sediment, which means "settling". The upper portion of regolith creates soil, which permits the growth of plants and crops that are crucial for human survival. The regions on the Earth where life can evolve belong to the biosphere. The biosphere is defined as all the Earth's living matter as well as all dead plants and animals that have not yet been completely decomposed. The biosphere has a maximum range of 20 kilometers in thickness and ranges from the depths of the oceans to the peaks of the highest mountains. It is primarily composed of various compounds of carbon, hydrogen and oxygen. Continents, or continental masses, refer to the major land areas of the world. Continental masses comprise roughly 30% of the surface of the Earth and average approximately 800 meters in altitude.

The continents are underlain by ancient rocks, dating as far back in time as 3.9 billion years. An interesting point, however, is that the materials which comprise the continents all resulted from the geological cycle that transformed the Earth from its primitive state to its modern one. No remnants of any materials from the Earth's infant stage have ever been found in the continents. Research has shown that the most accurate way to analyze the continents is to organize them into several large regions where the surface morphology and the various rocks display similar traits. These regions are called physiographic provinces. Examples include mountains, plains, plateaus, and shields. A mountain is a physiographic province defined as a landmass that stands 400 meters higher or more than its surroundings. Cordilleras, a Spanish term meaning "strings", is a pseudonym for the various mountain belts of the Earth. A cordilleras has several individual parts based on morphology, including mountain ranges, mountain systems, and mountain chains. Plains represent a second type of physiographic province. Because of the minimal variations between their lowest and highest points, plains are quite flat.

Beneath the plains are sediments, and the addition of new layers of these sediments causes the surface area of plains to grow. Plains are most often found in coastal regions or large regions within the interiors of the continents. A high-standing area within which the rock strata are generally horizontal is a third physiographic province called a plateau. Plateaus can be viewed as elevated plains. Usually, they result when the sediments underlying a former plains area cement together and subsequently elevate. Not all plateaus are underlain by sediments; some are formed by layers of volcanic rocks. Shields, the fourth physiographic province, are low-lying regions which form when several ancient mountain belts join together. Shield areas are relatively thick and rigid continental blocks. The regions on the Earth where life can evolve belong to the biosphere. The biosphere is defined as "the totality of the Earth's living matter and, in addition, dead plants and animals that have not yet been completely decomposed." The biosphere has a maximum range of 20 kilometers in thickness and ranges from the depths of the oceans to the peaks of the highest mountains. It is primarily composed of various compounds of carbon, hydrogen, and oxygen.

The Liquid Layer A computer-generated model of the Hydrosphere detailing the average daily temperature of the Earth's water supply ( The liquid layer of the Earth is called the hydrosphere and it represents the entire conglomeration of water bodies enveloping the earth's surface. The hydrosphere consists of the rivers, streams, lakes and oceans, while its sub-category, the cryosphere, is made up of the temporarily frozen, solid water bodies such as ice, snow and glaciers. The liquid layer of the earth covers approximately three-quarters of the earth's surface, of which oceans comprise ninety-seven percent. The distribution of the liquid layer of the earth is shown on Table 4. The daily changes in the liquid layer is explained by the "hydrologic cycle." The Sun's heat evaporates the water of the hydrosphere. The newly-created water vapor rises into the atmosphere, cools, condenses, and becomes precipitation, falling back onto the land and into the oceans, lakes, and rivers. The hydrologic cycle describes the movement of water in its three states: solid, liquid and gas.

The evaporation and precipitation of the water, the hydrosphere of planet Earth, recycles and rejuvenates the Earth and its water supply each and every day. Evaporation and precipitation across the Earth is in total balance, though evaporation is greater than precipitation over the oceans and the reverse is true over the land. Water vapor usually averages twelve days in the atmosphere before coming back down to Earth again as rain or snow. This difference is corrected by the flow of rivers into the oceans and balance is maintained. Table 3 (Batten & Dott, 131) The hydrosphere has three main functions which make it so important to the planet Earth. First, water shapes the earth's surface by eroding certain areas and relocating those materials. Ocean waves are a primary instrument of erosion. Surf zone abrasion is an example of this. The sediment carried by the waves smashes into the beach and the constant action wears down the surf zone, smoothing and flattening the land. Second, the oceans serve as basins for the accumulation of almost all of the substances available on Earth. The rivers of the hydrosphere collect materials and sediment and bring them out to the interconnected oceans.

