Overview
Seen from space, the Earth is mostly blue, because water covers almost three-fourths of its surface. This chapter explores the great oceans and continents. You learn how water and land are shared unevenly: the Northern Hemisphere holds much more land, the Southern is mostly ocean. You find out why, on a planet full of water, fresh water is still scarce, and what each of us can do to save it. You meet the five oceans, from the huge Pacific to the small Arctic, and discover that they are really one connected body full of marine life. You locate the Indian Ocean with the Arabian Sea and the Bay of Bengal on either side of India. The chapter shows how the ocean brings the monsoon but also cyclones and tsunamis, such as the disaster of December 2004, and how early warning saves lives. You see why continents can be counted as four to seven, learn the usual seven by size, explore islands including India's own, and learn about India's research in Antarctica. Finally, you understand why oceans are called the planet's lungs and why we must protect them from plastic, pollution and overfishing.
हिंदी में पढ़ें
नीले ग्रह के पाँच महासागर और सात महाद्वीप, मीठा पानी, द्वीप, समुद्री आपदाएँ और महासागरों की रक्षा क्यों ज़रूरी है।
Learning Objectives
- Describe how water and land are distributed on the Earth and between the hemispheres
- Explain why fresh water is scarce and suggest ways to save it
- Name and locate the five oceans in order of size
- Explain how oceans bring rain and describe cyclones and tsunamis
- Explain why continents can be counted in different ways and list the seven continents by size
- Define an island and name India's two major island groups
- Describe India's scientific work in Antarctica
- Explain the importance of oceans for life and how to protect them
Topics in this chapter
7 topics · tap a topic title to jump straight to it.
The blue planet: how water and land are shared
1Think first
2The idea, in plain words
Look at a photograph of the Earth taken from space. The first thing you notice is blue, everywhere. Early astronauts were so struck by this that they lovingly called the Earth the blue planet.
Mostly water. The blue is water. Almost three-fourths of the Earth's surface (about 71 per cent) is covered by water, and only a little more than one-fourth (about 29 per cent) is land. The very large bodies of salt water are called oceans. Their smaller parts, partly closed in by land, have other names such as sea, bay and gulf. The Arabian Sea and the Bay of Bengal are examples near India.
Land. In the same photograph, brown and green patches show land. A large body of land is called a landmass, and a very large continuous stretch of land is called a continent. The white swirls you see are clouds.
Not shared equally. If you look at the Earth from above the North Pole and then from above the South Pole, you notice a difference. The Northern Hemisphere has much more land; the Southern Hemisphere is mostly ocean.
| Hemisphere | Water (about) | Land (about) |
| Northern | 61 per cent | 39 per cent |
| Southern | 81 per cent | 19 per cent |
| Whole Earth | 71 per cent | 29 per cent |
So most of the world's people, cities and farms are in the Northern Hemisphere, where most of the land is. India is one of them.
Why this matters. Oceans and continents together shape the Earth's climate: where it rains, how hot or cold it gets, and how winds blow. That in turn affects every plant and animal, including human beings, our history, our culture and our daily lives.
The ocean in Indian tradition. The emblem of the Indian Navy carries the motto Sham no Varunah, meaning 'Be auspicious to us, O Varuna'. Varuna is a Vedic deity linked with the oceans, the sky and water. This shows how long the sea has been part of India's thinking.
- Earth's surface: about 71% water + about 29% land
- Northern Hemisphere: more land; Southern Hemisphere: more water
3Worked example
- From space the Earth looks mostly blue because about 71 per cent of its surface is water.
- The Arabian Sea and the Bay of Bengal are parts of the Indian Ocean.
- Indian Navy motto: Sham no Varunah, an invocation to Varuna.
4Your turn
Which hemisphere has more land?
5Remember this
Salt water and fresh water
1Think first
2The idea, in plain words
There is water almost everywhere on the Earth, so why do we hear about a 'water crisis' and see people in many towns waiting for water tankers? The answer is in what kind of water it is.
Most water is salty. The oceans hold most of the water on our planet, about 97 out of every 100 litres. But seawater is salty. Humans and most land animals cannot drink it, and crops cannot be watered with it.
Fresh water is scarce. Only a small share, about 3 out of every 100 litres, is fresh water, and much of that is frozen. Fresh water is found in:
- glaciers and ice sheets, mostly near the poles and on high mountains;
- rivers and lakes;
- the atmosphere, as water vapour and clouds;
- under the ground, where it is called groundwater and reaches us through wells and hand pumps.
So the water we can actually use for drinking, cooking, bathing and farming is only a tiny part of all the Earth's water.
