Microbiology/Genetics

Life Could Have Originated Earlier than Thought

Diamond fragments set new limit for life occurrence

By Gabriel Gache, Science News Editor

3rd of July 2008, 11:18 GMT

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Image of a zircon crystal containing possible evidence that life was present on Earth some 4.25 billion years ago

Currently, it is widely considered that life first appeared on our planet approximately 3.5 billion years ago in the outcome of a period that is currently known as the Late Heavy Bombardment, which saw the Earth under a rain of debris coming from out of space. Such an effect would have most likely prevented the evolution of any living being on the planet and destroyed life preceding its onset. But a new finding indicates that life may have been present here as much as 750 million years prior to that time, otherwise put, 4.25 billion years ago.

On Earth, carbon is usually found in the form of lightweight isotopes, mostly due to the presence of life. If we consider light carbon isotopes as an indicator for life in any world, then this would basically mean that life appeared on our planet more than 4.25 billion years ago. As evidence stands one of the oldest found mineral deposits in the world, located in the Jack Hills, Australia.

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

By analyzing the occurrence of radioactive elements inside the Jack Hills zircon deposits, Geisler and his fellow colleague researchers discovered that the ratio of carbon-13 and carbon-12 in small pieces of diamond is exceedingly low, suggesting the possibility of life presence. On the other hand, researchers cannot say for certain whether or not the lighter carbon isotopes have been created by life or they are of natural occurrence.

"We can't say now that we have unambiguous evidence of life before the Late Heavy Bombardment," said Geisler.

Even though light carbon isotopes can be created during chemical reactions between inorganic chemicals, it is highly improbable that this is the case since they cannot account for the ratios between light and heavy isotopes. Alternatively, the concentration of carbon isotopes may have existed on Earth ever since the planet was formed.

"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 of the Scripps Institution of Oceanography.

TAGS:

life | carbon | isotope ratio | zircon | diamond

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