Life on Earth may have developed below rather than above ground, reveal scientists
How life on Earth came into existence is still one of the greatest mysteries in science but new research into the “deep biosphere” indicates that the first replicating life-forms on the planet may have originated deep underground rather than, as commonly believed, on the surface.
Scientists have now discovered microbes living and reproducing as deep as 5km (3.1 miles) below ground and studies have shown that they are likely to have survived in complete isolation from the surface biosphere for millions and perhaps even billions of years.
One of the latest studies into the deep biosphere has found that these microbes form a distinct subsurface community of genetically similar individuals despite living on opposite sides of the world. This global similarity of such an isolated life-form suggests that they may have evolved directly from a common ancestor that lived as long ago at the period when life on earth originated, some 3.5 billion years ago.
An increasing number of researchers believe that life could have first got going in the tiny cracks of underground rocks, fuelled not by the energy of sunlight but by chemical fuel in the form of hydrogen and methane which can be produced in certain types of rock under high temperatures and pressures.
The latest discovery of a closely-related, global community of microbes in the deep biosphere lends further support to the idea that life originated not in the “primordial soup” of surface lakes and seas, but in the tiny water-filled fissures found in underground rock, said Matt Schrenk of Michigan State University.
“Two years ago we had scant idea about what microbes are present in subsurface rocks or what they eat. Since then a number of studies have vastly expanded that database,” Dr Schrenk said.
“We’re getting this emerging picture not only of what sort of organisms are found in these systems but some consistency between sites globally – we’re seeing the same types of organisms everywhere we look,” he said.
The study, presented this week to the American Geophysical Union in San Francisco, compared DNA sequences of hydrogen-eating microbes extracted from rock fractures deep below North America, Europe, South Africa and Japan. To their surprise, the scientists found that they were closer than 97 per cent similar – making them virtually the same species, Dr Schrenk said.
“It is easy to understand how birds or fish might be similar oceans apart, but it challenges the imagination to think of nearly identical microbes 16,000km apart from each other in the cracks of hard rock at extreme depths, pressures and temperatures,” he said.
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