Why water becomes scarce. More people, more farms and more factories all need fresh water. When groundwater is pumped out faster than rain can refill it, wells run dry. When rivers and lakes are polluted, their water becomes unsafe. That is how a 'water crisis' can happen on a planet covered with water.
Saving water. Every family, school and town can help:
- Turn off taps while brushing teeth; fix leaking taps and pipes.
- Collect rainwater from rooftops and store it or let it soak into the ground.
- Reuse water, for example water used to wash vegetables can water plants.
- Use drip irrigation in farms so water goes straight to plant roots.
Think about it. Which of these do you see at home or in school? Can your class start one new water-saving habit this month?
- Earth's water: about 97% salty + about 3% fresh
- Fresh water sources = glaciers + rivers + lakes + atmosphere + groundwater
3Worked example
- Out of 100 litres of the Earth's water, about 97 are salty sea water.
- A hand pump draws up groundwater.
- Rooftop rainwater harvesting stores rain for later use.
4Your turn
Why can't we drink seawater directly?
5Remember this
The five oceans
1Think first
2The idea, in plain words
If you could sail a boat from India, could you reach America without ever touching land? Yes, because all the oceans are joined.
Five oceans. On a world map we usually name five oceans. From largest to smallest they are:
| Rank | Ocean | Where it is |
| 1 | Pacific Ocean | Between Asia and Australia on one side and the Americas on the other; the largest and deepest |
| 2 | Atlantic Ocean | Between the Americas and Europe and Africa |
| 3 | Indian Ocean | South of Asia, between Africa and Australia |
| 4 | Southern (Antarctic) Ocean | All around Antarctica |
| 5 | Arctic Ocean | Around the North Pole; the smallest, often frozen |
One world ocean. The lines that separate the oceans on a map are only conventions, agreements made by people. Nature does not follow them. Seawater keeps flowing from one ocean to another, and many plants and animals live in several oceans. So in a real sense there is one great world ocean with five names.
Our ocean. The Indian Ocean is the only ocean named after a country. It is bounded by Asia to the north, Africa to the west, Australia to the east and the Southern Ocean to the south. On either side of India are two of its arms: the Arabian Sea to the west and the Bay of Bengal to the east.
Life in the oceans. Anything that belongs to or lives in the sea is called marine. The plant life of a region is its flora and its animal life is its fauna. Marine flora includes tiny plants called algae and many kinds of seaweed. Marine fauna includes thousands of kinds of colourful fish, dolphins, whales, sharks, turtles, starfish and strange creatures of the deep. Coral reefs, built by tiny animals in warm shallow seas, are among the richest homes of life on Earth.
Layers of life. Each part of the ocean has its own living things, from the sunlit surface, where algae grow, to the cold, dark depths, where some fish make their own light.
- Oceans by size: Pacific > Atlantic > Indian > Southern > Arctic
- Marine = of the sea; flora = plants; fauna = animals
3Worked example
- The Pacific is the largest ocean; the Arctic is the smallest.
- The Arabian Sea lies west of India and the Bay of Bengal east of it.
- Algae and seaweed are marine flora; dolphins and whales are marine fauna.
4Your turn
Why are the boundaries between oceans called 'conventions'?
5Remember this
Oceans, monsoon rain and disasters
1Think first
2The idea, in plain words
Every summer, farmers across India look at the sky and wait for the monsoon. Where do those rain clouds come from? They come from the ocean.
The gift of rain. The Sun heats the ocean and water rises into the air as vapour. The vapour forms clouds, and winds carry them over the land, where they fall as rain. The monsoon rains that India depends on every summer begin over the Indian Ocean. Without them, crops would fail, rivers and wells would dry up, and all life would suffer.
Storms from the sea. The ocean can also be dangerous. Over warm seas, huge spinning storms called cyclones form. They bring very strong winds and extremely heavy rain, and can flood and damage coastal towns and villages. India's east coast on the Bay of Bengal often faces cyclones.
Tsunamis. A tsunami is a gigantic, powerful wave. It is usually caused by a strong earthquake or a volcanic eruption on the ocean floor. A tsunami can travel thousands of kilometres across the ocean and then rise into a wall of water that floods the coast.
The 2004 tsunami. On 26 December 2004, a powerful earthquake near Indonesia set off a tsunami in the Indian Ocean. It struck India and 13 other countries. More than two lakh people lost their lives. In India, the Andaman and Nicobar Islands and the coasts of Tamil Nadu and Kerala suffered terrible damage.
Warning in time. Tsunamis are rare, and they can often be detected before they reach the coast. Countries work together in early warning systems. The Indian Ocean Tsunami Warning System, to which India contributes, sends alerts so that people can move to higher ground in time.
