The continents, it seems, are like ships in a rocky sea, drifting on currents that extend hundreds of miles below Earth’s surface.
We are all adrift, the ground beneath us in constant, if imperceptible, motion. Huge slabs of Earth’s crust slide over the partially molten mantle, pulled at one end by the slab dipping into the mantle at subduction zones, pushed at the other by new crust welling up at midocean ridges. That, anyway, is classical plate tectonic theory, and it works fine for oceanic crust. But it has never quite explained the motion of continents, which are thicker than oceanic plates, extending deeper into Earth’s mantle. The pull of sinking plates and push of rising new crust don’t appear powerful enough to drive continental drift. Slab pull, which is thought to be the biggest force, and ridge push seem very small to be pushing something the size of a ...
