Continental crust
Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 11, Ch 3 "Interior of the Earth"; Class 11, Ch 4 "Distribution of Oceans and Continents"
Meaning
Continental crust is the part of the crust that makes up the continents. It is about 30 km thick on average and up to 70 km thick under the Himalayas. It is lighter than oceanic crust and is made mostly of granite (sial: silica + aluminium). Because it is light, it is not pulled down and destroyed at trenches. So it lasts very long. NCERT says some of its rocks are over 3,200 million years old, and the oldest known are about 4 billion years old.
Example
Under the Himalayas in northern India, the continental crust is about 70 km thick, the thickest on earth. The plates pushing together have piled it up there.
Don't confuse with
- Oceanic crust: it is thinner (about 5-10 km), heavier (basalt, or sima) and young (nowhere older than about 200 million years).