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The minimum ages of some of the oldest Greenland rocks (Nutman et al., 1996, 1997) appear to overlap in time with a period of intense impacts peaking at 3850 ± 100 Ma as recorded on the Moon (Ryder, 1990).

Thermal and shock effects associated with the Late Heavy Bombardment era (Tera et al., 1974) are presumed to have rendered early Earth unsuitable for the emergence of life until after the massive bombardments ceased (e.g., Maher and Stevenson, 1988).

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However, stable isotope fractionations of the bioessential elements (e.g., C, N, and S) produced by different metabolic styles can be preserved in ancient sediments (Schidlowski et al., 1983). Timeline of early Earth history and recent advances made in investigating oldest biogeochemical records.

This permits understanding of the development of early life inferred from chemical and isotopic information, rather than solely on interpretation of microfossil-like shapes (e.g., Schopf, 1993; Mc Kay et al., 1996) (Fig. Listed are ages for oldest rock sequences, and of isotopic evidence for life in oldest sediments.) conditions (Holland, 1984) and a tectonic style reflecting higher heat flow through the crust than at present.

3850 Ma, interpreted as the age of crystallization of the magmatic protolith by Nutman et al. If this interpretation is correct, then the BIF is at least as old as 3850 Ma.

Carbon isotopic evidence of bio-organic activity during deposition of the BIF sediments (Mojzsis et al., 1996) would then suggest that the emergence of life on this planet occurred much earlier than previously thought (Hayes, 1996; Holland, 1997).

As long as liquid water, energy sources, and organic building blocks were present, life could have emerged on these worlds as well.

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