Jeffrey Alt is a marine geologist studying the evolution of the ocean crust—the rock material that covers almost three-quarters of the Earth’s surface. Dr Alt uses stable isotopes of carbon, sulfur and oxygen to trace the effects of microbial activity in the volcanic basement of oceanic crust, and his work ranges to study of uptake of carbon and sulfur in oceanic basement and the return of this material back into the deep earth and recycling back to the crust and atmosphere at subduction zones.