Chapter 2 Atmospheric Structure and Composition

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION CHAPTER 2 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC AtmosphericNOT FOR SALE OR DISTRIBUTION StructureNOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALEand OR DISTRIBUTION CompositionNOT FOR SALE OR DISTRIBUTION

CHAPTER AT© A Jones GLANCE & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ■ Origin of the Earth and Atmosphere ■ Atmospheric Composition ▸ Carbon Cycle ▸ Constant and Variable Gases © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC ■ Faint Young Sun Paradox NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ■ Atmospheric Structure ■ Summary ■ Key Terms ■ Review Questions © Jones & Bartlett■ Questions Learning, for Thought LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

he atmosphere is a collection of gases held the upward-directed force of buoyancy. is balance is near the Earth by gravity. It is also pulled away termed hydrostatic equilibrium. is extremely thin from the Earth© Jones because & a Bartlettvacuum exists Learning, in the LLCand delicate zone known ©as theJones atmosphere & Bartlett makes Learning, life LLC Tharsh conditions of space. One of the most funda- as we know it possible on the planet. When you look in NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION mental properties of the universe—the second law of the sky the atmosphere appears to continue innitely, thermodynamics—states that energy (and, therefore, but if Earth were the size of an apple, the atmosphere mass, because energy and mass are related by Einstein’s would have the thickness of the apple’s skin. theory of relativity) moves from areas of higher concen- Technically, the atmosphere is a subset of the air tration© Jones (in this & case, Bartlett Earth’s lowerLearning, atmosphere) LLC to areas of because ©it isJones composed & Bartlett solely of gases.Learning, By contrast, LLC air lowerNOT concentration FOR SALE (outer OR space). DISTRIBUTION e atmosphere thus containsNOT not only FOR gases SALE but also OR aerosols DISTRIBUTION—solid and represents a place where a balance is generally achieved liquid particles suspended above the surface that are too between the downward-directed gravitational force and tiny for gravity to pull downward. Solid aerosols include

11 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION.

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© Jonesice crystals,& Bartlett volcanic Learning, soot particles, LLC salt crystals from © Jones & Bartlett Learning, LLC the ocean, and soil particles; liquid aerosols include NOT FOR SALE OR DISTRIBUTION NOT FORclouds SALE and fog OR droplets. DISTRIBUTION Because the atmosphere is composed of the lightest elements gravitationally attracted to the Earth, many assume that it has little or no mass. Compared with the mass of the solid Earth© Jones (6 × 10 &24 kg; Bartlett or 6 × Learning,1021 LLC © Jones & Bartlett Learning, LLC metric tons) and oceansNOT (1.4 × FOR 1021 kg;SALE or 1.4 OR × 10 DISTRIBUTION18 NOT FOR SALE OR DISTRIBUTION metric tons), the atmosphere is indeed light. But the atmosphere has a substantial total mass of 5 × 1018 kg (5 × 1015 metric tons)! e ©mass Jones of the & air Bartlett is in constant Learning, motion, LLC giving © Jones & Bartlett Learning, LLC considerable impact to the surface environment. For NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION example, a tornado can cause catastrophic devastation to a location. In the case of a tornado, the mass of air has substantial acceleration. According to Newton’s second law of motion, force is the product of mass and © Jonesacceleration. & Bartlett e Learning, two factors combine, LLC in this situation, © Jones & Bartlett Learning, LLC NOT FORto produce SALE a ORforce DISTRIBUTION capable of devastation. NOT FOR SALE OR DISTRIBUTION e atmosphere is an extremely complex entity that FIGURE 2.1 The Orion Nebula. Courtesy of NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA), and the Hubble Space Telescope Orion Treasury must be viewed simultaneously on many levels, both Project Team. temporally and in three spatial dimensions (west–east, north–south, and vertical).© AtmosphericJones & Bartlett processes Learning, can LLC © Jones & Bartlett Learning, LLC be di cult to understand. To appreciate the nature of attracted the bulk of the elements that composed the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION the atmosphere properly, we must rst understand the nebula. Planets formed as balls of dust gravitationally origins of the atmosphere and its changes since the collected over various orbits about the primitive Sun. origin of the planet. Earth was one such ball of dust. As it grew the elements fused together and collapsed under their own weight © Jones & Bartlett Learning, LLC and gravity. As© Earth Jones grew & in Bartlett size, its gravity Learning, increased LLC ▸ OriginNOT ofFOR the SALE Earth OR DISTRIBUTION proportionately.NOT Friction FOR caused SALE the OREarth DISTRIBUTION materials to and Atmosphere melt. Melting was also encouraged by frequent impacts with large planetesimals, which were essentially small According to the best scienti c information, the uni- planets of condensed debris moving over wildly eccentric verse is thought to have begun 13.8 billion years ago. orbits about the Sun. ese planetesimals contributed © JonesAt that& Bartlett time all matter Learning, in the universe LLC was con ned to ©heavier Jones elements & Bartlett and mass Learning, to the growing LLC Earth while NOT FORa single SALE space. OR An DISTRIBUTION explosion of unimaginable propor- NOTshattering FOR and SALE melting OR its hotDISTRIBUTION surface. A collision between tion sent this matter—mostly hydrogen—outward in all Earth and a planetesimal is thought to have created the directions. Over time, gravity caused matter to collect Moon. Remnants of early solar system planetesimals in various areas of space to form galaxies. Within the are present today in the vast asteroid eld between galaxies smaller amounts ©of Jonesmatter condensed & Bartlett gravita- Learning,Mars LLC and Jupiter. e Oort cloud© —aJones collection & Bartlett of icy Learning, LLC tionally into stars. Star formationNOT FOR began SALE to occur OR when DISTRIBUTION comets and dust that surroundsNOT the outer FOR edges SALE of our OR DISTRIBUTION hydrogen was compressed under its own gravitational solar system—also acts as a relic of conditions present weight. If the mass involved was su ciently large, in the early stages of solar system formation. nuclear fusion—a process that converts lighter elements In these early times Earth’s atmosphere is believed (principally hydrogen) into heavier elements (primar- to have consisted of light and inert (noble) gases such ily helium)—began.© Jones & Such Bartlett reactions Learning, released amazingLLC as hydrogen, helium,© Jones neon, & and Bartlett argon. Learning,ese gases were LLC quantitiesNOT of radiant FOR energySALE while OR DISTRIBUTIONcreating (fusing) all e ectively sweptNOT away FOR as the SALE solar wind OR —radioactiveDISTRIBUTION matter heavier than hydrogen. particles from the Sun moving through space at nearly Occasionally, a star exploded, sending heavier ele- the speed of light—developed. Today, Earth is largely ments outward through the galaxy. Vast clouds of dust, devoid of noble gases as a result. So how did the atmo- © Jonescalled & Bartlettnebula ( FIGURELearning, 2.1), formed, LLC and the original ©sphere Jones that & we Bartlett know today Learning, form? LLC NOT FORgravitational SALE ORaccumulation DISTRIBUTION process began anew. Our NOT FOR e composition SALE OR of the DISTRIBUTION atmosphere can be explained solar system is believed to have formed from a nebula by looking at volcanic activity, which is rather limited approximately 5 billion years ago. e Sun gravitationally over Earth’s surface today but was apparently widespread

