1. Earth's Structure & Layers

If you could slice Earth open, you would see it is built in layers, like an onion — each made of different material and getting hotter toward the center.

From the outside in:

• Crust — the thin, solid outer shell of rock we live on (continents and ocean floor).
• Mantle — the thick layer of hot rock below the crust. It is mostly solid but flows very slowly over time, and its motion drives the plates above it.
• Outer core — a layer of liquid iron and nickel. Its swirling motion creates Earth's magnetic field.
• Inner core — a ball of solid iron and nickel at the center. It is the hottest part, but stays solid because of the enormous pressure.

The crust and the very top of the mantle together form a rigid shell that is broken into moving pieces called tectonic plates (Lesson 2).

⚠️ Common misconception: the inner core is hotter than the outer core, yet it is solid — extreme pressure keeps it from melting.

💡 Tip: remember the order Crust → Mantle → Outer core → Inner core. The outer core is liquid, the inner core is solid, and it gets hotter all the way down.