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Earth Science: Earth’s Weather, Water, and Atmosphere
Atmosphere’s Evolution
The chemical composition of the atmosphere has changed significantly over the 4.6-billion-year history of Earth. The
composition of the atmosphere has been influenced by a number of processes, including the “outgassing” of volatile
materials originally trapped in Earth’s interior during its formation; the geochemical cycling of carbon, nitrogen,
hydrogen, and oxygen compounds between the surface, the ocean, and the atmosphere; and the evolution of life.
Principal Terms
chemical evolution: the synthesis of amino acids and other complex organic molecules—the precursors of living
systems—by the action of atmospheric lightning and solar ultraviolet radiation on atmospheric gases
photosynthesis: the biochemical synthesis of glucose and molecular oxygen from carbon dioxide and water by
chlorophyll-containing organisms in the presence of sunlight
prebiotic: relating to the period of time before the appearance of life on Earth
primordial solar nebula: an interstellar cloud of gases and dust that condensed by the action of gravitational forces
to form the bodies of the solar system about 5 billion years ago
solar ultraviolet radiation: biologically lethal solar radiation in the spectral interval between approximately 0.1 and
0.3 micron (1 micron = 0.0001 centimeter)
T Tauri stars: a class of stars that exhibits rapid and erratic changes in brightness
volatile outgassing: the release of the gases and liquids, such as argon, water vapor, carbon dioxide, and nitrogen
sulfur, trapped within Earth’s interior during its formation
VOLATILE OUTGASSING
About 5 billion years ago, a cloud of interstellar gas and dust, called the primordial solar nebula, began to condense
under the influence of gravity. This condensation led to the formation of the sun, moon, Earth, the other planets and
their satellites, asteroids, meteors, and comets. The primordial solar nebula was composed almost entirely of
hydrogen gas, with a smaller amount of helium, still smaller amounts of carbon, nitrogen, and oxygen, and still smaller
amounts of the rest of the elements of the periodic table. About the time that the newly formed Earth attained its
approximate present mass, gases that were released from the planet’s interior could be retained by Earth’s gravity
instead of escaping into space, thus forming a gravitationally bound atmosphere. It is believed that the atmospheres
of the other terrestrial planets, Mars and Venus, also formed in this manner. The release of gases and other volatiles
in this manner is called volatile outgassing. The period of extensive volatile outgassing may have lasted for many tens
of millions of years. The outgassed volatiles or gases had roughly the same chemical composition as present-day
volcanic emissions: 80 percent water vapor by volume, 10 percent carbon dioxide by volume, 5 percent sulfur dioxide
by volume, 1 percent nitrogen by volume, and smaller amounts of hydrogen, carbon monoxide, sulfur, chlorine, and
argon.
The water vapor that outgassed from the interior eventually reached the saturation point, which is controlled by the
atmospheric temperature and pressure. Once the saturation point was reached, the atmosphere could not hold any
additional gaseous water vapor. Any new outgassed water vapor that entered the atmosphere would have
precipitated out of the atmosphere in the form of liquid water. The equivalent of several cubic kilometers of liquid
water released from Earth’s interior in gaseous form precipitated out of the atmosphere and formed the oceans. Only
small amounts of water vapor remained in the atmosphere, ranging from a fraction of a percent to several percent by
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volume, depending on atmospheric temperature, season, and latitude.
The outgassed atmospheric carbon dioxide, being somewhat water soluble, dissolved in the newly formed oceans
and subsequently formed carbonic acid through its reaction with water. Once formed, carbonic acid can dissociate
into ions of hydrogen, bicarbonate, and carbonate. The carbonate ions reacted with ions of calcium and magnesium in
the ocean water, forming first insoluble carbonate salts, which precipitated out of the ocean and accumulated as
seafloor carbonate sediments, eventually accumulating in sufficient quantities to form beds of carbonate rock. Most of
the outgassed atmospheric carbon dioxide formed carbonates, leaving only trace amounts of gaseous carbon dioxide
in the atmosphere (about 0.035 percent by volume). Sulfur dioxide, the third most abundant component of volatile
outgassing, was chemically transformed into other sulfur compounds, including sulfuric acid and other sulfates in the
atmosphere. Eventually, the sulfates formed atmospheric aerosols and gravitated out of the atmosphere to settle on
the surface.
