Iron oxide minerals are found in rocks around the globe. Some are magnetic, and some of them rust—especially when exposed to water and oxygen. These characteristics provide clues about the history of these minerals.

Utah State University geoscientists describe a new forensic tool for determining the timing of geochemical oxidation reactions in iron-oxide minerals occurring in the Earth’s crust, which could shed light on how and when large, unexplained gaps in the rock record—known as “unconformities”—developed.

“A challenge for geoscientists is accurately constraining when rocks resided in the near-surface environment,” says Alexis Ault, associate professor in USU’s Department of Geosciences. “It’s tricky to pinpoint the timing of such processes, because the geologic evidence has often been erased.”