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Did newborn Earth harbour life?

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http://space.newscientist.com/article/dn14245-did-newborn-earth-harbour-life.html?DCMP=ILC-hmts&nsref=news3_head_dn14245

Did newborn Earth harbour life?

Life on Earth might have emerged about 750 million years earlier than previously thought, new research suggests.

Researchers have found unusually light isotopes of carbon, a common indicator of life, in the Earth's oldest mineral deposit, found in the Jack Hills in Western Australia. The carbon dates to more than 4.25 billion years ago, a time known as the Hadean period.

Life is largely considered to have emerged around 3.5 billion years ago, after a violent period known as the Late Heavy Bombardment, in which a large amount of space debris walloped and may have sterilised the Earth.

But the Jack Hills find suggests life might have existed well before that time, although researchers caution it is too early to draw a definite conclusion.

"We now have an indication that it might be life," says mineralogist Thorsten Geisler of the Institute for Mineralogy at the University of Münster in Germany.

Geisler and colleagues dated samples from the Jack Hills area by measuring the abundance of radioactive elements in zircon deposits. They then analysed the concentration of carbon-13 and carbon-12 found in small pieces of diamond and graphite trapped within the zircon.
Organic material

They found the ratio of carbon-12, a lighter isotope of carbon, to carbon-13 was unusually high. Light carbon suggests the presence of organic material.

But it is too early to say for certain whether the carbon might indicate life. "We can't say now that we have unambiguous evidence of life before the Late Heavy Bombardment," Geisler told New Scientist.

That's because certain non-biological chemical reactions can also create light carbon, although the ratio is so skewed towards the lighter isotope that these reactions can't easily account for it.

A reservoir of light carbon might also indicate that simple organic compounds might have existed on Earth, priming the environment for the later emergence of life.

"When I see that, that's really good news, because we need a reservoir of reduced carbon compound to set the stage for the origin of life," says Jeffrey Bada, a chemist at the Scripps Institution of Oceanography in La Jolla, California, US.

Journal reference: Nature (vol 454, p 92)

TAGGED: BIOLOGY, EARTH SCIENCES, EVOLUTION


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