In this illustration of a thermal model, a cold oceanic plate (blue) sinks into the hot mantle (red). Shallow earthquakes are more common, and do not lead to diamond formation, whereas earthquakes at depth could lead to formation of diamonds. Temperatures in the descending slab are compatible with retaining fluids until the depth of diamond formation. Credit: Illustration by Steven Shirey, Peter van Keken, Lara Wagner and Michael Walter/Carnegie Institution for Science