Disaster management. Planning to prevent, prepare for and respond to events that cause loss of life and property is called disaster management. India has a National Disaster Management Authority (NDMA) for all kinds of disasters.
| Event | Cause | Main danger |
| Cyclone | Very warm sea and spinning winds | Strong winds, heavy rain, floods on the coast |
| Tsunami | Earthquake or volcano under the sea | Giant waves that flood the coast |
- Ocean water -> vapour -> clouds -> rain on land
- Tsunami = giant wave from an undersea earthquake or volcanic eruption
3Worked example
- The monsoon rains that feed Indian farms begin over the Indian Ocean.
- The 26 December 2004 tsunami hit the Andaman and Nicobar Islands, Tamil Nadu and Kerala.
- The Indian Ocean Tsunami Warning System sends early alerts.
4Your turn
What usually causes a tsunami?
5Remember this
Continents: how many and how big
1Think first
2The idea, in plain words
Ask five people how many continents there are and you might get different answers! Some say seven, some say six, and a few say five or even four. Surprisingly, they can all be right.
Why counts differ. A continent is a very large, continuous stretch of land. But where one continent ends and another begins is partly a matter of choice:
- North and South America are usually counted as two, but they are joined by a narrow strip of land, so some count them as one, 'America'.
- Europe and Asia form one single landmass. Because their histories and cultures developed very differently, they are usually counted as two. Geologists often treat them as one continent, Eurasia.
- Africa and Eurasia are usually two, but sometimes counted as one.
| Count | Continents |
| Four | Africa-Eurasia, America, Antarctica, Australia |
| Five | Africa, America, Antarctica, Australia, Eurasia |
| Six | Africa, Antarctica, Australia, Eurasia, North America, South America |
| Seven | Africa, Antarctica, Asia, Australia, Europe, North America, South America |
The usual count: seven. The list of seven is the one most widely used, and we use it too. In order of size, from largest to smallest, they are: Asia, Africa, North America, South America, Antarctica, Europe and Australia.
Asia, our continent. India is part of Asia, the largest continent by far. Asia alone covers almost one-third of all the land on Earth and has more people than any other continent.
The Olympic rings. The five rings of the Olympic Games stand for five inhabited continents: Africa, America, Asia, Australia and Europe. Antarctica is left out because no one lives there permanently.
Size, not shape. A diagram that shows each continent as a block of equal squares helps us compare sizes, even though it does not show real shapes. For example, Africa is larger than North America, and Antarctica is larger than both Europe and Australia.
- Asia > Africa > North America > South America > Antarctica > Europe > Australia
- Eurasia = Europe + Asia
3Worked example
- Seven continents, largest to smallest: Asia, Africa, North America, South America, Antarctica, Europe, Australia.
- Europe plus Asia together are called Eurasia.
- The five Olympic rings stand for five inhabited continents.
4Your turn
Which is the smallest continent in the seven-continent list?
5Remember this
Islands, and India in Antarctica
1Think first
2The idea, in plain words
Look carefully at a world map and you will see many small pieces of land that are not part of any continent. What are they?
Islands. A piece of land surrounded by water on all sides is an island. Continents are also surrounded by water, but they are so huge that we do not call them islands. There are lakhs of islands on our planet, from tiny rocks to very large lands.
The largest island. Greenland, in the far north near the Arctic Ocean, is the largest island in the world. It is so big that you would need to add up the areas of the ten largest States of India to equal it. Most of it is covered with thick ice.
India's islands. India has more than 1,300 small islands. There are two major groups:
| Island group | Sea | Side of India |
| Andaman and Nicobar Islands | Bay of Bengal | East |
| Lakshadweep Islands | Arabian Sea | West |
Antarctica, the frozen continent. Antarctica, around the South Pole, is the coldest continent. It is almost entirely covered by a thick sheet of ice, so it looks like a white cap at the bottom of the globe. Fierce winds blow, and no one lives there permanently. Only scientists stay there, in research stations.
India in Antarctica. Since 1981, the Indian Antarctic Programme has been sending expeditions to Antarctica. In 1983 India set up its first research station there, named Dakshin Gangotri. Two more stations were set up later. About 40 teams of Indian scientists have worked in this faraway land, studying especially how the Earth's climate and environment have changed over time. The scientists' settlement even has a library and a post office!
Why study ice? Antarctic ice was formed from snow that fell over thousands of years. Tiny bubbles of old air are trapped inside it. By studying ice and rocks, scientists learn about the climate of the past, which helps them understand how the climate may change in future.
