Earth’s crust

Definition

Earth's crust is the outermost layer of the planet, composed primarily of solid rocks and minerals. It includes both the continental crust, which forms the landmasses, and the oceanic crust beneath the oceans.

5 Must Know Facts For Your Next Test

1. Earth's crust varies in thickness from about 5 km under the oceans to up to 70 km under continental mountains.
2. The crust is divided into tectonic plates that float on the semi-fluid asthenosphere below.
3. Continental crust is mostly composed of granite, while oceanic crust is mainly basalt.
4. The Mohorovičić discontinuity, or Moho, marks the boundary between Earth's crust and its mantle.
5. Plate tectonics involving movement of Earth's crust cause geological phenomena such as earthquakes and volcanic activity.

Review Questions

• What are the primary differences between continental and oceanic crust?
• How does the thickness of Earth's crust vary across different regions?
• What role does Earth's crust play in plate tectonics?

Related terms

Mantle:

The layer directly beneath Earth's crust composed of semi-solid rock that flows slowly over time.

Tectonic Plates: Large slabs of lithosphere that move over Earth's asthenosphere causing seismic activity.

Lithosphere:

The rigid outer layer of Earth consisting of the crust and upper mantle.