The ancient supercontinent Pangea took hundreds of millions of years to break up into what we know as the seven continents. For 40 million years the land masses of what are now North America and Africa moved at a rate of one millimeter per year.

But 200 million years ago, and for 10 million years, the tectonic plates accelerated, breaking apart at a rate of 20 millimeters a year, or around the same rate at which fingernails grow, before slowing down once more. Turns out, the plates have two distinct speeds, a fast one and a slow one, that they switch between.