As a result, fine-grained, course-grained and evaporite sediments can all be found in the oceans. Also, terrigenous sediment, materials eroded by waves, carried by rivers, and blown by the wind, combine with pelagic sediment--marine organic materials referred to as deep-sea ooze--dissolve into the ocean waters and collect on the ocean floor. However, the hydrosphere is not just pure water. Through erosion and movement of sediment, several compounds have become dissolved in the water. Three to four percent of ocean water is mineral matter in solution, of which seventy-five percent is sodium chloride (NaCl--common table salt). Most of this mineral matter is contained in the oceans and only a minimal amount exists in the lakes and streams. Most importantly, the hydrosphere's third function is to be used as an essential building block and sustainer of virtually all life forms. However, one must not ignore the fact that although most people think of this as virtually the only important function of the liquid layer, the importance is actually in the proper operation of all of the functions and the successful interaction of the hydrosphere and the solid and gas layers.

The Gas Layer The outermost layer of Earth is the gas layer, better known as the atmosphere. The atmosphere is composed primarily of nitrogen and oxygen, but is also comprised of several trace gases such as carbon dioxide (CO2) and water vapor. All of these gases, which together form what is commonly called "air", are held to the Earth by the pull of gravity and each serves an important function. Carbon dioxide gas provides a barrier which keeps heat from escaping the Earth; this is known as the "greenhouse effect." The "greenhouse effect" caused by carbon dioxide in the atmosphere serves to maintain a temperature on Earth great enough to sustain life. Yet, if the amount of carbon dioxide gas were to increase drastically, too much heat would be trapped in the atmosphere, making it too hot for many organisms to survive. This causes a frightful problem wherein a certain balance of CO2 gas must be maintained to ensure that life may be maintained on the planet. Carbon dioxide also serves as the lifeline to most plants, allowing them to breath by taking in the carbon dioxide and emitting oxygen gas. Another gas, ozone (O3) screens out the harmful ultraviolet rays emanating from the sun.

One of the most abundant gases in the atmosphere, oxygen, is needed for animals to breath and live. This graph shows the range of predictions made as to the global-mean surface temperature during the next eighty years ( The gas layer is constantly moving around the Earth in the form of wind and filling the openings of the solid layer of Earth that have not yet been penetrated by water. The movement of wind is created by the uneven pattern of the Sun's heat on Earth, wherein the heat is greater near the equator than at the poles. This causes the equatorial air to expand, become less dense, and move toward the poles, where it will cool, contract, become more dense and flow toward the equator. However, the Coriolis effect modifies this pattern by forcing the air to clump into wind belts. The Coriolis effect causes any body that moves freely with respect to the rotating solid of the Earth to veer toward the right in the Northern Hemisphere and towards the left in the Southern Hemisphere. The Coriolis effect manipulates the movement of the Earth's gaseous layer and the flow of air becomes curved east in the north and west in the south instead of merely moving north and south between the poles.

A satellite image of cloud movements and formations over Europe, with the political boundaries artificially superimposed ( The atmosphere works as a geological agent of movement and erosion in two ways: wind and rock weathering. Winds are often extremely violent and can do extensive damage and erode land in a short period of time. Rock weathering, though, also erodes land but in a much slower process. Rock weathering slowly loosens material so that streams, gravity, and other instruments may carry it to the oceans. The atmosphere's interaction with the hydrosphere, the liquid layer of the Earth, is extremely important, as the gas layer holds water vapor (water in a gaseous state, caused by heat from the sun) and redistributes it back to the Earth's surface. The gas layer's role in the hydrologic cycle is to carry the evaporated water and cool it back down, then release it as precipitation. Without an atmosphere, water vapor would merely escape into space and the Earth's water supply would deplete. The atmosphere is the reason why rain is possible on the planet Earth. Conclusion The differentiation process that occurred on Earth was both lengthy and complicated.

