December 15, 2010

New Evidence Supports ‘Snowball Earth’ Hypothesis

Researchers in Britain and Australia have discovered evidence that parts of the open ocean may have experienced a catastrophic global freeze some 700 million years ago, which nearly wiped out life on Earth.

The event, dubbed "Snowball Earth", created such turbulent seas that microorganisms barely survived, and created conditions so harsh that most life is believed to have perished, the scientists said.

The researchers claim to have found deposits in the remote Flinders Ranges in South Australia that show unambiguous signs of turbulent oceans.  The sediments date to the Sturtian glaciation some 700 million years ago, during one of two major ice ages of the Cryogenian period associated with the "Snowball Earth" theory. 

These sediments, the scientists said, prove that parts of the open ocean waters must have existed during that period, and may have supported microscopic life.

The snowball earth hypothesis claims that the Earth's land and oceans were thrown into a deep freeze unlike any other in history.

"For the first time, we have very clear evidence that storms were affecting the sea floor," said lead researcher Dr. Dan Le Heron of Royal Holloway, University of London.

"That means we have to have pockets or oases within this 'Snowball Earth' that are free of ice," he told BBC News.

"We see a very particular type of feature in sedimentary rocks called 'hummocky cross-bedding'."

"These features can only form where storm waves sweep up sand from the ocean floor, slosh it back and forth and create a bed of sandstone," he explained.

Such ocean pockets could explain how some microorganisms survived the spectacular ice age and went on to thrive and diversify during the later Cambrian period.

"This could be one of the ideal places for early organisms to start thriving and for evolution to really start kicking in," Dr. Le Heron said.

However, the "Snowball Earth" hypothesis remains only a theory.  And while many scientists agree about the evidence for a deep freeze, debate continues over the causes and the degree to which the entire planet froze during the Sturtian and Marinoan glaciations.  Indeed, some scientists question how any life at all could have survived such an event.

"The paper supports the idea that the Earth was not completely frozen throughout one of the extreme glaciations in the late Precambrian," said Professor Doug Benn of the University Centre in Svalbard.

"The Snowball model was ground-breaking in its time, but now it has to be replaced by a more dynamic - and even more interesting - picture of how the Earth functioned in the distant past," said Benn, who acknowledges he is more of a believer in a "Slushball Earth" or "Softball Earth" theory.

The findings were published in the journal Geology.


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