Columbia began to break up about 1.5 billion years ago, and its fragments moved around the Earth independently for several hundred million years, he said. About a billion years ago, the fragments came together again to form a new supercontinent, called Rodinia. Rodinia lasted until about 700 million years ago before it too broke into several fragments.

These chunks moved independently until 250 million years ago, when the supercontinent Pangea formed, Rogers said. Pangea then began to break up almost immediately to form the world's present continents.

This sequence of formation and dispersal of supercontinents is clearly caused by movements deep within the Earth in a layer scientists call the mantle, he said. The exact mechanism is still being worked out, and hopefully the discovery of Columbia will contribute to understanding it.

Magnetic and geologic evidence for supercontinents becomes less certain and more controversial as the age of the supercontinent increases, Rogers said. For that reason, the shape of Columbia and even its existence is less certain than that of Rodinia.

Originally trained as petrologist and geochemist, the UNC scientist came up with his ideas while traveling in the Orkney Islands off Scotlands north coast. He based them on data he collected in India, East Africa and Saudi Arabia as U.S. leader of a joint Indian and U.S. cooperative study of the Precambrian evolution of southern India and on data published by other scientists.

Geologists date ancient rocks by measuring radioactive decay of uranium and lead isotopes. Comparisons of such information and rock types around the world reveal what regions used to be connected.

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Contact: David Williamson
david_williamson@unc.edu
919-962-8596
University of North Carolina at Chapel Hill
18-Mar-2002