What is the earth’s crust?
Don’t be confused with the crusts from a slice of toast; the crust we’re talking about here is very different and much bigger.
The “crust” describes the outermost shell of a terrestrial planet. Our planet’s thin, approximately 40 – 60km deep crust — just 1% of Earth’s mass — contains all known life in the universe.
The layers of the planet
Earth has three layers: the crust, the mantle, and the core. The crust is made of solid rocks and minerals. Beneath the crust is the mantle, primarily concrete stones, and minerals, but includes patches of semi-solid magma. At the center of the Earth is a hot, dense metal core.
How the Earth’s crust was made
Billions of years ago, the Earth started as a hot, sticky, glue-like ball of rock. The heaviest material, mostly iron and nickel, sank to the center of the new planet and became its core. The molten material that surrounded the core was the early mantle.
Over millions of years, the mantle cooled. Water trapped inside minerals erupted with lava, a process called “outgassing.” As more water was outgassed, the mantle solidified. Materials that initially stayed in their liquid phase during this process, called “incompatible elements,” ultimately became Earth’s brittle crust.
From mud and clay to diamonds and coal, Earth’s crust is composed of igneous, metamorphic, and sedimentary rocks. Forces created Earth’s crust, which continues to be shaped by the planet’s movement and energy. The Earth’s crust is divided into two types: oceanic crust and continental crust.
Tectonic plates and the crust
The Earth’s crust is broken into plates, and it was once believed that convection currents in the mantle slowly moved the crust around.
It is now thought that a mechanism called slab pull drives the movement of tectonic plates. Slab pull occurs when older, denser tectonic plates sink into the mantle at subduction zones. As these older sections of plates sink, newer and less thick sections are pulled behind. Sinking in one place leads to plates moving apart in other places.
The movement of the plates, and the activity inside the Earth, is called the theory of plate tectonics.