Over the course of nearly 4.5 billion years, the Earth has transformed from a molten protoplanet to a world with clear, beautiful oceans, majestic mountains, and an atmosphere that can sustain human, animal, and plant life. While the process was tedious, the results are undeniable. Had the Earth not differentiated into solid, liquid, and gas layers, life never would have evolved. But will life as we know it continue forever on Earth? Today's research suggests otherwise. Most scientists believe that several billion years from now the sun will burn out, killing any and all life forms remaining on the Earth. A more immediate problem faces the life-forms on Earth. Because of human negligence, (mainly in the form of pollution), the solid, liquid, and gas layers of the Earth are being threatened. The extent of the damage is unknown at this time. Should humans continue, however, to pollute the oceans, destroy the land and erode the ozone layer, the consequences will be frightening. The differentiation process took billions of years; reversing it may not take as long. Glossary of Terms Atmosphere : The gas layer of the Earth, primarily consisting of nitrogen, oxygen, carbon dioxide, and water vapor.

Bedrock : Large quantities of solid rock which form the primary composition of the crust. Chemical Fractionation : A concentration of relatively light elements which distilled to form a granitic residue. Continental Masses : The major land areas of the world. Cordilleras : Spanish for "strings". Refers to the Earth's mountain belts. Corlolis Effect : Effect that causes any body of air that moves freely with respect to the rotating solid of Earth to move towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere Cryosphere : A sub-category of the hydrosphere consisting of the temporarily frozen, solid water bodies including snow, ice, and glaciers. Greenhouse Effect : Occurs when carbon dioxide gas provides a barrier which keeps heat from escaping the Earth. It serves to maintain a temperature on Earth great enough to sustain life. Hydrologic Cycle : The cyclic movement of water through evaporation, precipitation, wind transport, stream flow, percolation, and related processes. Hydrosphere : The liquid layer of the Earth. The entire conglomeration of water bodies enveloping the Earth's surface. Lithosphere : The uppermost portion of the Earth's mantle.

Outgassing Hypothesis : Hypothesis which states that atmosphere gases arose from the interior of the Earth through igneous activity, such as volcanoes. Photochemical Dissociation Hypothesis : Hypothesis which states that intense ultraviolet radiation triggered photochemical reactions which caused the evolution of the modern-day atmosphere on Earth. Physiographic Province : A large continental region where the surface morphology and various rocks display similar traits to each other. Plains : A physiographic province with little variation between its lowest and highest points. Plateau : A physiographic province. It is a high standing area whose rock strata are horizontal. Regolith : A sheet of loose particles covering the bedrock. It plays a vital role in plant growth by creating soil. Rock Weathering : A form of erosion which slowly loosens material so that streams, gravity, and other instruments carry it to the oceans. Sediment : Regolith which is transported to a different location by nature. Surf Zone Abrasion : One method of shaping the Earth's surface caused by ocean waves which erode certain areas. Resources Batten, Roger L. and Robert H. Dott. Evolution of the Earth.

New York: McGraw-Hill Book Company, 1971. Landes, Kenneth K. Physical Geology and Man. New York: Prentice-Hall, Inc., 1948. Menard, H.W. Geology, Resources, and Society. San Francisco: W.H. Freeman and Company, 1974. Porter, Steven C. and Brian J. Skinner. The Dynamic Earth. New York: John Wiley and Sons, 1989. Sanders, John E. Principles of Physical Geology. New York: John Wiley and Sons, 1981. Atmosphere A planet's climate is decided by its mass, its distance from the sun and the composition of its atmosphere. Earth's atmosphere is 78% nitrogen, 21% oxygen, and 1% other gases. Carbon dioxide accounts for just 0.03 - 0.04%. Water vapour, varying in amount from 0 to 2%, carbon dioxide and some other minor gases present in the atmosphere absorb some of the thermal radiation leaving the surface and emit radiation from much higher and colder levels out to space.

These radiatively active gases are known as greenhouse gases because they act as a partial blanket for the thermal radiation from the surface and enable it to be substantially warmer than it would otherwise be, analogous to the effect of a greenhouse. This blanketing is known as the natural greenhouse effect. Without the greenhouse gases, Earth's average temperature would be roughly -20°C. T The atmosphere is a cloud of gas and suspended solids extending from the Earth's surface out many thousands of miles, becoming increasingly thinner with distance but always held by the Earth's gravitational pull. The atmosphere is made up of layers. it surrounds the Earth and holds the air we breathe; it protects us from outer space; and holds moisture (clouds), gases, and tiny particles. In short, the atmosphere is the protective bubble we live in. This protective bubble consists of several gases (listed in the table to the right) with the top four making up 99.998% of all gases. Of the dry composition of the atmosphere nitrogen, by far, is the most common. Nitrogen dilutes oxygen and prevents rapid burning at the Earth's surface. Living things need it to make proteins. Oxygen is used by all living things and is essential for respiration.

