Layers of The Earth

Layers of the Earth.


Think about that egg yolk again. Where in the hard-boiled egg do you find it? In the center, right? The same is true of the core of the earth. It is in the very middle of our planet. But, if we can’t see it, how do we know it’s there or what it looks like?

Geologists have used seismic waves to determine the different materials that compose the earth. Seismic waves are energy waves that travel through Earth, most often as the result of an earthquake or sometimes from an explosion. These waves travel at different speeds through different materials. Therefore, by measuring the speed of the waves, scientists have determined the composition of the earth.

The core has two layers, called the inner core and the outer core. Let’s take a look at how they’re similar and how they’re different.

Geologists think the liquid outer core spins, creating a magnetic field. Earth’s magnetic field is responsible for sheltering the earth from the Sun’s strong, solar winds.


Let’s move on to the mantle of the earth. Similar to the white of a hard-boiled egg that is between the yolk and the shell, the mantle sits between the core and the crust.

The mantle has two layers—the lower mantle and the upper mantle. Due to tremendous heat and pressure, the solid rock of most of the upper mantle can slowly move. Geologists call the ability of solid rock to flowplasticity. This region of the upper mantle is the asthenosphere.

The lower mantle sits just outside Earth’s core. The upper mantle, including the asthenosphere, sits just below the crust. Let’s take a look at how they’re similar and how they’re different.


As you walk home or to the store, think about where you’re standing. Is it concrete, dirt, or on a hill? No matter where you walk, you’re walking on the crust of the earth. You would be on the crust even if you were walking along the bottom of the ocean.

This outermost layer, which is like the shell of an egg, is also part of the lithosphere. The lithosphere is the crust and the uppermost, rigid portion of the mantle. It can vary in thickness. It is thinnest under the oceans and thickest in the mountains.

The lithosphere is a rigid shell made up of plates. In order to understand what the plates are like, imagine taking a hard-boiled egg and cracking it all over. Don’t peel it; just crack it. It’s still all together on the outside of the egg, but it’s broken into “plates.” The plates of the lithosphere move slowly about on the plastic asthenosphere beneath.

Crust or lithosphere facts:

  • thickness can range from 5-100 km; average thickness is 30 km
  • temperature can range from 0-700°C; average temperature is 25°C
  • thinnest under oceans
  • thickest in the mountains
  • made of large plates that move


Geologists use geosphere to refer to all of Earth’s interior—the crust, mantle, and core of Earth, collectively. The geosphere interacts with the other important spheres of Earth, such as the hydrosphere, atmosphere, and biosphere.

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