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Ice-free 'oases' found on Snowball Earth

Posted on 15/12/2010

A “dropstone”, deposited by an iceberg during the Snowball Earth. Evidence for violent storms – and hence ice-free “oases” – has been discovered between dropstone-rich layers in Australia

Between 600 and 700 million years ago, our planet froze solid in an event dubbed Snowball Earth. How life survived this deep freeze has puzzled scientists for over a decade.

Now geologist, Dr Dan Le Heron of Royal Holloway, University of London may have found the answer. His team has uncovered evidence for large 'ice-free oases' that could have harbored life and helped animals beat the chill. The findings are published today (14 December) in the leading journal Geology.

Exploring the remote Flinders Ranges in South Australia, the team found features formed by violent storms, sandwiched between ancient sediments that were laid down by the global ice sheets.

The features – known to geologists as hummocky cross bedding – are only formed by storm waves in the sea. Patches of sea remained ice free, allowing violent waves to sweep up sand from the sea floor, and leave their mark. In order to form, the surface of the sea had to be free of ice.

Dr Le Heron said: "This is an incredibly exciting discovery. What we've found is the clearest evidence yet that large areas of the Earth's oceans remained ice-free during Snowball Earth. Such 'oases' would have been key for the survival of life... and indeed our own existence today.



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