What is the Lithosphere? – World Atlas

Lithosphere refers to the hard, rocky outer layer of any terrestrial planet or natural satellite. On Earththe lithosphere is mainly composed of crust and the solid outer part of the stem coat. One of the major spheres of the Earth, the lithosphere is primarily the terrestrial component comprising solid landmasses such as continents and islands on which all biological life exists. The lithosphere is seriously affected by human activities such as mining, deforestation, agriculture, overgrazing and urbanization.

Why is it called lithosphere?

A diagram showing the extent of the lithosphere on Earth.

The term lithosphere is derived from the Greek words lithoswhich means rocks or stones, and sphaeros, which means sphere. The lithosphere or rocksphere thus designates the hard and rocky outer layer of the Earth, made up of the crust and the upper mantle. The lithosphere can extend to a depth of more than 100 km. Beneath the lithosphere is the asthenosphere, which refers to the weakest, hottest, and deepest part of the upper mantle. The lithosphere stays hard longer and deforms elastically, while the asthenosphere deforms viscously. The lithosphere is therefore less ductile than the asthenosphere.

History of the concept of lithosphere

The concept of the lithosphere as the solid outer layer of the Earth was first proposed by English mathematician Augustus Edward Hough Love in his 1911 monograph. The concept was further developed by American geologist Joseph Barrell, who introduced the term lithosphere. Canadian geologist Reginald Aldworth Daly further reinforced these concepts. The work of Love, Barrell and Daly is widely revered by the geophysicist and geologist communities, serving as the backbone of the theory of tectonic plates.

Composition of the lithosphere

The composition of the lithosphere varies depending on whether it is on land or under the oceans. It is known that the earth’s crust is not homogeneous and is composed of different layers of rock, including sedimentary (at the top), metamorphic (middle) and basalt rocks (bottom). In addition, the lithosphere is fragmented into several large tectonic plates which move slowly but continuously at an average speed of about 10cm.

Types of lithosphere

There are mainly two types of lithosphere: oceanic and continental.

oceanic lithosphere

ocean lithosphere
The seabed is part of the lithosphere.

Oceanic lithosphere refers to the lithosphere associated with the oceanic crust found beneath the seas and oceans. Oceanic lithosphere includes mafic crust and ultramafic mantle and tends to be comparatively denser than continental lithosphere. Young oceanic lithosphere is typically found on mid-ocean ridges, while old oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge, recycling at the mid-ocean ridge. oceanic. subduction areas.

This thickening of the oceanic lithosphere usually occurs through conductive cooling, where the hot asthenosphere is converted into a lithospheric mantle. It should be noted that the oceanic lithosphere is relatively younger than the continental lithosphere, and the oldest oceanic lithosphere is around 170 million years old.

Continental lithosphere

Layer of soil and rock on the earth’s crust forming the lithosphere.

Continental lithosphere refers to the lithosphere associated with continental crust. The average thickness of this lithosphere varies between 40 km and 280 km. The continental lithosphere represents approximately 40% of the earth’s surface and 70% of the volume of the earth’s crust. Scientists believe that the Earth originally had no continental crust, but eventually the fractional differentiation of oceanic crust led to the formation of continental crust.

The continental lithosphere is therefore quite old than the oceanic lithosphere, and the oldest parts of the continental lithosphere are found under the cratons. However, due to its relatively low density, continental lithosphere is not recycled in subduction zones, as it cannot subduct more than 100 km.

Subducted lithosphere

Several 21st century geophysical studies have revealed that there may be many large chunks of recycled lithospheric elements that have been subducted up to 2900 km into the mantle. There is a strong belief that some pieces of the lithosphere may still be floating in the upper mantle, and some pieces may descend about 400 km while still physically attached to continental plates higher on the Earth’s surface.

Importance of the lithosphere

Roots of plants growing in the lithosphere.

Being one of the main spheres of the Earth, the lithosphere greatly helps in the flourishing of life on the planet. The upper part of the lithosphere which chemically interacts with the other three spheres is called the pedosphere. Besides being a rich source of minerals, the lithosphere provides our forests, grasslands, agricultural lands, and lands for human settlements. The movement of tectonic plates is also responsible for the formation of mountains, volcanoes and continents.

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