NCERT Solutions for Class 7 Geography Social Science Chapter 3 Our Changing Earth

(i) The movement of molten magma inside the earth results in the movement of plates.

(ii)  The movement of the Earth is divided on the basis of the forces which cause them. The forces that act in the interior of the earth are called endogenic forces, and the forces that work on the surface of the earth are called exogenic forces.

(iii) Erosion is defined as the wearing away of the landscape by different agents like water, wind and ice. The process of erosion and deposition creates different land-forms on the surface of the earth.

(iv)  When a river overflows its banks, it results in the flooding of the area surrounding it. When it floods, it deposits a layer of fine soil and other material called sediments, thus forming a fertile layer of soil called flood plains.

(v) When the wind blows, it lifts and transports sand from one place to another. When the wind stops blowing, the sand falls and gets deposited in the low hill-like structures. These are called sand dunes. They are mostly found in desert areas.

(vi) The sea waves deposit sediments along the seashores. This results in the formation of beaches.

(vii) The sea waves deposit sediments along the seashores. This results in the formation of beaches.

(i) b

(ii) c

(iii) a

(iv) a

(v) b

(i)  Some rocks have the shape of a mushroom because, in deserts, wind erodes the lower section of the rock more than the upper section, which makes the base of the rock narrow and the upper part wide, giving it the shape of a mushroom.

(ii)  Flood plains are very fertile because at times when river water overflows, it results in the flooding of the neighbouring areas. This deposits a layer of fine soil and other sediments on the banks of the river, which leads to fertile flood plains.

(iii)  When the cavities in the sea caves become bigger and bigger, only the roof of the caves are leftover, which forms sea arches. Further, due to erosion, the roof vanishes and only the walls stay intact, turning the sea caves into stacks.

(iv)  When the lithospheric plates move, the surface of the earth vibrates and then these vibrations travel outwards from the epicentre in the form of waves, which leads to sudden movement and results in the collapse of buildings.