Class 6 Notes

Class 6 Geography Notes Chapter 5 (Major Domains of the Earth) – The Earth Our Habitat

Philoid

Philoid

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study here the detailed notes for Chapter 5: Major Domains of the Earth, from the NCERT Class 6 Geography textbook 'The Earth Our Habitat', tailored for exam preparation.

Chapter 5: Major Domains of the Earth

1. Introduction

  • The Earth is the only planet known to have life.
  • Life exists because of the presence and interaction of three essential components or domains:
    • Lithosphere: The solid portion of the Earth.
    • Atmosphere: The gaseous layers surrounding the Earth.
    • Hydrosphere: The water bodies on Earth.
  • The narrow zone where these three domains meet, overlap, and interact, supporting life, is called the Biosphere.

2. Lithosphere (The Domain of Land)

  • Definition: The solid outer part of the Earth, consisting of the crust (rocks) and the thin layers of soil containing nutrient elements which sustain organisms.

  • Etymology: 'Lithos' means Stone (Greek).

  • Two Main Divisions:

    • Continents: Large, continuous masses of land.
    • Ocean Basins: Huge depressions on the Earth's surface filled with water (the basins themselves are part of the lithosphere).

  • Elevation: Land surface elevation is measured from the sea level (taken as zero).

  • Highest Point: Mount Everest (8,848 meters above sea level). (Note: Height may vary slightly in different sources/updates, but NCERT value is key).

  • Lowest Point (Greatest Depth): Mariana Trench (11,022 meters below sea level) in the Pacific Ocean.

  • Continents:

    • There are seven major continents, separated by large water bodies.
    • Listed in order of size (Largest to Smallest):
      1. Asia:
        • Largest continent.
        • Covers about one-third of the total land area.
        • Lies mostly in the Eastern Hemisphere.
        • The Tropic of Cancer passes through Asia.
        • Separated from Europe by the Ural Mountains (on the west).
        • The combined landmass of Europe and Asia is called Eurasia (Europe + Asia).
      2. Africa:
        • Second largest continent.
        • The Equator (0° latitude) runs almost through the middle.
        • A large part lies in the Northern Hemisphere.
        • The only continent through which the Tropic of Cancer, the Equator, and the Tropic of Capricorn pass.
        • The Sahara Desert, the world's largest hot desert, is located here.
        • Bounded by oceans and seas on all sides.
        • The Nile River, the world's longest river, flows through Africa.
      3. North America:
        • Third largest continent.
        • Linked to South America by a very narrow strip of land called the Isthmus of Panama.
        • Lies completely in the Northern and Western Hemispheres.
        • Surrounded by three oceans: Arctic (North), Atlantic (East), Pacific (West).
      4. South America:
        • Lies mostly in the Southern Hemisphere.
        • Surrounded by two oceans: Pacific (West), Atlantic (East).
        • The Andes, the world's longest mountain range, runs through its length from north to south.
        • Home to the Amazon River, the world's largest river by discharge volume.
      5. Antarctica:
        • Completely in the Southern Hemisphere.
        • A huge continent, centered around the South Pole.
        • Permanently covered with thick ice sheets (hence called the 'White Continent').
        • No permanent human settlements.
        • Many countries have research stations here (e.g., India's Maitri and Dakshin Gangotri).
      6. Europe:
        • Much smaller than Asia.
        • Lies to the west of Asia.
        • The Arctic Circle passes through it.
        • Bounded by water bodies on three sides.
      7. Australia:
        • Smallest continent.
        • Lies entirely in the Southern Hemisphere.
        • Surrounded on all sides by oceans and seas.
        • Often called the 'Island Continent'.

  • Isthmus: A narrow strip of land joining two large landmasses (e.g., Isthmus of Panama).

  • Strait: A narrow passage of water connecting two large water bodies like seas and oceans (e.g., Palk Strait between India and Sri Lanka).

3. Hydrosphere (The Domain of Water)

  • Definition: Refers to the water component of the Earth.

  • Etymology: 'Hudor' means Water (Greek).

  • Components: Includes water in all its forms – oceans, seas, rivers, lakes, ice caps, glaciers, underground water, and water vapour in the atmosphere.

  • Water Distribution:

    • More than 71% of the Earth is covered with water ('Blue Planet').
    • More than 97% of the Earth's water is found in the oceans (saline/salty, unfit for human use).
    • Only about 2.5-3% is freshwater.
    • Most freshwater is locked in ice sheets and glaciers, or as groundwater. A very small fraction is available as surface water (rivers, lakes).

