Oceanic 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
Oceanic crust is the crust under the oceans. It is thin, about 5-10 km (mean about 5 km). It is made of dense, heavy basalt (sima: silica + magnesium). New oceanic crust keeps forming at mid-ocean ridges. Old crust keeps sinking back into the mantle at trenches. So no oceanic crust is older than about 200 million years.
Example
Near the Andaman Islands, the oceanic crust of the Indian plate subducts (slides down) beneath the Burma microplate. This is how old ocean floor gets destroyed. The same process feeds Barren Island volcano.
Don't confuse with
- Continental crust: it is thicker (about 30 km, up to 70 km), lighter (granite, or sial) and much older (up to about 4 billion years).
Related concepts
- Crust
- Continental crust
- Conrad discontinuity
- Mohorovicic discontinuity
- Mantle
- Asthenosphere
- Lithosphere