What Is the Earth's Mantle Made Out Of?

We cannot see the mantle of the earth except for the rare times that lava runs out of volcanoes. It is the layer of the earth that lies beneath the surface. The temperature is unimaginably hot and no living creatures could live in the earth's mantle.


The earth's mantle is a layer of rock beneath the crust that is 1800 miles thick. The deepest part of the mantle is hotter than the area near the Moho so that the deepest rocks are molten. Below the mantle is the earth's core: the molten outer core which is 1400 miles thick and the solid inner core which is 800 miles thick.


The earth's tectonic plates are found in the lithosphere which is an area that incorporates the crust and the uppermost part of the mantle. Between the crust and the mantle is a region called the Mohorovicic Discontinuity, known for short as the Moho. Under the lithosphere is a softer more pliable region called the asthenosphere.


Silicon, oxygen, aluminum, iron and magnesium are the elements which are found in the earth's mantle. When the earth experiences volcanic activity, molten hot iron and silicate lava rocks spew through the volcanic openings in the ocean's floor. These rocks are also rich in magnesium. When the lava cools, it solidifies as basalt which makes up the oceanic crust, a large part of the earth's surface.


The temperature inside the mantle increases by three degrees for each mile of depth. The deeper into the mantle, the hotter the temperature is until it reaches the hottest point of 7950 degrees Fahrenheit. The pressure within the mantle also increases as it gets deeper. Because of the increasing pressure and temperature, the minerals in the deepest parts of the mantle and even deeper in the core are denser than they are when they are found closer to the surface. The deepest part of the earth, its inner core, is formed by solid nickel and iron. It reaches a temperature of 12,600 degrees Fahrenheit.

Expert Insight

Geologists plot the seismic waves that they record during earthquakes to investigate the earth's core. By observing where and at what angles these waves are deflected, the geologists can map the innermost parts of the earth. A magnetic field emanates from the earth's core as well, due to the movement of electrical current in the molten metal. When heat is released from the core, it produces currents in the mantle which in turn can make the tectonic plates move.


About the Author

Lesley Barker, director of the Bolduc House Museum, authored the books "St. Louis Gateway Rail—The 1970s," published by Arcadia, and the "Eye Can Too! Read" series of vision-related e-books. Her articles have appeared in print and online since the 1980s. Barker holds a Bachelor of Arts in sociology from Washington University and a Master of Arts in Teaching from Webster University.