Earth's mantle

Earth's mantle is a thick layer of rock that lies between the outer crust of the Earth and its hot, liquid outer core. It is made mostly of silicate rock and is very heavy, weighing about 4.01×10²⁴ kg — that’s 86% of all the mass of the entire Earth!

This layer is about 2,900 kilometers or 1,800 miles thick, which makes up almost half of the Earth’s radius and more than three-quarters of its total volume. Even though it is solid rock, over very long periods of time, the mantle can flow slowly like thick caramel.

When parts of the mantle melt a little bit, it creates new crust under the oceans at places called mid-ocean ridges, and also helps form the continents where one piece of crust moves under another in areas known as subduction zones.

Structure

The Earth's mantle is the thick layer of rock between the outer crust and the core. It is made of special kinds of rocks called silicates and is very important for our planet.

The mantle has different layers. The top part, called the upper mantle, sits just below the Earth's crust. Below that is a layer called the transition zone, and the deepest part is the lower mantle. Each layer has its own minerals and properties, changing as you go deeper into the Earth. Scientists study these layers to learn more about our planet's structure and history.

Composition

The mantle is made of rocks, but it is hard to study because we cannot easily reach it. Sometimes, pieces of mantle rock can be found on the surface in special places called ophiolites, where parts of the ocean floor have moved onto continents. We can also find small pieces of mantle rock inside other rocks, such as basalts or kimberlites.

Most of what we know about the mantle comes from studying its top layer. Scientists are still learning whether the rest of the mantle has the same ingredients. The mantle's makeup has changed over time as magma has formed the Earth's crust. A study from 2018 suggested that a special kind of water, called ice VII, might exist deep in the mantle inside diamonds.

Temperature and pressure

In the mantle, temperatures range from about 500 kelvin at the top, near the crust, to around 4,200 kelvin at the bottom, close to the core. The temperature rises quickly at the very top and bottom of the mantle and increases more slowly in the middle. Even though these temperatures are much higher than what would melt the rocks at the Earth's surface, the mantle stays mostly solid. This is because the huge weight of the rocks above creates strong pressure, which stops the mantle from melting.

The pressure in the mantle starts at a few hundred megapascals near the surface and grows to about 139 GPa at the boundary with the core.

Movement

Main article: Mantle convection

The Earth's mantle moves because of heat differences between the surface and the core. Hot material rises, while cooler material sinks. This movement is called convection and helps shape the motion of Earth's plates.

Convection in the mantle is a complex process that works with the movement of plates. The mantle can flow very slowly over long periods, but it behaves like a solid under normal conditions. This slow movement helps create features like volcanoes and mountain ranges on Earth's surface.

Exploration

Scientists study the mantle mostly from the ocean floor because the oceanic crust is thinner than the crust on land. The first big attempt to explore the mantle, called Project Mohole, stopped in 1966 after many problems. The deepest it went was about 180 meters below the sea floor.

Later, the Deep Sea Drilling Project from 1968 to 1983 helped scientists understand how the Earth's plates move. In 2007, scientists tried to find areas where mantle rock was exposed and planned to drill very deep into the ocean floor. They also use computer programs to learn more about the mantle's history and composition. In 2023, they collected rock samples from deep below the ocean that might be from the mantle.