Thin layers thicker: the crust (about 7 times), the lithosphere and the asthenosphere are drawn thicker so you can see them; the deep layers are squeezed a little to make room. True scale: the crust is thinner than the skin of an apple.
Drag the slider, or press play, to travel 6,371 km down. Watch the temperature, the pressure and the density rise. (Numbers are approximate: scientists’ estimates for the deep Earth differ by a few hundred degrees.)
No hole has ever been drilled deeper than 12.3 km. Scientists learned about the layers from earthquake waves. P waves (push–pull) travel through solids and liquids; S waves (side to side) travel only through solids. The waves bend as the rock changes with depth, and the core bends them sharply or stops them, leaving shadow zones where seismometers record no direct waves.
Blue band: P-wave shadow zone (about 103°–142° from the earthquake). Red band: S-wave shadow zone (beyond about 103°). Ray paths are calculated from a simplified model of how wave speed changes with depth; real shadow-zone edges are a little blurred, and very faint waves do reach them.
Pictures always draw the crust far too thick. Choose a model size to see the real thicknesses.
| Layer | Thickness in the model |
|---|
A peach is a handy model: the skin is the crust, the juicy flesh is the mantle, and the stone is the core.
The cross-section you label in a test: crust, mantle, outer core and inner core, plus the lithosphere and asthenosphere. Switch between the labeled diagram, a blank one to test your memory, and a quiz where you place each label yourself. You can also download both versions or print a label worksheet.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back. On a phone, swipe the diagram sideways to see every number.
Ten questions about the layers, what they are made of and how we know.
Tap the layers from the outside to the centre. Tap a filled box to take a layer back.
Tap a fact, then tap the layer it describes. Check when all twelve are placed.
The crust is the thin rocky skin we live on. Below it the mantle is about 2,900 km of hot rock. Then comes the outer core, a layer of liquid iron and nickel, and finally the inner core, a solid ball of iron and nickel at the centre, 6,371 km down.
The four layers are named by what they are made of. Geologists also name the outer layers by how stiff they are. The lithosphere (the crust plus the top of the mantle, about 100 km thick) is cold and rigid and is broken into the tectonic plates. Below it, the asthenosphere is hot and soft enough to flow very slowly, so the plates can slide over it.
Earthquake waves travel faster in denser, stiffer rock and bend at every boundary. In 1909 Andrija Mohorovičić found a sudden speed-up about 30–50 km down: the base of the crust (the Moho). S waves never arrive more than about 103° from an earthquake, so something in the way must be liquid: the outer core. Beno Gutenberg measured the depth of the core (about 2,900 km) in 1913–14, and Harold Jeffreys showed in 1926 that it is liquid. In 1936 Inge Lehmann explained faint P waves inside the shadow zone with an inner core, which later work showed is solid.
Switch the 3D model between made of and how they behave, then press True scale to see how thin the crust really is. Travel to the centre and watch the density jump at 2,891 km. Move the seismometer into the shadow zone and see which waves still arrive.
| Layer | Depth | State | Made of | Temperature | Density |
|---|---|---|---|---|---|
| Crust | 0 to 5–70 km | solid | rock: granite-like (continents), basalt (oceans) | up to ~500 °C | 2.7–3.0 g/cm³ |
| Mantle | to 2,891 km | solid, flows very slowly | rock rich in silicon, oxygen, magnesium, iron | ~500 to ~3,700 °C | 3.3–5.6 g/cm³ |
| Outer core | 2,891–5,150 km | liquid | iron and nickel | ~3,700 to ~5,100 °C | 9.9–12.2 g/cm³ |
| Inner core | 5,150–6,371 km | solid | iron and nickel | ~5,100–5,200 °C | 12.8–13.1 g/cm³ |
| Layer | About | Behaviour |
|---|---|---|
| Lithosphere | 0–100 km (thinner under young ocean floor, up to 200 km or more under old continents) | cold and rigid; broken into tectonic plates |
| Asthenosphere | ~100–350 km | hot and weak; flows slowly, so the plates can move |
| Mesosphere (mantle below the asthenosphere) | ~350 to 2,891 km (some books start it at 660 km) | solid, stronger because of the pressure, flows very slowly |
| Outer core | 2,891–5,150 km | liquid |
| Inner core | 5,150–6,371 km | solid |
Continental crust is 30–70 km thick (thickest under mountains), made of lighter, granite-like rock, and some of it is about 4 billion years old. Oceanic crust is only 5–10 km thick, made of denser basalt, and is young: it is made at mid-ocean ridges and sinks back into the mantle at subduction zones, so none of it is much older than about 200 million years.
