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Evidence for Life on Earth before 3,800 Million Years Ago
NTRS Full-Text: Click to View  [PDF Size: 496 KB]
External Online Source: doi:10.1038/384055a0
Author and Affiliation:
Mojzsis, S. J.(Scripps Institution of Oceanography, La Jolla, CA United States)
Arrhenius, G.(Scripps Institution of Oceanography, La Jolla, CA United States)
McKeegan, K. D.(California Univ., W. M. Keck Foundation Center for Isotope Geochemistry, Los Angeles, CA United States)
Harrison, T. M.(California Univ., W. M. Keck Foundation Center for Isotope Geochemistry, Los Angeles, CA United States)
Nutman, A. P.(Australian National Univ., Research School of Earth Sciences, Canberra, Australia)
Friend, C. R. L.(Oxford Univ., Dept. of Geology and Cartography, Oxford, United Kingdom)
Abstract: It is unknown when life first appeared on Earth. The earliest known microfossils (approx. 3,500 Myr before present) are structurally complex, and if it is assumed that the associated organisms required a long time to develop this degree of complexity, then the existence of life much earlier than this can be argued. But the known examples of crustal rocks older than approx. 3,500 Myr have experienced intense metamorphism, which would have obliterated any fragile microfossils contained therein. It is therefore necessary to search for geochemical evidence of past biotic activity that has been preserved within minerals that are resistant to metamorphism. Here we report ion-microprobe measurements of the carbon-isotope composition of carbonaceous inclusions within grains of apatite (basic calcium phosphate) from the oldest known sediment sequences a approx. 3,800 Myr-old banded iron formation from the Isua supracrustal belt, West Greenland, and a similar formation from the nearby Akilia island that is possibly older than 3,850 Myr. The carbon in the carbonaceous inclusions is isotopically light, indicative of biological activity; no known abiotic process can explain the data. Unless some unknown abiotic process exists which is able both to create such isotopically light carbon and then selectively incorporate it into apatite grains, our results provide evidence for the emergence of life on Earth by at least 3,800 Myr before present.
Publication Date: Nov 07, 1996
Document ID:
(Acquired May 09, 1998)
Report/Patent Number: NASA/CR-96-207592, NAS 1.26:207592
Document Type: Technical Report
Publication Information: Nature; p. 55-59; Volume 384
Contract/Grant/Task Num: NAGw-2881
Financial Sponsor: NASA; Washington, DC United States
Organization Source: Scripps Institution of Oceanography; La Jolla, CA United States
Description: 5p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
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