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Monday, 8 July, 2002, 09:19 GMT 10:19 UK
Ancient rock points to life's origin
Chromite: A mineral from beneath an ancient ocean
The new data come from a huge chunk of the rock that lay beneath the sea floor 2.5 billion years ago. Tim Kusky, of St Louis University, US, says it is the first large intact piece of oceanic mantle ever found from our planet's earliest period, the Archean. Located not far from the Great Wall of China, the ancient mantle rocks are preserved in a highly faulted belt 100 kilometres (62 miles) long. It may also contain clues as to when life developed on Earth. Origin of life Working with researchers from Peking University, Kusky found the rock section where last year the same team discovered the Earth's oldest complete section of oceanic crust.
The minerals, including an unusual type of chromite (iron chromium oxide) deposit previously only known from deep ocean floor rocks, appear to have been deformed at extremely high temperatures before they were completely crystallized by volcanic heat. This indicates that the rocks were moving away from mid ocean ridges, say scientists. This suggests that the continents were moving more than 500 million years earlier than was previously believed. Thermal vents The discovery that ancient tectonic plates were shifting could throw some light on the origin of life on Earth.
Because such volcanic vents are associated with tectonic movements Kusky says that it is possible that life developed and diversified around these vents as the plates started spreading. The research is published by the Geological Society of America.
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