Origin of life from apatite dating
One possible explanation for this zircon age distribution is that the ~2700 Ma grains are metamorphic in origin, the ~3650 Ma grains are igneous, and the oldest grains are xenocrysts inherited from an older rock.
Together, these conditions would presumably have restricted the number of suitable environments for life to emerge. 1), then the best sources of information to understand this phenomenon are water-laid sediments preserved in the geologic record. Ancient (3800 Ma) water-sculpted terrains have been recognized on Mars, and liquid water appears to exist beneath the icy crust of Jupiter's moon Europa. Such organisms could have survived thermal assaults from giant impacts, especially if sequestered deep in the oceans or in rocks away from a destructive surface zone bathed both in the intense ultraviolet radiation of the early Sun and a rain of extraterrestrial debris ~4 b.y. To better understand this early era, we have to unravel the timing of events from a heavily modified early Archean rock record. M., 1999, Geochronology and thermochronology by the Ar method, 2nd ed.: New York, Oxford University Press, 269 p. R., 2000, Age significance of U-Th-Pb zircon data from early Archaean rocks of West Greenland A reassessment based on combined ion-microprobe and imaging studies Comment: Chemical Geology (in press). R., and Mason, B., 1977, Petrogenesis and geochemistry of metabasaltic and metasedimentary enclaves in the Amîtsoq gneisses, West Greenland: American Mineralogist, v. EARLY ARCHEAN (3500 Ma) HISTORY OF WEST GREENLAND The diverse rock types present in the Isua district of West Greenland are all contained within extensive early Archean (36003900 Ma) gneisses dominantly of tonalitic-granodioritic composition (Black et al., 1971; Nutman et al., 1996) (Fig. This multiply metamorphosed terrane, termed the Itsaq Gneiss Complex (Nutman et al., 1996), contains 3850 Ma on Akilia Island The oldest known sediment (Nutman et al., 1997), and the oldest known rock with evidence of biological processes active during time of deposition (Mojzsis et al., 1996), is a layer ~3 m thick of BIF within a body of amphibolite on the southern tip of Akilia island, West Greenland (Fig. This BIF on Akilia was chosen as the type locality for the Akilia association, a term used for volcano-sedimentary enclaves found throughout the Itsaq Gneiss Complex that are not part of the larger and better preserved Isua supracrustal belt (Mc Gregor and Mason, 1977).
Existing evidence points to a 3850 Ma age for granitoids intruding BIF on Akilia island, but the great significance of this age for early terrestrial evolution leads us to continue our geochronological investigations in more detail. S., and Moorbath, S., 1998, Initial Pb of the Amîtsoq gneiss revisited: Implication for the timing of the early Archaean crustal evolution in West Greenland: Chemical Geology, v.