Rock that sank 90 km into Earth reveals sudden shift from warm to cold

A rock from Goodenough Island in Papua New Guinea travelled more than 90 kilometres into a subduction zone about 4.4 million years ago, University of Göttingen researchers report in Nature Geoscience. Tiny grains of coesite trapped in garnet reveal the extreme pressure it faced, while its minerals show the descent began under warm conditions before shifting to a colder thermal regime.