Schopf, J .
The Oldest Records of Life.
During the past decade there has been an upsurge of interest in the oldest evidence of life, that preserved in Archean (>2,500-Ma-old) geologic units. Such evidence is widely regarded to extend to ~3,500 Ma ago: molecular biomarkers and isotopic data have been interpreted as providing insight into the physiology of Archean microbes, and stromatolites and microbial fossils have been reported from more than 50 Archean geologic units, including 13 deposits in the 3,200- to 3,500-Ma-old age range.
Despite this body of evidence, some workers have claimed that “true consensus for life’s existence” dates only from 1,900 Ma ago (Moorbath, 2005, Nature 434, 155), a timing for the beginning of the known fossil record more than a billion-and-a-half years younger than, and thus very much at odds with, that presented in modern textbooks.
It is certainly true that because of the scarcity of Archean rocks and the metamorphism to which such deposits have been subjected -- results of geologic recycling and tectonism over their protracted history -- evidence of Archean life is markedly less abundant and well preserved than that known from the younger, Proterozoic, Precambrian. Nevertheless, uncertainty about the oldest records of life stems largely from doubts raised about the biological origin of certain of the oldest putative fossils known, microbe-like microscopic filaments reported from the ~3,465-Ma-old Apex chert of Western Australia. These doubts have now been laid to rest. The paleoenvironment, carbonaceous composition, mode of preservation, and morphology of these permineralized organic-walled filaments, coupled with new evidence of their cellularity provided by two- and three-dimensional Raman imagery, support a biogenic interpretation. The Apex filaments, together with the presence in similarly aged deposits of stromatolites, microfossils, and carbon isotopic evidence of biological activity, establish that the antiquity of life on Earth extends at least to ~3,500 Ma ago.
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1 - University of California Los Angeles, CSEOL-Gelogy Bldg, Los Angeles, California, 90095-1567, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 1:15 PM