Look at a map and South America seems to slot into Africa like two torn halves of a page. In 1912 Alfred Wegener argued this was no coincidence — the continents had once been joined and had since drifted apart. He had no force that could move them, so geologists dismissed the idea for half a century. The proof came from the bottom of the ocean: new seafloor erupts along undersea ridges and spreads outward, and as it cools it records the direction of Earth’s magnetic field. Because that field flips over geological time, the floor carries a striped barcode of reversals — and the stripes are mirror-symmetric about every ridge. The continents really do move, carried on vast plates.
It is the organising idea of all of geology. Earthquakes, volcanoes, mountain ranges and the slow rearrangement of the continents are all the visible edges of a few dozen rigid plates riding a churning interior.
This is the identical fact set, re-told at a different altitude. Switch any time — the reader keeps your place in the idea, not the prose.