Crust
Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 9, Ch 2 "Shaping of the Earth's Surface"; Class 11, Ch 3 "Interior of the Earth"
Meaning
The crust is the outermost layer of the earth. It is solid and brittle, which means it cracks instead of bending. It is thin under the oceans (mean about 5 km) and thicker under the continents (about 30 km on average). It is thickest, about 70 km, under the Himalayas. The ocean crust is made of dense basalt, and the continental crust is mostly lighter granite. At its base is the Mohorovicic discontinuity (Moho), where seismic wave speeds jump sharply.
Example
Under the Himalayas in northern India, the crust is about 70 km thick. Under the Indian Ocean floor, it is only about 5-10 km thick.
Don't confuse with
- Lithosphere: the lithosphere is the crust plus the uppermost mantle, 10-200 km thick, and it is broken into plates. The crust is only the top part of it.
Related concepts
- Oceanic crust
- Continental crust
- Conrad discontinuity
- Mohorovicic discontinuity
- Mantle
- Asthenosphere
- Lithosphere