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© Jones & billionsBartlett of yearsLearning, ago as the LLC early Earth cooled slowly from© Jonesrole & in Bartlett maintaining Learning, the temperature LLC of the planet at a its primordial molten state. As volcanic material cooled, level comfortable for life in its present form. Earth’s NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION gases were released through the process of outgassing, early atmosphere apparently contained far more CO2 which primarily involved diatomic nitrogen (N2) and than today’s and little or no O2. So where did most of carbon dioxide (CO2), with lesser amounts of water the CO2 go a er outgassing in the primitive atmosphere, vapor, methane (CH4), and sulfur. e condensation and how did O2 come to replace it? of water vapor into© liquid Jones water & in Bartlett the cool atmosphere Learning, LLC e evolution of Earth’s© Jones atmospheric & Bartlett composition Learning, LLC formed clouds and NOTprecipitation. FOR SALE Precipitation OR DISTRIBUTION collected (including O2) involves signiNOT cant FOR interactions SALE withOR theDISTRIBUTION in low-elevation areas of the planet and accumulated biosphere, hydrosphere, and lithosphere. About 3.5 billion over time to form the oceans. years ago an interesting development occurred in the Our planet is unique in the solar system because of extensive waters of primordial Earth that profoundly the© presence Jones of& liquidBartlett water. Learning, is is a consequence LLC of a ected the© Jones evolution & ofBartlett the atmosphere. Learning, Single-celled LLC many related, and interacting, factors—some of which organisms, called prokaryotes, began to appear. ese NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION include distance to the Sun and atmospheric composi- simple ancestors of bacteria and green algae absorbed tion. Because water is essential to life, it is not surpris- nutrients directly from the surrounding environment. ing that Earth is the only planet known to support life. Prokaryotes released CO2 to the atmosphere as a byproduct of fermentation, the process by which simple © Jones & Bartlett Learning, LLC © Jonesorganisms & Bartlett acquire Learning, energy through LLC the breakdown of NOT FOR SALE▸ Atmospheric OR DISTRIBUTION Composition NOT FORfood. SALE e evolution OR DISTRIBUTION of prokaryotes led to more complex, o en multicellular, organisms called eukaryotes, which Today, the dry atmosphere consists primarily of N2 and contain more complex internal structures and release diatomic oxygen (O2). Diatomic nitrogen is a stable gas even more CO2 into the atmosphere in the process of that comprises 78% of the present-day atmospheric respiration. Most life on Earth is believed to have TABLE 2.1 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC volume ( ). e abundance of N2 has increased evolved from the further development of eukaryotes. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION as a percentage of the total atmospheric volume pri- Prokaryotes and eukaryotes would have had to develop marily because it is not removed as e ectively from in the oceans, however, because without oxygen in the the atmosphere as are most other atmospheric gases. atmosphere the protective ozone (O ) layer could not residence time 3 e —the mean length of time that an have formed to protect terrestrial life from the harmful individual© Jones molecule & Bartlett remains Learning, in the atmosphere—of LLC ultraviolet© Jones (UV) radiation & Bartlett emitted Learning, by the Sun. LLC Over N2 is believed to be approximately 16.25 million years. NOT FOR SALE OR DISTRIBUTION time, CONOT2 continued FOR to SALE accumulate, OR DISTRIBUTIONas it became a larger e next-most abundant gas in the present-day dry and larger component of the atmospheric volume. atmosphere is oxygen, comprising approximately 21% By about 3 billion years ago another major de- of the atmospheric volume. About 0.93% of the remain- velopment in the history of life on Earth apparently ing 1% of the dry atmosphere is composed mostly of caused another major change to the atmospheric com- © Jones & Bartlettargon (Ar), Learning, and a wide array LLC of atmospheric trace gases© Jonesposition. & Bartlett e early Learning, evolution LLCof eubacteria, and later, NOT FOR SALEconstitute OR the DISTRIBUTION remainder. Of these, CO2 is the fourth-NOT FORprotists, SALE and OReventually DISTRIBUTION aquatic green plants led to a most abundant gas in the dry atmosphere, representing signi cant extraction of CO2 from the atmosphere in 0.041% of the dry atmosphere, or 407 parts per million photosynthesis—the process by which green plants (ppm), as of June 2016. It plays an especially important use sunlight to synthesize food. O2 is released into the © Jones & Bartlett Learning, LLCatmosphere as a byproduct© of Jones photosynthesis. & Bartlett As green Learning, LLC plants began to populate Earth, rst in the oceans and TABLE 2.1 CompositionNOT FOR of the DrySALE Atmosphere OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION later on land a er the presence of O2 gradually led to the formation of ozone (O3) and the O3 layer—atmospheric Gas Percentage of Air CO2 decreased in concentration while atmospheric O2 simultaneously increased. Today most of the atmospheric ©Nitrogen Jones (N 2&) Bartlett Learning,78.08 LLC CO is stored© Jones in vast & quantitiesBartlett ofLearning, sedimentary LLC rock, 99.03 2 NOT FOR SALE OR DISTRIBUTION originallyNOT extracted FOR from SALE the atmosphere OR DISTRIBUTION by living things. Diatomic oxygen (O2) 20.95 e amount of atmospheric O2 present today represents a Argon (Ar) 0.93 similar percentage to that of CO2 in the early atmosphere.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Carbon dioxide (CO2) 0.041 Carbon Cycle NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION All others 0.003 e process described above essentially represents the atmospheric component of the carbon cycle, the

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© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC CO2 in NOT FOR SALE OR DISTRIBUTION NOTatmosphere FOR SALE OR DISTRIBUTION Combustion of fuels Diffusion Respiration © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT PhotosynthesisFOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

Dissolved CO2 © Jones & Bartlett Learning, LLC ©Photosynthesis Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Respiration

Death and decay Death and decay Fossil fuels Carbonates © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning,in sediment LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

