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We inhabit the planet’s outermost layer, the crust, which varies in thickness. Under continents it stretches about 30 km (18.6 mi) deep, while beneath the oceans it tapers to roughly 5 km (3.1 mi). In regions like the Alps, the crust can reach up to 100 km (62 mi) beneath the surface.
About 2,897 km (1,800 mi) beneath the surface lies Earth’s core, a region roughly the size of Mars. It is divided into a liquid outer core and a solid inner core that can reach temperatures of 5,538 °C (10,000 °F). The inner core endures extreme pressure equivalent to 3.5 million atmospheres, driving tectonic plate motion and, ultimately, mountain building on our planet’s surface.
The mantle, the planet’s largest layer, sits between the core and the crust. While cooler than the searing core, it contains molten rock that feeds volcanic eruptions, especially in zones 100–200 km (62–124 mi) below the surface. The mantle’s upper boundary meets the crust to form the lithosphere, which supports the continents and ocean basins. Heat conducted from the core through the mantle powers the convective currents that shape the lithosphere.
NASA’s studies suggest the Moon has a core structure similar to Earth’s. Its solid inner core measures about 241 km (150 mi) in radius, surrounded by a liquid outer core rich in iron. Unlike Earth, the Moon may also host a partially molten shell encasing this outer core.
