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Published 1992 | public
Journal Article

The fate of organic matter during planetary accretion: preliminary studies of the organic chemistry of experimentally shocked Murchison meteorite

Abstract

It is possible that Earth's biologic precursors were delivered by late-impacting asteroids or comets, and it is possible that these objects were a source of Earth's volatile inventory. To understand the behavior of organic matter in carbonaceous meteorites during hypervelocity impact (1–2 km s^(−1)), three samples of the Murchison (CM2) carbonaceous chondrite were shocked to 19, 20 and 36 GPa and analyzed by very sensitive thermal-desorption photoionization mass spectrometry (SALI). Thermal-desorption (25–800 °C) SALI mass spectra of unshocked Murchison reveal indigenous aliphatic, aromatic, sulfur and organosulfur compounds. Samples shocked to ≈20 GPa exhibit little or no loss of organic matter relative to the unshocked material. This is consistent with the earlier work of Tyburczyet al. (1986) which showed that incipient devolatilization of Murchison occurs at peak shock pressures near 20 GPa. The small amount of organic matter lost appears to have occurred by volatilization of elemental sulfur, amines and aliphatic compounds. In the sample shocked to 36 GPa, approximately 70% of the organic matter was volatilized as a result of impact. The residual organic matter desorbed at somewhat higher temperatures and displayed a different chemical signature. In particular, the shocked material has a lower alkene/alkane ratio than that of the starting material. The preliminary data suggest that it is unlikely that the indigenous organic matter in carbonaceous chondrite-like planetesimals could have survived impact on the Earth in the later stages of Earth's accretion. However, chemical reactions that produce organic compounds with greater thermal stabilities may occur during impact or subsequent to impact by condensation of the impact-produced vapor plume.

Additional Information

© 1992 Kluwer Academic Publishers. Received December 17, 1991. The authors would like to thank J. F. Kerridge and M. H. Engel for thorough and constructive reviews. TNT and CHB acknowledge financial support from Gas Research Institute grant 5087-260-1626 and technical assistance from L. Jusinski, W. Olson, and S. Young at SRI International. E. Gelle and M. Long provided assistance with the shock experiments. TJA acknowledges ,financial support from NASA grants NAGW-1941 and NAGW-1953. JAT acknowledges financial support from NSF Grant EAR86-09782. Contribution #5094, Division of Geological and Planetary Science, California Institute of Technology.

Additional details

Created:
August 20, 2023
Modified:
October 18, 2023