fifty five million years ago, one trillion tonnes of methane suddenly burst out of the ocean, shooting up the temperatures and killing thousands of species in the ocean depths. The first evidence of this prehistoric event was unearthed by researchers in 1991. But they were not sure of the causes that led to such an extraordinary outburst. Now scientists have started understanding the mystery behind the outburst. They say that the Earth can create dramatic climate changes, without human interference ( New Scientist , Vol 158, No 2132).

To unravel the mystery, researchers drilled a 2,100-metre hole into the Maud Rise, a submarine ridge beneath the Weddell Sea off Antarctica. G eologists James Kennett from the University of California at Santa Barbara, usa , and Lowell Stott of the University of Southern California, Los Angeles, usa, examined the sediment removed from the hole. They found evidence of a sudden mass extinction of organisms living on the sea-floor at the end of the Palaeocene era. Nearly half to two-thirds of all animals on the sea-floor had vanished within 1,000 years.

Earlier studies had shown similar extinctions in marine sediments in the Caribbean and European region during the same period. Kennett and his colleague say that it was a global event