The crust is not one-size-fits-all. You’ve got oceanic crust (dark, dense, and thin) and continental crust (pale, fluffy, and thick). Think of oceanic crust as the heavy, salty cracker; continental crust is the soft, chewy bread.
Guess which one is older? Continental crust. Some chunks of it are 4 billion years old. Oceanic crust is a teenager; it gets recycled every 200 million years. It sinks back into the mantle, melts, and gets reborn.
That means the rock under the Atlantic is younger than your great-grandma’s kitchen table. But the rock under Wyoming? Practically a dinosaur bone.
