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Saturday, March 27, 1999 Published at 19:15 GMT


'Oldest ever' fossils found

Disturbances in the Earth's crust destroyed many fossils

The oldest and tiniest fossils yet identified will be unveiled at a meeting in Strasbourg next week.

The bacterial creatures, which resemble "pond slime", were found in North West Australia and are estimated to be approximately three-and-a-half billion years old.

Bacteria and algae like them are believed to have filled the primitive, super-heated oceans of the world during the earliest stages of life on this planet.

Hyperactive crust

The task of the team of Swiss and Austrian geologists who discovered the fossils was complicated by the massive problems associated with identifying fossils so small.

When the hyperactive state of the Earth's crust is taken into consideration, the project would appear to have been all but impossible.

Over millions and millions of years, the continents have crashed into each other, split apart, been submerged, melted down and re-emerged again.

The vast majority of fossils formed from algae and bacteria will have been folded, fractured and cooked by heat and pressure many times.

Breathable atmosphere

But the scientists reasoned that since the action of modern micro-organisms produces deposits of a limestone called dolomite, then dolomite approximately 3.5 billion years old would be a good place to start looking for their ancestors.

They found some 3.45 billion-year-old dolomite in the Pilbara range in North West Australia. After etching it with acid they found the fossils using an electron microscope.

It is believed that the fossils are of a cyanobacteria - an organism that still forms thick mats in warm shallow seas today.

But in the early pre-Cambrian period, they played a vital role in the development of more complex species by being among the first life forms to use sunlight to help them absorb carbon dioxide and release oxygen and therefore making the atmosphere breathable.

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