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Chapter 1 of 10
Inside the Earth
Four layers, mostly inferred.
The layers
A thin rocky crust sits on the mantle, which behaves as a very slow-moving solid. Below that is a liquid outer core and a solid inner core, both mostly iron.
- The crust is 5 to 70 km thick, a skin compared with the 6,400 km radius.
- Movement in the liquid outer core generates the magnetic field.
How we know
Seismic waves from earthquakes bend and reflect at boundaries between materials. Reading those arrivals worldwide is how the interior was mapped without ever reaching it.