Inside the Earth

The Earth is not a solid ball of rock. It is layered like an onion, and each layer behaves differently. From the outside in: a thin crust, a thick rocky mantle, a molten outer core, and a solid inner core.

The crust is the cool, brittle skin we live on — only 5–70 km thick, thinner than an apple’s skin compared to the whole fruit. Below it the mantle makes up most of the planet by volume: hot, solid rock that can slowly flow like extremely stiff putty over millions of years.