FIGURE 2.2 The global carbon© cycle.Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION continuous movement of carbon through the Earth– biological processes. Residence time associated with ocean–atmosphere system. Carbon can exist in various the biosphere may be examined on a number of levels. Earth–ocean–atmosphere reservoirs—the components Carbon is held directly in the biosphere as long as the of a system© Jones that e ectively & Bartlett store matterLearning, and/or LLC energy living organism© remains Jones alive. & Bartlett Once the Learning,organism dies, LLC for a certainNOT period FOR of SALE time, a OR er which DISTRIBUTION they allow for carbon exits thisNOT sink FOR as the SALE remains OR of theDISTRIBUTION organism the movement (ﬂ u x ) of that matter and/or energy to decay. Some of this carbon may become buried naturally another component of the system. Carbon reservoirs and transported into the rock reservoir. is process is include the atmosphere, which houses CO2; the bio- e ective in marine environments where an abundance sphere, which comprises all living matter; and the oceans, of organic matter lters to the ocean oor, building huge © Joneswhich & Bartlett include dissolved Learning, carbonates LLC (FIGURE 2.2). Over ©layers Jones of organic & Bartlett matter Learning, over time. Some LLC of the decay- NOT FORtime carbonSALE cyclesOR DISTRIBUTION among these various reservoirs. e NOTing carbon FOR dissolves SALE OR directly DISTRIBUTION into water, becoming part carbon residence time is di erent for each reservoir, with of the oceanic carbon reservoir, and some reenters the the rates of exchange directly related to the size of the atmosphere through diﬀ usion. Much oceanic biomass reservoir. e largest carbon reservoir, comprising the eventually solidi es into sedimentary rock. Finally, the vast majority of carbon in ©the Jones Earth–ocean–atmosphere & Bartlett Learning, atmosphere LLC represents the smallest© Jonescarbon sink, & Bartlett and the Learning, LLC system, is sedimentary rock,NOT which FOR may SALE store OR carbon DISTRIBUTION carbon exchange rate to this reservoirNOT FOR is rapid—only SALE OR DISTRIBUTION for billions of years. about 100 years. e second-largest reservoir is the oceans, which e natural carbon cycle is being disrupted by human act as a sink for atmospheric CO2 by absorbing many activities. Since the dawn of the Industrial Revolution in gigatons of CO from the atmosphere each year. Over the late 1700s, people have been burning ever-increasing © Jones2 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC time CO2 is transported from the atmosphere into the quantities of fossil fuels—deposits of carbon primarily in deep oceanNOT layers FOR in SALEa slow process.OR DISTRIBUTION Once the CO2 is the form of coal,NOT oil, and FOR natural SALE gas. FossilOR DISTRIBUTION fuels contain transported into the deep ocean, it may remain there carbon that was removed from the atmosphere long ago for many thousands of years. through natural processes and stored in the vast rock e biosphere (including soil) is also a reservoir reservoir. Normally, this carbon would be re-released © Jonesthat & acts Bartlett as a sink Learning, for CO2 from LLC the atmosphere. It is ©back Jones to the & atmosphere Bartlett Learning,over millions LLCof years. However, NOT FORthen SALEtransported OR andDISTRIBUTION stored elsewhere in the system. NOThumans FOR are SALE extracting OR and DISTRIBUTION releasing this material back For example, the vast majority of carbon in the rock to the atmosphere in very short periods of time. e reservoir was extracted from the atmosphere through atmospheric quantity of CO2 increased from 270 ppm

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410 © Jones & Bartlett Learning, LLC © Jones & BartlettAtmospheric Learning, CO2 at MaunaLLC Loa Observatory NOT FOR SALE OR400 DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 390 400 380 370 380 360 350 © Jones & Bartlett Learning, LLC 360 © Jones & Bartlett Learning, LLC 340 NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

330 rts per Million ppm 2 320 Pa 340

CO 310 300 320 © Jones290 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT280 FOR SALE OR DISTRIBUTION NOT1960 FOR1970 SALE 1980 OR 1990 DISTRIBUTION 20002010 270 Year 260

00 FIGURE 2.4 The Keeling curve. 11 1000 2100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Data from: Scripps Institution of Oceanography and NOAA Earth System Research Laboratory. © Jones & Bartlett Learning, LLCYear © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FORof atmospheric SALE OR CO DISTRIBUTION is considered the culprit for the FIGURE 2.3 Exponential rise in atmospheric carbon dioxide 2 observed increases in temperature of Earth’s surface in over the past 1000 years. the last several decades.

in 1800 to 407 ppm© today, Jones with & the Bartlett bulk of the Learning, increase LLC © Jones & Bartlett Learning, LLC occurring since 1950 (FIGURE 2.3). Constant and Variable Gases NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Whereas clues of the atmospheric concentration of Constant gases are those that have relatively long resi- CO2 in the distant past come from chemical analysis dence times in the atmosphere and that occur in uniform of air bubbles trapped in ice, CO2 concentration has proportions across the globe and upward through the been measured directly since 1957 atop Mauna Loa in bulk of the atmosphere. ese gases include nitrogen, Hawaii—a© Jones site & asBartlett far removed Learning, as possible LLC from local oxygen, ©argon, Jones neon, & Bartletthelium, krypton, Learning, and LLCxenon. sourcesNOT of FOR pollution. SALE eOR time DISTRIBUTION series of atmospheric CO2 VariableNOT gases FOR are those SALE that OR change DISTRIBUTION in quantity from since 1957 is known as the Keeling curve (FIGURE 2.4), place to place or over time (TABLE 2.2). ey generally have named for Charles Keeling, the climatologist who showed shorter residence times than constant gases, as various that CO2 released from fossil fuel combustion would processes combine to cycle the gases through reservoirs. accumulate signi cantly in the atmosphere. e most abundant variable gas is water vapor, which © Jones & Bartlett e Keeling Learning, curve not LLC only veri es the rapid increase© Jonescan &occupy Bartlett as much Learning, as 4% of theLLC lower atmosphere by NOT FOR SALEsince 1957, OR butDISTRIBUTION it also reveals the seasonal cycle of CONOT2. FORvolume. SALE Higher OR percentages DISTRIBUTION of water vapor are impos- Maximum concentrations occur in early spring in the sible because atmospheric processes (cloud formation northern hemisphere, where most of the world’s middle- and precipitation) limit the amount that may be present and high-latitude forests are located. e relative lack in the atmosphere for any location. e atmosphere is of photosynthetic activity© Jones during & theBartlett dormant Learning, northern LLCe cient in ridding itself of© excess Jones water & Bartlettvapor. Learning, LLC winter months causesNOT a buildupFOR SALE of atmospheric OR DISTRIBUTION CO2 e amount of water vaporNOT in FOR the atmosphere SALE OR varies DISTRIBUTION into March. Likewise, minimum atmospheric CO2 in widely across space because water and energy must be northern hemisphere autumn results from the buildup available at the surface for evaporation to occur. Water of biomass throughout the northern hemisphere’s spring vapor content is maximized over locations with abundant and summer months. energy and surface water, so the wettest atmospheres © Jones e long-term & Bartlett exponential Learning, growth in theLLC atmospheric occur over© Jonestropical &waters Bartlett and rain Learning, forest regions. LLC In CONOT2 concentration FOR SALE concerns OR DISTRIBUTION most climatologists and addition,NOT water FOR vapor SALE is largely OR limited DISTRIBUTION to the lower environmental scientists. Carbon dioxide is an inte- atmosphere because as height increases, atmospheric gral component of Earth’s energy balance because it water vapor is increasingly likely to condense to liquid absorbs energy that is radiated from the Earth and then water in the cooler, high-altitude conditions. © Jones & Bartlettreemits energy Learning, back downward LLC to the Earth, thereby© Jones &Surprisingly, Bartlett Learning, some locations LLC that experience little NOT FOR SALEkeeping OR the DISTRIBUTIONsurface warmer than it would be if the CONOT2 FORprecipitation SALE ORmay DISTRIBUTIONhave abundant water vapor in the were not present. is phenomenon is known as the atmosphere. e maximum amount of water vapor that greenhouse eﬀ ect. e rapid increase in the quantity may exist in the atmosphere is directly related to air

