The serpent’s tails coil together menacingly. A horn juts sharply from its head. The creature looks as if it might be swimming through a sea of stars. Or is it making its way up a sheer basalt cliff? For Bruce Masse, an environmental archaeologist at Los Alamos National Laboratory, there is no confusion as he looks at this ancient petroglyph, scratched into a rock by a Native American shaman. “You can’t tell me that isn’t a comet,” he says.

In Masse’s interpretation, the petroglyph commemorates a comet that streaked across the sky just a few years before Europeans came to this area of New Mexico. But that event is a minor blip compared to what he is really after. Masse believes that he has uncovered evidence that a gigantic comet crashed into the Indian Ocean several thousand years ago and nearly wiped out all life on the planet. What’s more, he thinks that clues about the catastrophe are hiding in plain sight, embedded in the creation stories of cultural groups around the world.