Friday, March 20, 2009

Origin of life: Doubt cast on oldest trace of life - not so old, new research says

As ScienceDaily tells it, (Feb. 28, 2009), a 1996 study argued that the small island called Akilia in southwest Greenland featured apparent evidence for life at 3.82 billion years ago.

That's certainly remarkable because, as the release explains,

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.
The 1996 group
... 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.
Well yes, but ... it's not like finding something definite like stromatolites ...

They may have jumped swiftly to conclusions.

Anyway, that's what other researchers thought: Martin J. Whitehouse at the Swedish Museum of Natural History and Nordic Center for Earth Evolution led a team that dated the graphite 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.
Still pretty old, when you think of it ...

(Note: The photo is a view of Akilia's rocks from SpaceDaily.)

Journal reference:

1. M J Whitehouse, J S Myers & C M Fedo. The Akilia Controversy: field, structural and geochronological evidence questions interpretations of >3.8 Ga life in SW Greenland. Journal of the Geological Society, 2009; 166 (2): 335-348 DOI: 10.1144/0016-76492008-070
Adapted from materials provided by Geological Society of London, via AlphaGalileo.

See also:

Podcast: Chemist Charles Garner on chemical evolution

Why the Huygens probe - sadly - probably won't tell us much.

Mars red but not dead?

NASA says, could be life on Mars, could be rocks

Origin of life: What can the Saturnian moon Titan tell us?

Origin of life: Alien origin taken seriously? Ghost of Francis Crick smiles wanly

Origin of life: A meatier theory? Or just another theory?; Origin of life: There must be life out there vs. there can't be life out there; Origin of life: Oldest Earth rocks may show signs of life, in which case ... ; Origin of life: Positive evidence of intelligent design?; Origin of life: But is being greedy enough?; Origin of life: Ah, that "just so happens" intermediate series of chemical steps
Why should the search for Darwin's "warm little puddle" be publicly funded?