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(CFCs) © Jones & Bartlett Learning, LLC © Jones. Humans & Bartlett have had Learning, at least some LLC in uence in the TABLE 2.2 Concentrations of Variable Gases concentration of all these gases, and CFCs are entirely NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION of the Atmosphere human derived. Collectively, these gases make up only a small amount of the atmosphere, but they can have Gas ppm of Air important implications for some processes.

Water vapor (H2Ov) © Jones0.1–40,000 & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Carbon dioxide (CO2) ∼407 ▸ Faint Young Sun Paradox Evidence contained in sedimentary rocks and sedi- Methane (CH ) ∼1.8 4 ments, ice sheets, and fossils reveals that Earth’s average temperature has remained within a range of about 15 C° Hydrogen© Jones(H ) & Bartlett Learning,∼0.6 LLC © Jones & Bartlett Learning, LLC 2 (27 F°) for most, if not all, of its geological history. is NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION implies that even global-scale shi s in mean environ- Nitrous oxide (N2O) ∼0.31 mental conditions, from ice ages to ice-free conditions Carbon monoxide (CO) ∼0.09 on Earth, have occurred within a range of temperature variability that is smaller than the summer to winter © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Ozone (O3) ∼0.4 temperature di erence at most locations outside the NOT FOR SALE OR DISTRIBUTION NOTtropics. FOR SALE OR DISTRIBUTION

Fluorocarbon 12 (CCl2F2) ∼0.0005 is fact has caused considerable consternation for many climate scientists because of an apparent contradiction between what is known about energy released © Jones & Bartlett Learning,during LLC the evolution of stars, such© Jonesas our Sun, & Bartlettand evi- Learning, LLC temperature. When high temperatures combine with dence of Earth’s temperature through geological time. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION a nearby surface water source, high amounts of water Stars obtain energy through the constant nuclear fusion vapor are usually present. For example, the Red Sea re- of hydrogen into heavier elements. ese reactions cause gion tends to have high quantities of atmospheric water stars to expand gradually and grow hotter and brighter vapor despite the lack of precipitation. is region is dry over time. Eventually, stars expend their sources of not because© Jones water vapor & Bartlett is unavailable Learning, but because LLC the energy and extinguish© Jones themselves. & Bartlett We can Learning, assume that LLC region lacksNOT a means FOR by SALE which OR the precipitation DISTRIBUTION process energy emittedNOT from FORthe early SALE Sun ORwas aboutDISTRIBUTION 25% to can occur easily. 30% less than that emitted today, because this pattern As implied by the Red Sea example, deserts are is observed throughout the life cycle of other stars like generally not the regions of lowest atmospheric water the Sun. We also know that even small changes in solar vapor content. Instead, polar regions are normally the output can induce drastic climatic changes on Earth. © Jonesdriest & locationsBartlett on Learning, Earth. is LLCis because little energy is ©If Jones solar output & Bartlett today were Learning, decreased LLC by 25% to 30%, NOT FORpresent SALE in cold OR air DISTRIBUTION to evaporate water. Furthermore, as NOTtemperatures FOR SALE would ORquickly DISTRIBUTION plummet to a point whereby air cools, water vapor readily condenses to form clouds Earth would be entirely frozen. Because the young Sun and perhaps precipitation, thereby minimizing the mass must have been weak, at rst glance it would appear that of water vapor in the atmosphere. So the regions with Earth must have been frozen for the rst 3 billion years the least water vapor tend© to Jonesbe the coldest & Bartlett locations Learning, on of its LLC history. But evidence does ©not Jones support & the Bartlett notion Learning, LLC Earth. Over such locationsNOT in winter, FOR theSALE water OR vapor DISTRIBUTION that Earth was ever below freezingNOT on FOR a global SALE annual OR DISTRIBUTION content may approach zero. e total will never actually average basis. Furthermore, little credible evidence has reach zero because there is always at least some water been found for widespread glaciation during the rst half vapor present in the lower atmosphere, but the total of Earth’s existence. is apparent contradiction between reaches about 0.00001% of the atmospheric volume in a weak Sun but relatively warm global conditions is the central Antarctica.© Jones & Bartlett Learning, LLC faint young Sun© Jones paradox &. Bartlett Learning, LLC SeveralNOT other FOR variable SALE gases OR are DISTRIBUTION important. Among How couldNOT temperatures FOR SALE have been OR above DISTRIBUTION freezing these, CO2 is most abundant. As stated earlier, the vari- during the early times of geological history? How could able nature of CO2 stems from its increasing quantity Earth maintain a small variance in temperature over time over time, since the late 1700s. e rate of increase is if the Sun were much weaker in the early history of the © Jonesabout & Bartlett0.4% per year Learning, or by about LLC 35% since 1800. Other ©planet? Jones How & Bartlett could temperatures Learning, maintain LLC themselves NOT FORnotable SALE variable OR gases DISTRIBUTION include CH4, nitrous oxide (N2O), NOTover FORtime as SALE the Sun OR grew DISTRIBUTION hotter? carbon monoxide (CO), tropospheric ozone (O3), and e most logical answer to these questions is that a family of chemicals known as chloroﬂ uorocarbons the Earth–ocean–atmosphere system must have some

