For half a century, geologists have been baffled by perforations in a piece of quartzite, a type of rock, in Western Australia. The markings are identical in shape to burrows made in sands by crustaceans.

But what confounded scientists is that the original sandy sediment is a billion years older than the oldest known animals.

Now, an international team of scientists including Bruce Runnegar, a UCLA professor emeritus of Earth, planetary and space sciences, has resolved the mystery.

The researchers used radioactive minerals to measure the age of sand in the burrows and found that the sand was more than a billion years younger than the quartzite around it — meaning that the burrows could indeed have been created by animals.

Read the full news release.