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Analogues for the early synthesis of organic matter on Mars

Michael H. Engel, School of Geology & Geophysics

100 East Boyd Street

The University of Oklahoma, Norman, Oklahoma 73019 USA

Randall S. Perry, Department of Earth and Space Sciences

University of Washington, Seattle, Washington 98195

On Earth, organic matter is found in association with sediments and sedimentary rocks.� Sedimentary rocks that have undergone slight to moderate metamorphism may also contain remnants of organic matter incorporated prior to deformation.� Igneous rocks, however, may only contain organic matter if it is introduced via fluid migration into fractures subsequent to crystallization.� The Martian meteorites collected to date are all igneous rocks.� Thus, the chances that they contain indigenous organic matter, biotic or abiotic, are remote.� Whether the organic material in fractures of ALH84001 is indigenous or is contamination resulting from an extended residence time on Earth prior to collection, remains unresolved.� What is clear, however, is that the current collection of Martian meteorites is far from ideal with respect to determining the types of organic compounds that may have been incorporated into sediments on the Martian surface.� Carbonaceous meteorites consist of material derived from the solar nebula 4.5 billion years ago.� They also exhibit varying degrees of aqueous processing thought to have occurred on a parent body(s) in the region of the asteroid belt during the early stages of formation of the solar system.�� Life appears to have existed on Earth for as far back in time as the rock record extends (~3.8 Ga).� Thus, the only record for the solar system organic inventory that preceded life�s origin on Earth or Mars are carbonaceous meteorites.� In particular, the CI and CM carbonaceous meteorites contain many of the building blocks for life as we know it.� It is interesting to note, however, that of the twenty protein amino acids common to all organisms, only eight have been observed in carbonaceous meteorites. �A hypothesis is presented to account for the absence of the remaining twelve amino acids that are essential for life and how their presence or absence can be used to determine if life was present in ancient rocks from Mars.� In summary, carbonaceous meteorites collected at the time of or shortly after impact provide the most reliable record of the solar system�s organic inventory during the early stages of its formation.� They provide the best analogue for what organic synthesis and aqueous processing may have been like on planetary surfaces prior to life�s origin.��

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