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© Jones & typeBartlett of internal Learning, regulator LLC that keeps temperatures within© Jones &A secondBartlett explanation Learning, is that LLC ammonia (NH3) caused a reasonable range regardless of changes to solar output the early greenhouse e ect. is hypothesis was proposed NOT FOR SALE OR DISTRIBUTION NOT FOR SALEover time. OR DISTRIBUTION is regulator must have been present in by Carl Sagan and George Mullen of Cornell University the early atmosphere. How would this have happened? in the late 1970s and was based on the observation that Examining the radiation balance of Earth today reveals NH3 behaves as a strong greenhouse gas. e problem that surface temperatures are only indirectly caused by with this argument is that experiments have shown that incoming solar radiation—© Jonesinsolation & Bartlett—being Learning, absorbed LLCNH3 is easily broken up by© UV Jones radiation & Bartlett in oxygen-free Learning, LLC at the surface. If surfaceNOT receipt FOR ofSALE solar radiation OR DISTRIBUTION alone conditions, such as in the NOTatmosphere FOR before SALE the OR arrival DISTRIBUTION determined temperatures, average Earth temperatures of photosynthesis. Nevertheless, the NH3 explanation is would be about −18°C (0°F). Instead, the transfer of still plausible because shielding by other gases may have energy (either from the Sun or Earth) absorbed in the allowed NH3 to accumulate in the lower atmosphere atmosphere© Jones down & Bartlett to the surface Learning, augments LLC radiation and be an© important Jones & greenhouse Bartlett Learning,gas. LLC received at the surface directly from the Sun. Certain A third explanation, proposed by Harvard scientists NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION gases in the atmosphere, such as H2O and CO2, are in the early 2000s, is that in the pre-photosynthesis known to be e cient absorbers of energy escaping the Earth, the planet’s oxygen-devoid atmosphere made surface. Much of this energy is then reemitted back down conditions ideal for oxygen-intolerant microbes called to reheat the surface. is process—the greenhouse methanogens. ese methanogens (so-named because © Jones & Bartlette ect—is responsibleLearning, for LLC the life-supporting tempera-© Jonesthey & release Bartlett CH4 asLearning, a waste product) LLC likely allowed CH4 NOT FOR SALEtures we OR enjoy DISTRIBUTION today. e net result is that the averageNOT FORto produce SALE a ORstrong DISTRIBUTION greenhouse e ect, which would temperature of Earth is raised from −18°C (0°F) to a have warmed Earth even though the Sun emitted less more comfortable 15°C (59°F). radiation at the time. It is well known that CH4 is a So which greenhouse gases could have helped highly e ective greenhouse gas. Once oxygen entered the early Earth to remain© Jones relatively & Bartlett warm? Learning,e two most LLCthe atmosphere from photo©synthesis, Jones & the Bartlett methanogens Learning, LLC abundant greenhouse gases in today’s atmosphere are began to die o and CH became less important as a NOT FOR SALE OR DISTRIBUTION 4NOT FOR SALE OR DISTRIBUTION water vapor and CO2. As far as we can tell, the quantity greenhouse gas. In today’s oxygen-rich atmosphere the of water vapor has remained relatively constant since concentration of CH4 is extremely minute—an average primordial times. Until recently it was assumed that of only 1.8 ppm in the atmosphere. Some geoscientists the wide uctuations of CO2 over time caused Earth’s surmise that the demise of the methanogens caused temperature© Jones to& remainBartlett relatively Learning, stable LLCvia the green- Earth’s ©rst Jones global ice & ageBartlett and perhaps Learning, contributed LLC to houseNOT e FORect. SALEat argument OR suggestsDISTRIBUTION that during times subsequentNOT ice FORages. SALE OR DISTRIBUTION in Earth history when the Sun was relatively weak, such Regardless of the explanation, most of Earth’s history as in Earth’s early atmosphere, the high concentrations is thought to have been dominated by somewhat higher of CO2 may have e ectively absorbed large amounts of temperatures than exist today, or at least temperatures radiation emitted from Earth and reemitted much of that that are not far below those now. e debate over the © Jones & Bartlettradiation backLearning, downward LLC in the greenhouse e ect. Just© Jonesexplanation & Bartlett of the Learning, faint young LLC Sun paradox lingers on. NOT FOR SALEas the solar OR outputDISTRIBUTION began to increase, the onset of plantNOT FOR SALE OR DISTRIBUTION evolution and proliferation would have been removing enough atmospheric CO2 to keep the insolation and ▸ Atmospheric Structure temperatures on Earth fairly constant. But if excessive© levels Jones of CO &2 Bartlettindeed caused Learning, Earth LLC e atmosphere may be divided© Jones into & a seriesBartlett of layers Learning, LLC to remain warm despiteNOT aFOR weak SALESun, such OR concentra- DISTRIBUTIONbased on thermal qualitiesNOT (FIGURE FOR 2.5). SALE e lowest OR layer DISTRIBUTION tions probably would have been too high to allow the of the atmosphere is called the troposphere. is is generation of organic molecules, so life could not have a very thin zone con ned to the rst 8 to 20 km (5 to existed easily. Furthermore, no geological evidence has 12 mi) above Earth’s surface, yet this atmospheric layer been found to suggest that CO2 concentrations were ever contains approximately 75% of the mass of the atmo- large© Jones enough &to haveBartlett created Learning, such a strong LLC greenhouse sphere. © eJones compressibility & Bartlett of air Learning, allows its weight LLC to e NOTect. Speci FOR cally, SALE in an OR oxygen-free DISTRIBUTION atmosphere such exert a downwardNOT FOR force SALE on, andOR compress, DISTRIBUTION the lower as early Earth would have had, CO2 levels of about eight atmosphere. is layer therefore also contains air of the times today’s concentrations would have produced the greatest mass per unit volume: density. mineral siderite (FeCO3) in the top layers of the soil e term “troposphere” is derived from the Greek © Jones & Bartlettas iron reacted Learning, with the LLC CO2, but not enough FeCO©3 Jonesword & meaningBartlett “to Learning, turn.” is indicatesLLC that the tropo- NOT FOR SALEhas been OR found DISTRIBUTION in relic soils to support this hypothesis.NOT FORsphere SALE is a region OR in DISTRIBUTION which mass is constantly overturn- Better explanations for the faint young Sun paradox ing, largely as a result of thermodynamic (heat-driven) were sought. processes. Most insolation passes through the atmosphere

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Thermosphere 100 60

90 © Jones & Bartlett Learning, LLC © Jones & Heterosphere Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 80 Mesopause 50

70 © Jones & Bartlett Learning, LLC © Jones40 & Bartlett Learning, LLC 60 Mesosphere NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

50 Altitude (miles) Stratopause 30 Altitude (kilometers) 40

Ozone (O3 ) layer 20 Isothermal 10 Tropopause layer 10 Mt. Everest © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Troposphere 0 NOT FOR SALE OR DISTRIBUTION 0 NOT FOR SALE OR DISTRIBUTION

0 Degrees F 20 32 40 60 80 –80 –60 –40 –20 –100 –140 –120

0 Degrees C 10 © Jones & Bartlett Learning, LLC 20 30 © Jones & Bartlett Learning, LLC –10 –90 –80 –70 –60 –50 –40 –30 –20 NOT FOR SALE OR DISTRIBUTIONTemperature NOT FOR SALE OR DISTRIBUTION

FIGURE 2.5 The vertical structure of the atmosphere.