The fourth most abundant outgassed compound, nitrogen, is almost completely chemically inert in the atmosphere
and thus was not readily transformed in large quantities, as was sulfur dioxide. Only minor amounts of nitrogen would
be converted to various oxides by the action of lightning, to be trapped as nitrogen oxide salts in minerals. Unlike
carbon dioxide, nitrogen is relatively insoluble in water and, unlike water vapor, does not condense out of the
atmosphere. For these reasons, nitrogen built up in the atmosphere to become its major constituent (78.08 percent by
volume). Accordingly, outgassed volatiles led to the formation of Earth’s atmosphere, oceans, and the earliest,
prebiotic carbonate rocks.
CHEMICAL EVOLUTION
It has been demonstrated in laboratory experiments that molecular nitrogen, carbon dioxide, and water vapor in the
early atmosphere would have been acted upon by solar ultraviolet radiation and atmospheric lightning. In the process,
molecules of formaldehyde and hydrogen cyanide were chemically synthesized in the early atmosphere. These
molecules were precipitated and diffused out of the atmosphere into the oceans. In the water, formaldehyde and
hydrogen cyanide entered into chemical reactions that eventually led to the chemical synthesis of amino acids—the
building blocks of proteins in living systems. The synthesis of amino acids and other compounds from nitrogen,
carbon dioxide, and water vapor in the atmosphere is called chemical evolution. Chemical evolution preceded and
provided the material for biological evolution.
For many years, it was thought that the early atmosphere was composed of ammonia, methane, and hydrogen rather
than of carbon dioxide, nitrogen, and water vapor. Experiments show, however, that ammonia and methane are
chemically unstable and are readily destroyed by both solar ultraviolet radiation and chemical reaction with the
hydroxyl radical, which is formed from water vapor. In addition, ammonia is very water soluble and is readily removed
from the atmosphere by precipitation. Hydrogen, the lightest element, is readily lost from a planet by gravitational
escape. Thus, an early atmosphere composed of methane, ammonia, and hydrogen would be very short lived, unless
these gases were produced at a rate equal to their destruction or loss rates (an equilibrium state). These gases are
also known to be extremely efficient “greenhouse gases,” even more effective than carbon dioxide; their presence in
the primordial atmosphere in any substantial amount would have maintained an extraordinarily high atmospheric
temperature, by which many of the materials that were formed would thermally decompose. Today, methane and
ammonia are very minor components of the atmosphere, at concentrations of 1.7 parts per million by volume and 1
part per billion by volume, respectively. Both gases are produced by microbial activity at the ground surface, and
methane is released during coal mining and oil production, and from seafloor accumulations of methane hydrate.
Clearly, microbial activity and microbes were nonexistent during the prebiotic phase of the planet. The atmospheres of
the outer gas giant planets—Jupiter, Saturn, Uranus, and Neptune—all contain quantities of hydrogen, methane, and
ammonia. It is believed that the atmospheres of these planets, unlike the atmospheres of the terrestrial planets—
Earth, Venus, and Mars—are captured remnants of the primordial solar nebula resulting from the greater ability of the
gravitational fields of those large planets to capture such light materials, preventing them from being drawn toward the
sun. Because of the outer planets’ great distance from the sun and their very low temperatures, hydrogen, methane,
and ammonia are stable and long-lived constituents of their atmospheres. This is not true of hydrogen, methane, and
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ammonia in Earth’s atmosphere.
Some have suggested that at the time of its formation, Earth may have also captured a remnant of the primordial solar
nebula as its very first atmosphere. Such a captured primordial solar nebula atmosphere would have been composed
of mostly hydrogen (about 90 percent) and helium (about 10 percent), the two major elements of the nebula. Even if
such an atmosphere had surrounded the very young Earth, it would have been very short lived. As the young sun
went through the T Tauri phase of its evolution, very strong solar winds (the supersonic flow of protons and electrons
from the sun) associated with that phase would have quickly dissipated this remnant atmosphere. In addition, there is
no geochemical evidence to suggest that early Earth ever possessed a primordial solar nebula remnant atmosphere.
