Chap.2. ‘Ocean and Continents’ Notes Class 6 NCERT Social Science

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Chapter Notes: Ocean and Continents

Introduction

• Earth’s Appearance from Space: The Earth is often called the “blue planet” because its surface is mostly covered with water, which makes it appear blue when viewed from space.
• Water coverage: Approximately three-fourths of the Earth’s surface is covered by water.
• Oceans: The largest water bodies on Earth are known as oceans.
• Landmass:
  • Brown areas seen from space represent land.
  • Land covers a little over one-fourth of the Earth’s surface.
  • Large bodies of land are called landmasses, and continuous expanses of land are known as continents.
• Role of Oceans and Continents:
  • Oceans and continents have a significant impact on Earth’s climate.
  • They influence all life forms, including plants, animals, and humans.
  • Their effects can be seen throughout history, culture, and daily life.
• Cultural Reference: The Indian Navy’s emblem includes the motto Sam noh Varunah, invoking the Vedic deity Varuna, associated with the oceans, sky, and water.

1. Distribution of Water and Land:

• Distribution of Water and Land:
  • Oceans and continents are not evenly distributed between the Northern Hemisphere and Southern Hemisphere.
  • Oceans include smaller extensions such as seas, bays, and gulfs.
• Hemispheres and Water Proportions:
  • The Southern Hemisphere holds more water compared to the Northern Hemisphere.
  • The proportion of water to land differs in both hemispheres. Students are encouraged to discuss and estimate this proportion in groups.
• Ocean Connectivity:
  • All oceans are interconnected and together hold the majority of Earth’s water.
  • However, most of this water is saline (salty), making it unfit for drinking by humans and most land animals.
• Freshwater Resources:
  • Freshwater is a very small proportion of Earth’s total water and is found in glaciers, rivers, lakes, the atmosphere, and underground sources (called groundwater).

2. Oceans

1. The Five Oceans:

The five oceans of the world:

1. Pacific Ocean – Largest ocean.
2. Atlantic Ocean – Second largest.
3. Indian Ocean – Third largest.
4. Southern Ocean – Fourth largest, surrounding Antarctica.
5. Arctic Ocean – Smallest ocean.

Ocean Boundaries: The boundaries between these oceans are based on conventions and geographical lines, but in reality, all oceans are interconnected. Seawater constantly flows across different oceans, supporting marine life.

2. Marine Life:

• Marine Flora (plants): Includes tiny algae and seaweeds.
• Marine Fauna (animals): Includes fish, dolphins, whales, and many deep-sea creatures.
• Different parts of the ocean, from the surface to the deep sea, host unique and diverse species of plants and animals.

4. Oceans and Disasters:

• Clouds seen from space represent weather systems that bring rain to continents. For example, monsoon rains in India originate in the ocean and are vital for agriculture.
• Oceans and Storms: Oceans also generate storms, such as cyclones, which involve extreme rainfall and strong winds. These storms can cause severe damage to coastal areas.
• Tsunami:
  • A tsunami is a large, powerful ocean wave caused by underwater earthquakes or volcanic eruptions.
  • Tsunamis can travel over long distances and cause significant flooding and damage in coastal regions.

3. Continents

1. Continents:

The map of oceans also shows the continents. Depending on how they are grouped, there are four to seven continents. Different ways to count continents:

1. Four Continents: Africa-Eurasia, America, Antarctica, Australia.
2. Five Continents: Africa, America, Antarctica, Australia, Eurasia.
3. Six Continents: Africa, Antarctica, Australia, Eurasia, North America, South America.
4. Seven Continents: Africa, Antarctica, Asia, Australia, Europe, North America, South America (this is the most widely used classification). The diagram in Fig. 2.3 shows the relative sizes of the seven continents.

2. Islands:

• Islands are smaller landmasses surrounded by water on all sides.
• While continents are also surrounded by water, their large size prevents them from being categorized as islands.
• There are thousands of islands across the planet, varying greatly in size.

4. Oceans and Life:

1. Water Cycle:

• Oceans are an essential part of the Earth’s water cycle.
• Rainfall originates from the oceans. Without oceans, the Earth would become a desert.
• You will learn more about this cycle in Science, but the oceans are the primary source of rain through evaporation.

2. Oceans as ‘Planet’s Lungs’:

• More than half of the Earth’s oxygen comes from the flora (plants and algae) in the oceans.
• Oceans are vital in producing oxygen and are often called the “lungs of the planet” because of this role.

2. Regulation of Climate:

• Oceans regulate the Earth’s climate. Their large bodies of water absorb heat, helping to stabilize global temperatures.
• Without oceans, the Earth’s climate would be far more extreme.