- Island = land with water on all sides (smaller than a continent)
- India: 1,300+ islands; 2 major groups
3Worked example
- Greenland is the world's largest island.
- Lakshadweep lies in the Arabian Sea; the Andaman and Nicobar Islands lie in the Bay of Bengal.
- Dakshin Gangotri (1983) was India's first research station in Antarctica.
4Your turn
In which sea are the Lakshadweep Islands?
5Remember this
Oceans and life: why we must protect them
1Think first
2The idea, in plain words
Take a deep breath. Some of the oxygen you just breathed in was very likely made in the ocean! The oceans affect our lives every day, even when we live far from the sea.
Rain and climate. Oceans send water vapour into the air, which falls as rain on the continents. This is part of the Earth's water cycle, which you will study in Science. Without oceans there would be no rain, and the land would become a desert. Oceans also store heat and slowly release it, which keeps the Earth's climate steady.
The planet's lungs. Tiny plants and algae in the sea make more than half of the world's oxygen. That is why oceans are called 'the planet's lungs'.
Oceans and people. Since early times, people have used the oceans:
- to travel and migrate to new lands;
- to trade goods such as spices, cloth and grain;
- for food, through fishing;
- for military campaigns and defence.
Coastal peoples all over the world have songs, stories and festivals about the sea, about sea gods and goddesses, sea monsters and treasures, showing both its dangers and its blessings.
Oceans in danger. Scientists have found that human activity is harming the oceans:
- Several million tonnes of plastic waste enter the oceans every year. Turtles, fish and birds swallow it or get tangled in it.
- Sewage, chemicals and oil spills pollute the water.
- Overfishing, catching fish faster than they can breed, makes many kinds of fish fewer every year.
Our responsibility. The United Nations marks 8 June as World Oceans Day to remind everyone how much we depend on the ocean for oxygen, food and medicine. Protecting the oceans is everyone's job: say no to single-use plastic, never throw waste on beaches or into rivers (rivers carry it to the sea), and support rules against overfishing.
- Oceans -> vapour -> rain on land (water cycle)
- Threats to oceans = plastic + pollution + overfishing
3Worked example
- Algae and other sea plants make more than half of the world's oxygen.
- A plastic bag dropped in a river can end up in the sea and harm a turtle.
- World Oceans Day is 8 June.
4Your turn
Why are the oceans called 'the planet's lungs'?
5Remember this
Key Concepts
- Ocean
- One of the very large bodies of salt water covering most of the Earth's surface.
- Sea, bay, gulf
- Smaller parts of an ocean, partly enclosed by land, such as the Arabian Sea or the Bay of Bengal.
- Continent
- A very large, continuous expanse of land; seven are commonly counted.
- Landmass
- A large body of land.
- Blue planet
- A name for the Earth, which looks mostly blue from space because water covers about three-fourths of it.
- Fresh water
- Water that is not salty, found in glaciers, rivers, lakes, the atmosphere and underground.
- Groundwater
- Fresh water stored under the ground, reached by wells and hand pumps.
- Marine
- Related to or found in the seas and oceans.
- Flora and fauna
- The plant life and the animal life of a region.
- Algae
- Tiny plants that grow in water; in the oceans they make much of the world's oxygen.
- Cyclone
- A huge spinning storm over a warm sea that brings very strong winds and heavy rain.
- Tsunami
- A giant, powerful sea wave usually caused by an earthquake or volcanic eruption under the ocean.
- Disaster management
- Planning to prevent, prepare for and respond to disasters; in India led by the NDMA.
- Eurasia
- Europe and Asia considered together as one continent.
- Island
- A piece of land smaller than a continent, surrounded by water on all sides.
- Dakshin Gangotri
- India's first research station in Antarctica, set up in 1983.
- Overfishing
- Catching fish faster than they can breed, so their numbers fall.
End-of-Chapter Trial Paper & Test Questions
Topic-wise questions to test your understanding of every concept in this chapter.
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Explain the terms continent, ocean and island. / महाद्वीप, महासागर और द्वीप शब्दों को समझाइए।
Show answer
A continent is a very large continuous stretch of land, an ocean is a very large body of salt water, and an island is a smaller piece of land surrounded by water on all sides. / महाद्वीप भूमि का बहुत बड़ा लगातार फैला भाग है, महासागर खारे पानी का बहुत बड़ा जलाशय है, और द्वीप चारों ओर से पानी से घिरा भूमि का छोटा भाग है।
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Why is the Earth called the blue planet? / पृथ्वी को नीला ग्रह क्यों कहा जाता है?
