Corsetti Melts ‘Snowball Earth’ Theory of Ice Age
By Usha Sutliff, USC News Service
When Frank Corsetti headed to the hottest spot in North America to investigate one of the coldest times in Earth’s history, he didn’t expect his findings to challenge a widely held scientific theory.
The “snowball Earth” theory—coined in 1992—postulates that roughly 700 million years ago, thick glaciers covered most of the planet, devastating life.
“We were in a microbial world during this period in Earth’s history that is thought to have lasted up to 10 million years,” says Corsetti, an assistant professor of earth sciences in USC College. “Life was abundant, but it was microscopic. We were dealing with ‘simple’ prokaryotic and eukaryotic cells.”
The hardy prokaryotes were the first organisms on the planet and survived the so-called snowball Earth; they remain one of the most pervasive of all living things. The more complex eukaryotes are thought to have been more susceptible to extinction in the extreme temperatures. But without microbial fossils from that time period to study, there was no way to prove or disprove these assumptions.
It wasn’t until a trip to Death Valley in 2000 with David Pierce and Stanley Awramik, both of UC Santa Barbara, that Corsetti realized that fossils in Death Valley, trapped in a glacial deposit, contained prokaryotes and eukaryotes deposited before and during the ice age, suggesting that both kinds of organisms survived the big freeze.
“There are two ways to think of it: Either life is more robust than we thought, or perhaps conditions were not as bad as we previously thought,” Corsetti says. Perhaps Earth was more like a slushball than a snowball, he adds, with oceans either ice-free or partially covered.
Either way, the discovery has Corsetti rethinking a theory he once accepted. “This finding makes it difficult to accept the ‘hard’ version of the snowball Earth theory. If there was a hard snowball, there should have been a major effect on life,” he says.
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