The Earths Mantle

The Earths mantle lies beneath the crust. The boundary between the crust and the mantle was discovered by Andre Mohorovicic, a Croation seismologist. The boundary is deeper under the continents that it is under the ocean floors. Mohorovicic discovered the Mohorovicic Discontinuity (Moho boundary) when he looked at the speed earthquake waves travel inside the body of the Earth.

Interior layers of the Earth, USGS

Major layers inside the Earth, USGS

Moho boundary
At the Moho boundary between the Earths mantle and the crust the density of the rock changes from 2.9 grams per cubic centimeter to 3.4 grams per cubic centimeter. This increase in density increases the speed that p waves travel through the body of the earth. The waves are also slightly deflected by the change in density of the rocks at the boundary.

Mantle and crustal rocks
Mantle and crustal rocks have different mineral compositions. Typical rocks found in the mantle have more magnesium and iron than crustal rocks. Peridotite is the dominant rock of the upper mantle.

Common minerals
Minerals commonly found in the rocks include olivine, pyroxene and garnets. The crust has a variety of igneous, sedimentary and metamorphic rocks that are lighter and less dense than peridotite.

Olivine, pyroxene and garnet minerals
Olivine, pyroxene and garnet minerals are found in rocks from the Moho boundary to a depth of 410 kilometers. Between 400 kilometers and 650 kilometers beneath the Earth's surface the minerals are under so much heat and pressure they become unstable.

Minerals recrystallize
The minerals recrystallize into minerals that are stable at this heat and pressure without melting. Below 650 kilometers all the minerals become unstable and the rocks melt when they reach the Earth's outer core.

Temperature in the mantle
The upper mantle has a temperature range between 500 degrees and 900 degrees Celsius near the crust. Deep in the Earth at the boundary with the Earth's core the rock temperature is about 4000 degrees Celsius.

Pressure in the mantle and outer core
Only the extreme pressure keeps the rocks in the mantle from melting. At the boundary between the mantle and the outer core the rocks melt and become molten.

More Planet Earth Links

Iceland Volcanoes Did you know volcanoes in Iceland formed because of the Mid Atlantic Ridge and a hot spot?

Tectonic Plate Boundaries Find out about the major types of crustal plates and the boundaries around them.

Earths Atmosphere Find out which layer meteors burn up, where the International Space station is located and more.

Lithosphere Find out if you know the two types of crusts that make up this layer of the Earth and which one is younger?

What are Northern Lights? Find out how the solar wind powered, by great storms on the Sun, create the Northern Lights.

The Earths Mantle Is the mantle molten rock or solid rock? Find out what we know about this large layer of the Earth.

Planet Earth Find out about our planet from the Earth's core to the outer reaches of our atmosphere.

Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.

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