3. Human Interaction with Oceans:

• Migration: Oceans have allowed people to migrate to new regions.
• Trade: From ancient times, seas have facilitated trade of goods between countries.
• Military campaigns: Historically, seas and oceans were used for conducting military operations.
• Food Source: Fishing has provided a rich source of food for coastal communities.

4. Cultural Impact:

• Many coastal cultures have myths and legends about the oceans, including stories of sea gods, goddesses, and monsters.
• Oceans are seen both as a source of danger and blessing.

Key Revision Points

These key points summarize the chapter’s main ideas and concepts about oceans, continents, and human interaction with the marine environment.

1. Earth’s Water Distribution:

• The Earth’s surface is covered by almost 75% water, which is why it is called the “Blue Planet.”
• Water bodies like oceans dominate the Earth’s surface, while land covers about one-fourth.

2. Oceans:

• Five major oceans: Pacific, Atlantic, Indian, Arctic, and Southern.
• Oceans are interconnected, and their boundaries on maps are more conventional than natural.
• Oceans play a crucial role in regulating climate, sustaining marine life, and providing oxygen.

3. Continents:

• There are seven widely recognized continents: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.
• Geologically, Europe and Asia can be combined as ‘Eurasia’, but they are traditionally treated as separate continents.

4. Islands:

• Islands are smaller landmasses surrounded by water.
• Greenland is the largest island, and India has over 1,300 islands.
• Islands play a role in biodiversity and geography.

5. Ocean and Life:

• Oceans produce over half of the world’s oxygen and influence the water cycle, essential for rainfall and agriculture.
• Oceans have influenced human history through migration, trade, culture, and food sources like fishing.

6. Oceans and Natural Disasters:

• Oceans are responsible for some natural disasters like tsunamis, cyclones, and storms.
• Tsunamis are caused by underwater earthquakes or volcanic eruptions, and they can cause widespread damage to coastal regions.

7. Water Scarcity:

• Despite the abundance of water, only a small proportion of Earth’s water is freshwater, which leads to water scarcity.
• Most of the Earth’s water is in the oceans, and it is salty and not suitable for drinking or farming.

8. Human Impact on Oceans:

• Human activities like pollution and overfishing are damaging marine ecosystems.
• Plastic waste and other pollutants harm marine life, and efforts are needed globally to protect oceans.

9. Disaster Management and Tsunami Warning System:

• India has disaster management systems to handle events like tsunamis, which are monitored through early warning systems, including the Indian Ocean Tsunami Warning System.

10. Cultural Significance:

• Oceans and seas are important in mythology and culture, symbolized in the Indian Navy’s emblem, invoking Varuna, the deity of water.

Don’t Miss out Section

1. Indian Navy Emblem:
   • The Indian Navy’s emblem includes the motto “Sam noh Varunah” (ŚhamnoVaruṇah), which translates to “Be auspicious to us, O Varuna.”
   • Varuna is a Vedic deity associated with oceans, sky, and water.
2. Indian Ocean Geography:
   • The Indian Ocean is bounded by Asia (north), Africa (west), Australia (east), and the Southern Ocean (south).
   • Arabian Sea lies to the west of India, and the Bay of Bengal lies to the east.
3. 2004 Tsunami:
   • On 26 December 2004, a powerful tsunami struck countries around the Indian Ocean due to an earthquake in Indonesia. It resulted in the loss of over 200,000 lives.
   • India’s Andaman and Nicobar Islands, along with the Tamil Nadu and Kerala coasts, were severely impacted.
   • Indian Ocean Tsunami Warning System and National Disaster Management Authority are in place to mitigate such disasters.
4. Olympic Rings:
   • The Olympic rings represent the gathering of athletes from five inhabited continents: Africa, America, Asia, Australia, and Europe.
5. Greenland and Indian Islands:
   • Greenland is the largest island in the world.
   • India has over 1,300 islands, including the Andaman and Nicobar Islands (Bay of Bengal) and the Lakshadweep Islands (Arabian Sea).
   • India’s Antarctica Programme explores Antarctica, where the first Indian base station ‘Dakshin Gangotri’ was established in 1983.
6. World Oceans Day (June 8):
   • The United Nations declared this day to emphasize the ocean’s importance as the planet’s lungs, a key source of food and medicine.
   • Ocean pollution is a major concern, with millions of tonnes of plastic waste dumped yearly, threatening marine life. Overfishing is also causing a decline in marine species.
   • Protecting oceans is a collective responsibility for the future of the planet.