Earth's Layers and Structure

The Four Layers of Earth#

Earth is not a solid, uniform ball — it is made of distinct layers with different compositions, temperatures, and states of matter. Scientists have discovered these layers through the study of seismic waves — vibrations caused by earthquakes that travel through Earth's interior.

The Four Main Layers#

1. Crust (outermost layer)

• Thickness: 5–70 km thick (thinnest under oceans, thickest under mountains)
• State: Solid rock
• Temperature: Near surface temperature (~15°C) up to ~200°C at the bottom
• Composition: Oceanic crust (basalt rock); continental crust (granite rock)
• This is where we live — all continents and ocean floors are part of the crust

2. Mantle

• Thickness: About 2,900 km — the thickest layer
• State: Mostly solid, but behaves plastically (like very thick, slow-moving putty)
• Temperature: 200°C–4,000°C
• Composition: Dense, iron-rich silicate rock (peridotite)
• Key fact: The upper mantle flows very slowly in convection currents, driving plate tectonics

3. Outer Core

• Thickness: About 2,300 km
• State: Liquid iron and nickel
• Temperature: 4,000°C–5,100°C
• Key fact: The movement of liquid iron generates Earth's magnetic field, which protects us from harmful solar radiation

4. Inner Core (innermost layer)

• Thickness/Radius: About 1,220 km radius
• State: Solid iron and nickel (even though it is the hottest layer!)
• Temperature: ~5,100°C–6,000°C (similar to the surface of the sun)
• Key fact: The inner core is solid despite extreme heat because of the enormous pressure from all the layers above it