Show answer
Almost three-fourths of the Earth's surface is covered with water, so it looks mostly blue when seen from space. / पृथ्वी की लगभग तीन-चौथाई सतह पानी से ढकी है, इसलिए अंतरिक्ष से देखने पर वह अधिकतर नीली दिखती है।
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Which hemisphere has more land, and what does this mean for where people live? / किस गोलार्ध में अधिक भूमि है, और इसका लोगों के रहने पर क्या असर है?
Show answer
The Northern Hemisphere has much more land than the Southern, so most of the world's people, cities and farms are found there. / उत्तरी गोलार्ध में दक्षिणी गोलार्ध से बहुत अधिक भूमि है, इसलिए दुनिया के अधिकतर लोग, शहर और खेत वहीं हैं।
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If the Earth has so much water, why is there talk of a water crisis? / यदि पृथ्वी पर इतना पानी है तो जल संकट की बात क्यों होती है?
Show answer
Most of the water is salty sea water that we cannot drink or use for farming, and fresh water is only a small share that is being overused and polluted. / अधिकांश पानी खारा समुद्री पानी है जिसे हम न पी सकते हैं न खेती में लगा सकते हैं, और मीठा पानी बहुत कम है जिसका अधिक उपयोग और प्रदूषण हो रहा है।
-
Name the five oceans from the largest to the smallest. / पाँच महासागरों के नाम सबसे बड़े से सबसे छोटे क्रम में लिखिए।
Show answer
From largest to smallest, they are the Pacific, the Atlantic, the Indian, the Southern and the Arctic Ocean. / सबसे बड़े से सबसे छोटे क्रम में वे प्रशांत, अटलांटिक, हिंद, दक्षिणी और आर्कटिक महासागर हैं।
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What is a tsunami, and what happened on 26 December 2004? / सुनामी क्या है, और 26 दिसंबर 2004 को क्या हुआ था?
Show answer
A tsunami is a giant wave caused by an undersea earthquake or volcano; on 26 December 2004 an earthquake near Indonesia caused a tsunami that killed more than two lakh people in 14 countries, including India. / सुनामी समुद्र के नीचे भूकंप या ज्वालामुखी से उठी विशाल लहर है; 26 दिसंबर 2004 को इंडोनेशिया के पास भूकंप से उठी सुनामी ने भारत सहित 14 देशों में दो लाख से अधिक लोगों की जान ले ली।
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Why can the number of continents be counted as four, five, six or seven? / महाद्वीपों की संख्या चार, पाँच, छह या सात क्यों गिनी जा सकती है?
Show answer
Some landmasses are joined, such as Europe and Asia or North and South America, so they can be counted either as one continent or as separate ones. / कुछ भूभाग आपस में जुड़े हैं, जैसे यूरोप और एशिया या उत्तर और दक्षिण अमेरिका, इसलिए उन्हें एक महाद्वीप या अलग-अलग महाद्वीप गिना जा सकता है।
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Name India's two major island groups and the seas they lie in. / भारत के दो प्रमुख द्वीप समूहों और उनके समुद्रों के नाम बताइए।
Show answer
The Andaman and Nicobar Islands lie in the Bay of Bengal, and the Lakshadweep Islands lie in the Arabian Sea. / अंडमान और निकोबार द्वीपसमूह बंगाल की खाड़ी में हैं, और लक्षद्वीप द्वीपसमूह अरब सागर में हैं।
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What has India done in Antarctica? / भारत ने अंटार्कटिका में क्या किया है?
Show answer
Since 1981 India has sent expeditions to Antarctica, set up its first station Dakshin Gangotri in 1983 and later two more, and its scientists study the climate and environment there. / 1981 से भारत अंटार्कटिका में अभियान भेज रहा है, 1983 में पहला केंद्र दक्षिण गंगोत्री बनाया और बाद में दो और, और उसके वैज्ञानिक वहाँ जलवायु और पर्यावरण का अध्ययन करते हैं।
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Why are oceans called the planet's lungs, and how are they threatened? / महासागरों को पृथ्वी के फेफड़े क्यों कहा जाता है, और उन्हें क्या खतरे हैं?
Show answer
Sea plants and algae produce more than half of the world's oxygen, but plastic waste, pollution and overfishing are harming marine life. / समुद्री पौधे और शैवाल दुनिया की आधी से अधिक ऑक्सीजन बनाते हैं, पर प्लास्टिक कचरा, प्रदूषण और अत्यधिक मछली पकड़ना समुद्री जीवन को नुकसान पहुँचा रहे हैं।
Related Laws & Principles
Explore allFoundational laws & principles behind this chapter. Each one opens a full page — what it says, why it matters, five practice questions and the mistakes to avoid.