Dec. 4 (UPI) -- New scientific findings suggest glacial meltwater helped eukaryotes survive Earth's most extreme ice age, so-called Snowball Earth.
Scientists hypothesize that between 650 and 700 million years ago, an extreme icehouse climate froze Earth's oceans solid, cutting off the oxygen supply for marine life.
To better understand how early life forms survived these frigid, oxygen-deprived conditions, researchers analyzed iron formations in ancient rocks deposited by glaciers in Australia, Namibia and California. By studying iron levels in the 700-million-year-old rocks, scientists were able to estimate the abundance and distribution of oxygen in the oceans during Snowball Earth.
Scientists published the results of their analysis this week in the journal PNAS.
"The evidence suggests that although much of the oceans during the deep freeze would have been uninhabitable due to a lack of oxygen, in areas where the grounded ice sheet begins to float there was a critical supply of oxygenated meltwater," lead study author Maxwell Lechte, an earth scientist and postdoctoral researcher at McGill University in Canada, said in a news release. "This trend can be explained by what we call a 'glacial oxygen pump'; air bubbles trapped in the glacial ice are released into the water as it melts, enriching it with oxygen."
Previously, scientists estimated life would have had to wait out Snowball Earth in meltwater puddles on top of Earth's frozen shell, but the latest findings suggest oxygenated marine environments were able to persist beneath the ice.
"The fact that the global freeze occurred before the evolution of complex animals suggests a link between Snowball Earth and animal evolution," Lechte said. "These harsh conditions could have stimulated their diversification into more complex forms."
The work of Lechte and his colleagues focused exclusively on oxygen, but of course, oxygen isn't the only ingredient needed to sustain life. Early eukaryotes would have needed food, too.
The study's authors hope followup research will help scientists better understand how food webs were maintained in marine habitats oxygenated by glacial meltwater. Food webs in niche Arctic and Antarctic ecoystems, like communities of organisms living in pockets of sub-glacial meltwater, could offer clues.
"This study actually solves two mysteries about the Snowball Earth at once," said Galen Halverson, McGill professor and study co-author. "It not only provides explanation for how early animals may have survived global glaciation, but also eloquently explains the return of iron deposits in the geological record after an absence of over a billion years."