2006
2006 June 6. STUDY
SHOWS OUR ANCESTORS SURVIVED 'SNOWBALL EARTH' -
Earth Observatory. Excerpt:
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." |
