Overview (The Solar System)
About 4.5 to 4.6 billion years ago, the primordial solar nebula, a part of a large interstellar cloud of gas and dust, began to contract under the influence of gravity. This contraction led to the formation of the Sun and the rest of the Solar system including the Earth. The primordial solar Nebula was composed mostly 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.
As the Solar nebula contracted, its rotational speed increased to conserve angular momentum. Most of its mass contracted to its center, there becoming the proto-Sun, while the remaining matter was spun off into an equatorial disk. Within the disk, matter condensed from the gaseous state into small, solid grains. Only materials with high melting-point temperatures could condense near the developing proto-Sun; materials with lower melting points condensed farther out. The small solid grains collided with each other and stuck together in a process called accretion that led to the growth of larger bodies called planetesimals. Continued accretion resulted in fewer but larger planetesimals that eventually grew into protoplanets and finally planets, such as Earth.
About the time that the newly formed Earth was reaching its approximate present mass, it may have acquired a temporary atmosphere of hydrogen, helium, methane, ammonia, water...
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Methods of Study (The Solar System)
Information about the origin, early history, and evolution of the Earth’s atmosphere comes from a variety of sources. Information on the origin of Earth and other planets is based on theoretical computer simulations. These computer models simulate the collapse of the Primordial solar nebula and the formation of the planets. Astronomical observations of what appear to be equatorial disks and the possible formation of planetary systems around young stars 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 and the geochemical cycling and 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 these experiments, mixtures of gases simulating the Earth’s early atmosphere are energized by ultraviolet radiation, electrical discharges, or heated rocks, simulations of energy sources available on the early Earth. The resulting products are analyzed by chemical techniques.
One of the parameters affecting atmospheric photochemical reactions, chemical evolution, and the origin of life was the flux of solar ultraviolet radiation incident on the early Earth. Astronomical...
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Context (The Solar System)
Studies of the origin and evolution of the atmosphere have provided new insights into the processes and parameters responsible for global change. Understanding the history of the atmosphere provides insight into its future. Today, atmospheric changes being studied for their possible long-term effects include the buildup of greenhouse gases like carbon dioxide and the depletion of ozone in the stratosphere. 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 and possible remedies. Studies of the origin and evolution of the atmosphere have also provided new insights into the origin of life and the possibility of life outside the Earth.
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Further Reading (The Solar System)
Ahrens, C. Donald. Essentials of Meteorology: An Invitation to the Atmosphere. 5th ed. Florence, Ky.: Brooks/Cole, 2007. An updated version of a classic meteorology textbook. Explains tricky concepts in an easy-to-understand way. Suitable for students and nonscientists.
_______. Meteorology Today. 8th ed. Florence, Ky.: Brooks/Cole, 2006. A common text used for introductory meteorology college courses but can also be understood by general audiences. Comes with a CD-ROM learning aid, which includes chapter tests and multimedia tutorials.
Chaisson, Eric, and Steve McMillan. Astronomy Today. 6th ed. New York: Addison-Wesley, 2008. Very well-written college-level textbook for introductory astronomy courses with an entire chapter on the formation of the planets.
Fraknoi, Andrew, David Morrison, and Sidney Wolff. Voyages to the Stars and Galaxies. Belmont, Calif.: Brooks/Cole-Thomson Learning, 2006. A textbook for introductory astronomy courses that offers several sections dealing with the origin of the solar system and planetary atmospheres.
Freedman, Roger A., and William J. Kaufmann III. Universe. 8th ed. New York: W. H. Freeman, 2008. College-level introductory astronomy textbook with several sections on the origin of the solar system, including coverage of planetary atmospheres.
Hartmann, William K. Moons and Planets. 5th ed. Belmont, Calif.:...
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