EVOLUTION OF ATMOSPHERIC OXYGEN
There is microfossil evidence for the existence of fairly advanced anaerobic microbial life on Earth by about 3.8 billion
years ago. The ability to carry out photosynthesis evolved in one or more of these early microbial species. Through
photosynthesis, the organism utilizes water vapor and carbon dioxide in the presence of sunlight and chlorophyll to
form glucose and molecular oxygen. The glucose molecules are subsequently used by the organism for food and for
biopolymerization into starches and celluloses. The production of oxygen by photosynthesis was a major event on
Earth and eventually transformed the composition and chemistry of the early atmosphere as oxygen built up to
become the second most abundant constituent of the atmosphere (20.90 percent by volume). It has been estimated
that atmospheric oxygen reached only 1 percent of its present atmospheric level 2 billion years ago, 10 percent of its
present atmospheric level about 550 million years ago (at the beginning of the Paleozoic), and its present atmospheric
level as early as 400 million years ago.
The evolution of atmospheric oxygen had important implications for the evolution of life. Because molecular oxygen is
a very effective oxidizing agent and would have been harmful to existing anaerobic life-forms, the presence and
buildup of oxygen required the evolution of respiration and aerobic organisms. Accompanying and directly controlled
by the buildup of atmospheric oxygen were the origin and evolution of atmospheric ozone, which is chemically formed
from oxygen. The evolution of atmospheric ozone resulted in the shielding of Earth’s surface from biologically lethal
solar ultraviolet rays. The development of the atmospheric ozone layer and its accompanying shielding of Earth’s
surface permitted early life to evolve such that it could leave the safety of the oceans and go ashore for the first time
in the history of the planet. Prior to the evolution of the atmospheric ozone layer, early life was restricted to a depth of
several meters below the ocean surface. At this depth, the ocean water offered shielding from solar ultraviolet
radiation. Theoretical computer calculations indicate that atmospheric ozone provided sufficient shielding from
biologically lethal ultraviolet radiation for the evolution of non-marine organisms once oxygen reached about one-tenth
of its present atmospheric level.
VENUS AND MARS
Calculations indicate that the atmospheres of Venus and Mars also formed as a consequence of volatile outgassing of
the same gases that led to the formation of Earth’s atmosphere—water vapor, carbon dioxide, and nitrogen. In the
case of Venus and Mars, however, the outgassed water vapor may never have existed in the form of liquid water in
quantities comparable to those on Earth. Because of Venus’s closer distance to the sun (108 million kilometers versus
150 million kilometers for Earth), its lower atmosphere was too hot to permit the outgassed water vapor to condense
out of the atmosphere. Thus, the outgassed water remained in gaseous form in the atmosphere and, over geological
time, was decomposed by solar ultraviolet radiation into molecular hydrogen and oxygen. The very light hydrogen gas
quickly escaped from the atmosphere of Venus, and the heavier oxygen combined with surface minerals to form a
highly oxidized surface. In the absence of liquid water on the surface of Venus, the outgassed carbon dioxide
remained in the atmosphere and built up to become the overwhelming constituent of Venus’s atmosphere, about 96
percent by volume. The outgassed nitrogen accumulated to make up about 4 percent by volume of the atmosphere of
Venus. The present-day carbon dioxide and nitrogen atmosphere of Venus is massive—its atmospheric surface
pressure is about 90 atmospheres (compared to the surface pressure of Earth’s atmosphere of only 1 atmosphere). If
the outgassed carbon dioxide in Earth’s atmosphere had not been dissipated via dissolution in the oceans and
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carbonate formation, the planet’s surface atmospheric pressure would presumably be about 70 atmospheres, with
carbon dioxide accounting for about 98 to 99 percent of the atmosphere and nitrogen about 1 to 2 percent. Thus, the
atmosphere of Earth would closely resemble that of Venus. The carbon dioxide-rich atmosphere of Venus causes a
very significant greenhouse temperature enhancement, giving the surface of Venus a temperature of about 750
kelvins, which is hot enough to melt lead. The surface temperature of Earth is only about 288 kelvins, a range at
which water can exist in equilibrium between all three phases, as solid, liquid, and gas.
