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A new study published in this week's issue of Science concludes that tectonic movement on earth may have started 500 million years earlier than 1.9 billion years ago, a date suggested by current theory. Timothy Kusky and colleagues at St. Louis University, along with researchers from Washington University in St. Louis, found the oldest complete section of oceanic sea floor on the planet last summer. Oceanic earth crust is usually "recycled" back into the mantle through subduction, but a few fragments survive in mountain belts that form during the collision of two tectonic plates. That is exactly what happened with Kusky's sample, found in a mountain belt in the Eastern Hebei Province in China. The sample turned out to be about 2.5 billion years old, dating back to the Archean¿earth's earliest geologic time period.
"This discovery shows that the plate tectonic forces that create oceanic crust on the earth today were in operation more than 2.5 billion years ago," Kusky says. He thinks that these findings could help shed a light on when the first complex organisms evolved on earth: "Because hot volcanic vents on the sea floor have provided the nutrients and temperatures needed for life to flourish and develop, it's possible that life developed and diversified around these vents as plate tectonics began."
