Another article reiterating that C13 isotope depletion is not a biomarker: Controversy Over World’s Oldest Traces Of Life.
Research carried out in 1996 argued that a five metre wide outcrop of rock on the island contained graphite with depleted levels of 13C. Carbon isotopes are frequently used to search for evidence of early life, because the lightest form of carbon, 12C (atomic weight 12), is preferred in biological processes as it requires less energy to be used by organisms. This results in heavier forms, such as 13C, being less concentrated, which might account for the depleted levels found in the rocks at Akilia. ...
The new research, led by Martin J. Whitehouse at the Swedish Museum of Natural History and Nordic Center for Earth Evolution, casts doubt on this interpretation. The researchers present new evidence demonstrating that the cross-cutting relationships are instead caused by tectonic activity, and represent a deformed fault or unconformity. If so, the age of the intrusive rock is irrelevant to the dating of the graphite, and it could well be older. Because of this, the scientists turned their attention to dating the graphite-containing rocks themselves, and found no evidence that they are any older than c. 3.67 billion years.
"The rocks of Akilia provide no evidence that life existed at or before c. 3.82 Ga, or indeed before 3.67 Ga," they conclude.
The age of the Earth itself is around 4.5 billion years. If life complex enough to have the ability to fractionate carbon were to exist at 3.8 billion years, this would suggest life originated even earlier. The Hadean eon, 3.8 – 4.5 billion years ago, is thought to have been an environment extremely hostile to life. In addition to surviving this period, such early life would have had to contend with the ‘Late Heavy Bombardment’ between 3.8 and 4.1 billion years ago, when a large number of impact craters on the Moon suggest that both the Earth and the Moon underwent significant bombardment, probably by collision with asteroids.
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5 comments:
@OIM "because the lightest form of carbon, 12C (atomic weight 12), is preferred in biological processes as it requires less energy to be used by organisms. This results in heavier forms, such as 13C, being less concentrated, which might account for the depleted levels found in the rocks at Akilia"
OIM, are you disputing that the C12 to C13 ratio in biological organisms is enhanced relative to nonbiological carbon?
I had always thought that the reason for this had to do with preferential osmosis across the cellular membrane, rather than it "requires less energy to be used by organisms".
Tom,
This is the modern equivalent of vitalism.
The fact that a lack of c13 isotope can indicate biological activity does not mean that it does indicate biological activity.
Similarly, the fact that carbon can be biological (e.g. carbohydrates) does not mean all carbon is alive.
Graphite and diamonds are not biological organisms.
I refer you to my post on the subject.
I agree with you. Carbon IS a component of Life on Earth, but deposits of it does NOT mean one finds evidence for life. If those guys are looking for evidence for life by relying on carbon deposits, then they're not going to get very far. Carbon isn't the only "biomolecule" out there.
Raptor,
Have you any physical evidence of a non carbon based life form?
No, I don't. But, if I found deposits of, oh say....copper, does that mean I found a penny? No. I mean is it doesn't necessarily mean life is present. Remember that carbon isn't the only "biomolecule." And, besides, finding material that coincidentally makes up something else, doesn't mean that "something" was there. Carbon doesn't only make up life you know.
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