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BBC: Fossil gives clue to big chill (21 April 2006)
The gateway between the Atlantic and Pacific at the bottom of the globe opened up 41 million years ago, according to a study of old fish teeth. The research in Science pushes back the date of the forging of Drake Passage to twice as long ago as once thought. US geologists believe it kick-started the ocean current that swirls around Antarctica, helping to bring about a dramatic cooling effect. The continent was transformed from lush forest to the icy landscape of today.
The world was a very different place then. Levels of carbon dioxide were three to four times today's levels and it was so warm that alligators sunned themselves in the high Arctic. But some 30 million years ago, there was a dramatic shift in climate from "greenhouse" to "icehouse". The rapid cooling swept over the Antarctic and, over the course of several million years, its pine trees were replaced by glaciers.
South America and Antarctica were once joined by a land bridge. (Image: Science)
Scientists believe the formation of the ocean current that circulates around Antarctica played a key role in the cooling as it deflects warm streams of water coming from the equator.