Life might have emerged on Earth 300m years earlier than thought, scientists say


Electron microscope images show graphite specks trapped in old zircon crystals.
BELL ET AL, UNIVERSITY OF CALIFORNIA, LOS ANGELES

Scientists say they have found evidence that life may have begun on Earth 300 million years earlier than previously thought.

A discovery in Western Australia suggests that living organisms may have existed as long as 4.1bn years ago. That dramatically reduces the time between the Earth forming (about 4.6 billion years ago) and the emergence of life.

US scientists, led by Dr Mark Harrison, from the University of California at Los Angeles, found specks of graphite with the hallmark of biological origin trapped within immensely old zircon crystals from Jack Hills, Western Australia.

The graphite was enriched with 12C, a “light” carbon isotope, or atomic strain, normally associated with living things, the scientists say in a study published in the journal Proceedings of the National Academy of Sciences.

"This study extends the terrestrial carbon isotope record around 300 million years beyond the previously oldest-measured samples from south-west Greenland,” the scientists wrote.

However, they cautioned that some non-biological processes could also produce the light form of carbon, notably meteorite impacts.

But the amount of extra-terrestrial carbon needed to account for the findings made meteorites an unlikely source.

“A biogenic origin seems at least as plausible,” the scientists said.

  1. http://www.pnas.org/content/early/2015/10/14/1517557112
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