text:  They form current that come up, and they drive the surface material apart, and that's constantly replaced up in the center, and it goes back down at the edges. And that is analogous to what happens in the Kilauea fire pit. They've got a lot of photographs of the kind of mechanism that's been proposed for the plates. We know when new material comes up, it must go someplace, otherwise the Earth would be expanding constantly, and then they...