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Melting the snowball earth theory

Geoscientists in Scotland have found evidence against the controversial theory that the Earth was completely frozen for periods of many millions of years.

Drs Dan Condon, Tony Prave and Doug Benn at the University of St Andrews are the latest in a line of geoscientists testing a recently proposed theory that the Earth was completely covered in ice for as long as ten million years.

The ‘Snowball Earth’ theory, a term coined by geologists in 1992, supported a hypothesis going back to 1948 which has been described as something of a classic scientific detective story. Signs of extensive glaciers at sea level around the tropics over 600 million years ago, which appear to defy the laws of nature, have perplexed geologists for decades.

The snowball hypothesis is something of a ‘hot’ topic in the field of Geosciences, particularly in the US, with firm camps set on either side of theory.

By examining sections of rocks in the West of Scotland, Ireland, Namibia and California, the St Andrews team have joined a small but growing number of scientists across the globe looking critically and openly debating the ‘Snowball Earth’ model.

Proponents of the Snowball Earth model claim that this supposed freeze would have caused severe environmental stress upon early life, resulting in repeated mass extinctions, and the aftermath (or ‘thawing’) period may have kick-started the evolution of complex (multi-cellular) life on Earth.

But Drs Condon, Prave and Benn, from the University’s School of Geography and Geosciences, have joined the scientific snowball fight and argue against the notion that the earth was completely frozen, with basic but fundamental observations which have significant ramifications for the Snowball Earth hypothesis.

In a paper published in the latest edition of the scientific journal, ‘Geology’, they detail how they have found evidence of sedimentary material, which could only have been derived from floating ice on open oceanic waters – indicating that the Earth’s oceans could not have been frozen during the supposed ‘big freeze’.

“We are claiming namely, that in reality there was not a totally frozen snowball Earth, and that even during the coldest conditions large regions remained ice-free. If the Earth’s oceans were not totally covered in thick sea-ice, there would have been areas of open seas which would have offered refuge for early marine life forms. This means that there would have been places in which marine micro-organisms lived and survived during the glaciation,” said Dr Condon.

“While others have approached the debate with a geochemical argument, by examining isotopes of carbon, we have approached it by looking at the glacial rocks themselves. Not only did we examine the section in Namibia upon which the Snowball Earth model is based, we also examined samples from the West of Scotland; County Donegal, Ireland; and Death Valley, California, which would have formed during the ancient glaciations. What is important, and different about our findings is that we have found physical evidence for the glacial rocks being deposited in an environment where there were areas of open seas, contradictory to the ‘hard’ Snowball model.”

The only geoscientists studying this area in Scotland, Drs Condon, Prave and Benn examined in some detail a suite of rocks South West of Oban, directly North of Jura, called the ‘Port Askaig Tillite’, which are supposed to record snowball Earth glaciations. However, they have found that the rocks similarly contain evidence that Earth’s oceans remained unfrozen during the putative Snowball events.

“What is interesting about the Port Askaig Tillite, is that it was the first rock unit ever described (in 1871) to be attributed to these ancient glaciations, thus the roots of the Snowball Earth model are firmly grounded on Scottish soil,” said Dr Prave.

PICTURE CAPTION: An area of Scottish rocks under study: View of A’ Chuli and Eileach an Naoimh looking southwest (photo taken from the highest point on Garbh Eileach).

ENDS

NOTE TO EDITORS: DRS CONDON PRAVE AND/OR BENN WILL BE AVAILABLE FOR INTERVIEW TODAY ON 01334 462381. PLEASE CALL DIRECT.

PICTURE EDITORS: EMAILABLE PICS OF THE AREAS OF ROCKS UNDER STUDY IN SCOTLAND ARE AVAILABLE – CONTACT GAYLE COOK FOR COPIES (CONTACT DETAILS BELOW)

Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook on 01334 467227, mobile 07900 050103, or email gec3@st-andrews.ac.uk Ref: snowball earth pr 060302 View the latest University news at http://www.st- andrews.ac.uk/extrel/press.htm

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