Let’s start with the oceanic crust. This is the crust that sits under all the world’s oceans. It’s the shy one that you almost never see, but it makes up about 60% of the Earth’s surface.
Imagine a gigantic, dark, dense cookie. That’s oceanic crust. It’s made mostly of a rock called basalt, which is super heavy and rich in iron and magnesium. Think of it as the gym rat of the crust world—dense, muscular, and always sinking.
It’s also thin, only about 5 to 10 kilometers thick. That’s like the thickness of a single slice of bread compared to the whole loaf. Because it’s so dense, it sits lower, letting water fill the giant bathtubs we call oceans.
And here’s a funny thing: oceanic crust is constantly being recycled. Old crust gets pushed back into the Earth’s mantle, like a really bad leftover. So it never gets much older than about 200 million years. That’s young in Earth years—basically a teenager!