It is also necessary for combustion or burning. Argon is used in light bulbs, in double-pane windows, and to preserve the original Declaration of Independence and the Constitution. Plants use carbon dioxide to make oxygen. Carbon dioxide also acts as a blanket that prevents the escape of heat into outer space. These percentages of atmospheric gases are for a completely dry atmosphere. The atmosphere is rarely, if ever, dry. Water vapor (water in a 'gas' state) is nearly always present up to about 4% of the total volume. In the Earth's desert regions (30°N/S) when dry winds are blowing, the water vapor contribution to the composition of the atmosphere will be near zero. Water vapor contribution climbs to near 3% on extremely hot/humid days. The upper limit, approaching 4%, is found in tropical climates. The table below shows the changes in atmospheric composition with the inclusion of different amounts of water vapor. The earth's atmosphere is a very thin layer wrapped around a very large planet. Two gases make up the bulk of the earth's atmosphere: nitrogen ( ), which comprises 78% of the atmosphere, and oxygen ( ), which accounts for 21%. Various trace gases make up the remainder.

Based on temperature, the atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere. Energy is transferred between the earth's surface and the atmosphere via conduction, convection, and radiation. Ocean currents play a significant role in transferring this heat poleward. Major currents, such as the northward flowing Gulf Stream, transport tremendous amounts of heat poleward and contribute to the development of many types of weather phenomena. Cambridge University Graphic The atmosphere is divided into five layers. It is thickest near the surface and thins out with height until it eventually merges with space. 1) The troposphere is the first layer above the surface and contains 70 to 80 per cent of the Earth's atmosphere. Weather occurs in this layer. 2) Many jet aircrafts fly in the stratosphere because it is very stable. Also, the ozone layer absorbs harmful rays from the Sun. 3) Meteors or rock fragments burn up in the mesosphere. 4) The thermosphere is a layer with auroras. It is also where the space shuttle orbits. 5) The atmosphere merges into space in the extremely thin exosphere. This is the upper limit of our atmosphere. National Geographic Video U.S.

Weather Service Graphic The inhabitants of our planet live in the Troposphere. Earth's atmosphere varies in density and composition as the altitude increases above the surface. The lowest part of the atmosphere is called the troposphere (and it extends from the surface up to about 10 km (6 miles). The gases in this region are predominantly molecular Oxygen ( O2 ) and molecular Nitrogen ( N2 ). All weather is confined to this lower region and it contains 70 to 80 per cent of the Earth's atmosphere and 99% of the water vapor. The highest mountains are still within the troposphere and all of our normal day-to-day activities occur here. The high altitude jet stream is found near the tropopause at the the upper end of this region. The layer above this is the Stratosphere, this is where the Ozone Layer is formed. The atmosphere above 10 km is called the stratosphere. The gas is still dense enough that hot air balloons can ascend to altitudes of 15 - 20 km and Helium balloons to nearly 35 km, but the air thins rapidly and the gas composition changes slightly as the altitude increases.

Within the stratosphere, incoming solar radiation at wavelengths below 240 nm. is able to break up (or dissociate) molecular Oxygen ( O2 ) into individual Oxygen atoms, each of which, in turn, may combine with an Oxygen molecule ( O2 ), to form ozone, a molecule of Oxygen consisting of three Oxygen atoms ( O3 ). This gas reaches a peak density of a few parts per million at an altitude of about 25 km (16 miles). The Ozone Layer absorbs ultra-violet radiation from the Sun. Without the Ozone Layer life as we know would cease to exist on our planet. Ozone is important because it is the only atmospheric gas which absorbs light in the B region of UVB rays. The Ozone layer extends from a height of 20 kilometers to 60 kilometers above the Earth's surface. The air is very thin at these altitudes. If all of the Ozone in the Earth's atmosphere were compressed into a single layer at the Earth's surface, it would only be 3 millimeters thick-basically two stacked pennies! The gas becomes increasingly rarefied at higher altitudes.

