A HUNT for signs of the earliest life on Earth has instead turned up the earliest evidence yet for plate tectonics. This pre-dates previous evidence by more than a billion years and will go some way to settling a debate about whether plate tectonics began early in Earth鈥檚 history, or much later.
Until now, the earliest evidence for the theory 鈥� which describes the motion of the plates that make up the Earth鈥檚 crust 鈥� came from the discovery of 2.5-billion-year-old 鈥渙phiolites鈥�. These are a distinctive sequence of rocks from the ocean floor that end up on land and are regarded as a sign of plate tectonics.
Harald Furnes of the University of Bergen in Norway and his colleagues were looking for signs of life in the Isua supracrustal belt, a 3.8-billion-year-old rock formation in south-western Greenland. Instead they found 鈥渟heeted dikes鈥�, the banded rocks that make up ophiolites, and rocks nearby resembling those beneath islands that sit above today鈥檚 subduction zones 鈥� where one plate slides beneath another (Science, vol 315, p 1704). This suggests plate tectonics got going at least 3.8 billion years ago.
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