Like Venus, Mars has an atmosphere, though extremely thin, composed primarily of carbon dioxide (about 95 percent
by volume) and nitrogen (about 3 percent by volume). The total atmospheric surface pressure of Mars is only about 7
millibars (1 atmosphere is equivalent to 1,013 millibars). There may be large quantities of outgassed water in the form
of ice or frost below the surface of Mars, but in the absence of liquid water, the outgassed carbon dioxide has
remained in the atmosphere. The smaller mass of the atmosphere of Mars compared to the atmospheres of Venus
and Earth may be attributable to the smaller mass of the planet and, accordingly, the smaller mass of gases that could
have been trapped in the interior of Mars during its formation. In addition, the amounts of gases trapped in the
interiors of Venus, Earth, and Mars during their formation apparently decreased with increasing distance from the sun.
Venus appears to have trapped the greatest amounts of gases and was the most volatile-rich planet. Earth trapped
the next greatest amounts, and Mars trapped the smallest amounts.
STUDY OF EARTH’S ATMOSPHERE
Information about the origin, early history, and evolution of Earth’s atmosphere comes from a variety of sources.
Information on the origin of Earth and other planets is based on theoretical computer simulations, with ever-increasing
empirical data input from celestial observation. These computer models simulate the collapse of the primordial solar
nebula and the formation of the planets. Astronomical observations of what appears to be the collapse of interstellar
gas clouds and the possible formation of planetary systems have provided new insights into the computer modeling of
this phenomenon. Information about the origin, early history, and evolution of the atmosphere is based on theoretical
computer models of volatile outgassing, the geochemical cycling of the outgassed volatiles, and the photochemistry of
the outgassed volatiles. The process of chemical evolution, which led to the synthesis of organic molecules of
increasing complexity—the precursors of the first living systems on the early Earth—is studied in laboratory
experiments in which mixtures of gases simulating Earth’s hypothetical early atmosphere are energized by solar
ultraviolet radiation and atmospheric lightning. The resulting products are analyzed by chemical techniques. A key
parameter affecting atmospheric photochemical reactions, chemical evolution, and the origin of life was the flux of
solar ultraviolet radiation on the early Earth. Astronomical measurements of the ultraviolet emissions from young sunlike stars have provided important information about the probable ultraviolet emissions from the sun during the early
history of the atmosphere.
Geological and paleontological studies of the oldest rocks and the earliest fossil records have provided important
information on the evolution of the atmosphere and the transition from an oxygen-deficient to an oxygen-rich
atmosphere. Studies of the biogeochemical cycling of the elements have provided important insights into the later
evolution of the atmosphere. Thus, studies of the origin and evolution of the atmosphere are based on a broad crosssection of science, involving astronomy, geology, geochemistry, geophysics, and biology as well as atmospheric
chemistry.
SIGNIFICANCE
Studies of the origin and evolution of Earth’s atmosphere have provided new insights into the processes and
parameters responsible for global change. Understanding the history of the atmosphere provides a sound basis for
better understanding its future. Today, several global environmental changes are of national and international
concern, including the depletion of ozone in the stratosphere and increasing global temperatures caused by the
buildup of greenhouse gases in the atmosphere. The study of the evolution of the atmosphere has provided new
insights into the biogeochemical cycling of elements between the atmosphere, biosphere, land, and ocean.
Understanding this cycling is a key to understanding environmental problems. Studies of the origin and evolution of
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the atmosphere have also provided new insights into the origin of life and the possibility of life outside Earth.
FURTHER READING
Ackerman, Steven A., and John A. Knox. Meteorology: Understanding the Atmosphere. 3d ed. Sudbury, Mass.:
Jones and Bartlett Learning, 2012. Provides an overview of the atmosphere and atmospheric phenomena,
beginning from the evolution of the early terrestrial atmosphere. Suitable for university-level readers.
Ahrens, C. Donald. Essentials of Meteorology: An Invitation to the Atmosphere. Belmont, Calif.: Brooks/Cole
Cengage Learning, 2012. Covers various topics in weather and the atmosphere. Discusses topics such as
tornadoes and thunderstorms, acid deposition and other air pollution topics, humidity and cloud formation, and
temperature.