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FORbefore SALE being absorbedOR DISTRIBUTION by the Earth’s surface. e heated NOT AccordingFOR SALE to oneOR formDISTRIBUTION of Charles’ law, in an surface then warms the air directly above it through ideal gas (which the atmosphere approximates), the process of conduction. is gives the lowest lay- density decreases as temperature increases if pressure ers of the atmosphere buoyancy and causes the air to remains constant. Air that is warmer than surround- rise in a process known as© convection Jones &. BartlettEventually Learning, this ing LLC air thus rises. Because Earth© is Jones not heated & Bartlett equally Learning, LLC air cools and sinks. BecauseNOT this FOR vertical SALE movement OR DISTRIBUTION is and relatively warm air rises, NOTthe troposphere FOR SALE does OR DISTRIBUTION integral to the development of most weather-related not have a uniform depth. Instead, the troposphere processes, the troposphere is sometimes referred to as is thicker near the equator than near the poles. Near the “weather sphere.” the equator the layer is approximately 20 km (12 mi) Because the atmosphere is heated primarily from Earth’s thick, whereas near the poles in winter the thickness surface and© Jones because &the Bartlett compression Learning, of atmospheric LLC gas is only about 8© km Jones (5 mi). & Roughly Bartlett the Learning, same amount LLC decreasesNOT with FORheight SALE (as the weightOR DISTRIBUTION of the atmosphere of atmosphericNOT mass FOR exists SALE over theOR two DISTRIBUTION locations, above it decreases), a decrease of temperature usually but the density of that air is less over the equator and occurs with increasing height through the troposphere. greater over the poles. is decrease is known as the environmental lapse e top of the troposphere is called the tropo- © Jonesrate &. Bartlett rough the Learning, troposphere, LLC air cools at an average ©pause Jones. &is Bartlettfeature marks Learning, the boundary LLC between the NOT FORrate of SALE 6.5 C° /kmOR (or DISTRIBUTION 3.5 F°/1000 ), although this value NOTtroposphere FOR SALE below and OR the DISTRIBUTION next layer of the atmosphere may vary widely from place to place and from day to above (Figure 2.5). e average temperature at the tro- day, and even on an hourly basis. popause is about −57°C (−70°F), which represents quite

9781284126563_CH02.indd 18 12/04/17 12:43 PM Atmospheric Structure 19

° ° © Jones & aBartlett decrease Learning,from the 15 LLCC (59 F) average temperature© Jones &Some Bartlett of the Learning,diatomic oxygen LLC (O2) that enters the of the surface. atmosphere from photosynthesis near the surface reaches NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION e layer above the troposphere is the stratosphere. the stratosphere over time. Because O2 molecules ef- Temperatures remain somewhat constant from the tro- fectively absorb UV radiation at wavelengths between popause upward into the stratosphere for about 10 km 0.12 and 0.18 µm, the O2 reaching the stratosphere is (6 mi). Any zone of relatively constant temperature with exposed to incoming harmful radiation. When this radi- height, such as this ©one, Jones is called & an Bartlett isothermal Learning, layer. LLCant energy strikes O2 molecules, © Jones a chemical & Bartlett reaction Learning, in LLC Above the isothermalNOT layer FORtemperatures SALE actually OR DISTRIBUTION increase the presence of light that NOTsplits theFOR molecular SALE bonds—OR DISTRIBUTION with height through the rest of the stratosphere. is photodissociation—is triggered and two monatomic increase of temperature with height—a temperature oxygen (O) atoms are liberated. Because O is inherently inversion—is caused by the absorption of UV radia- unstable, it bonds quickly and easily with other atoms and tion© byJones the triatomic & Bartlett form ofLearning, oxygen (O 3LLC), or ozone. molecules.© SomeJones of these & Bartlett O atoms chemicallyLearning, bond LLC with e so-called ozone layer in the stratosphere occurs an O molecule to form an O molecule that e ectively NOT FOR SALE OR DISTRIBUTION 2 NOT FOR SALE3 OR DISTRIBUTION because of several processes that have important impli- absorbs UV radiation at wavelengths between 0.18 and cations for terrestrial life on the planet. To understand 0.34 µm. But in the absorption process the O3 becomes the workings of the ozone layer we must rst review photodissociated into O and O2, and the O then bonds the nature of radiation reaching Earth from the Sun. with another O2 to form O3. e process then repeats © Jones & BartlettInsolation Learning,arrives in Earth’s LLC atmosphere in a wide range© Jonesendlessly, & Bartlett ensuring Learning, that oxygen LLC is continuously being NOT FOR SALEof wavelengths OR DISTRIBUTION, which are measured in micrometersNOT FORreworked SALE into OR O3 inDISTRIBUTION the stratosphere. UV radiation at (millionths of a meter [µm]). Shorter wavelengths are wavelengths between 0.18 and 0.34 µm is e ectively associated with more intense (and therefore more harm- “absorbed”—actually used in chemical processes with ful to living things) energy than longer wavelengths. emitted heat as a byproduct—such that only the UV e Sun emits more© energyJones at & a Bartlettwavelength Learning, of about LLCradiation at wavelengths between© Jones 0.34 and& Bartlett 0.40 µm Learning,lters LLC 0.5 µm than at any other wavelength, with successively to Earth’s surface. is harmful radiation can cause skin NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION less energy emitted at successively shorter and longer cancer, cataracts, and other problems if we are exposed wavelengths (FIGURE 2.6). By convention, energy from to it in large doses, but at least we are protected from the solar origin shorter than 4.0 µm is usually referred much more harmful shorter UV wavelengths. to as shortwave radiation in the atmospheric sci- Early in geological history, the rst organisms must ences.© Jones Wavelengths & Bartlett of the peakLearning, amounts LLC of shortwave have formed© Jones in murky & waters Bartlett because Learning, no O2 (and, LLC there- radiationNOT FOR occur SALE in the visible OR DISTRIBUTION part (0.4 to 0.7 µm) of the fore, no ONOT3) existed FOR to SALEprotect themOR DISTRIBUTIONfrom UV radiation. electromagnetic spectrum—the full assemblage By the time life evolved into shallow water areas and of all possible wavelengths of electromagnetic energy. onto land surfaces, O2 released from photosynthesis Any insolation with wavelengths less than 0.4 µm is had built a stratospheric O3 layer. Life has never been too intense to allow terrestrial life to exist. UV radiation exposed to excessive amounts of UV radiation and has © Jones & Bartlettfalls between Learning, wavelengths LLC of 0.01 and 0.40 µm, making© Jonesnever & adaptedBartlett to it.Learning, Increasing exposureLLC to UV radiation NOT FOR SALEUV radiation OR DISTRIBUTION harmful to living organisms. Fortunately, NNOT2 FORis damaging SALE toOR terrestrial DISTRIBUTION life. absorbs electromagnetic radiation of wavelengths below Humans have contributed to thinning the fragile 0.12 µm. But how does the ozone layer protect us from O3 layer over the past half-century by producing CFCs. UV radiation at wavelengths between 0.12 and 0.40 µm? Most general uses for CFCs involved refrigeration both © Jones & Bartlett Learning, LLCas a gas (Freon) and as an© insulating Jones & substance Bartlett (foam Learning, LLC NOT FOR SALE OR DISTRIBUTIONand Styrofoam). CFCs wereNOT also FOR used SALE as a propellant OR DISTRIBUTION For 6000 K for aerosol sprays. When chlorine from CFCs and For 6000 K bromine are released to the atmosphere, they can make their way upward to the stratosphere where they readily bond with monatomic oxygen atoms. Such a bond © Jones & Bartlett Learning, LLC10 µm © Jones & Bartlett Learning, LLC For 300 K does not allow the O to bond with O2 to produce the NOT FOR SALE OR DISTRIBUTION O3 that wouldNOT FORabsorb SALE UV radiation. OR DISTRIBUTION e result is that

