Rocks are portals to the past. They tell us how and when they formed, and what the air and oceans were like at the time. They preserve evidence of ancient life. They can even tell us if they were exposed to radiation. The decay of uranium, for example, can bore thin “tunnels” in the rock. And one team of scientists wants to look for traces of something else: dark matter.

Dark matter appears to account for about 85 percent of all the matter in the universe. Yet so far, it’s never been detected. We know it’s there only because it exerts a gravitational pull on the visible matter around it. It appears to keep the galaxies in clusters from flying away from each other, for example.

The leading theory says that dark matter consists of some new type of subatomic particle, which should pass through Earth in torrents. But extensive efforts to catch them haven’t yielded even a single confirmed particle.

A team from Sweden and the U.S. has suggested looking for signs of dark matter in ancient rocks. The idea is that dark matter particles could have left “tracks” in the rocks — no more than a few millionths of an inch long.

One group tried to find such tracks a quarter century ago, but saw no trace of them. The new group wants to use the more-sensitive microscope technology that’s available today. The scientists would examine bits of rock drilled from deep below the surface — rocks that might contain evidence of dark matter.

Script by Damond Benningfield