Heat left over from when the Earth formed, plus heat from radioactive elements (uranium, thorium, potassium) slowly breaking down, keeps the inside hot. In the crust the temperature rises by about 25–30 °C for every kilometre down near the surface; further down the rise slows. That heat drives slow convection currents in the mantle, which help move the plates, and keeps the outer core stirring to make the magnetic field.
The melting point of iron rises with pressure. At the centre the pressure is about 360 GPa, more than 3.5 million times the air pressure at sea level, so even at about 5,200 °C the iron stays solid. The outer core is a little cooler but under less pressure, so it is liquid.
| Value | |
|---|---|
| Average radius of the Earth | 6,371 km |
| Average density of the Earth | 5.5 g/cm³ (crust rock only about 2.7–3.0, so the inside must be much denser) |
| Share of Earth’s volume | crust under 1%, mantle about 83–84%, core about 16% |
| Deepest hole ever drilled | 12.3 km (Kola Superdeep Borehole, Russia, 1989): about 0.2% of the way to the centre |
| Pressure at the centre | about 360 GPa |
From the outside in: the crust, the mantle, the outer core and the inner core. Geologists also describe the outer part by how it behaves: the rigid lithosphere (crust plus the top of the mantle) sits on the soft, slowly flowing asthenosphere.
Key takeaway: crust, mantle, outer core, inner core.Only the outer core. It is molten iron and nickel, about 2,260 km thick. The mantle is solid rock, even though it can flow very slowly over millions of years, and magma only forms in small pockets where the rock partly melts.
Key takeaway: only the outer core is liquid.The mantle: about 2,900 km thick and about 84% of the Earth’s volume. The crust is the thinnest, from 5 km under the oceans to about 70 km under big mountain ranges.
Key takeaway: the mantle is thickest; the crust is thinnest.About 5,200 °C, roughly as hot as the surface of the Sun. Estimates differ by a few hundred degrees because nobody can measure it directly; scientists combine earthquake data with experiments that squeeze iron to core pressures in the lab.
Key takeaway: about 5,200 °C.Mostly from earthquake waves. P and S waves change speed and bend at each layer, and S waves cannot cross the liquid outer core, leaving a shadow zone. Other clues: the Earth’s average density (5.5 g/cm³) is much higher than surface rock, mantle rocks brought up by volcanoes, meteorites, the magnetic field, and lab experiments at high pressure.
Key takeaway: earthquake waves are our X-ray of the Earth.No. The deepest hole ever drilled, the Kola Superdeep Borehole in Russia, reached 12.3 km in 1989 and stopped because the rock was too hot (about 180 °C) for the drill. That is only about 0.2% of the way to the centre. Ocean drilling projects are trying to reach the mantle where the crust is thinnest.
Key takeaway: 12.3 km is the record: nowhere near the mantle.The crust is named by what it is made of: lighter rock above the Moho. The lithosphere is named by how it behaves: the rigid outer shell made of the crust plus the cold top part of the mantle, about 100 km thick. The lithosphere is what is broken into tectonic plates.
Key takeaway: crust = what it is made of; lithosphere = how it behaves.Because of the enormous pressure, more than 3 million times the air pressure at the surface. Pressure raises the melting point of iron, so the inner core stays solid even though it is hotter than the liquid outer core.
Key takeaway: pressure keeps the inner core solid.From the outer core. Liquid iron swirls as heat escapes from the core, and moving metal makes electric currents that create a magnetic field: the geodynamo. The field protects us from much of the solar wind and lets a compass work.
Key takeaway: the moving liquid iron in the outer core.The boundary between the crust and the mantle, named after Andrija Mohorovičić, who found it in 1909 because earthquake waves suddenly travel faster below it. It is about 5–10 km down under the oceans and 30–70 km under the continents.
Key takeaway: the crust–mantle boundary.