WBBSE Class 6 Geography Chapter 5 Water Land Air Introduction
1. The blanket of air that envelopes the Earth and is held close to it because of the Earth’s gravitational force is called the Atmosphere. The atmosphere extends up to a height of 10000km to 15000 km above the Earth’s surface.
2. The lowest layer of the atmosphere extending up to 16km above the Earth’s surface, is known as the Troposphere.
3. The next layer after the troposphere up to a height of 50 km from the Earth’s surface is known as the Stratosphere.
4. The layer, above the stratosphere up to a height of 80 km from the Earth’s surface is known as the Mesosphere.
5. Above the mesosphere till 300 km from the Earth’s surface is the Thermosphere. Air becomes very thin in this layer. Gases in this layer are in an ionized state. So this layer is also known as the Ionosphere.
6. The outermost layer of the atmosphere, above the thermosphere where artificial satellites and space stations are located, is known as the Exosphere.
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7. The solid and thin outermost layer of the Earth is called the Crust.
8. The concentric layer in between the crust and the core is known as the Mantle.
9. The innermost layer; after the mantle around the center of the Earth, is known as the Core.
10. The solid landmass, made up of mostly rocks and soil is known as the Lithosphere. It forms only one-quarter of the Earth’s surface.
11. The total water content of the Earth in liquid, vapour or solid form together form the Hydrosphere.
12. Three-fourths of the Earth’s surface is water. No other planet in the solar system contains water to such a great extent. Thus, Earth appears blue from space and is called the Blue planet.
WBBSE Class 6 Earth Atmosphere Notes
13. The cyclic movement of water through solid, liquid and gaseous states from the Earth’s surface to the air and back on Earth is known as the Water cycle or the Hydrological cycle.
14. The movement of continents on the Earth’s surface under the influence of the convection currents generated in the magma present in the Earth’s interior is known as Continental drift.
15. Around 200 million years ago, there was only one unified continent or supercontinent. It was known as the Pangaea or, Pangea.
16. Pangaea was surrounded by a huge water mass or super ocean, known as the Panthalassa.
17. Difference in temperature in the Earth’s interior generates currents, known as Convention currents.
18. Land, water and air on Earth together create an environment that can support and sustain life. This region of the Earth occupied by living organisms is called the Biosphere. The numbers of plant and animal species in the biosphere are almost 35 thousand and 1.5 million respectively,
19. Human beings, an important part of the biosphere, interact with the environment. The more negative activities of human beings on the environment, the higher the degree of degradation of the environment.
20. The increase in the average temperature of the Earth’s atmosphere because of the heat trapped by the greenhouse gases in the air is called global warming.
Burning of fossil fuels and emissions from the factories lead to an increase of greenhouse gases (CO2, CH4, NO2 etc.) in the atmosphere.