This lesson will explain what the continental crust is, describe its composition and properties, and discuss the history of how the continental crust was formed.
Imagine a swimming pool covered from end to end with rafts and floatation devices – so many floatation devices, that you can barely see what’s underneath. This image is similar to how the earth is constructed.
The entire surface of the earth – whether above water or underneath it – floats on a sea of hot magma, just like the rafts float on the pool water.This floating surface is called the earth’s crust. The crust is the topmost layer of the earth.
It is ridiculously thin when compared to the rest of the earth’s interior – so thin that it wouldn’t show up on most diagrams if drawn to scale. But despite being tiny compared to the rest of the layers, the crust can be a whopping 70 kilometers thick!
What is the Continental Crust?
There are two types of crust: continental and oceanic. Continental crust is the crust under which the continents are built and is 10-70 km thick, while oceanic crust is the crust under the oceans, and is only 5-7 km thick. The deepest mine shaft ever built, called Western Deep in South Africa, currently reaches 3.9 km, which is tiny compared to the continental crust. Forty percent of the earth’s surface is currently covered with continental crust.
It’s important to note that not all continental crust is above sea level. The main defining characteristic of continental crust is that it is made of different types of rock than oceanic crust.
Formation of the Continental Crust
The crust isn’t one large piece; rather, it’s more like an egg shell that has been cracked repeatedly. The crust contains sections, called plates. Just like the floatation devices resting on top of a pool of water, these plates are continually on the move.
When they hit each other, slide along each other, or move away from each other, you can get earthquakes and volcanoes.The continental crust formed through these interactions between plates. When two plates collide, one plate can subduct beneath the other.
Subduction is simply the process by which one plate moves underneath another plate. When this happens, the crust can be pushed upwards, forming continental plates or raising the level of current continental plates to form mountains.
Properties and Composition
The continental crust is between 10 km and 70 km thick, depending on the location.
As you descend through the crust, the temperature increases from surface temperature to between 300 degrees Celsius and 500 degrees Celsius. The pressure gradually increases from 1 atm (atmosphere) to an incredible 91,000 atm!The composition of the crust is largely a mixture of rock that is both felsic and granitic. This is what makes it continental crust, though continental crust also tends to be above sea level. Felsic rock is igneous rock that is rich in the elements that make up feldspar and quartz. Granitic rock refers to rock that is granular; that is, its structure contains granules.
The average density of this rock that makes up the continental crust is 2.7 grams per cubic centimeter.
The earth’s crust is the topmost and thinnest layer of the earth, which floats on the magma underneath. This crust is broken into plates, and when plates collide, they can produce continental crust – crust that is thicker and therefore above sea level. Continental crust is between 10 km and 70 km thick, reaches temperatures as high as 500 degrees Celsius, pressures as high as 91,000 atmospheres, and is made up of rock that is mostly felsic and granitic.
Properties of the Continental Crust
|*10-70 km thick *Formed by subduction when two plates collide*Composed of felsic and granitic rock *Average density of 2.7 grams per cubic centimeter|
Explore this video lesson on the continental crust, then achieve these goals:
- Discuss the continental crust and contrast it with oceanic crust
- Recount the way in which the continental crust is formed
- List some of the properties of the continental crust