This GSEB Class 8 Social Science Notes Chapter 2 What is Around Us? covers all the important topics and concepts as mentioned in the chapter.
What is Around Us? Class 8 GSEB Notes
→ The Earth is a member of the solar system. Among all the members of the solar system, only Earth has got suitable temperature, air and water required to sustain life.
→ There are four major spheres on Earth:
- Atmosphere and
→ Lithosphere: The solid part on which we live is known as the lithosphere. This layer occupies about 29 % of the surface of the Earth and is almost 64 km to 100 km thick. Landforms like mountains, plateaus, plains, valleys, etc. are seen on the lithosphere.
→ As we move towards the centre of the Earth, the temperature increases.
→ Rocks, which are in molten state in the interior of the Earth are known as ‘Magma’.
→ Many gases present in the interior rise up due to pressure and heat. But the pressure of rocks on Earth’s surface is equally strong. Thus a balance is maintained and the Earth’s crust does not break. However, if this balance is disturbed the crust breaks and a volcano erupts.
→ Lithosphere is useful in many ways. It is the home of mankind. It gives space for constructing homes, obtaining fresh water and land for cultivation as well as forests and useful minerals for industries.
→ Hydrosphere: The liquid component of Earth is called ‘Hydrosphere’. It includes oceans, seas, bays, straits, lakes, ponds, rivers, etc. The hydrosphere covers about 71 % of the Earth’s surface.
→ A water body that carries huge amount of water is known as an ‘Ocean’. Pacific, Atlantic, Indian and ‘ Arctic are the four oceans on Earth and they are connected to each other. These oceans are huge and deep and have valleys which are as deep as 10 to 11 km at their bottom. Ocean beds have features similar to that of the Earth’s surface with mountains, plateaus, vast plains, valleys, etc.
→ Oceans contain about 97 % of water on Earth and about 1 / 3rd of remaining water is trapped in ice-caps and glaciers.
→ Only some water is accumalated in lakes, while some flows into rivers and some is stored in the interior of the Earth as ground water.
→ The amount of potable water (water fit for drinking) or fresh water is very less. Fresh water being precious should be used with care and should not be wasted. Life cannot be sustained without fresh drinking water.
→ Moisture for rain, which is the main source of fresh water, comes from oceans. Valuable chemicals, fish, salt, minerals, etc. are obtained from seas and oceans. A large variety of aquatic life is sustained in oceans and seas. The tremendous force of waves, tides and ocean currents is a potential source for generating electricity. Oceans are also useful as waterways.
→ The sphere of air that wraps the Earth from all sides is called ‘Atmosphere’. It extends up to about 1600 km from the surface of the Earth and it cannot be seen clearly with the naked eye.
→ Various gases like nitrogen, oxygen, carbon dioxide, ozone, hydrogen, water vapour, dust particles, smoke, salt particles, micro-organisms, etc. make up the atmosphere, which is colourless, odourless and transparent.
→ Atmosphere contains about 78 % nitrogen, 21 % of oxygen, and 1 % other gases.
→ As we go higher from the surface of the Earth, the amount of these gases decreases. Carbon dioxide being heavy is found in more in the lower layer of air.
→ Ozone gas comprises a small proportion of air. This gas absorbs the ultra-violet rays of the Sun thus protecting the Earth from excessive heat of the Sun. This gas is more in proportion in the morning in open grounds or areas near the sea.
→ Oxygen and nitrogen gases sustain life on Earth. Nitrogen reduces the intensity of oxygen.
→ The most important component of atmosphere is water. Water evaporates due to heat and stays in the atmosphere in the form of water vapour.
→ The process of cooling of vapour is called ‘Condensation’. Various forms of moisture – dew, fog, clouds and precipitation are seen due to condensation.
→ Sound is heard only in the presence of atmosphere. Radio broadcasts and television are possible only due to atmosphere.
→ The dust particles in the atmosphere prove that sunrays spread in all directions.
→ That part of the lithosphere, hydrosphere and atmosphere where the living world exists is called ‘Biosphere’. This is one of the important spheres on Earth as this is the only planet in the solar system ‘ that has the biosphere. Biosphere includes human, beings, animals, vegetation and minute insects.
→ Human life is dependent on biosphere.
→ Biosphere is divided into:
- Non-living (Abiotic) and
- Living (Biotic).
→ The non-living or abiotic division includes lithosphere, hydrosphere and atmosphere. The living or biotic division includes micro-organisms, plants and animals.
→ The balance of the various spheres of Earth has been disturbed due to activities undertaken (knowingly or unknowingly) by humans for their own development.
→ All these activities affect the biosphere.