Rock that sank over 90 kilometres into Earth reveals a sharp shift in thermal gradient

A rock found on Goodenough Island indicates an unexpected thermal gradient change during its descent deep within Earth's crust. Researchers estimated that this rock traveled over 90 kilometres into a subduction zone about 4.4 million years ago. Initial warm conditions shifted to a cold thermal regime as it descended further into the Earth. Both shearing stress and the youth of the subduction zone may explain this temperature change.