To Sano et al., this suggests either that the apatites ``grew about 1,500 Myr ago, or that they grew earlier than that but were subsequently affected by recrystallization, and/or diffusive exchange''.3.65 Ga) volcano-sedimentary terranes are locked in granitoid gneiss complexes that have experienced high degrees of metamorphism and deformation, the origin and mode of preservation of carbonaceous material in the oldest metasedimentary rocks remain a subject of vigorous debate.
report a 207Pb/206Pb date of 1,459 /-160 Myr for apatite grains 25 mum in diameter, containing inclusions of isotopically light carbon, from a granulite grade BIF (typically 70% quartz, 10% magnetite, 20% mafic phases and sulphides) from Akilia island, Greenland, that was lithified before 3,850 Myr (refs 1,2).
But if other isotopes (U-Pb and Pb-Pb) are used, the apatites are estimated at just 1,504 /-336 (2sigma) and 1,459 /-160 (2sigma) Myr old.
ABSTRACT: The age and origin of the quartz-amphibole-pyroxene (qap) gneiss from the island of Akilia, southern West Greenland, have been the subject of intense debate since the light C-isotope composition of graphite inclusions in apatite was interpreted to indicate the presence of Earth's earliest biological activity.
Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 half-life there will be 0.5 gram of the parent isotope left.Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists. Recognition that radioactive decay of atoms occurs in the Earth was important in two respects: Principles of Radiometric Dating Radioactive decay is described in terms of the probability that a constituent particle of the nucleus of an atom will escape through the potential (Energy) barrier which bonds them to the nucleus.The energies involved are so large, and the nucleus is so small that physical conditions in the Earth (i.e. The rate of decay or rate of change of the number N of particles is proportional to the number present at any time, i.e.By definition, D* = N-1) (2) Now we can calculate the age if we know the number of daughter atoms produced by decay, D* and the number of parent atoms now present, N.The only problem is that we only know the number of daughter atoms now present, and some of those may have been present prior to the start of our clock. The reason for this is that Rb has become distributed unequally through the Earth over time.This finding could also be consistent with evidence from molecular biology that places the ancestry of primitive bacteria living in extreme thermal environments near the last common ancestor of all known life.