Kerry has taught for eleven years in grades 4-8 and is currently a 5th grade classroom teacher. Kerry also has a master's degree and is a certified reading specialist.
What Is Earth's Crust?
When you step outside, what do you see underneath your feet? You likely find yourself standing on grass or pavement, and if you take a closer look you will notice dirt, sand, and rocks as well. This is Earth's crust, the outermost layer that covers our planet like a shell, and also the only one that sustains life!
What Is the Crust Made Of?
Earth's crust is the thinnest of all the layers that make up the planet. Imagine peeling a hard-boiled egg for a moment. The yolk and the egg whites make up nearly all of the egg, with an extremely thin shell that surrounds those edible insides. The Earth is constructed very much like this egg, and the shell represents Earth's crust. It is very, very thin compared to the other layers! Of course, there are very obvious differences between an eggshell and the Earth's crust.
For starters, Earth's crust is made up of rock. The type of rock depends on the type of crust: oceanic or continental. Let's learn more about each.
Oceanic crust is crust that sits beneath the ocean. It is much thinner than continental crust and can range from three to six miles thick. This is probably close to how far you travel to get to school or the grocery store, so you can imagine how thin the crust under the ocean actually is! Oceanic crust is mostly made up of basalt, which is rock that comes from cooled and hardened lava. This is because crust beneath the ocean forms when volcanoes erupt and the lava hardens into new rock, or crust. Since new crust is always being formed, oceanic crust is much younger than continental crust. The oldest oceanic crust that has been found is only 270 million years old. This is very young, considering the Earth itself is approximately 4.5 billion years old!
Continental crust is crust that makes up the continents on Earth. It's much thicker than oceanic crust - it can range from approximately 20 to 30 miles thick. This is about how far a marathon runner travels during a race! The type of rock that makes up the continental crust is different from oceanic crust as well. Granite is the most common type of rock found here, though it is almost never found in oceanic crust. Since the continental crust is much thicker, and does not separate to allow lava to flow through like the oceanic crust does, continental crust is also much older. Some parts of the continental crust have been around for billions of years, almost since the Earth was first created!
Movement of the Earth's Crust
Believe it or not, the Earth's crust is constantly moving. It's broken into 12 pieces, or plates. These plates move ever so slightly over the other layers of Earth, sometimes creating movement or reactions that we can see. For example, when the oceanic crust separates and lava flows through, this is because the Earth's plates are moving away from each other, allowing new crust to form. In other cases, the plates of Earth crust move toward each other, creating mountains or even causing one plate to slide beneath the other! When this happens, Earth's crust is actually destroyed as it disappears into the layer beneath it. Because of this movement, the Earth's crust is constantly changing.
The Earth's crust is the outermost layer of our planet; it's a thin shell that surrounds the entire Earth. There are two types of crust: oceanic crust and continental crust. Oceanic crust is very thin and is mostly made up of basalt, which comes from lava. Continental crust is thicker than oceanic crust, is much older than oceanic, and is mostly made up of granite, which is usually only found in this type of crust. The Earth's crust is separated into plates, which are always shifting and changing.
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