Earth's crust facts for kids

Earth cutaway from the core to the exosphere

The Earth's crust is our planet's hard, rocky outer layer. Think of it like the skin of an apple, but for the Earth! It's actually very thin compared to the rest of the Earth, making up less than 1% of its total size.

The crust is made of different kinds of rocks, including igneous, metamorphic, and sedimentary rocks.

Right below the crust is a much thicker layer called the mantle. The crust and the very top part of the mantle together form something called the lithosphere. The lithosphere isn't one solid piece; it's broken into huge sections called tectonic plates. These plates are always slowly moving, which causes things like earthquakes and volcanoes!

There are two main types of Earth's crust:

• The continental crust is the part under the land where we live. It's thicker, usually between 30 km (20 mi) and 50 km (30 mi) deep. It's mostly made of lighter rocks, like granite.
• The oceanic crust is found under the oceans. It's thinner, only about 5 km (3 mi) to 10 km (6 mi) deep. This type of crust is made of denser rocks, like basalt.

The deeper you go into the crust, the hotter it gets. This is because of geothermal energy, which is heat coming from inside the Earth. Where the crust meets the mantle, temperatures can be super hot, from 200°C (392°F) to 400°C (752°F)! Even though it gets hot deep down, the crust is the coldest layer overall because its surface is exposed to the atmosphere.

What is the Earth's Crust Made Of?

Even though you might see lots of sedimentary and metamorphic rocks on the surface, Igneous rocks actually make up over 90% of the Earth's crust by volume! They are just often covered up.

A group of minerals called feldspars makes up about half of the crust's material. Another very common mineral is quartz. You can also find other minerals like mica and hornblende.

Only a small part (about 8%) of the Earth's crust is made of minerals that are not silicates. These include things like carbonates, sulfides, chlorides, and oxides.

Here are some of the most common elements found in the Earth's crust:

All other elements are found in very tiny amounts, making up less than 1% of the crust.

How Did the Earth's Crust Form?

The Earth's crust and mantle started forming about 100 million years after our planet itself formed, which was about 4.6 billion years ago. At first, the crust was very thin. It probably changed a lot because the tectonic plates were shifting much faster than they do now.

The early crust was also hit many times by asteroids. This was very common during a time called the Late Heavy Bombardment, which destroyed parts of the crust over and over.

Today, the oldest oceanic basalt crust we have is only about 200 million years old. But most of the continental crust is much, much older! The oldest continental rocks found on Earth are called cratons. These are between 3.7 and 4.28 billion years old. They have been found in places like Western Australia, Canada's Northwest Territories, and the Fennoscandian Shield. Some tiny crystals called zircons, found in Western Australia, are even older, at least 4.3 billion years old!

On average, the Earth's continental crust is about 2.0 billion years old. Most of the very old crustal rocks (formed before 2.5 billion years ago) are found in these cratons. These old continental crusts and the mantle below them are less dense than other parts of the Earth. This means they are not easily destroyed when the plates move around.

New continental crust forms when major mountain-building events happen. This often occurs at the same time that huge supercontinents, like Rodinia, Pangaea, and Gondwana, are forming. The crust grows as island arcs (chains of volcanic islands) and granite and metamorphic fold belts come together. This process is helped by the subduction of the mantle below the crust, which creates a stable base for the crust to float on.

Images for kids

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  Thickness of Earth's crust (km)

See also

In Spanish: Corteza terrestre para niños