Water and land on the Earth
Seen from space the Earth looks blue, so early astronauts fondly called it the "blue planet".
Almost three-fourths of the Earth's surface is covered with water; the largest water bodies are oceans. A large continuous expanse of land is a continent. Water and land are not shared equally between the Northern and Southern Hemispheres.
In the figure : The share of water and land on the Earth.
Rule 1: More water than land — Seawater is salty and unfit for most land animals to drink. Freshwater is a very small share, found in glaciers, rivers, lakes, the air and underground (groundwater).
- Easy : Seawater is not fit for drinking.
- Medium : Even with so much water we face scarcity because usable freshwater is little.
- Exam-type : What is groundwater? Answer: freshwater stored under the ground.
Rule 2: The two hemispheres differ — The Northern Hemisphere has more land; the Southern Hemisphere has more water.
- Easy : The Southern Hemisphere can be called the "water hemisphere".
- Medium : In the two maps drawn from above the poles, the circles are parallels and the radiating lines are meridians.
- Exam-type : Which hemisphere has more land? Answer: the Northern Hemisphere.
Even with so much water, saving freshwater is our responsibility.
Thinking all ocean water is usable. It is salty.
Water ¾, land ¼; salty water is plenty, fresh is little. Memory clue : 3 : 1 (water : land).
Spot the difference
| Term | Meaning | Example |
|---|---|---|
| Ocean | The largest water bodies | The Pacific Ocean |
| Continent | A large continuous landmass | Africa |
| Freshwater | Rivers, lakes, glaciers, groundwater | The Ganga river |
| Groundwater | Freshwater under the ground | Well water |
Practice questions
- 1How much of the Earth is covered with water?
- 2Why is the Earth called the "blue planet"?
- 3What is a continent?
- 4Where is freshwater found?
- 5Why is seawater not fit to drink?
- 6Which hemisphere has more water?
- 7Why do people speak of a "water crisis" despite so much water?
- 8Suggest two ways to save water at home or school.
Show answers (try them yourself first)
- 1Almost three-fourths.
- 2Because water makes it look blue from space.
- 3A large continuous expanse of land.
- 4In glaciers, rivers, lakes, the atmosphere and groundwater.
- 5Because it is salty.
- 6The Southern Hemisphere.
- 7Because the freshwater that can be used for drinking and farming is very small and not evenly available.
- 8Any two: repair leaking taps, harvest rainwater, close the tap while brushing.
The five oceans
The monsoon rain that India expects every summer begins over the ocean; without it our farming would suffer.
The Earth has five oceans: Pacific, Atlantic, Indian, Southern (Antarctic) and Arctic. They are connected; the boundary lines on a map are only conventions.
In the figure : The five oceans in order of size.
Rule 1: Oceans are connected and full of life — Seawater keeps flowing between oceans, so many plants and animals live in more than one. Marine plants include algae and seaweed; animals include fish, dolphins and whales.
- Easy : The Pacific is the largest ocean.
- Medium : The Indian Ocean is third largest and the Arctic is the smallest.
- Exam-type : What are the limits of the Indian Ocean? Answer: Asia to the north, Africa to the west, Australia to the east, the Southern Ocean to the south.
Rule 2: Oceans and disasters — Oceans bring rain but also cyclones and tsunamis. A tsunami is a huge wave caused by a strong earthquake or volcanic eruption on the sea floor.
- Easy : Monsoon rain comes from clouds formed over the sea.
- Medium : On 26 December 2004 a tsunami caused by an earthquake in Indonesia struck 14 countries including India; more than two lakh people died.
- Exam-type : How are people protected from tsunamis? Answer: through the Indian Ocean Tsunami Warning System, to which many countries including India contribute.
Early warning and disaster management save lives; India has the National Disaster Management Authority.
Thinking oceans are completely separate. They are connected.
Size order: Pacific > Atlantic > Indian > Southern > Arctic. Memory clue : P-A-I-S-A (Please Always Inspect Sea Areas).
Spot the difference
| Term | Meaning | Example |
|---|---|---|
| Pacific Ocean | The largest ocean | Contains the world's deepest parts |
| Indian Ocean | Third largest | Arabian Sea and Bay of Bengal are parts |
| Tsunami | Giant wave from a sea-floor quake | 26 December 2004 |
| Marine flora/fauna | Plants and animals of the sea | Algae, dolphins |
Practice questions
- 1Name the five oceans.
- 2Which is the largest ocean?
- 3Which is the smallest ocean?
- 4What is a tsunami?
- 5Name the two parts of the Indian Ocean on either side of India.
- 6Why are ocean boundaries called only "conventions"?
- 7State one difference between a cyclone and a tsunami.
- 8What is the use of a tsunami warning system?
Show answers (try them yourself first)
- 1Pacific, Atlantic, Indian, Southern and Arctic.
- 2The Pacific Ocean.
- 3The Arctic Ocean.
- 4A huge wave caused by an earthquake or volcanic eruption at the bottom of the sea.
- 5The Arabian Sea in the west and the Bay of Bengal in the east.
- 6Because seawater and sea life move freely between oceans; nature has no such boundaries.
- 7A cyclone is a storm with strong winds and rain; a tsunami is a huge wave caused by a sea-floor earthquake.
