Source: Exploring Society – The Earth: Our Habitat, Class VI, Pages 30–38 Class: VI | Subject: Geography
Section 1. The Four Domains of the Earth 🌍
Earth is the only planet with life – land, water, and air are all present here. The surface of the earth has three main parts that meet, overlap, and interact.
| Domain | Definition |
|---|
| Lithosphere | The solid portion of the earth – rocks of the crust and thin layers of soil |
| Hydrosphere | All water on earth – in the form of ice, liquid water, and water vapour |
| Atmosphere | Gaseous layers surrounding the earth – oxygen, nitrogen, carbon dioxide, and other gases |
| Biosphere | The narrow zone where land, water, and air meet – contains all forms of life |
🔑 Lithos = Stone | Atmos = Vapour | Hudor = Water | Bios = Life
Section 2. Lithosphere 🌍
- The Lithosphere = solid part of earth; made of rocks of the crust and thin layers of soil.
- Two main divisions: Continents (large landmasses) and Ocean basins (huge water bodies).
- Elevation of land is measured from sea level = zero.
- Highest point: Mt. Everest – 8,848 m | Greatest depth: Mariana Trench – 11,022 m (Pacific Ocean)
Section 3. Continents ⚙️
Seven continents separated by large water bodies. Greater part of land lies in the Northern Hemisphere.
| Continent | Key Facts |
|---|
| Asia | Largest (one-third of earth's land area); separated from Europe by Ural Mountains |
| Europe | Much smaller than Asia; Arctic Circle passes through it |
| Africa | 2nd largest; only continent through which Tropic of Cancer, Equator, and Tropic of Capricorn all pass; has Sahara (world's largest hot desert) and Nile (world's longest river) |
| North America | 3rd largest; linked to South America by Isthmus of Panama |
| South America | Has Andes (world's longest mountain range) and Amazon (world's largest river) |
| Australia | Smallest continent; entirely Southern Hemisphere; called island continent |
| Antarctica | Completely Southern Hemisphere; South Pole near centre; permanently covered with thick ice; no permanent human settlements; India's stations: Maitri and Dakshin Gangotri |
🔑 Europe + Asia = Eurasia
- Isthmus – narrow strip of land joining two landmasses
- Strait – narrow passage of water connecting two large water bodies
Section 4. Hydrosphere 🌍
- Earth = blue planet – more than 71% water, 29% land.
- More than 97% of earth's water is in oceans – too salty for human use. Only 2.5% is fresh water.
- Despite being a blue planet, we face a shortage of usable water.
| Type | % |
|---|
| Ocean water (salty) | 97.5% |
| Fresh water | 2.5% |
Section 5. Oceans ⚙️
Five major oceans – all interconnected. Three movements of ocean water: waves, tides, currents.
| Ocean | Key Facts |
|---|
| Pacific | Largest; covers one-third of earth; Mariana Trench lies here |
| Atlantic | 2nd largest; S-shaped; most indented coastline; busiest for commerce |
| Indian | 3rd largest; only ocean named after a country (India); triangular shape |
| Southern | Encircles Antarctica; extends to 60° south latitude |
| Arctic | Smallest; surrounds the North Pole; within the Arctic Circle |
Section 6. Atmosphere ⚙️
- Thin blanket of gas around earth; provides air to breathe; protects from sun's harmful rays.
- Height: about 1,600 km.
- Five layers (surface upward): Troposphere → Stratosphere → Mesosphere → Thermosphere → Exosphere
| Gas | % | Role |
|---|
| Nitrogen | 78% | Growth of living organisms |
| Oxygen | 21% | Breath of life |
| CO₂ + others | 1% | CO₂ keeps planet warm; essential for plants |
- Density maximum at sea level, decreases upward.
- Air moves from high pressure → low pressure = wind.
Section 7. Biosphere 🌿
- Narrow zone where land, water, and air meet – only place on earth where life exists.
- Organisms: microbes to mammals; divided into plant kingdom and animal kingdom.
- Human impacts: cutting forests → soil removal; waste into water → water unusable; increase in CO₂ → global warming.
- Need to limit use of earth's resources to maintain balance between the domains.
Common Confusions ⚠️
| Confusion | Clarification |
|---|
| Lithosphere vs Atmosphere | Lithosphere = solid land/rocks; Atmosphere = gaseous air layer around earth |
| Hydrosphere vs Biosphere | Hydrosphere = all water; Biosphere = narrow zone where land + water + air meet and life exists |
| Isthmus vs Strait | Isthmus = narrow strip of LAND; Strait = narrow passage of WATER |
| Australia vs other continents | Australia = only continent surrounded on ALL sides by ocean – hence "island continent" |
Memory Aids 💡
| What to Remember | Mnemonic |
|---|
| Four domains | 💡 LAHB – Lithosphere, Atmosphere, Hydrosphere, Biosphere |
| Five oceans in size order | 💡 PAISE – Pacific, Atlantic, Indian, Southern, Arctic |
| Five atmosphere layers (bottom → top) | 💡 "Try Sitting More Than Everybody" – Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere |
| Africa has all three latitudes | 💡 Africa wears THREE BELTS – Cancer (top), Equator (middle), Capricorn (bottom) |
Exam Corner 🎯
| Question | Answer Pointer | Ref |
|---|
| Q1(a) Four major domains | Lithosphere, Hydrosphere, Atmosphere, Biosphere | p.37 |
| Q1(b) Major continents | Asia, Europe, Africa, N.America, S.America, Australia, Antarctica | p.37 |
| Q1(c) Two continents entirely in Southern Hemisphere | Australia and Antarctica | p.37 |
| Q1(d) Layers of atmosphere | Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere | p.37 |
| Q1(e) Why 'blue planet'? | More than 71% of earth covered by water | p.37 |
| Q1(f) Why Northern Hemisphere = Land Hemisphere? | Greater part of land mass lies in Northern Hemisphere | p.37 |
| Q1(g) Why Biosphere important? | Only zone with land + water + air together; all life depends on it for survival | p.37 |
| Q2(a) Range separating Europe from Asia | Ural Mountains | p.38 |
| Q2(b) N.America linked to S.America by | Isthmus of Panama | p.38 |
| Q2(c) Major atmospheric constituent by % | Nitrogen (78%) | p.38 |
| Q2(d) Domain of solid rocks | Lithosphere | p.38 |
| Q2(e) Largest continent | Asia | p.38 |
| Q3(a) Deepest point on earth | Mariana Trench (Pacific Ocean) | p.38 |
| Q3(b) Ocean named after a country | Indian Ocean | p.38 |
| Q3(c) Narrow contact zone of land, water and air | Biosphere | p.38 |
| Q3(d) Europe + Asia together | Eurasia | p.38 |
| Q3(e) Highest mountain peak | Mt. Everest | p.38 |
| Map Skills | Mark: Europe, Asia, Antarctica, S.America, Australia, Indian Ocean, Pacific Ocean, Atlantic Ocean, Ural Mountains, Isthmus of Panama | p.38 |
Abbreviation Legend
| Abbreviation | Full Form |
|---|
| CO₂ | Carbon dioxide |
| km | Kilometres |
| m | Metres |
