Watching plates move

Plates move about as fast as your fingernails grow — roughly 2–10 cm a year. That sounds trivial, but over millions of years it opens oceans and builds mountains.

Today we no longer have to infer it: GPS stations bolted to the ground measure plate motion directly, confirming the speeds and directions predicted by seafloor magnetic stripes. Wegener was right all along — he just lacked the tools to prove it.