At heights of 80 km (50 miles), the gas is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. The existence of charged particles at this altitude and above, signals the beginning of the ionosphere a region having the properties of a gas and of a plasma. Visionlearning | Earth Science | Composition of Earth's Atmosphere Composition of Earth's Atmosphere ozone : a form of oxygen, O3, produced by the reaction of sunlight with O2 pressure : the application of force; the weight of air in the atmosphere surface : the outside or external part; the topside face of something Glossary Terms The fact that the moon's surface is covered with meteorite impact craters is obvious to us today. Though the moon is not far from us, impact craters are few and far between on Earth. As it turns out, Earth has received just as many incoming meteorites as the moon, but the presence of the atmosphere has determined the fate of many of them. Small meteorites burn up in the atmosphere before ever reaching Earth.

Those that do hit the surface and create an impact crater are lost to us in a different way – the craters are quickly eroded by weather generated in the atmosphere, and the evidence is washed away. The moon, on the other hand, has no atmosphere, and thus every meteor aimed at the moon hits it, and the craters have remained essentially unchanged for 4 billion years (Figure 1). Figure 1: Craters on the far side of the moon (L) and Manicouagan crater in Quebec (R). Image courtesy of NASA. Composition of Earth's atmosphere The early Greeks considered "air" to be one of four elementary substances; along with earth, fire, and water, air was viewed as a fundamental component of the universe . By the early 1800s, however, scientists such as John Dalton recognized that the atmosphere was in fact composed of several chemically distinct gases, which he was able to separate and determine the relative amounts of within the lower atmosphere. He was easily able to discern the major components of the atmosphere: nitrogen, oxygen, and a small amount of something incombustible, later shown to be argon.

The development of the spectrometer in the 1920s allowed scientists to find gases that existed in much smaller concentrations in the atmosphere , such as ozone and carbon dioxide. The concentrations of these gases, while small, varied widely from place to place. In fact, atmospheric gases are often divided up into the major, constant components and the highly variable components, as shown in Table 1 and Table 2. Nitrogen (N2) Nitrogen oxides (NO, NO2, N20) trace​ Table 2: Variable Components. Amounts vary over time and location. Although both nitrogen and oxygen are essential to human life on the planet, they have little effect on weather and other atmospheric processes. The variable components, which make up far less than 1 percent of the atmosphere , have a much greater influence on both short-term weather and long-term climate . For example, variations in water vapor in the atmosphere are familiar to us as relative humidity.

Water vapor, CO2, CH4, N2O, and SO2 all have an important property: They absorb heat emitted by Earth and thus warm the atmosphere, creating what we call the "greenhouse effect." Without these so-called greenhouse gases, the Earth's surface would be about 30 degrees Celsius cooler – too cold for life to exist as we know it. Though the greenhouse effect is sometimes portrayed as a bad thing, trace amounts of gases like CO2 warm our planet's atmosphere enough to sustain life. Global warming, on the other hand, is a separate process that can be caused by increased amounts of greenhouse gases in the atmosphere. In addition to gases, the atmosphere also contains particulate matter such as dust, volcanic ash, rain, and snow. These are, of course, highly variable and are generally less persistent than gas concentrations , but they can sometimes remain in the atmosphere for relatively long periods of time. Volcanic ash from the 1991 eruption of Mt. Pinatubo in the Philippines, for example, darkened skies around the globe for over a year. Though the major components of the atmosphere vary little today, they have changed dramatically over Earth's history, about 4.6 billion years.

The early atmosphere was hardly the life-sustaining blanket of air that it is today; most geologists believe that the main constituents then were nitrogen gas and carbon dioxide, but no free oxygen. In fact, there is no evidence for free oxygen in the atmosphere until about 2 billion years ago, when photosynthesizing bacteria evolved and began taking in atmospheric carbon dioxide and releasing oxygen. The amount of oxygen in the atmosphere has risen steadily from 0 percent 2 billion years ago to about 21 percent today. Comprehension Checkpoint Nitrogen and oxygen, which make up more than 99% of Earth's atmosphere, have a bigger influence on climate than other components of the atmosphere. a.true b.false Measuring the atmosphere We now have continuous satellite monitoring of the atmosphere and Doppler radar to tell us whether or not we will experience rain anytime soon; however, atmospheric measurements used to be few and far between. Today, measurements such as temperature and pressure not only help us predict the weather, but also help us look at long-term changes in global climate (see our Temperature module). The first atmospheric scientists were less concerned with weather prediction, however, and more interested in the composition and structure of the atmosphere.

