Earth's continents may have formed far earlier than thought

摘要

THE planet's continental crust may have emerged 500 million years earlier than previously estimated. Pinning down when land emerged could help us understand the conditions in which life began. Today, new oceanic crust rises at mid-ocean ridges where tectonic plates drift apart. Continental crust is usually much older, formed from volcanism where plates crash into each other, thrusting a thicker, less-dense layer above sea level. Weathering of continental crust adds nutrients to the oceans, which may have helped support primordial life. The big question is: when did continental crusts start forming? To answer that, Desiree Roerdink at the University of Bergen in Norway and her colleagues analysed 30 ancient rock samples from six sites in Australia, South Africa and India. These contained barite, which can form in hydrothermal vents - fissures in the ocean floor where warm, mineral-rich waters react with seawater.