# The Continental Crust: Definition, Formation & Composition

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• 0:00 Floating Surface
• 0:50 What is the Continental Crust?
• 1:34 Formation of the…
• 2:21 Properties and Composition
• 3:17 Lesson Summary

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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

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.

## Floating Surface

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.

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