The two most important instruments for taking measurements in Earth's atmosphere were developed hundreds of years ago: Galileo is credited with inventing the thermometer in 1593, and Evangelista Torricelli invented the barometer in 1643. With these two instruments, temperature and pressure could be recorded at any time and at any place. Of course, the earliest pressure and temperature measurements were taken at Earth's surface . It was a hundred years before the thermometer and barometer went aloft. While many people are familiar with Ben Franklin's kite and key experiment that tested lightning for the presence of electricity, few realize that kites were the main vehicle for obtaining atmospheric measurements above Earth's surface . Throughout the 18th and 19th centuries, kite-mounted instruments collected pressure, temperature, and humidity readings; unfortunately, scientists could only reach up to an altitude of about 3 km with this technique. Figure 2: Scientist launches a radiosonde. Instruments for collecting data are in the white and orange box.

image © NASA Jet Propulsion Laboratory Unmanned balloons were able to take measurements at higher altitudes than kites, but because they were simply released with no passengers and no strings attached, they had to be retrieved in order to obtain the data that had been collected. This changed with the development of the radiosonde, an unmanned balloon capable of achieving high altitudes, in the early 1930s. The radiosonde included a radio transmitter among its many instruments, allowing data to be transmitted as it was being collected so that the balloons no longer needed to be retrieved. A radiosonde network was developed in the United States in 1937, and continues to this day under the auspices of the National Weather Service. Comprehension Checkpoint What was an advantage of the radiosonde over earlier data collection instruments? a.The radiosonde was easy to retrieve. b.The radiosonde did not need to be retrieved. Temperature in the atmosphere Through examination of measurements collected by radiosonde and aircraft (and later by rockets), scientists became aware that the atmosphere is not uniform.

Many people had long recognized that temperature decreased with altitude – if you've ever hiked up a tall mountain, you might learn to bring a jacket to wear at the top even when it is warm at the base – but it wasn't until the early 1900s that radiosondes revealed a layer, about 18 km above the surface , where temperature abruptly changed and began to increase with altitude. The discovery of this reversal led to division of the atmosphere into layers based on their thermal properties. Figure 3: This graph shows how temperature varies with altitude in Earth's atmosphere. The lowermost 12 to 18 km of the atmosphere , called the troposphere, is where all weather occurs – clouds form and precipitation falls, wind blows, humidity varies from place to place, and the atmosphere interacts with the surface below. Within the troposphere , temperature decreases with altitude at a rate of about 6.5° C per kilometer. At 8,856 m high, Mt. Everest still reaches less than halfway through the troposphere.

Assuming a sea level temperature of 26° C (80° F), that means the temperature on the summit of Everest would be around -31° C (-24° F)! In fact, temperature at Everest's summit averages -36° C, whereas temperatures in New Delhi (in nearby India), at an elevation of 233 m, average about 28° C (82.4° F). At the uppermost boundary of the troposphere , air temperature reaches about -100° C and then begins to increase with altitude. This layer of increasing temperature is called the stratosphere. The cause of the temperature reversal is a layer of concentrated ozone . Ozone's ability to absorb incoming ultraviolet (UV) radiation from the sun had been recognized in 1881, but the existence of the ozone layer at an altitude of 20 to 50 km was not postulated until the 1920s. By absorbing UV rays, the ozone layer both warms the air around it and protects us on the surface from the harmful short-wavelength radiation that can cause skin cancer.

It is important to recognize the difference between the ozone layer in the stratosphere and ozone present in trace amounts in the troposphere . Stratospheric ozone is produced when energy from the sun breaks apart O2 gas molecules into O atoms ; these O atoms then bond with other O2 molecules to form O3, ozone. This process was first described in 1930 by Sydney Chapman , a geophysicist who synthesized many of the known facts about the ozone layer . Tropospheric ozone, on the other hand, is a pollutant produced when emissions from fossil-fuel burning interact with sunlight. Above the stratosphere , temperature begins to drop again in the next layer of the atmosphere called the mesosphere, as seen in the previous figure. This temperature decrease results from the rapidly decreasing density of the air at this altitude. Finally, at the outer reaches of Earth's atmosphere, the intense, unfiltered radiation from the sun causes molecules like O2 and N2 to break apart into ions . The release of energy from these reactions actually causes the temperature to rise again in the thermosphere, the outermost layer.

