SCIENTISTS studying ancient soils have found remnants of organic life dating back 2.6 billion years.
It is believed the South African soil discovery reveals the earliest known evidence for terrestrial life. This would push back the boundaries of life on earth by an amazing 1.4 billion years.
The consequences of the discovery are important to experts investigating global warming, fears over the current erosion of the protective layer, and understanding why the earth is rich in oxygen.
Crucially, it means the earth was protected by an ozone shield before 2.6 billion years ago. This allowed the organisms to grow - no more than a mouldy, glowing mat of photosynthetic blue-green algae. Its ancient remnants have many chemical similarities to modern blue-green algae growing in fresh water.
It is already known that micro-organisms flourished in the oceans at least 3.8 billion years ago. But exactly when these tiny micro-organisms took the crucial evolutionary move to colonise on land has mystified scientists.
The discovery reveals that the early life forms were no more than mould growing on top of the soil during a rainy season.
To date, the oldest undisputed remnants of terrestrial biomass have been 1.2 billion-year-old microfossils found in Arizona.
However, a research team which studied samples taken from Mpumalanga province, South Africa, found a paleosol dating to between 2.6 and 2.7 billion years ago which contained organic carbon.
A paleosol is a layer of ancient soil - in this case buried and preserved where it formed. Researchers were able to date the paleosol accurately because the 55ft thick layer found at Schagen was trapped between a layer of 2.7 billion-year-old serpentine and a 2.6 billion-year-old quartzite bed. This dated the soil to between 2.6 and 2.7 billion years ago.
Further tests confirmed that the carbon was not a remnant of later petroleum migration, but was biological in origin and had always been part of the soil.
Dr Hiroshi Ohmoto, professor of geochemistry and director of the Penn State Astrobiology Centre, will publish details of his findings in this week's issue of Nature.
He said: ''Our work shows that the organic matter in this soil very probably represents remnants of microbial mats that developed on the soil surface between 2.6 and 2.7 billion years ago. This places the development of terrestrial biomass more than 1.4 billion years earlier than previously reported.
''Our finding may then imply that an ozone shield developed before 2.6 billion years ago. The ozone shield would have protected land-based biological forms from the effects of cosmic radiation.''
He added: ''Development of the ozone shield requires an oxygen-rich atmosphere. Our finding of ancient biomats on land is an important addition to a growing line of evidence suggesting that the rise of atmospheric oxygen took place more than 2.6 billion years ago.'' The rise of oxygen was crucial to life on the planet.
Proving that the carbon in the soil is biological in origin and that it accumulated during soil formation is a complex process. Eventually, the Penn State scientists were able to agree that the organic carbon was the remnant of life which had developed on the soil surface.
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