The Earth has three different layers to it. The crust is the part of the Earth right on top where people live. The crust is subdivided into two types, oceanic and continental.
Oceanic crust is found under oceans, and it is about four miles thick in most places. A feature unique to oceanic crust is that there are areas known as mid-ocean ridges where oceanic crust is still being created. Magma shoots up through gaps in the ocean’s floor here. As it cools, it hardens into new rock, which forms brand new segments of oceanic crust. Since oceanic crust is heavier than continental crust, it is constantly sinking and moving under continental crust.
Continental crust varies between six and 47 miles in thickness depending on where it is found. Continental crust tends to be much older than the oceanic kind, and rocks found on this kind of crust are often the oldest in the world. Examples of such rocks are those in Quebec, Canada which are estimated to be about 4 billion years old.
What is the difference between Oceanic and Continental Crust?
- Oceanic crust is dominated by mafic and ultramafic intrusive igneous rocks whereas continental rocks are dominated by granitic (felsic) intrusive igneous rocks.
- The difference in density has an impact on isostacy of crust floating on the semi-fluid upper mantle (asthenosphere), with continental crust (about 2.7g/cm3) rising or floating above oceanic crust (about 3.5 g/cm3).
- The continental crust is by far the older of the two types of crust.
- The mantle, oceanic crust, and continental crust all have different compositions due to a process called partial melting.
- Because continental crust is less dense than oceanic crust it floats higher on the mantle, just like a piece of Styrofoam floats higher on water than a piece of wood does.