Chapter: 04. Major Water Bodies
Major Water Bodies
Water is an incredible part of our Earth! It covers a huge portion of our planet and comes in many different forms, from giant oceans to small lakes and flowing rivers. These water bodies are super important for all life on Earth. Not only do they provide drinking water for humans and animals, but they also support all the amazing plants and animals that live underwater.
Water covers about 71% of the Earth’s surface!
Oceans
Oceans are huge areas of water. There are five main oceans in the world:
The Southern Ocean (also called the Antarctic Ocean) About 71% of the Earth’s surface is covered by oceans, and they hold about 97% of all the water on Earth!
The Pacific Ocean
The Pacific Ocean is the largest ocean and covers more than one-third of the globe.
Shape: It’s almost circular. Borders: It’s bordered by new fold mountains that have many active volcanoes, forming what is known as the ‘Ring of Fire’. Southern Part: It merges with the Atlantic and Indian oceans in the south. Deepest Part: The deepest part of the Earth’s crust, the Mariana Trench, is located here near the Philippines. Quick Fact: The Mariana Trench is about 11,000 meters deep. A large stone would take more than an hour to reach its bottom! Other Trenches: Other important trenches include the Philippine (Mindanao) Trench, the Japan Trench, and the Kuril Trench.
The Atlantic Ocean
The Atlantic Ocean is shaped like the letter ‘S’.
Size: It’s much smaller than the Pacific Ocean, about half its size. Coastline: Even though it’s smaller, the total length of its coastline is longer than the combined coastlines of the Pacific and Indian oceans. Busiest Ocean: It’s the busiest ocean in the world because many trade and transportation routes pass across it. Borders: Europe and Africa are on its east coast, while the two Americas are on its western border. Mid-Atlantic Ridge: In the middle of the Atlantic Ocean, there is a submerged (underwater) mountain range. Some of its high peaks or ridges form islands, like Iceland, which are volcanic. The Indian Ocean
The Indian Ocean is roughly triangular in shape.
Area: It covers one-fifth of the total area of all oceans. Naming: India is located at the head of this ocean, which is why it’s named after the country. Location: It lies mainly in the Southern Hemisphere. Parts: The Arabian Sea and the Bay of Bengal are two important parts of the Indian Ocean to its north. Borders: Asia is to its north, Australia to its east, and Africa forms its western shore. The Arctic Ocean
The Arctic Ocean is the northernmost ocean.
Location: It lies north of North America, Europe, and Asia. It’s mostly within the Arctic Circle. Temperature: Because of its location, it remains frozen for most of the year. Size & Depth: It is the smallest and shallowest ocean. It surrounds the North Pole. The Southern Ocean (Antarctic Ocean)
This ocean surrounds the continent of Antarctica.
Formation: It’s formed by the merging of the Pacific, Atlantic, and Indian oceans. Size: It is the fourth largest ocean in the world. Importance of Oceans
Oceans are vital for many reasons:
Resources: They are huge storehouses of oil and mineral resources. Aquatic Life: They support a wide variety of aquatic (water-dwelling) life. Trade Routes: They make international trade easier by providing routes for ships. Climate Moderation: They help moderate the climate of coastal areas. Water vapor evaporates from ocean and sea surfaces, which later falls as rain, playing a key role in the water cycle. Food Supply: They are a major source of food for many people around the world. Energy: They possess enormous energy in the form of tidal waves.
Sustainable Development Goals (SDGs): SDG 14: Life Below Water
Our oceans are facing a huge problem with pollution, especially plastic waste.
Plastic Pollution: Plastic waste makes up 80% of all marine pollution. Millions of tons of plastic are thrown into our oceans each year. Future Outlook: By 2050, it’s estimated that plastic will likely outweigh all fish in the sea if we don’t change our ways. Degradation Time: Plastic takes thousands of years to degrade! Even then, it often breaks down into tiny pieces called microplastics, but it doesn’t fully disappear. Harm to Marine Life: Plastic pollution has a terrible effect on ocean animals and their habitats: Suffocation: Animals can get trapped or choked by plastic. Entanglement: They can get tangled in plastic debris. Laceration: Sharp plastic can cause cuts and injuries. Infections: Injuries can lead to infections. Internal Injuries/Poisoning: Animals often mistake plastic for food and eat it, causing internal injuries or poisoning. Urgent Need: There is an urgent need for the world to act to ensure that marine resources can be used sustainably (meaning, we use them in a way that doesn’t harm them for future generations).
