Popigai: The Crater of Diamonds

The Earth is bombarded by thousands of micrometeorites every day, but only once in tens of millions of years does an asteroid large enough arrive to leave a lasting mark on the geography of a region and the geology of its underlying rocks. The Popigai Crater in northern Siberia, located about 550 kilometers north of the Arctic Circle, is the result of one such impact event. The Popigai Crater was formed about 35 million years ago when an asteroid, estimated to be 5 to 8 kilometers in diameter, slammed into what is now the Taymyr Peninsula of northern Siberia, Russia. The impact instantly melted some 1,750 cubic kilometers of rock, about half of which was ejected into the atmosphere. Some of this material travelled high into the air and landed thousands of kilometers away on other continents, leaving behind a crater roughly 100 kilometers wide and 8 to 10 kilometers deep. A digital elevation model shows the topography of the crater and the surrounding area. Credit: NASA The region where the asteroid struck is rich in a type of metamorphic rock composed of garnet, graphite, and the minerals that form gneiss (typically feldspar, quartz, and mica). The graphite-garnet gneiss basement rock was overlain by about 1.5 kilometers of sedimentary cover. The asteroid blasted through this sedimentary layer and into the underlying gneiss, where the immense heat and pressure caused the flakes of graphite in the Archean graphite-garnet gneiss to be instantaneously transformed into diamond. The heat and pressure generated by the impact rippled through the surrounding rocks, melting everything in their path. At a distance of about 12 kilometers from the point of impact, the conditions were likely still too extreme for diamonds to form or survive. Just beyond this zone, around 13 kilometers out, the temperature and pressure dropped enough to allow the formation of stable diamonds.