Earth's Layers & Interior
Crust, mantle, core & seismic evidence
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Earth's Layers & Interior
The ground under your feet goes down 6,371 km (3,959 miles) to the center of the Earth, but we have never actually seen below about 12 km (7.5 miles). Almost everything scientists know about Earth's interior comes from studying seismic waves: vibrations that travel through the planet when earthquakes occur.
The Four Layers
Earth is made up of four distinct layers, each with different materials and properties:
Crust (0–70 km / 0–43 miles deep)
The outermost layer, made of silicate rock (granite and basalt). The crust is extremely thin compared to the rest of Earth, like the skin of an apple. Oceanic crust (under the oceans) is denser and thinner than continental crust (under the land).
Mantle (70–2,900 km / 43–1,800 miles deep)
The largest layer, making up about 84% of Earth's volume. Made of iron and magnesium silicates. The mantle is solid rock, but over millions of years it flows very slowly, like an extremely thick liquid.
Outer Core (2,900–5,150 km / 1,800–3,200 miles deep)
Made of liquid iron and nickel. Convection currents in the liquid outer core generate Earth's magnetic field, which protects us from harmful solar radiation.
Inner Core (5,150–6,371 km / 3,200–3,959 miles deep)
The center of Earth, made of solid iron and nickel. Even though the inner core is hotter than the outer core, the extreme pressure keeps it solid.
Lithosphere and Asthenosphere
Scientists also use two other terms that cut across layer boundaries:
How We Know: Seismic Waves
When an earthquake occurs, it sends vibrations through the planet in two main types:
Here is the key discovery: S-waves stop at the outer core. Because S-waves can only travel through solids, their stopping proved that the outer core must be liquid.