CBSE Class 6 Geography notes on the lithosphere

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. 

FAQs

1. What is a lithospheric plate?

The lithosphere is divided into certain plates that float on the hot molten magma beneath them. These plates keep on moving very slowly. We don’t feel the movement because it is very, very slow. The plates can be thought of as pieces of a cracked shell that rest on the hot, molten magma and fit snugly against one another. There are seven major plates and a few minor plates.

2. What is the biosphere?

The biosphere is a part of the Earth that harbors life. The biosphere represents a zone comprising the atmosphere (air), hydrosphere (water), and lithosphere (land). It is a thin layer around the surface of the Earth. If we visualize the Earth as the size of an apple, the biosphere would be as thick as its skin. Every living form is dependent on each other within the biosphere. The biosphere provides us with conditions favorable for survival, and in turn, we help maintain its existence.

3. Why is the atmosphere important?

• The atmosphere provides us with oxygen to breathe
• It provides the carbon dioxide to the plants for respiration 
• The atmosphere maintains the temperature for the survival of living organisms on Earth
• The atmosphere protects us from ultraviolet radiation
• It helps maintain the water cycle and the rock cycle
• The atmosphere plays a role in the transport of pollen grains and, therefore, facilitates pollination
• The atmosphere acts as a medium for us to fly drones and aeroplanes
• The atmosphere creates a path for the birds to fly
• Without the atmosphere, life on Earth wouldn’t be possible

4. What are some fun facts about Earth?

• Earth is the third planet from the Sun and the only astronomical object known to support life.
• Earth revolves around the Sun for 365 days. A period is known as an Earth year.
• The Earth is one of the densest and largest planets.
• More than half of the Earth is covered by water bodies like oceans, rivers, and seas.
• Earth is round, but it is not a perfect sphere.
• More than 7.7 billion humans depend on the Earth’s lithosphere, biosphere, and atmosphere for their survival. 
• If an earthquake of more than 12 magnitude hits Earth, it will rip the Earth apart. We have never had an earthquake of more than 9.6 magnitudes. 

5. What is the lithosphere?

The lithosphere is the solid crust or the hard top layer of the Earth. It contains rocks and minerals and is covered by soil and grass. Humans use the landforms to develop their habitats. The lithosphere provides us with a solid surface where we can cultivate crops to produce our food and grow grass for animals to feed on. We build our homes and offices on its surface. We carry out activities like walking, running, playing, and swimming in the lithosphere. It also contains important minerals.

6. How is the lithosphere helpful for humans?

• We cultivate plants and crops in the lithosphere. Without the lithosphere, we won’t be able to produce food.
• The lithosphere provides nutrients and minerals to support the growth of plants. 
• The lithosphere provides minerals like iron, aluminum, and nickel that act as raw materials for industries. Precious metals like gold and diamonds are extracted from the deepest layers of the lithosphere. 
• The lithosphere provides us with a solid surface where we humans build our homes, offices, and other structures. 
• We extract fuels like coal and petroleum from the lithosphere. 
• The movement of the lithospheric plates leads to the development of earthquakes. This allows the Earth to keep constantly changing and form new habitats.
• The lithosphere holds water bodies such as lakes, rivers, and oceans that are very important for life on Earth.

7. How many chapters in Geography in the CBSE Class 6 textbook?

There are eight chapters in total in Geography CBSE textbooks. These chapters cover all the essential information regarding the domains of the Earth. Special emphasis has been made on educating the students about the geography of our country India. It is important to be acquainted with the geography of one’s own country to understand its landforms and resources better.