Approximately 250 million years ago, something nearly wiped out life on Earth; 90% of marine animals and 80% of land animals were snuffed out in the geologic blink of an eye. Researchers now believe they've found the culprit: an 8 to 11 km (5 to 7 mile) asteroid that stuck the Earth off the coast of Australia. The impact happened so long ago, there isn't a crater, but geologists have found several clues that lead to this spot, including deposits of "shocked quartz" which can only be formed in a violent event like an asteroid strike.