Interplanetary organic material

Piazzarello, S., Cooper, G. W. and Flynn, G. J. (2006) The nature and distribution of the organic material in carbonaceous chondrites and interplanetary dust particles. In Meteorites and the Early Solar System II, eds. Lauretta, D. S. and McSween, H. Y., Jr. Tucson University of Arizona Press, pp. 625-651. A comprehensive, up-to-date review of organic matter in carbonaceous chondrites, but not for the faint-hearted. 

Carbon compounds in the solar system can be traced in planetary atmospheres, on planetary surfaces, comets, asteroids, meteorites and in the interplanetary medium. Gas and solid state chemistry within the solar nebula was responsible for new organic material (49,50). Many organic compounds have been identified on outer solar system bodies, some of them originating in the surface ices through energetic processing (4). 

The importance of exogenous delivery of organic matter to the early Earth is critically dependent on the survivability of organic compounds during the delivery process. It is presently unclear exactly how much organic material would escape destruction during asteroid, comet and interplanetary dust particle infall to the Earth s surface. 

The shock waves produced by meteorite impacts give rise not only to the obvious craters seen on planets and their satellites but also to subtle effects seen only with chemical and petrographic examination of the shocked material. Shock waves in the interplanetary and interstellar medium play an important role in the formation of stars and planets, including the Solar System. They also produce important chemical effects in interstellar clouds of dust and gas—including the production of rather complex organic molecules. 

Meteorites from the asteroid belt are a potential source of some of the purine bases present in RNA. As asteroids travel in their orbits between Mars and Jupiter they collide with each other and pieces are broken off that vary in size from large bodies (potential meteorites) to dust particles. If the energy of the collision is great enough, this material is propelled out of its orbit into the interplanetary medium and some of the material eventually reaches the Earth. Approximately 10 kg of asteroidal material reached the primitive Earth s surface (6). This corresponds to a layer of material weighing 2x10 kg/m if spread uniformly over the surface of the Earth. The carbon content of the soluble organics present (1%) is equivalent to a layer of carbon compounds 25 m thick on the primitive Earth. Since meteorites contain about 1 ppm of purines and pyrimidines, then about lO kg of these compounds were on the primitive Earth. 

Regardless of what the early Earth s atmosphere was like, the planet was undoubtedly bombarded then, as now, by extraterrestrial material such as meteorites. The presence of organic compounds in meteorites was recognized since the mid-19th century, when Berzelius analyzed the Alais meteorite. Today the presence of a complex array of extraterrestrial organic molecules in meteorites, comets, interplanetary dust and interstellar molecules is firmly established, and has lead some to propose them as sources of the prebiotic organic compounds necessary for the origin of life (109-112). 

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