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 12 October 2008 00:17 BST

'Oldest evidence' found of life on Earth

Thursday, 03 Jul 2008 15:04
New evidence has questioned when life began on Earth
A team of Australian scientists believe they have found evidence that life on Earth began millions of years earlier than thought.

Previous evidence for ancient life stretches back to at least 3.5 billion years ago, in the form of single-celled organisms.

But now scientists from Curtin University of Technology say they have found a key indicator to the earliest life forms in diamonds from Jack Hills in Western Australia.

They believe that the 4.2 billion-year-old diamonds found trapped inside the Jack Hills zircon crystals are the oldest-known samples of Earth's carbon.

The high concentrations of carbon 12, or 'light carbon', within these crystals is said to be remarkable as it is a feature usually associated with organic life.

Writing in the journal Nature, the researchers argue that their finding reignites debate on the early evolution of life on Earth, suggesting that a simple life form existed on Earth 700 million years earlier than previously thought.

"We believe this find to be the oldest terrestrial light carbon reservoir discovered so far," said project leader Dr Alexander Nemchin.

"We interpret the range of light carbon values observed in these inclusions as a unique chemical marker that opens up the possibility of biological activity during the period not long after the Earth's formation."

He added: "The discovery challenges our fundamental understanding of processes active in the early history of the Earth. It suggests that life may well have appeared on Earth long before the period of heavy-meteorite bombardment believed by some to have initiated the emergence of life on Earth.

"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."
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