Isotopic evidence for extraterrestrial organic material in the Martian meteorite, Nakhla

In this paper, we report on new C-14 and C-13 isotopic analyses of organic and carbonate phases in pristine samples of the martian meteorite, Nakhla ( fell 1911AD). We undertook water and acid extractions of soluble phases as well as a study of insoluble material. We used 14C to differentiate between extraterrestrial organic material and recent terrestrial contamination. Re sults indicate that most of the organic matter in Nakhla is released by 6N HCl and there appear to be two isotopically distinct sources of extraterres trial organics with delta C-13 Of -33 parts per thousand and -15 parts per thousand and low C-14. We estimate that at least 75% of the organic materia l released by 6N HCl acid etching is extraterrestrial. We conclude that thi s acid-labile component is likely similar to polymeric organics observed in CM2 chondrites (Gilmour and Pillinger, 1994) and could have accumulated on the Martian surface from the accumulation of meteoritic material and comet ary debris and cosmic dust. We also determined that the terrestrial organic contamination is characterized by approximately modem C-14 values and delt a C-13 of -25 parts per thousand. Copyright (C) 2000 Elsevier Science Ltd.