The thermosphere extends to about 500 km above Earth's surface , still a few hundred kilometers below the altitude of most orbiting satellites. Comprehension Checkpoint All weather, including clouds, wind, and precipitation, occurs in the a.troposphere. Pressure in the atmosphere Figure 4: Pressure and density decrease rapidly with altitude. Atmospheric pressure can be imagined as the weight of the overlying column of air. Unlike temperature, pressure decreases exponentially with altitude. Traces of the atmosphere can be detected as far as 500 km above Earth's surface , but 80 percent of the atmosphere's mass is contained within the 18 km closest to the surface. Atmospheric pressure is generally measured in millibars (mb); this unit of measurement is equivalent to 1 gram per centimeter squared (1 g/cm2). Other units are occasionally used, such as bars, atmospheres, or millimeters of mercury. The correspondence between these units is shown in the table below. bars 760 mm Hg Table 3: Correspondence of atmospheric measurement units .

At sea level, pressure ranges from about 960 to 1,050 mb , with an average of 1,013 mb. At the top of Mt. Everest, pressure is as low as 300 mb. Because gas pressure is related to density , this low pressure means that there are approximately one-third as many gas molecules inhaled per breath on top of Mt. Everest as at sea level – which is why climbers experience ever more severe shortness of breath the higher they go, as less oxygen is inhaled with every breath. Though other planets host atmospheres , the presence of free oxygen and water vapor makes our atmosphere unique as far as we know. These components both encouraged and protected life on Earth as it developed, not only by providing oxygen for respiration , but by shielding organisms from harmful UV rays and by incinerating small meteors before they hit the surface . Additionally, the composition and structure of this unique resource are important keys to understanding circulation in the atmosphere, biogeochemical cycling of nutrients , short-term local weather patterns, and long-term global climate changes. Summary Earth's atmosphere contains many components that can be measured in different ways.

This module describes these different components and shows how temperature and pressure change with altitude. The scientific developments that led to an understanding of these concepts are discussed. Key Concepts Earth's atmosphere is made up of a combination of gases. The major components of nitrogen, oxygen, and argon remain constant over time and space, while trace components like CO2 and water vapor vary considerably over both space and time. The atmosphere is divided into the thermosphere, mesosphere, stratosphere, and troposphere, and the boundaries between these layers are defined by changes in temperature gradients. Pressure decreases exponentially with altitude in the atmosphere. Our knowledge about the atmosphere has developed based on data from a variety of sources, including direct measurements from balloons and aircraft as well as remote measurements from satellites. Further Reading troposphere Report The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth. The troposphere is bonded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on bottom by the surface of the Earth. The troposphere is wider at the equator (10mi) than at the poles (5mi).

The troposphere contains 75 percent of atmosphere's mass- on an average day the weight of the molecules in the air is14.7 lb..(sq. in.)- and most of the atmosphere's water vapor. Water vapor concentration varies from trace amounts in Polar Regions to nearly 4 percent in the tropics. Most prevalent gases are nitrogen (78 percent) and oxygen (21 percent), with the remaining 1- percent consisting of argon, (.9 percent) and traces of hydrogen ozone ( a form of oxygen), and other constituents. Temperature and water vapor content in the troposphere decrease rapidly with altitude. Water vapor plays a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet's surface. The troposphere contains 99% of the water vapor in the atmosphere. Water vapor concentrations vary with latitudinal position(north to south).

They are greatest above the tropics, where they might be as high as 3% and decrease toward the polar regions Carbon dioxide is present in small amounts, but its concentration has nearly doubled since 1900.Like water vapor, carbon dioxide is a greenhouse gas which traps some of the Earth's heat close to the surface and prevents its release into space. Scientists fear that the increasing amounts of carbon dioxide could raise the Earth's surface temperature during the next century, bringing significant changes to worldwide weather patterns. Such changes may include a shift in climatic zones and the melting of the polar ice caps, which could raise the level of the world's oceans. The uneven heating of the regions of the troposphere by the sun ( the sun warms the air at the equator more than the air at the poles )causes convection currents, large-scale patterns of winds that move heat and moisture around the globe. In the Northern and Southern hemispheres, air rises along the equator and subpolar ( latitude about 50 to about 70 north and south ) climatic regions and sinks in the polar and subtropical regions.

