Earth’s Crust

Earth's continental crust may have emerged 500 million years earlier than scientists had previously estimated. Pinning down when our planet's land emerged could help us understand the conditions in [blank] primitive life began. Today, the new oceanic crust rises at mid-ocean ridges where tectonic plates drift apart. Continental crust is usually [blank] older, formed from volcanism where plates crash into each other, thrusting a thicker, less-dense layer above sea level. The weathering of the continental crust adds [blank] to the ocean, a process that may have played a role in supporting primordial life. The big question is: when did continental crusts start forming? To try to answer that, Desiree Roerdink at the University of Bergen in Norway and her colleagues analyzed 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 [blank] warm, mineral-rich waters react with seawater.