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Thursday, 30 November, 2000, 15:39 GMT
Life's leap to land
Planet
Life has flourished in the oceans for four billion years
Life made the transition to land more than a billion years earlier than previously thought, according to new geological evidence.

Organic material discovered within South African rocks suggests that microbes made the leap from the oceans to land about 2.6 billion years ago.

Until now, 1.2 billion-year-old fossils of blue-green algae found in Arizona contained the earliest record of terrestrial life.

The discovery gives scientists new information about the presence of life-sustaining oxygen in the Earth's atmosphere.

An ozone shield and an oxygen rich atmosphere around the planet would have been needed for life on land to emerge.

Organic matter

The rocks come from what is now the Eastern Transvaal district of South Africa.

They contain fossilised remnants of mats of photosynthetic bacteria, organisms that generate oxygen from water and atmospheric carbon dioxide.

"This places the development of terrestrial biomass more than 1.4 billion years earlier than previously reported," said Yumiko Watanabe, of the Pennsylvania State University, US, in the scientific journal Nature.

The researchers believe there may be even earlier fossil evidence of life on land, perhaps in Australia or Canada.

The finding also has implications for the search for life on other planets.

Collaborating scientists at the American space agency Nasa's Astrobiology Institute said they planned to search for signs of ozone around other planets in a future mission.

"The suggestion that an ozone shield existed as early as 2.6 billion years ago boosts our chances in the search for life on planets orbiting other stars," said astrobiologist Dr Michael Meyer.

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