Recently, researchers using data from Grace (Gravity Recovery and Climate Experiment satellite program) announced that they had found the possible remains of an enormous crater a mile below the East Antarctic ice sheet — the result of an impact that may have wiped out 90 percent of life on earth some 250 million years ago.

To look back to that catastrophe — called the Permian-Triassic extinction — you have to imagine all of earth's continents merged in a single great land mass surrounded by a single great ocean. It's possible that the collision that caused this newfound crater — four or five times as big as the crater from the impact that is believed to have extinguished the dinosaurs 65 million years ago — may have helped create a rift that began to drive the continents apart.