# The Three Layers of the Earth: Crust, Mantle & Core

Maria Airth, Elizabeth Friedl
• Author
Maria Airth

Maria has taught University level psychology and mathematics courses for over 20 years. They have a Doctorate in Education from Nova Southeastern University, a Master of Arts in Human Factors Psychology from George Mason University and a Bachelor of Arts in Psychology from Flagler College.

• Instructor
Elizabeth Friedl

Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.

Learn about the three layers of the Earth: the crust, mantle, and core. Discover what scientific principle causes the different layers of the Earth and their properties. Updated: 10/30/2021

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## What are the Three Layers of the Earth?

The question, ''How many layers does the Earth have?'' has a complex answer. When referring to the rocky portion of the Earth, there are three layers of the Earth. However, the planetary rock referred to as Earth does not just consist of the rocky layers: which is where the complexity arises.

Thinking of just the rocky layers, what are the three layers of the Earth? Earth's layer's names are:

• Crust: the outer layer of rock on which humans and animals live and plants grow.
• Mantle: a semi-solid magma layer consisting of iron, magnesium, and silicon.
• Core: centrally located solid mass of metal (inner core) and a liquid mass of iron and nickel (outer core).

These three layers make up the rocky portion of the Earth and are similar to the layers found on many of the rocky planets in the solar system.

### How Many Layers Does the Earth Have?

It is already easy to see why the question of how many layers make up the Earth is difficult to answer because within the three main layers the core can be seen to have two layers (inner and outer). This is true for the other layers as well.

As well as the individual layers of each of the main three layers of the rocky Earth, the Earth also consists of many layers of the atmosphere, the gaseous bubble surrounding the planet. The Earth's atmosphere is made up of five layers that extend 10 miles out from the surface of the planet.

This lesson will focus on the rocky layers of the Earth with the understanding that these are not the culmination of all the layers that make up the planet Earth.

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• 0:06 Earth's Core
• 1:32 The Mantle
• 2:44 The Lithosphere
• 3:32 The Crust
• 4:48 The Lesson Summary
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## Core

It is logical to start an exploration of the Earth's layers by going to its center, the core. The core of the Earth consists of a solid metal inner core and a liquid metal outer core. In this image, the core is represented by the central-most ball of yellow (inner core) and the surrounding area of orange (outer core).

These two layers are defined as a single layer, the core, due to their metal makeup, their similarities to each other, and basic differences from the other layers. The core begins about 1800 miles below the surface of the Earth (where the outer core begins) and continues slightly more than 2000 miles to the Earth's ultimate center.

### Inner Core

The inner core of the Earth consists of extremely hot (over 9000 degrees F) metal (mostly iron and nickel) under incredible pressure (as much as 3.6 million atmospheres of pressure). It is this extreme pressure that makes the inner core solid. The temperature is hot enough to melt iron, but the pressure is too high to allow the melting process to occur.

Thus, the inner core is a solid ball of hot, high-pressure metal. It is interesting to note that some scientists refer to the inner core as a plasma acting as a solid instead of just a simple solid. This is due to the fact that its heat should melt the iron, but the pressure prohibits the melting. These characteristics lend the material to be defined as a plasma (like the sun) rather than a solid.

### Outer Core

Unlike the inner core, the outer core is liquid. It is about 2000 miles thick and is made up of iron and nickel. It is similar in most ways to the inner core however, it is not under as much pressure as the inner core, thus the extreme temperature melts the metals creating a flowing liquid outer core. It is the movement within the outer core that creates the core's magnetism effect on the Earth's crust. This magnetic field creates the Earth's North and South Poles.

## Mantle

Moving out from the core, the next layer is the mantle. The mantle makes up about 84% of the Earth's total volume. Starting about 20 miles below the Earth's surface, the mantle extends approximately 1800 miles towards the Earth's core, making it the largest layer of Earth. In comparison to the outer core, it is about the same thickness, but due to its much larger circumference (being further out in the spherical planetary layers), it is much larger in total volume than the outer core.

The mantle is considered semi-solid, with flowing molten iron, magnesium, and silicon making up its layer. The mantle, like the core, is made up of a combination of other layers of the mantle. These layers are:

1. Asthenosphere
2. Central Mantle
3. Lower Mantle

Like the layers in the core, these mantle layers are similar in many ways, but are subtly different enough to constitute recognizing them as a separate layer of the mantle itself.

### Asthenosphere

The upper mantle is made of the lithosphere and the asthenosphere. However, the lithosphere is shared between the crust and the mantle, so, the uppermost layer of the mantle proper is the asthenosphere. Starting approximately 60 miles below the Earth's surface, the asthenosphere extends down about 400 miles. This layer of the mantle moves like a convection oven with the current pushing hot molten magma towards the Earth's crust, sometimes breaking through in the form of volcanos and/or causing earthquakes when the lithosphere above is stressed due to the movement below.

### Central Mantle

The central layer of the mantle is known as the transition zone due to the transformation seen in rocks in this layer. The transition zone extends from 250 miles to 410 miles below the Earth's surface. Rocks transition from their surface structures to a much denser form. It is believed that this increase in the density of rock in the central area of the mantle prohibits slabs of the lithosphere (lower area of the crust and upper mantle) that falls into the mantle from falling completely through the mantle.

The central mantle, or transition zone, holds as much water, in the form of hydroxide, as can be found in all the Earth's oceans on the surface of the planet. Due to the high temperature and pressure found in the mantle, the hydroxide ion is trapped in the rock structures that enter the central mantle. It is believed that this water can enter the mantle during subduction (when slabs of tectonic plates are pushed into the asthenosphere and fall into the transition zone).

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#### What are the three layers of the Earth's mantle?

The three main layers of the Earth are: crust, mantle, and core.

These three layers each have multiple layers as well.

• Crust: the main crust and the lithosphere (bottom of crust shared with upper mantle).
• Mantle: lithosphere (shared with crust), asthenosphere, central mantle (transition zone) and lower mantle.
• Core: inner core (solid) and outer core (liquid).

#### What are the three layers of earth and which one do we live on?

The crust, mantle, and core are the three main layers of the Earth. The only layer that can support life is the crust. Scientists have studied most of the Earth's crust but have yet to study the entire ocean bed floor (the thinnest part of the crust).

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