Bandy, A. R., ed. The Chemistry of the Atmosphere: Oxidants and Oxidation in the Earth’s Atmosphere.
Cambridge, England: Royal Society of Chemistry, 1995. Collects essays and lectures first presented at the
Priestely Conference at Bucknell University. Covers such topics as atmospheric chemistry, the ozone layer,
and the causes and remedies of air pollution. Somewhat technical. Suitable for the reader with some
background in the subject.
Berner, Robert A. The Phanerozoic Carbon Cycle: CO2 and O2. New York: Oxford University Press, 2004.
Discusses climate and atmosphere of the Paleozoic, Mesozoic, and Cenozoic eras. Also covers aspects of
weathering and erosion on the carbon cycle. Suited to undergraduates. Contains references for each chapter
and indexing.
Brimblecombe, Peter. Air Composition and Chemistry. 2d ed. New York: Cambridge University Press, 1996.
Provides a thorough account of atmospheric chemistry and the techniques and protocol involved in determining
the makeup and properties of air. Appropriate for readers with some background in chemistry and
mathematics. Illustrations, maps, bibliography, and index.
Hobbs, Peter V. Introduction to Atmospheric Chemistry. Cambridge, England: Cambridge University Press,
2000. Provides a sound introduction to atmospheric chemistry, beginning with the early evolution of the
planet’s atmosphere. Written at the college level.
Holland, H. D. The Chemical Evolution of the Atmosphere and Oceans. Princeton, N.J.: Princeton University
Press, 1984. A comprehensive and technical treatment of the geochemical cycling of elements over geological
time and the coupling between the atmosphere, ocean, and surface. Covers the origin of the solar system, the
release and recycling of volatiles, the chemistry of the early atmosphere and ocean, the acid-base balance of
the atmosphere-ocean-crust system, and carbonates and clays.
Levine, Joel S., ed. The Photochemistry of Atmospheres: Earth, the Other Planets, and Comets. Orlando, Fla.:
Academic Press, 1985. A series of review papers dealing with the origin and evolution of the atmosphere, the
origin of life, the atmospheres of Earth and other planets, and climate. Compares the origin, evolution,
composition, and chemistry of Earth’s atmosphere with the atmospheres of the other planets. Contains two
appendices that summarize atmospheric photochemical and chemical processes.
Lewis, John S., and Ronald G. Prinn. Planets and Their Atmospheres: Origin and Evolution. New York:
Academic Press, 1983. A comprehensive, textbook treatment of the formation of the planets and their
atmospheres. Begins with a detailed account of the origin and evolution of solid planets via coalescence and
accretion in the primordial solar nebula. Discusses the surface geology and atmospheric composition of each
planet.
Marshal, John, and R. Alan Plumb. Atmosphere, Ocean and Climate Dynamics: An Introductory Text.
Burlington, Mass.: Elsevier Academic Press, 2008. An excellent introduction to atmospheres and oceans.
Discusses the greenhouse effect, atmospheric structure, oceanic and atmospheric circulation, and climate
change. Suitable for advanced undergraduates and graduate students with some background in advanced
mathematics.
Voronin, P., and C. Black. “Earth’s Atmosphere as a Result of Coevolution of Geo- and Biospheres.” Russian
Journal of Plant Physiology 54 (2007): 132-136. Covers the evolution of the atmosphere’s composition and
factors altering the gas composition. Provides background content on photosynthesis and chemolithotrophy.
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Highly technical. Appropriate for readers with a strong chemistry or geology background.
Yung, Yuk Ling, and William B. DeMore. Photochemistry of Planetary Atmospheres. New York: Oxford
University Press, 1999. Examines the atmospheric chemistry of all of the planets in the solar system, with a
focus on photochemical processes. Intended for the advanced reader. Illustrations, bibliography, and index.
Joel S. Levine
Article Citation
Levine, Joel S. "Atmosphere’s Evolution." Earth Science: Earth’s Weather, Water, and Atmosphere. Ed. Margaret
Boorstein and Richard Renneboog. Salem Press, 2012. Salem Science Web. 13 Jan. 2013.
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