THE world鈥檚 continents have lumped together into a giant land mass not once but at least three times in Earth鈥檚 history.
John Rogers of the University of North Carolina has pieced together a picture of a 1.9 billion-year-old supercontinent from the scars of rifts in ancient rocks. The land mass, which he calls Columbia, existed just as single-celled life on Earth started to develop nuclei. He says the massive lump included bits of Africa, India, Australia, America, Greenland and Siberia (Gondwana Research, vol 5, p 5).
The most famous supercontinent, called Pangaea, formed just 250 million years ago. And geologists believe another one, called Rodinia, formed about a billion years ago.
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