Geologists study how earthquake waves travel through the planet to understand its inner structure. They are still refining their interpretations, but the evidence suggests the following:
Earth has a solid, dense, iron-rich inner core surrounded by a fluid outer core, also mainly iron.
The next layer out, the mantle, is split into the lower and upper mantle. Though it is solid rock, parts of the mantle slowly deform. Hotter rock rises and cooler rock sinks through convection, driving the movement of the Earth's plates.
Above the mantle lies the crust upon which we live. The lithosphere incorporates the crust and part of the upper mantle.
Image: Artwork showing the Earth's internal layers (credit: Jose Antonio Peñas/SPL)
Our planet develops its inner heat.
Dr Iain Stewart explains how the Earth developed its inner heat during a time known as the Hadean eon, about 4.5 billion years ago.
Iain Stewart explains how the Earth's crust is divided.
Dr Iain Stewart visits the Mid-Atlantic Ridge in Thingvellir, Iceland, a place where it's possible to see the divide between two of the Earth's plates on land.
Liz Bonnin uses a plum to explain what's happening inside the Earth.
Reporting from Eyjafjallajokull volcano in Iceland, Liz Bonnin explains the Earth's inner structure using a plum to show the different layers inside our planet. She explains why hot bits of the mantle that are rising melt to form magma.
Anna Grayson traces the geological history of the Lizard in Cornwall.
Anna Grayson explains the geological history of a region of southern Cornwall called the Lizard. The rocks that form the Lizard are unique - it is possible to see rocks and minerals that formed deep inside the Earth.
Professor Dan Lathrop investigates Earth's core.
The molten metal of Earth’s outer core creates our planet’s magnetic field. But exactly how it does it has remained a mystery. So Professor Dan Lathrop built a model to investigate.
The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by either their chemical or their rheological properties. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of Earth's internal structure is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanic activity, analysis of the seismic waves that pass through Earth, measurements of the gravity field of Earth, and experiments with crystalline solids at pressures and temperatures characteristic of Earth's deep interior.