Friday, July 11, 2008
Pinpointing when in earths history life began has been a big challenge for science. Naturally the further back you go, the scarcer the evidence becomes. At the moment the general agreement is that microfossils found in ancient rocks, together with other clues, like the banded iron formations, are proof of that life was established here on earth by around 3.5 billion years ago, but more equivocal evidence has suggested that the beginning may be yet earlier. However it is usually thought that the late heavy bombardment that tails off around 3.8 billion years ago imposes a limit on the antiquity of life’s origin. Interesting then, that recent research on to isotopic carbon ratios in ancient Australian rocks indicates that some kind of biological process may have been at work up to 4.25 billion tears ago. Living organisms concentrate the lighter isotope of carbon, and we aren’t aware of any other natural processes that do this to any significant extent, so the presence of high levels of C12 in the carbon inclusions found in these ancient zircon deposits is curious to say the least.