mardi 26 juillet 2011

Through the mists of time: how we discovered the age of the Earth



"Where did we come from?" It's a central human question that drives us to wonder about origins—of humans, life, the Earth, the Universe. The age of the Earth is central to that question, and it has been taken on by human cultures for millennia. But only in the last couple centuries have we obtained the means to unequivocally determine that age from actual evidence. The road was a long one.

In the late 1700s, geology was in its infancy. Rock layers (of any type) were only starting to be recognized as something other than deposits from a catastrophic, world-wide flood. James Hutton, a Scottish scientist, became enthralled with the fantastic histories he saw recorded in the rocks of his homeland. At a now-famous seaside outcrop on the eastern coast of Scotland, he saw nearly horizontal layers of red sandstone on top of completely vertical layers of a much different, gray sedimentary rock. He was the first to grasp the significance of that spatial relationship.

de Ars Technica

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