Look at a map of the world. See how the east coast of South America fits into the west coast of Africa like puzzle pieces? That's not a coincidence. About 200 million years ago, all the continents were smooshed together in one giant supercontinent called Pangaea. Then they started drifting apart — and they're still moving today, right under your feet.

The secret is that Earth's surface isn't one solid shell. It's broken into huge pieces called tectonic plates, like a cracked eggshell that's still held together. These plates float on top of a layer of hot, gooey rock called the mantle. The mantle flows very, very slowly — about as fast as your fingernails grow.

What makes the mantle flow? Heat from deep inside the Earth. The planet's core is as hot as the surface of the sun, and that heat has to go somewhere. Hot rock rises up like bubbles in boiling water, cools near the surface, then sinks back down. This creates giant loops of flowing rock, churning endlessly beneath the crust.

Those flowing loops drag the tectonic plates along with them — like crackers floating on top of slowly stirred soup. Some plates drift apart. Some crash together. Some slide past each other. The continents are passengers riding on these plates, moving about two inches per year. That's slow, but over millions of years, it adds up.

So Pangaea started breaking up. First it split into two huge chunks: Laurasia in the north and Gondwana in the south. The Atlantic Ocean was born as a narrow crack between them. Magma bubbled up through the crack, cooling into new ocean floor and pushing the continents farther apart with every pulse.

Then Gondwana broke apart. South America peeled away from Africa. India drifted north and eventually smashed into Asia so hard it crumpled the crust upward, creating the Himalayas. Australia wandered off toward the Pacific. Antarctica slid south and froze over. Every continent found its own path.

The continents are still moving. North America and Europe drift apart by about an inch and a half each year — the Atlantic Ocean gets wider while you sleep. The Pacific Ocean is slowly shrinking. Millions of years from now, Africa will bump into Europe and close the Mediterranean Sea. California will slide north. The continents will be somewhere completely new.

So that's how the puzzle came apart. Heat from the core stirs the mantle, the mantle drags the plates, and the plates carry the continents on the slowest road trip in history. You're standing on a giant raft of rock, floating on an ocean of flowing stone, going somewhere new — two inches at a time.