Heat rises, cold falls, and like a pan of soup on a hot stove, the earth boils, exceedingly slowly. The boiling is called convection: columns of heat rise from the earth’s hot core, move up through the viscous solidity of the mantle, cool at the crust, roll over and fall back down. The crust that rolls along the top of the mantle is broken into continental plates which move with the boil, pushing up and apart where heat is rising, sinking under and down where the cold falls. And thus the continents are recycled. It’s all just physics. But certain parts of the continents called cratons – places in, for instance, Canada, South Africa, Australia — don’t recycle. They just sit there while their plates move around them, they’re a couple hundred kilometers deep, they’re like stable keels, and how they manage the stability has been a mystery. Continue reading