Radiant Intensity increased amounts of UV radiation reach the surface, where adverse e ects on organisms occur. Although O3 0.5 µm is found throughout the stratosphere, if all stratospheric Wavelength © Jones & Bartlett Learning, LLC © Jonesozone & Bartlettwere compressed Learning, to the LLC surface it would create NOT FOR SALEFIGURE 2.6OR Emitted DISTRIBUTION energy by wavelength for the Sun andNOT FORa layer SALE only 3OR mm DISTRIBUTION thick. Since the U.S. ban on CFC Earth, assuming a surface temperature of 6000 K for the production took e ect on January 1, 1996, the ozone Sun and 300 K for the Earth. layer has shown some signs of recovery.

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© Jones & Bartlette ozone formation Learning, process LLC is responsible for the © JonesSimilar & to Bartlett the troposphere, Learning, temperatures LLC in the me- temperature inversion in the stratosphere. As O molecules sosphere decrease with height. e temperature inversion NOT FOR SALE OR DISTRIBUTION 3 NOT FOR SALE OR DISTRIBUTION absorb UV radiation, they acquire energy. e O3 at the characteristic of the stratosphere is not present in the top of the stratosphere has the rst opportunity to gain mesosphere because it is too high for photodissociated energy (and, therefore, temperature, because temperature O2 to encounter other oxygen atoms or molecules to is a measure of the energy or heat content of matter) bond with quickly enough to absorb the incoming UV from incoming UV radiation.© Jones Its temperature, & Bartlett therefore, Learning, radiation. LLC Instead, the increased© density Jones and & proximity Bartlett Learning, LLC is higher than for moleculesNOT lower FOR in theSALE stratosphere. OR DISTRIBUTION to the surface and stratosphericNOT heat sources FOR SALEbelow the OR DISTRIBUTION e process of O3 production and dissociation hap- mesosphere make the lower mesosphere warmer than pens in the stratosphere because this is the uppermost the top of this layer. Temperatures at the mesopause layer for which atmospheric density is high enough average approximately −84°C (−120°F). to allow ©O Jonesand O2 to& meetBartlett and bondLearning, quickly LLCenough Few processes© Jonesof consequence & Bartlett to weather Learning, and climate LLC so that incoming UV radiation is absorbed e ectively. are known to occur in the mesosphere in part because NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Temperatures rise to approximately −18°C (0°F) at the so little atmospheric mass exists in this zone. Charged stratopause, which is about 48 km (29 mi) above the particles from the Sun that are captured by Earth’s surface. e stratopause is the boundary between the magnetic eld in the mesosphere can disrupt telecom- stratosphere and the layer above it. munications during their release of energy. ese same © Jones & Bartlette layer above Learning, the stratosphere LLC is the mesosphere, ©charged Jones particles & Bartlett are also Learning, responsible LLC for the northern NOT FORfrom SALE the Greek OR pre DISTRIBUTION x meso-, which means “middle.” NOTlights FOR (aurora SALE borealis OR; FIGURE DISTRIBUTION 2.7) and southern lights Although this layer does sit near the middle of the (aurora australis). But even these processes have minimal atmosphere from an altitude perspective—in the region e ect on Earth’s weather and climate. between the stratopause and about 80 km (50 mi) above From the surface up through the mesosphere, the the surface—the low-density© Jonesmesosphere & Bartlett does not repre- Learning,proportion LLC of atmospheric gases© isJones about the& Bartlettsame as Learning, LLC sent the middle of the atmosphere by density or volume. that at the surface, except for the greater concentration NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Because of the compressibility of gases, the middle of the of O3 in the stratosphere. e rst three “spheres” of the atmosphere by density and volume is only about 5.5 km atmosphere are thus sometimes collectively known as (3.4 mi) above the surface—well within the troposphere. the homosphere, which means “same sphere.” Above

