Layers of the Earth

Crust

Mantle

Outer core

Inner core

This process is called the geodynamo.

Short for the Mohorovičić discontinuity, where seismic waves suddenly speed up.

The enormous pressure at the center keeps the iron and nickel solid.

Oceanic crust (thin, dense basalt) and continental crust (thick, lighter granite).

Mantle

The rigid outer shell made of the crust and uppermost mantle, broken into tectonic plates.

Crust: silicate rocks (granite, basalt). Mantle: dense silicate rock rich in iron and magnesium (peridotite). Core: iron and nickel.

Chemical: crust, mantle, core. Mechanical: lithosphere, asthenosphere, mesosphere (lower mantle), outer core, inner core.

Hot, weak, partly plastic zone of the upper mantle beneath the lithosphere; tectonic plates move over it.

Oceanic: about 5–10 km. Continental: about 30–50 km, up to about 70 km under large mountain ranges.

Oceanic crust (basalt) is denser than continental crust (granite).

About 6,371 km.

About 2,900 km.

The core–mantle boundary, about 2,900 km deep.

Roughly 5,000–6,000 °C, similar to the surface of the Sun.

Pressure comes from the weight of overlying rock. Heat is left over from Earth's formation and is added by radioactive decay.

It increases with depth, from about 2.7–3.0 g/cm³ in the crust to about 13 g/cm³ in the inner core.

This was an early clue that Earth's interior holds a dense metallic core.

P (primary) waves: compressional, fastest, travel through solids and liquids. S (secondary) waves: shear waves, slower, travel only through solids.

S waves

S waves cannot pass through it, leaving a large S-wave shadow zone on the side of Earth opposite an earthquake.

A band about 104°–140° from an earthquake where no direct P waves arrive, because they bend (refract) as they enter the core.

Danish seismologist Inge Lehmann in 1936, from faint P waves recorded inside the shadow zone, which she explained as waves deflected by a distinct inner core.

Heat from the core and from radioactive decay: hot rock slowly rises, cools and sinks over millions of years.

Divergent: plates move apart (mid-ocean ridges). Convergent: plates collide (subduction zones, mountain ranges). Transform: plates slide past each other (San Andreas Fault).

One plate (usually denser oceanic lithosphere) sinks beneath another into the mantle, forming deep trenches and volcanic arcs.

A plume of hot mantle material that melts through a plate away from plate boundaries, building a chain of volcanoes as the plate moves (Hawaii).