In a new study led by University of Chicago geophysicist Sunyoung Park, evidence was found of a layer of surprisingly fluid-rock located in the Earth’s mantle. The finding was made by measuring lingering movement registered by GPS sensors in the wake of a deep earthquake in the Pacific Ocean near Fiji.

The study demonstrates a new method of measuring the fluidity of the Earth’s mantle, which could have implications for how the planet transports heat, and cycles and mixes materials between the crust, core, and mantle over time.