Friday , September 25 2020
NCERT 5th Class (CBSE) Social Science: Movements of the Earth – Their effect

NCERT 7th Class (CBSE) Social Science: The Changing Face of the Earth

Question: Define “Lithospheric Plates”.

Answer: According to the theory, the lithosphere is broken up into number of pieces called tectonic or lithospheric plates. It consists of crust and outer parts of upper mantle. There are six major and 20 minor plates, all of which floats independently.

Question: Distinguish between endogenetic and exogenetic forces.

Answer: The difference is as follows:

Endogenetic Forces
Exogenetic Forces
1. These are internal changes.
1. These are external changes.
2. These changes are slow or continuous or sudden. These forces also cause horizontal or vertical movements.
2. These changes are the result of depositional work or erosional work by rivers, winds, glaciers etc. it can be noticeable in 100-1000 years. 
3. For example – Sudden: Earthquakes, Landslides or volcanic eruptions. Slow: Mountain building.
3. For example – Land forms caused by gradation of the earth.

Question: Why do tectonic plates move?

Answer: The rigid lithospheric plates float in the semi-molten rocks of the lower portion of the upper mantle, which is called asthenosphere. The temperature in the asthenosphere is high around 1600° C. At this temperature, the rocks are in a near molten state and they can flow in a thick and viscous way. Therefore tectonic plates are always moving.

Question: What is the difference between erosion and deposition?

Answer: The difference is as follows:

Erosion is the process of eroding or being eroded by wind, water or other natural agents.
Deposition is the process by which sediments settles out of the water or wind that is carrying it, and is deposited in a new location.

Question: What causes earthquakes?

Answer: Earthquakes:

  1. They are vibrations that move through the earth and over its surface.
  2. They are caused by disturbances that originate inside the earth.
  3. Sudden movements deep beneath the surface, like the rupture of rocks and the collision of tectonic plates, release an enormous amount of energy in the form of seismic or shock waves.
  4. These seismic waves travel to the surface and cause earthquakes.

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One comment

  1. it is quite a concept which you do a not understand.

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