RBSE Class 7 Social Science Notes Geography Chapter 3 Our Changing Earth

These comprehensive RBSE Class 7 Social Science Notes Geography Chapter 3 Our Changing Earth will give a brief overview of all the concepts.

RBSE Class 7 Social Science Notes Geography Chapter 3 Our Changing Earth

→ Lithospheric plates and their movement

• The lithosphere is broken into a number of plates known as the Lithospheric plates.
• These plates move around very slowly-just a few millimetres each year.
• The movement of these plates causes changes on the surface of the earth.
• The forces which act in the interior of the earth are called as Endogenic forces and the forces that work on the surface of the earth are called as Exogenic forces.
• Endogenic forces sometimes produce sudden movements and at the other times produce slow movements.

→ Volcanoes: A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly.

→ Earthquakes:

• When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth. These vibrations are called earthquakes.
• The place in the crust where the movement starts is called the focus. The place on the surface above the focus is called the epicentre. Greatest damage is usually dosest to the epicenter.
• There are three types of earthquake waves :
  (a) P waves or longitudinal waves,
  (b) S waves or transverse waves,
  (c) L waves or surface waves.
• An earthquake is measured with a machine called a seismograph. The magnitude of the earthquake is measured on the Richter scale.

→ Major Land Forms:

• The landscape is being continuously worn away by two processes-weathering and erosion.
• Weathering is the breaking up of the rocks on the earth’s surface.
• Erosion is the wearing away of the landscape by different agents like water, wind and ice.

→ Work of a River: The running water in the river erodes the landscape. Water falls, eruptions, arcades, plains and deltas are formed by the waters of rivers. 

→ Work of Sea Waves: The erosion and deposition of the sea waves gives rise to coastal landforms. They are sea caves, sea arches, stacks, sea cliff etc.

→ Work of Ice: Glaciers are “rivers of ice” which too erode the landscape by bulldozing soil and stones to expose the solid rock below. They are deep trough, beautiful lake, glaciers, snow etc.

→ Work of wind: An active agent of erosion and deposition in the deserts is wind. The topography made by winds are mushroom rocks,‘sand dimes, loess etc.