  • Oceans:

    • Major part of the Hydrosphere. They are all interconnected.
    • Ocean waters are always moving. The three chief movements are waves, tides, and ocean currents.
    • There are five major oceans (Largest to Smallest):
      1. Pacific Ocean:
        • Largest ocean. Spreads over one-third of the Earth.
        • Mariana Trench, the deepest part, lies here.
        • Almost circular in shape.
        • Bordered by Asia, Australia, North America, and South America.
      2. Atlantic Ocean:
        • Second largest ocean.
        • 'S' shaped.
        • Flanked by North and South America on the west, and Europe and Africa on the east.
        • Has a highly indented coastline, providing ideal locations for natural harbours and ports (busiest ocean for commerce).
      3. Indian Ocean:
        • The only ocean named after a country (India).
        • Almost triangular in shape.
        • Bounded by Asia (North), Africa (West), and Australia (East).
      4. Southern Ocean:
        • Encircles the continent of Antarctica.
        • Extends northward to 60 degrees south latitude.
      5. Arctic Ocean:
        • Located within the Arctic Circle, surrounds the North Pole.
        • Connected to the Pacific Ocean by the narrow Bering Strait.
        • Bounded by the northern coasts of North America and Eurasia.

4. Atmosphere (The Domain of Air)

  • Definition: The thin blanket of air (gaseous layer) that surrounds the Earth.

  • Etymology: 'Atmos' means Vapour (Greek).

  • Importance:

    • Provides the air we breathe (Oxygen).
    • Protects us from the harmful effects of the sun's rays (Ozone layer).
    • Controls temperature extremes.

  • Extent: Extends up to about 1,600 km, but the significant atmosphere is much lower. Held to the Earth by gravity.

  • Composition:

    • Nitrogen (N2): ~78% (important for the growth of living organisms).
    • Oxygen (O2): ~21% (essential for breathing).
    • Other Gases: ~1% by volume, including:
      • Carbon Dioxide (CO2): Absorbs heat radiated by the Earth, keeping the planet warm (greenhouse effect). Essential for plant growth. (Increase in CO2 due to burning fuels leads to global warming).
      • Argon (Ar)
      • Others (Helium, Ozone, Hydrogen, etc.)

  • Structure (Layers based on composition, temperature, etc., starting from Earth's surface):

    1. Troposphere:
      • Lowest and densest layer.
      • Height varies (average ~13 km).
      • Almost all weather phenomena (rain, fog, clouds, storms) occur here.
      • Temperature decreases with height.
    2. Stratosphere:
      • Lies above the troposphere (up to ~50 km).
      • Contains the Ozone layer, which absorbs harmful ultraviolet (UV) radiation from the sun.
      • Free from clouds, ideal for flying airplanes.
    3. Mesosphere:
      • Lies above the stratosphere (up to ~80 km).
      • Meteorites burn up in this layer upon entering from space.
      • Temperature decreases with height.
    4. Thermosphere:
      • Extends from ~80 km to ~400 km+.
      • Temperature increases rapidly with height.
      • Contains the Ionosphere, a layer with electrically charged particles (ions) that help in radio transmission (radio waves are reflected back to Earth).
    5. Exosphere:
      • Uppermost layer.
      • Very thin air.
      • Light gases like Helium and Hydrogen float into space from here.

  • Properties:

    • Density: Maximum at sea level, decreases rapidly as we go up.
    • Temperature: Generally decreases with increasing altitude in the Troposphere.
    • Pressure: Air exerts pressure on the Earth's surface. This varies with location and altitude. Air moves from areas of high pressure to areas of low pressure – this movement is called wind.

5. Biosphere (The Domain of Life)

  • Definition: The narrow zone of contact between the land (Lithosphere), water (Hydrosphere), and air (Atmosphere) where life exists.
  • Etymology: 'Bio' means Life (Greek).
  • Scope: Includes all living organisms – from microscopic microbes and bacteria to huge mammals, plants, and humans.
  • Interdependence:
    • All living organisms are linked to each other for survival.
    • Organisms are also dependent on the three non-living domains (land, water, air).
  • Ecosystems: The Biosphere consists of several distinct zones, each with its own type of climate, plant, and animal life (ecosystems). Broadly divided into the Plant Kingdom and the Animal Kingdom.
  • Human Impact & Balance:
    • Human activities like deforestation (clearing land), agriculture, industries, settlement construction, pollution (air, water, land), and exploitation of resources can disturb the delicate balance of the Biosphere.
    • Example: Increased CO2 emissions lead to global warming. Discharge of waste into water bodies makes them unusable.
    • It is crucial to use Earth's resources in a limited way to maintain the balance between the domains of nature.

This covers the key points from Chapter 5 as per the NCERT Class 6 textbook, structured for easy understanding and revision for government exams. Remember to refer to the textbook for diagrams and maps which are also important.

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