01

Start with the surface

Earth’s crust is a thin outer shell compared with the planet beneath it. Beneath the crust lies the much thicker mantle, followed by the core. These broad layers differ in composition and behaviour.

02

Rock that moves slowly

The mantle consists mainly of solid rock, but over geological timescales it can deform and flow. Calling it simply “liquid” misses this distinction. The rigid tectonic plates include the crust and the uppermost mantle.

03

A core in two parts

The outer core is liquid, while the inner core is solid. Temperature is not the only factor determining whether a material melts: pressure and composition matter too. The Earth cutaway is schematic, with layer boundaries simplified for clarity.

04

How can we know?

Scientists cannot drill to the core. Instead, they combine evidence including earthquake waves, gravity, magnetic fields, and laboratory studies. Changes in how seismic waves travel provide clues about the materials and boundaries inside the planet.

FOLLOW THE EVIDENCE

Sources & further reading

Sources checked 13 November 2026. These organisations provide reference material and do not endorse this website.