Hawaiian volcano

The Earth’s Interior
A look At The Inner Earth

Studying the earth's interior can help us to understand earthquakes, volcanoes, plate tectonics and more about the inner earths natural processes.

In general the earth's interior has been sorted by Gravity. Heavier elements like iron tend to sink toward the center or core of the earth. Lighter materials, the silicates, oxygen compounds and water have risen to become part of the crust. This action has created distinct layers within the earth and is still in process today.


The Inner Earth is composed of three main parts; the crust, the mantle, and the core as shown in the diagram of the earth's interior below:

  • The Crust - silicate rocks, primarily granite and basaltOceanic Crust - mostly basaltContinental Crust - igneous, metamorphic, and sedimentary rocks
  • The Mantle - iron and magnesium rich silicate rocksUpper MantleLower mantle
  • The Core - iron nickel alloyOuter core Inner core

The Crust
The crust of the earth is very slowly growing thicker. Volcanic activity is continually adding mass to the crust. Though the crust is solid it is made up of about 12 plates. They are called Tectonic Plates. These plates are in constant motion. The movement is caused by convection currents in the mantle. The movement is very slow, averaging about 2 inches a year. This is about like the growth of your fingernails.

  • The crust is about 0.5 % of the earth’s total mass.
  • The crust is made up of silicate rocks such as granite and basalt.
  • The continental crust is much thicker than the oceanic crust as shown here in the diagram of the earth's crust.
  • Oceanic crust - The crust under the oceans is about 10 km thick and is generally made up of rock rich in iron and magnesium. These are primarily basalt formed by volcanic action at the mid ocean ridges. The oceanic crust is denser than continental crust.
  • Continental crust (continental cratons) - Where there are continents the crust is about 30 to 50 km thick. It is made up of igneous, metamorphic, and sedimentary rocks. The continental crust is less dense than the oceanic crust. When the continental crust collides with oceanic crust through plate movement the continental crust rides over the top of the oceanic crust while the oceanic crust is pushed back down towards the mantle.
Earth's Interior - The Mantle

Much less is known about the mantle than the crust. The crust we can see, measure, dig and drill. The mantle is different. We have little direct contact with the inner earth. We can tell some things about the mantle by studying volcanoes and what comes out of them.

Much of what we believe is true about the earth's interior comes from studying Seismology. Seismology began as the study of earthquakes and the seismic waves they produced. These waves travel through the earth and move at different speeds in different materials. By studying these waves and how they move through the inner earth we can learn about the its structure.

The upper mantle

  • Is made up of rocks rich in magnesium and iron, and poor in silica; mostly peridotites.
  • It is about 400 km thick and is much denser than the crust.
  • It comprise 10% of the earth’s mass
The Lower mantle
  • It is more dense and contains a greater amount of iron than the upper mantle
  • It is about 1900 km thick
  • It makes up 41% of the earth’s mass
Earth's Interior - The core

The core is composed primarily of a nickel-iron alloy. There is an outer core that is liquid and an inner core that is solid.

  • Outer core Is about 2100 km thick. It makes up about 30 % of the Earth's total mass.
  • Inner coreIs about 1300 km thick. It makes up about 2 % of the Earth's total mass.
Some points to remember in studying the earth’s interior:
  • There are distinct layers to the earth’s interior.
  • Heavier elements tend to sink to the core
  • Lighter elements rise toward the surface
  • Much more is known about the crust than the mantle and core.
  • What we believe is true about the mantle and core comes from studying seismology.



Below you may download a blank copy of the inner earth for students to color and lable.Download a blank copy of The Earth's Interior PDF file here


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