- 8It warns coastal areas in time so that lives and property can be saved.
Continents and islands
The five Olympic rings stand for sportspeople gathering from all over the world; they represent five inhabited continents.
The number of continents can be anything from 4 to 7 depending on how we count; the most widely used list has seven. An island is a smaller piece of land surrounded by water on all sides.
In the figure : The seven continents and India's two island groups.
Rule 1: The count of continents depends on how we count — North and South America can be counted as one, America. Europe and Asia together form Eurasia. Africa and Eurasia are sometimes joined too. So the count can be 4, 5, 6 or 7.
- Easy : The list of seven is the one most used.
- Medium : Counting Europe and Asia separately gives seven; as one gives six.
- Exam-type : Which are the four continents? Answer: Africa-Eurasia, America, Antarctica, Australia.
Rule 2: Islands and the islands of India — Greenland is the largest island in the world. India has more than 1,300 small islands in two groups: Andaman and Nicobar in the Bay of Bengal and Lakshadweep in the Arabian Sea. India's first research base in Antarctica was "Dakshin Gangotri" (1983).
- Easy : The Andaman and Nicobar Islands are in the Bay of Bengal.
- Medium : Lakshadweep is in the Arabian Sea.
- Exam-type : What is the difference between a continent and an island? Answer: a continent is a very large landmass; an island is smaller and surrounded by water.
Antarctica is an icy, very cold continent; India has been doing research there since 1981.
Treating continent and island as the same. Continents are too large to be called islands.
Seven: Asia, Africa, North America, South America, Antarctica, Europe, Australia. Memory clue : "A A N S A E A" — seven first letters.
Spot the difference
| Term | Meaning | Example |
|---|---|---|
| Continent | A very large landmass | Asia |
| Island | Smaller land surrounded by water | Greenland |
| Eurasia | Europe and Asia taken together | Geologists often use it |
| Dakshin Gangotri | India's first base in Antarctica (1983) | Two more bases later |
Practice questions
- 1Name the seven continents.
- 2Which is the largest continent?
- 3Which is the smallest continent?
- 4What is an island?
- 5Which is the largest island in the world?
- 6Name India's two island groups and say where they are.
- 7How can the number of continents be anywhere between 4 and 7?
- 8Why is India's research in Antarctica important?
Show answers (try them yourself first)
- 1Asia, Africa, North America, South America, Antarctica, Europe, Australia.
- 2Asia.
- 3Australia.
- 4A smaller piece of land surrounded by water on all sides.
- 5Greenland.
- 6Andaman and Nicobar in the Bay of Bengal; Lakshadweep in the Arabian Sea.
- 7Some continents are joined, so they can be counted as one or two, for example America, Eurasia and Africa-Eurasia.
- 8It helps study how climate and environment have evolved.
Oceans and life
Since early times people have used the sea for travel, trade and fishing; almost every coastal society has tales and deities of the sea.
Oceans bring rain, regulate climate and produce more than half of the world's oxygen, which is why they are called "the lungs of the planet". Pollution and overfishing from human activity now threaten them.
In the figure : Uses of oceans and the threats they face.
Rule 1: Oceans support life — Oceans give rain (the water cycle), keep climate balanced, give fish as food and, through marine plants, give oxygen.
- Easy : Fish come from the sea.
- Medium : Without oceans there would be no rain and the Earth would be a desert.
- Exam-type : Why are oceans called "lungs"? Answer: they produce more than half of the world's oxygen.
Rule 2: Protecting oceans is our duty — Several million tonnes of plastic enter the sea every year and choke marine life. Overfishing also reduces sea life. 8 June is World Oceans Day.
- Easy : Do not throw plastic into the sea.
- Medium : Overfishing means catching more fish than nature can replace.
- Exam-type : Suggest two steps to protect oceans. Answer: use less plastic, do not dump waste into the sea, limit fishing.
World Oceans Day: 8 June.
Thinking the sea is too big to be polluted. Human waste is already harming it.
Ocean = rain + oxygen + food + trade routes. Memory clue : R-O-F-T (Rain, Oxygen, Food, Trade).
Spot the difference
| Term | Meaning | Example |
|---|---|---|
| Water cycle | Sea water evaporates and returns as rain | The monsoon |
| Overfishing | Catching too many fish | Fish numbers fall |
| Marine pollution | Waste and chemicals entering the sea | Plastic waste |
| World Oceans Day | Reminder of the ocean's importance | 8 June |
Practice questions
- 1Why are oceans called "the lungs of the planet"?
- 2When is World Oceans Day?
- 3Name one cause of marine pollution.
- 4What is overfishing?
- 5How do oceans help in making rain?
- 6For which purposes have people used the oceans?
- 7What danger does plastic pose to sea creatures?
- 8What would happen on Earth without oceans?
Show answers (try them yourself first)
- 1They produce more than half of the world's oxygen.
- 28 June.
- 3Dumping plastic waste into the sea.
- 4Catching far too many fish.
- 5Seawater evaporates, forms clouds and falls as rain over land.
- 6For travel, trade, fishing and military campaigns.
- 7They swallow it or get tangled in it and choke.
- 8There would be no rain, climate would go wrong and the Earth would become a desert.