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Mantle (geology)

earth science Maturity 7-9 Next article →

A mantle is a massive layer found inside a planetary body. It is positioned between the outer crust and the inner core. Mantles are typically the largest and most massive layers of a planet. They are often composed of rock or various types of ices. These layers are characteristic of bodies that have undergone differentiation by density. This process occurs when heavy materials sink toward the center and lighter materials stay near the surface.

Earth Internal Structure
Earth Internal Structure

In Earth's case, the mantle is a layer of silicate rock. It sits directly between the crust and the outer core. The mantle has a mass of 4.01 × 10^24 kg. This represents 67% of the total mass of the Earth. It also accounts for about 84% of Earth's total volume. While it is predominantly solid, it behaves like a viscous fluid over geological time. This means it flows very slowly, like extremely thick syrup, over millions of years.

The movement of the mantle drives important geological processes. At mid-ocean ridges, the mantle undergoes partial melting. This process produces new oceanic crust. At subduction zones, the mantle also undergoes partial melting. This specific melting produces continental crust. These cycles help shape the surface of our planet over vast amounts of time.

Earth Internal Structure
Earth Internal Structure

Different types of planets possess very different mantle compositions. Terrestrial planets, like Earth, have mantles made of silicate rock. For example, Mercury has a silicate mantle that is 28% of its mass. Venus has a silicate mantle making up around 70% of its mass. Mars has a silicate mantle that constitutes between 74% and 88% of its mass. Scientists believe chassignite meteorites may represent the mantle of Mars.

Earth Internal Structure
Earth Internal Structure

Other types of planets have mantles made of different materials. The ice giants, Uranus and Neptune, have mantles made of ice. These ice mantles are approximately 30,000 km thick. They compose 80% of the mass of both planets. This shows how the composition of a mantle depends on the planet's distance from the sun and its overall makeup.

Moons and asteroids can also possess mantles. Jupiter's moons Io, Europa, and Ganymede all have silicate mantles. Io has a silicate mantle covered by a volcanic crust. Ganymede has a silicate mantle covered by a thick layer of ice. Europa has a silicate mantle covered by ice and possibly liquid water. The Earth's moon also has a silicate mantle that is 1300 to 1400 km thick. This lunar mantle is the source of mare basalts.

Earth Internal Structure
Earth Internal Structure

Even smaller objects in space show these structures. The largest asteroids can have mantles as well. The asteroid Vesta is a notable example. It has a silicate mantle similar in composition to diogenite meteorites. Some moons, like Titan and Triton, have mantles made of ice or other solid volatile substances. This demonstrates that the mantle is a common feature across many different types of celestial bodies.

Earth Internal Structure
Earth Internal Structure

Understanding the mantle helps scientists learn about the history of the solar system. Researchers use textbooks like "Theory of the Earth" by Don L. Anderson to study these interiors. They also study mantle xenoliths and seismic discontinuities to understand composition changes. For instance, the lunar mantle contains a seismic discontinuity at a certain depth. This is likely related to a change in the mantle's chemical composition. By studying these layers, we learn how planets form and evolve.

Earth Internal Structure
Earth Internal Structure
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