9781284126563_CH02.indd 20 12/04/17 12:43 PM Summary 21

© Jones & theBartlett mesosphere Learning, gases stratify LLC into layers according ©to Jones▸ & Bartlett Learning, LLC their atomic weights because there is so little mass to Summary NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION “stir them up.” at region is termed the heterosphere. e atmosphere is a fragile and complex collection of e heterosphere corresponds to the nal thermal gases gravitationally attracted to Earth. It originated layer of the atmosphere, the thermosphere. Like the early in the history of the planet as volcanic materials stratosphere, the thermosphere is characterized by cooled and outgassed. e early atmosphere is believed temperatures that increase© Jones with & height—a Bartlett temperature Learning, LLCto have been composed primarily© Jones of & N 2Bartlett and CO2 ,Learning, but LLC inversion. Unlike theNOT stratosphere, FOR SALE however, OR whereDISTRIBUTION the O2 gradually replaced CONOT2 as the FOR second-most SALE OR abun- DISTRIBUTION inversion exists because of O3 absorption of insola- dant gas since the evolution and proliferation of simple tion, the thermospheric temperature inversion occurs organisms and green plants, which have stored carbon because the uppermost N2 and O2 molecules have the in their biomass and released O2 into the atmosphere rst© opportunityJones & Bartlett to absorb Learning, insolation. LLC eir position over the ©past Jones 3 billion & years.Bartlett Learning, LLC allows them to attain extraordinarily high tempera- NOT FOR SALE OR DISTRIBUTION CarbonNOT is stored FOR forSALE certain OR periods DISTRIBUTION of time within tures because Earth’s magnetic eld captures charged a number of reservoirs such as rock layers, the ocean, high-energy particles from the Sun. biomass, and the atmosphere. is cycle of carbon is e number of those molecules with such high important in the history of Earth. Its importance has temperatures is miniscule, however, because of the been challenged recently, however, by evidence suggest- © Jones & Bartlettsparseness Learning, of the atmosphere LLC at such heights. e total© Jonesing &that Bartlett methane-emitting Learning, microbes LLC may have played NOT FOR SALEmass of OR the DISTRIBUTION thermosphere accounts for only aboutNOT FORa greater SALE role ORthan DISTRIBUTION previously believed in Earth’s early 0.01% of the total atmospheric mass. e decrease of history by absorbing energy emitted by Earth via the density, mass, and volume of the atmosphere can be greenhouse e ect. is methane may have kept Earth’s expressed by the mean free path of a molecule—the temperatures within a narrow range of variability, despite distance an individual© Jones molecule & Bartlett must travel Learning, before LLCa weaker solar output. © Jones & Bartlett Learning, LLC encountering another molecule. e mean free path NOT FOR SALE OR DISTRIBUTION e troposphere is theNOT lowest FORlayer of SALE the atmosphere OR DISTRIBUTION at the surface is on the order of a micrometer. By and is where nearly all weather and climate processes contrast, in the thermosphere the mean free path is of importance occur. Temperatures in the troposphere on the order of a kilometer or more. Despite the fact usually decrease with height because of the increased that the individual molecules have very high amounts density in the most compressed part of the atmosphere— of© energy, Jones there & Bartlettare so few Learning, molecules toLLC contain the the part ©nearest Jones to the& Bartlettsurface—and Learning, because ofLLC prox- heatNOT that FOR even ifSALE you could OR somehow DISTRIBUTION survive for more imity to NOTthe surface, FOR SALEwhich absorbs OR DISTRIBUTION insolation more than a fraction of a second at those heights, you would e ectively than the air above it. e stratosphere is the freeze to death instantly even at temperatures above second layer from the surface and is characterized by 1100°C (2000°F)! increases in temperature with height—a temperature A thermopause does not exist; instead, the atmo- inversion—because of ozone absorption. In the meso- © Jones & Bartlettsphere simply Learning, merges slowly LLC into inter planetary space.© Jonessphere & Bartlett temperatures Learning, decrease LLCwith height for the same NOT FOR SALEIndividual OR gas DISTRIBUTION molecules may be gravitationally attractedNOT FORreason SALE they doOR in DISTRIBUTIONthe troposphere. e nal thermal to the planet for quite a distance into space. Most agree, layer of the atmosphere is the thermosphere, which is however, that the atmosphere extends no higher than characterized by a temperature inversion because of the about 1000 km (600 mi) above the Earth’s surface. direct absorption of incoming radiation by N2 and O2. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Key Terms Aerosol Density Greenhouse e ect Atmosphere© Jones & Bartlett Learning, LLCDi usion © Jones &Greenhouse Bartlett gasLearning, LLC BiosphereNOT FOR SALE OR DISTRIBUTIONElectromagnetic spectrum NOT FORHeterosphere SALE OR DISTRIBUTION Carbon cycle Environmental lapse rate Homosphere Charles’ law Eukaryote Hydrosphere Chloro uorocarbon (CFC) Evaporation Hydrostatic equilibrium Condensation Faint young Sun paradox Insolation © Jones & BartlettConduction Learning, LLC Fermentation© Jones & Bartlett Learning,Isothermal LLC layer NOT FOR SALEConstant OR gas DISTRIBUTION Flux NOT FOR SALE OR DISTRIBUTIONKeeling curve Convection Fossil fuel Lithosphere

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© JonesMean & freeBartlett path Learning, LLC Ozone (O3) © Jones & BartlettSink Learning, LLC Mesopause Photodissociation Solar wind NOT FOR SALE OR DISTRIBUTION NOT FORMesosphere SALE OR DISTRIBUTION Photosynthesis Stratopause Methane (CH4) Planetesimal Stratosphere Methanogen Prokaryote Temperature inversion Micrometer Reservoir ermosphere Nebula © Jones & BartlettResidence Learning, time LLC Tropopause© Jones & Bartlett Learning, LLC Newton’s second law of motionNOT FOR SALERespiration OR DISTRIBUTION TroposphereNOT FOR SALE OR DISTRIBUTION Nuclear fusion Second law of thermodynamics Ultraviolet (UV) radiation Oort cloud Shortwave radiation Variable gas Outgassing Siderite Wavelength Terms in© italics Jones also &appeared Bartlett in Chapter Learning, 1. LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Review Questions 1. Explain how Earth and its atmosphere formed. 5. What is residence time and why is it important? © Jones2. & BartlettHow is today’s Learning, atmosphere LLC similar to and dierent © Jones6. What & isBartlett the carbon Learning, cycle and how LLC does it operate? NOT FOR SALEfrom early OR Earth’s DISTRIBUTION atmosphere? NOT7. FORDescribe SALE the thermalOR DISTRIBUTION structure of the atmosphere. 3. Describe how oxygen came to comprise almost 8. What causes the thermal characteristics associ- 21% of the atmosphere today. ated with each thermal layer of the atmosphere? 4. Given that solar output has increased over the past 9. Compare and contrast the heterosphere and the 4.6 billion years, how© Joneshave Earth’s & Bartlett temperatures Learning, LLChomosphere. © Jones & Bartlett Learning, LLC remained fairly constantNOT overFOR that SALE same ORtime? DISTRIBUTION10. Why is there no dened topNOT to theFOR atmosphere? SALE OR DISTRIBUTION Questions for Thought

1. Give© Jonesas many examples& Bartlett of the Learning, second law LLC of ther- 3. Why are© the Jones auroras & not Bartlett visible Learning,in the tropical LLC modynamicsNOT FOR as SALE you can OR think DISTRIBUTION of, both related to parts of theNOT Earth? FOR SALE OR DISTRIBUTION and not related to the atmosphere. 2. Why do the aurora borealis and aurora australis occur in the mesosphere and not elsewhere in the atmosphere? © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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