Life on earth began 300m years early

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The Independent Online
Life on Earth began almost four billion years ago - 300 million years sooner than was previously thought, and only 200 million years after the Earth was sterilised by meteorite bombardments, according to new studies of ancient sedimentary rocks on Greenland.

And according to one British expert, the news could also mean that comets and meteorites originally provided the building blocks for self-reproducing molecules - the essential prerequisite for life.

The new research looked at rocks in the Itsaq Gneiss complex, in southwestern Greenland, and examined the ratios inside them of two carbon isotopes - atoms with the same chemical properties, but different atomic weights. Scientists have previously found that living organisms filter these isotopes in a way that inorganic processes do not, producing imbalances of different forms of isotopes. The new studies show that the rocks, which are among the Earth's oldest, have the telltale isotopic signature of life.

Following the new studies, published today in the science journal Nature, it is now thought that primitive life existed on Earth up to 3,850 million years ago - between 300 and 400 million years before the appearance of the microfossils which had previously been the earliest known evidence of life. Researchers had long suspected that life pre-dated the microfossil evidence, since those fossils are structurally complex, implying an already significant period of evolution.

The date for the first life would be only 100 million years after the Earth was heavily bombarded by meteorites which would have sterilised its surface - posing a problem for some who think that the new date implies an accelerated development of life.

However, the findings are not at odds with what we know about the contents of comets and meteorites, said Monica Grady, an expert in geology at the Natural History Museum.

Although not sufficient to produce life of themselves, such chemicals could have provided a kick-start to the development of life on this planet, she said. "We still don't understand some of the intervening steps, such as how you would get self-replication and a cell membrane. But my feeling is that comets and meteorites formed the first steps by producing the building blocks for life."

The age of the Greenland rocks closely matches that of the meteorite recently said to offer signs of life on Mars, which is between 3,600 and 4,000 million years old.