Upper Mantle

The upper mantle of the planet Earth is the geological layer which is located right below the crust. It is not made up of solid materials but it is rather a very thick, slow-moving liquid of molten rocks. The crust has been formed by these molten rocks that have been ejected from deep below over hundreds of millions of years. Layers upon layers of sediment that derive from once upon-a-time living creatures and vegetation lie on top of the crust. Consisting of the lithosphere and the asthenophere, it is estimated that the upper mantle measures about 217 miles (350 km) thick. The lithosphere in turn is also a part of the deep part of the crust, overlapping both.

As the upper mantle drifts slowly around the Earth surface, so does the crust lying on top of it. This geological process is called plate tectonics. According to the theory, plate tectonics have shaped the continents, islands, mountains, causing the strongest earthquake on the planet. The upper mantle and the crust move so slowly that it cannot be observed on a day to day, or a week to week, basis, for it takes millions upon millions of years to shape huge mountain ranges, such as the Andes or the Himalaya.

Composition

The top section of the upper mantle (the lithosphere) is rigid, almost solid, and it is 40-mile deep. It is composed of peridotites. A peridotite is a plutonic igneous rock, which consists of olivine. Olivine is in turn a yellowish green mineral made up of silicate containing iron and magnesium, mainly (Mg, Fe)2SiO4. Since peridotites are heavier than most of the rocks found in the Earth crust, they have a tendency to sink down deep into the bottom of the crust and the upper mantle.

The asthenosphere, on the other hand, consists of about 150 miles of molten rocks, which are made up mostly of silicon and magnesium, but it also contains smaller amount of magnesium, iron, aluminum, and calcium. Diamonds and other rocks also erupt onto the surface of the Earth from deep in the upper mantle in some places of the planet.

Below, Diagram/Drawing of Earth Geological Layers, Showing the Upper Mantle.