Science Spotlight: Marie Tharp
Marie Tharp was an incredible geologist and oceanographic cartographer (mapmaker). She created detailed maps of the ocean floor using sonar findings (a technology that uses sound waves to measure water depth). Her work led to the amazing discovery of the Mid-Atlantic Ridge, a vast underwater mountain range in the Atlantic Ocean. Her contributions were especially important because, at the time, women often faced challenges in scientific research. Her dedication to mapping and understanding the ocean floor has had a lasting impact on how we understand our Earth’s dynamic processes.
Seas
A sea is a part of an ocean that is smaller and shallower. Seas are usually located close to the edge of a land mass or continent.
Examples: You can find seas like the Caribbean Sea, the Bering Sea, the Arabian Sea, and the North Sea along the edges of continents. Did You Know? Sometimes, the term ‘sea’ is also used for large salty water bodies that are cut off from the open ocean, like the Caspian Sea and the Dead Sea.
Gulfs and Bays
Both gulfs and bays are indentations (curving inlets) made by the sea or a lake into a coastline, but they have some differences.
Gulf: A deep inlet of the sea almost surrounded by land, with a narrow mouth. Gulfs are generally more indented and enclosed than bays. Examples: Persian Gulf, Gulf of Mexico, Gulf of Carpentaria. Bay: An open, curving indentation made by the sea or a lake into a coastline. Examples: Bay of Bengal, Hudson Bay, Bay of Biscay.
Here’s a comparison between a gulf and a bay:Basis of comparisonBayGulfDefinitionA broad, semicircular inlet of sea; can be accessed by land from three sides.A water body where the water has eroded the coastline so deeply that it has a narrow opening.IndentationWide indentation of the seaDeep indentation of seaEnclosedLessComparatively moreFormationContinental drift and erosion of coastlineMovement of the earth’s plates
Straits
A strait is a narrow stretch of water that joins two large water bodies.
Example 1: The Strait of Gibraltar connects the Mediterranean Sea to the North Atlantic Ocean. Example 2: The Palk Strait connects the Bay of Bengal in the north-east with the Gulf of Mannar in the south-west.
Lakes
Lakes are small bodies of water which are surrounded by land on all sides. They are generally bigger and deeper than ponds.
Man-made Lakes: Some lakes are man-made, like reservoirs constructed with dams to store water (e.g., Bhakra Nangal dam). Natural Lakes: Lake Balkhash and Lake Baikal are examples of natural lakes. Inland Seas: Very large lakes are sometimes called inland seas, such as the Aral Sea, the Black Sea, and the Caspian Sea in Eurasia.
Lakes are important for:
Providing drinking water. Supplying water for agriculture. Leisure activities like fishing. Some Important Lakes:
Located in south-east Siberia. Oldest and deepest lake in the world (1,700 m deep). Contains 20% of the world’s total unfrozen freshwater reserve. The Five Great Lakes of the USA (Superior, Huron, Michigan, Ontario, Erie): A group of five huge freshwater lakes between the United States and Canada. Comprise the largest body of fresh water on Earth. About 34 million people in the US and Canada and over 3,500 species of plants and animals live in their basin. Popular for boating, fishing, and other recreational activities. Important for transportation of goods. Second largest lake in Europe. Situated in the north-western part of the European portion of Russia. One of Europe’s largest freshwater reservoirs. Lake Titicaca (Andes Mountains): A large, deep lake bordering Bolivia and Peru. Largest lake in South America in terms of water volume and surface area. Main reservoir of the Nile River. Lies mainly in Tanzania and Uganda, bordering Kenya.
