This diamond and the zircon surrounding it, as seen by an electron microscope, are both 4 billion years old.
Credit: Thorsten Geisler & Alexander Nemchin
Does carbon mean life?
However the study also raises the possibility that there are other non-organic processes that can concentrate the isotope carbon 12. "Alternatively, it requires some other process to create the light carbon values, which would then question the widely held assumption that light carbon means life," Nemchin added.
Co-author Martin Whitehouse, of the Swedish Museum of Natural History in Stockholm, acknowledges that while light carbon is a possible sign of life, it's not a unique indication. There are other non-biological processes that can create carbon 12, and at this stage in the research, they shouldn't necessarily be ruled out.
"The idea that life might have developed during a period when the Earth was subject to intense meteorite bombardment is definitely intriguing," says Whitehouse. "If it is a sign of life, then it would not only show that life could have developed in such a hostile extreme environment, but also that it probably developed more than once, only to be obliterated by successive meteorite impacts."
Ian Fitzsimons, head of the Applied Geology department at Curtin, and not one of the study authors, finds this aspect of the research the most interesting, because it would mean there was a non-organic system concentrating carbon 12. If this were proved it could invalidate a lot of the assumptions that the study and dating of early life are based upon.
"It would negate a large number of assumptions about carbon isotope signatures in rocks, and the physical and chemical processes operating on early Earth," said Fitzsimmons.
