The Inner Earth

A study of the inner earth helps us understand earthquakes, volcanoes, plate tectonics, and more. The earth’s interior has been sorted by Gravity. Generally heavier elements tend to sink toward the center. Lighter materials have risen to become pat of the crust. This action has created distinct layers and is still in process today.
The Inner Earth is composed of three main parts:

The Crust - silicate rocks, primarily granite and basalt
Oceanic Crust - mostly basalt
Continental Crust - igneous, metamorphic, and sedimentary rocks

The Mantle - iron and magnesium rich silicate rocks
Upper Mantle
Lower mantle

The Core - iron nickel alloy
Outer 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 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.
It is made up of silicate rocks such as granite and basalt.

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 Mantle
Much less is known about the mantle than the crust. The crust we can see, measure, dig and drill. 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 earths 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.

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

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

2100 km thick.
About 30 % of the Earth's total mass.

Inner core

1300 km thick.
About 2 % of the Earth's total mass.
In studying the earth’s interior:

There are distinct layers to the earth’s interior.
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.

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