solidEarth

Solid Earth refers to the planet’s solid interior, comprising the crust, mantle, and the solid inner core. The outer core, in contrast, is liquid and thus not part of the solid Earth. The solid Earth sits beneath the oceans and atmosphere and underlies the planet’s geologic and geophysical behavior.

The crust is the outermost solid shell, with continental crust rich in granitic rocks and oceanic crust dominated by basalt and gabbro. Beneath lies the mantle, extending to about 2,900 kilometers below the surface. The mantle is divided into the upper mantle, which includes the rigid lithosphere and the partially molten asthenosphere, and the lower mantle, which is more rigid. The inner core is a solid sphere about 1,220 kilometers in radius, surrounded by a liquid outer core that drives the geomagnetic field.

The solid Earth exhibits a range of physical properties, including varying mineral composition, density, and elastic stiffness. Seismic waves generated by earthquakes are the primary tool for studying its internal structure, revealing discontinuities and velocity changes with depth. Gravity, magnetism, and space-geodetic measurements also constrain the planet’s interior. Mantle convection, lithospheric deformation, and phase transitions within minerals govern how the solid Earth responds to forces and evolves over geological time.

Dynamic processes of the solid Earth include plate tectonics, driven by mantle convection; elastic deformations from tides and glacial rebound; and episodic crustal deformation associated with earthquakes and volcanism. Understanding the solid Earth is essential for interpreting geologic history, assessing natural hazards, and locating mineral and energy resources.