Air is deflected by the Earth's rotation as it moves between the poles and equator, creating belts of surface winds moving from east to west ( easterly winds ) in tropical and polar regions, the winds moving from west to east ( westerly winds ) in the middle latitudes. This global circulation is disrupted by the circular wind patterns of migrating high and low air pressure areas, plus locally abrupt changes in wind speed and direction known as turbulence. A common feature of the troposphere of densely populated areas is smog, which restricts visibility and is irritating to the eyes and throat. Smog is produced when pollutants accumulate close to the surface beneath an inversion layer ( a layer of air in which the usual rule that temperature of air decreases with altitude doesn't apply ), and undergo a series of chemical reactions in the presence pollutants from escaping into the upper atmosphere. Convection is the mechanism responsible for the vertical transport of heat in the troposphere while horizontal heat transfer is accomplished through advection. The exchange and movement of water between the earth and atmosphere is called the water cycle. The cycle, which occurs in the troposphere, begins as the sun evaporates large amounts of water from the earth's surface and the moisture is transported to other regions by the wind.

As air rises, expands, and cools, water vapor condenses and clouds develop. Clouds cover large portions of the earth at any given time and vary from fair weather cirrus to towering cumulus clouds. When liquid or solid water particles grow large enough in size, they fall toward the earth as precipitation. The type of precipitation that reaches the ground, be it rain, snow, sleet, or freezing rain, depends upon the temperature of the air through which it falls. As sunlight enters the atmosphere, a portion is immediately reflected back to space, but the rest penetrates the atmosphere and is absorbed by the earth's surface. This energy is then remitted by the earth back into atmosphere as long-wave radiation. Carbon dioxide and water molecules absorb this energy and emit much of it back towards the earth again. This delicate exchange of energy between the earth's surface and atmosphere keeps the average global temperature from changing drastically from year to year.

The troposphere contains 75% of the atmosphere's total mass In either space or time the troposphere is not constant Weather occurs in the troposphere The troposphere is 10 miles from the equator The troposphere is 5-7 miles above the poles Does not contain ozone The altitude of the tropopause at the poles is 5 miles The temperature in the troposphere can reach -80*C The troposphere contains ozone. True or False the troposphere can reach . What percentage of the total mass of the atmosphere does the troposphere contain? How high is the troposphere from the equator? What occurs in the troposphere? The height of the tropopause ceiling is not constant in time or space. True or False The altitude of the troposphere from the poles is . A.3 miles The troposphere is miles above earth. A.1to3 What goes on in the troposphere? weather What's so important about the troposphere?. it contains weather and the oxygen that we breath Is the troposphere the largest atmosphere? no How big is the troposphere?

It extends 5 to 7 miles above the earth BBC - GCSE Bitesize: The modern atmosphere Next Heat can be transferred from place to place by conduction [conduction: The transfer of heat energy through a material - without the material itself moving. ], convection [convection: The transfer of heat energy through a moving liquid or gas. ] and radiation [infrared radiation: Electromagnetic radiation emitted from a hot object. ]. Dark matt surfaces are better at absorbing heat energy than light shiny surfaces. Heat energy can be lost from homes in many different ways and there are ways of reducing these heat losses. The modern atmosphere You need to know the proportions of the main gases in the atmosphere. The Earth’s atmosphere has remained much the same for the past 200 million years. The pie chart shows the proportions of the main gases in the atmosphere. The composition of air The two main gases are both elements and account for about 99 percent of the gases in the atmosphere.

They are: about 4/5 or 80 percent nitrogen (a relatively unreactive gas) about 1/5 or 20 percent oxygen (the gas that allows animals and plants to respire and for fuels to burn) The remaining gases, such as carbon dioxide, water vapour and noble gases such as argon, are found in much smaller proportions. Page:

Question: Which gas forms 80% of Earth's atmosphere?
Answer: Nitrogen