Deep in the taiga of eastern Siberia stands a 40-meter-high mound of shattered limestone, 160 meters across at its base, with a ring-shaped crown and a smaller peak rising from inside the ring. It weighs roughly a million tons. Locals knew about it long before a Russian geologist named Vadim Kolpakov described it in 1949. Tree-ring evidence dates it to about 300 years old, young enough that somebody's great-great-great-grandparents could have watched it appear. For decades, the favorite explanation for the Patomskiy crater was a meteorite strike. Some said a super-dense meteorite punched into the ground and vanished. Others thought it was debris from the 1908 Tunguska event, or a natural gas pocket blowing out from below. V.S. Antipin and A.M. Fedorov, writing in Doklady Earth Sciences in 2008, found no meteorite signature in the rock chemistry. The mound's proportions match a volcanic cone's. At a 2010 conference at Saint Petersburg Mining Institute, researchers reviewed the geophysics and ruled out impact.…