A team of researchers affiliated with several institutions in Japan has found evidence that offers credence to a theory that subducted crust exists at the base of Earth’s upper mantle. In their paper published in the journal Nature, the group describes experiments they conducted in their lab involving pressurizing material believed to exist in the mantle, and what they found. Johannes Buchen, with the California Institute of Technology, has written a News & Views piece on the work in the same journal issue.