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Friday, June 09, 2006

Study Shows Our Ancestors Survived Snowball Earth

Seattle WA (SPX) Jun 07, 2006
It has been 2.3 billion years since Earth's atmosphere became infused with enough oxygen to support life as we know it. About the same time, the planet became encased in ice that some scientists speculate was more than a half-mile deep.
 
That raises questions about whether complex life could have existed before "Snowball Earth" and survived, or if it first evolved when the snowball began to melt.
 
New research shows organisms called eukaryotes -- organisms of one or more complex cells that engage in sexual reproduction and are ancestors of the animal and plant species present today -- existed 50 million to 100 million years before that ice age and somehow did survive. The work also shows that the cyanobacteria, or blue-green bacteria, that put the oxygen in the atmosphere in the first place, apparently were pumping out oxygen for millions of years before that, and also survived Earth's glaciation.
 
The findings call into question the direst models of just how deep the deep freeze was, said University of Washington astrobiologist Roger Buick, a professor of Earth and space sciences. While the ice likely was widespread, it probably was not consistently as thick as a half-mile, he said.
 
"That kind of ice coverage chokes off photosynthesis, so there's no food for anything, particularly eukaryotes. They just couldn't survive," he said. "But this research shows they did survive."
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