Our Earth consists of four main domains — the lithosphere, hydrosphere, and atmosphere. The hydrosphere includes all the water bodies of the Earth. The atmosphere constitutes the air surrounding the Earth. All the living organisms on Earth are a component of the biosphere. The lithosphere is where man and animals live and plants grow. It is also a reservoir for various natural resources. It is a home for different types of rocks on the Earth and the thin soil layers that contain nutrients and minerals that sustain organisms and support life on Earth. The Earth’s surface comprises three layers — crust, mantle and core. The crust is the outermost layer of the Earth. The crust and the outer part of the mantle contribute to form the lithosphere. The soil (pedosphere) is the part of the Earth where living organisms (biosphere), water bodies (hydrosphere), minerals (lithosphere), and air (atmosphere) coordinate and make life on the planet possible.
Evolution of lithosphere
- The Earth has a layered structure. The lithosphere is one of the layers of the Earth. Earth was in a volatile state in its primordial stage.
- Due to the gradual increase in density, the temperature started to increase. Therefore, the material inside started to segregate based on their concentration. This allowed heavier metals (like iron) to fall towards the Earth’s centre and the less dense ones to rise towards the Earth’s surface. This is how different layers of the Earth were formed.
- Take a bucket full of water and immerse some mud into it to understand this better. When water is mixed with the mud, it appears muddy. If you let this mixture settle for some time, you will observe that the water has become clean again as the mud particles have settled at the bottom of the bucket. This is because the mud particles have a higher density than the water. Similarly, on Earth, the density of every metal is different, due to which the metals with higher densities like iron and nickel sink towards the core. The metals which have a comparatively lower density, like aluminium, move towards the surface of the Earth.
- Over some time, cooling took place, resulting in the solidification of the lava due to condensation. This is how the crust was formed. The crust was the first layer to be formed.
- Changes in the lithosphere (crust) started to occur during the moon’s formation. This created a huge impact. The Earth, which had cooled and solidified again, started to heat up due to friction. Due to the increasing temperature, the dense materials again started to settle down at the bottom.
- Process of differentiation: The materials forming the Earth got separated into different layers. We got layers like the crust, mantle, and core. The layers have different densities.
Parts of lithosphere
There are two parts of the lithosphere — crust and upper mantle. The crust can be divided into — oceanic crust and continental crust. Oceanic crust is associated with the oceanic lithosphere; it exists in the oceanic bases. The continental crust is related to the continental lithosphere. We can find many mountain ranges, volcanoes, and huge planes in the continental lithosphere. We can also find volcanoes below the oceanic lithosphere. The oceanic crust is rich in two minerals — magnesium and silica, so it is called sima.
The continental crust contains mostly aluminum and silica, also called sial. Oceanic crust is thinner but denser than continental crust. Continental crust has lesser density, but it is thicker. This difference in density is because of the types of rocks they are made up of. There are three different rocks in the crust — igneous, sedimentary and metamorphic. Continental crust is a good mix of these three types of rocks, whereas the oceanic crust mainly consists of igneous rocks. Oceanic crust is mostly made up of rocks with a composition of basalt (a dark-colored rock). The continental is mostly made up of rocks with a composition of granite (a light-colored rock). The lithosphere is around 80-100 km thick.
Movement of the lithospheric plates
The lithosphere is the solid, outermost shell of the Earth. The whole lithosphere (land part) is broken into several plates. The blocks of landmass are known as lithospheric plates or tectonic plates. The lithosphere has seven large plates and several small plates. These plates move around very slowly. The movement is because of the molten magma inside the Earth. To understand this concept, let us take an example.
Have you ever observed boiling water? When water starts boiling, we notice bubbles develop on its surface due to the charges produced by the heat. The water bubbles keep dancing on the surface of the water. If we place a paper on this boiling water surface, we will notice that the paper moves here and there.
Similarly, the lithospheric plates lie on top of the hot molten magma. The hot magma goes up and down and moves circularly, like boiling water. So, the lithospheric plates on top keep moving continuously. We don’t feel the movement of the lithospheric plates because it occurs very, very slowly. When an earthquake occurs, the lithospheric plates move suddenly so that we can feel it. Earthquakes, volcanic activity, and mountain-building occur along the boundaries of these lithospheric plates. Their study helps geologists predict the onset of earthquakes, which helps us stay vigilant.
Formation of different types of rocks
- The molten material magma moves up and down, as discussed earlier. Sometimes it cools down and solidifies as it goes up. When this molten magma solidifies, the formation of Igneous rocks occurs. Igneous rocks are also called primary rocks as they were the first type of rocks to be formed.
- The deeper we go from the Earth’s surface towards the core, the temperature increases. So when the magma moves from the Earth’s surface towards the core, because of high temperature and pressure, the formation of a type of rock called metamorphic rock occurs. The name metamorphic is derived from the Greek term metamorphose, meaning change of form.
- If these two types of rocks undergo erosion, they break down and form sediments. These sediments fuse, compress and harden, and form sedimentary rocks. The name sedimentary is derived from the Latin term sediment; meaning settles down. These rocks may also contain fossils of plants, animals, and other microorganisms that once lived on them.
- Marble is formed from the sedimentary rock limestone when subjected to heat and pressure.
- This is how different types of rocks are formed in the lithosphere.
Lithosphere: Plateaus, plains, and mountains
- Plateaus: Plateau is a land with a flat top and a steep slope. A plateau looks like a tabletop. Plateaus cover about 1/3rd of the world’s land, so it is one of the major landforms of Earth.
- Plains: The plain is a large land area at the same elevation. Plains are formed as a result of erosion. Suppose there is a piece of land with a non-uniform elevation. With time, under the influence of wind and rain, the part of the elevated land erodes, giving way to land with a uniform elevation. Plains are also formed due to deposition; the wind and water carry soil with them and deposit it.
- Mountains: A mountain is a prominently elevated land with respect to its surroundings.
The Earth is in a constant state of change. We are discovering new things about it with every passing day. Geologists are continuously studying the complexities of the Earth better to understand our home and its place in the universe. There is still so much mystery that is left unknown.
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