In thin sections of the fine-grained parts of Akilia Qp rock sample G91-26, mapped apatites were found to be associated with graphite in about 20% of the occurrences.
Raman spectra of this carbonaceous material had strong G-band and small D-band absorptions indicative of crystalline graphite.
The half-life is the amount of time it takes for one half of the initial amount of the parent, radioactive isotope, to decay to the daughter isotope.
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.
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.
But if other isotopes (U-Pb and Pb-Pb) are used, the apatites are estimated at just 1,504 /-336 (2σ) and 1,459 /-160 (2σ) Myr old.
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.
On the basis of the age of these rocks, the emergence of the biosphere appears to overlap with a period of intense global bombardment.
Mark Harrison, Department of Earth and Space Sciences and IGPP Center for Astrobiology, University of California, Los Angeles, CA 90095-1567, USA published in GSA Today, April 2000 ABSTRACT Recent explorations of the oldest known rocks of marine sedimentary origin from the southwestern coast of Greenland suggest that they preserve a biogeochemical record of early life.