Signs of iceage found amid early animal evolution: Scientists
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Last Updated: Friday, March 05, 2010, 19:32
  
London: Confirming the theory that ice may have covered the entire earth in ancient time, geologists have found evidence that sea ice extended to the equator 716.5 million years ago.

Based on an analysis of ancient tropical rocks that are now found in remote northwestern Canada, a study by scientists at Harvard University bolster the theory of 'snowball earth' which say that our planet has, at times in the past, been ice-covered at all latitudes.

The team was able to determine, based on the magnetism and composition of these rocks, that 716.5 million years ago the rocks were located at sea-level in the tropics, at about 10 degrees latitude.

"Climate modelling has long predicted that if sea ice were ever to develop within 30 degrees latitude of the equator, the whole ocean would rapidly freeze over," lead author Francis Macdonald said.

"So our result implies quite strongly that ice would have been found at all latitudes during the Sturtian glaciation," Macdonald said.

This is the first time that the Sturtian glaciation has been shown to have occurred at tropical latitudes, providing direct evidence that this particular glaciation was a 'snowball earth' event, journal Science reported.

"Our data also suggest that the Sturtian glaciation lasted a minimum of five million years," Macdonald added.

According to Enriqueta Barrera, program director in NSF's Division of Earth Sciences, which supported the research, the Sturtian glaciation, along with the Marinoan glaciation right after it, are the greatest ice ages known to have taken place on Earth.

"Ice may have covered the entire planet then," says Barrera, "turning it into a 'snowball earth.''

The survival of eukaryotes -- life forms other than microbes such as bacteria -- throughout this period suggests that sunlight and surface water remained available somewhere on earth's surface. The earliest animals arose at roughly the same time.

Even in a snowball earth, Macdonald says, there would be temperature gradients, and it is likely that sea ice would be dynamic: flowing, thinning and forming local patches of open water, providing refuge for life.

"The fossil record suggests that all of the major eukaryotic groups, with the possible exception of animals, existed before the Sturtian glaciation," Macdonald says.

Scientists don't know exactly what caused this glaciation or what ended it, but Macdonald says its age of 716.5 million years closely matches the age of a large igneous province -- made up of rocks formed by magma that has cooled -- stretching more than 1,500 kilometres (932 miles) from Alaska to Ellesmere Island in far northeastern Canada.

This coincidence could mean the glaciation was either precipitated or terminated by volcanic activity.

PTI


First Published: Friday, March 05, 2010, 19:32


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