Pre history revisited
IT is time to rewrite the history of life on Earth. A Calcutta-based geologist, Pradip Bose, has found convincing evidence from a site close to Churhat, Madhya Pradesh: The first multi-celled animals evolved about 1.1 billion years ago. This finding will stretch back the chronology of animal life by about 500 million years. So far, findings in China had shown that multi-celled animals had evolved nearly 600 million years ago. But now, with Bose's discovery, scientists may begin to question Darwin's theory of evolution. Bose's paper, written along with two authors from Germany, is the cover story of latest issue of the reputed American journal Science.
Though microbiologists had predicted that coelomate metazoans existed at least one billion years ago, the Churhat find, Bose says, is the "first hard evidence". It could question Darwin's theory of evolution. The existence of such ancient multi-celled animals, suggests that "even such insignificant life forms could survive for so long".
Bose found wiggly groves on the surface of ancient sandstones on a road crossing in Churhat. The tracts were left by worm-like animals - about half-a-centimetre thick - while burrowing through the seafloor in ages gone by. If the findings are true, it provides the first evidence of macroscopic animals, says Charles Marshall, an expert on evolution from the University of California, Los Angeles, USA.
Bose has used the latest dating technique, called the vision track method and potassium argon dating, to establish the time period of the Churhat sandstone. According to the scientist, the trace fossils were preserved in the Churhat Sandstone, which contains sand beds that built up during storms about a billion years ago. The tops of many sand beds are covered with a microbial mat that and protected the sand below from disturbances. The mat is used as a source for food and oxygen, as the water within the sand layers is probably poor in oxygen.
An important and often controversial consideration for researchers analysing trace fossils is that physical processes can also create patterns in sedimentary rocks that appear to be similar to tracks left behind by animals. According to Adolf Seilacher, the German collaborator of Bose, the Churhat findings are best explained as the legacy of burrowing animals. The diameters, for instance, vary from tunnel to tunnel, but remain constant along each individual tunnel. The tunnels also do not resemble the structures commonly caused by physical processes. They are similar to younger trace fossils known to be produced by animals that developed from an embryo and that contain three outer membranes, as do worms, or what in the lexicon of scientists are called the 'triploblastic animals'.
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