Hawaii’s Deepest Secret

Earth’s concentric layers scale remarkably well to those of a peach. The atmosphere is proportionally as thick as the exterior fuzz. The crust corresponds to the skin, the iron core (although spherical rather than pointed) to the pit, and the rocky mantle, which constitutes eighty-four per cent of the volume of the planet, to the flesh of the fruit. The lower mantle is about eighteen hundred miles from Earth’s surface—roughly the distance from Manhattan to Denver—but is less accessible and less known to us than the face of Mars. The deepest holes ever drilled, in a bizarre late-Cold War competition between NATO and the Soviet Union, barely pricked the skin; they went about eight miles down.