Beryllium-10 is a radioactive isotope that is continuously produced by cosmic rays interacting with Earth's atmosphere. When it rains from the atmosphere and settles in the ocean, the isotope becomes incorporated into the extremely slow growth of some deep metal-rich crusts.

There seems to be too much of a radioactive element in rocks deep in the Pacific Ocean – how did it get there 10 million years ago?

Earth must have experienced something exceptional 10 million years ago. Our study of rock samples from the floor of the Pacific Ocean has found a strange increase in the radioactive isotope beryllium