🧩 Plate tectonics

Earth's outer shell is not one solid piece, it is broken into roughly a dozen major slabs of rock called tectonic plates, along with several smaller ones, all fitting together like pieces of a cracked eggshell around the planet. These plates float on a slowly shifting layer of hot, softened rock underneath, drifting a few centimetres a year in different directions. Because the plates are constantly moving, however slowly, the map of Earth's continents has actually looked completely different in the past and will keep changing in the future.

Scientists noticed that the coastlines of certain continents, like South America and Africa, look almost like matching puzzle pieces if you push them together on a map. That clue alone was not enough proof, but scientists later found matching rock layers, matching mountain ranges, and even fossils of the same ancient animals on continents now separated by entire oceans. Taken together, all this evidence convinced scientists that today's separate continents were once joined into one enormous supercontinent, before slowly drifting apart over hundreds of millions of years.

When two plates push directly into each other, the land between them can crumple upward into towering mountain ranges, since neither plate has anywhere else to go. When one plate instead slides underneath another, it can melt as it sinks deeper, sometimes fueling volcanoes on the plate above, while the spot where they meet often triggers frequent earthquakes. In other places, two plates simply slide sideways past each other, grinding and occasionally getting stuck, then suddenly slipping and shaking the ground.

Tectonic plates drift at roughly the same speed your fingernails grow, just a few centimetres each year, which is far too slow for anyone to ever notice or feel directly. Scientists measure this tiny movement using extremely precise satellite equipment that can detect ground shifting by even a fraction of a centimetre. Even at that snail-like pace, drifting plates can add up to enormous distances over millions of years, enough to carry a continent all the way across an ocean.