Alfred Wegener was a German scientist who, in 1912, proposed that Earth's continents were once joined together in a single giant landmass he called Pangea. He noticed that the coastlines of South America and Africa fit together like puzzle pieces, and that identical fossils and rock formations appeared on opposite sides of the Atlantic Ocean. He called his idea continental drift — the theory that continents slowly move across Earth's surface over millions of years.
Almost nobody believed him. Other scientists argued that solid continents couldn't possibly plow through solid ocean rock, and Wegener was mocked and dismissed for decades. He died in Greenland in 1930 without ever seeing his theory accepted. It wasn't until the 1960s that scientists discovered seafloor spreading — new ocean crust forming at mid-ocean ridges — which finally proved that plates really do move, and that Wegener had been right all along.
Volcanoes were one of the key clues that helped piece Pangea back together. Volcanoes cluster along the edges of tectonic plates, where plates collide, pull apart, or grind past each other. When you map volcano locations back onto a reconstruction of Pangea, they trace the same collision zones that eventually tore the supercontinent apart — the same boundaries Wegener had identified from coastline shapes and fossils alone, without any modern technology.