JUST as the Earth was emerging from a 10-million-year freeze it was buffeted by violent global storms. Evidence of raging storms and huge waves has been discovered in sedimentary rocks formed 635 million years ago when the global ice age dubbed 鈥淪nowball Earth鈥� was ending.
During the snowball, ice up to a kilometre thick covered most of the planet, some geologists think. A few have suggested the ice prompted the evolutionary leap from single to multicellular organisms that seems to have occurred at around the same time (New 杏吧原创, 12 April 2003, p 30).
Philip Allen from the Swiss Federal Institute of Technology, Zurich, and Paul Hoffman from Harvard University have evidence that when the ice melted, the planet was flung into a period of brutal weather. They have found ripples in sedimentary rocks laid down 635 million years ago in Australia, Brazil, Canada, Namibia and Svalbard in the Arctic Ocean left by giant ocean waves. The monster swells whipped up by persistent winds must have been 7 to 12 metres high.
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Allen and Hoffman suggest the hurricanes were caused by the large differences in temperature between the shrinking ice and the growing oceans around the equator (Nature, vol 433, p 123). But Hoffman says any link between Snowball Earth and evolution is far from proven.