A saltwater (brackish) lake in Odisha, eastern India. In winter, it becomes the largest ground for migratory birds in the Indian subcontinent. Home to many threatened species of plants and animals. Knowledge of India: Chilika Lake is a World Heritage Site. Its area varies between 900 to 1165 sq. km. It is connected to the Bay of Bengal by a 32 km long channel. Many islands are present, including Krushnaprasad, Nalaban, Kalijai, Somolo, and Birds Islands. It provides a livelihood for more than 2 lakh (200,000) fishermen.
Rivers
A river is a stream of water that flows in a channel from high ground to low ground, eventually reaching a lake or a sea. Rivers are a crucial source of fresh water on Earth.
Source: The place where a river originates, usually in a hill or a mountain. Mouth: The place where a river ends its journey, typically where it enters the sea or a lake. Course of a River
The journey of a river has three different stages:
Generally located in the mountains where the land is steep. The river flows very swiftly at this stage. After the river descends to the plains from the mountains. The speed of its flow decreases considerably as it moves through areas with a gentler slope. Near its mouth, where the slope is negligible (very flat). The river’s flow has nearly halted at this stage.
Important Rivers Around the World
World’s longest river (6,695 km). Flows into the Mediterranean Sea. Amazon River (South America): Second longest river in the world (6,640 km). Flows through South America.
Mississippi River (USA): An important river in the USA. One of Europe’s longest and most important rivers. Flows through six European countries. Source in the Alps Mountains in Switzerland. Europe’s second-longest river. Longest river in the European Union region. Flows through or along the borders of ten European countries. Indus River (South Asia): Major south-flowing river in South Asia. Was the cradle (birthplace) of the Indus Valley Civilization. Ganga River (India/Bangladesh): Most important river of India. Flows through India and Bangladesh. Huang He (Yellow River) (China): Main river of northern China, east central, and eastern Asia. Believed to be the cradle of the Chinese civilization. Third-longest in the world. Ob River (Western Siberia): An important river in western Siberia. Murray River (Australia): Australia’s longest river, rises in the Australian Alps.
Importance of Rivers
Rivers are an extremely valuable resource for many reasons:
Fertile Soils: River valleys and plains provide fertile soils, which are great for growing crops in abundance. Water Supply: River water is used for human and animal consumption. Rivers provide plenty of water to support large settlements and cities. Transport: Rivers provide a way to transport people and goods from one place to another, helping trade to grow. Energy: River water is a crucial source of energy. It’s used to power hydroelectric plants, generating electricity that helps industries to grow. Recreation: Rivers also offer opportunities for recreational activities like boating and fishing.
Pollution of Water Bodies
Pollution is one of the biggest threats our Earth faces today. Almost all human activities create waste, which causes pollution. Water pollution happens when harmful waste is discharged (released) into water bodies. It affects all kinds of water resources on Earth: oceans, seas, rivers, and lakes.
Causes of Water Pollution
Households, industries, and surface run-off are the main causes of water pollution. This pollution harms both humans and other living organisms. Here are some examples:
Liquid Waste from Thermal Power Plants: This waste increases the dissolved oxygen content of river water initially, leading to a sudden rise in microbe population. This, in turn, reduces the overall oxygen level in the river, making it difficult for other organisms to survive. Surface Run-off: This is water from rain, melting snow, or other sources that flows over land. When it flows from farms, it carries organic and inorganic fertilizers into water bodies. This promotes the excessive growth of algae (called an algal bloom), which uses up the dissolved oxygen in the water. Other living organisms, including fish, cannot survive in these low-oxygen conditions. Untreated Liquid Waste: Untreated liquid waste from kitchens and toilets is often released directly into rivers. This can expose people who use river water to serious diseases like typhoid, cholera, and amoebic dysentery. Oil Spills: An oil spill happens when crude oil leaks into the sea, usually during transportation from one country to another. This can be due to accidents or natural hazards like hurricanes, which can overturn oil tankers. Harmful Effects of Oil Spills: Oil spills are very harmful for fish, birds, and other animals that depend on oceans and seas. For example, birds’ feathers get covered in oil, and they can get poisoned when they try to clean themselves. Water is incredibly important for sustaining life on Earth. We should always be careful while using water and take steps to save our water resources.
Important Terms (Glossary)
Trenches: A long narrow hole in the ground (often deep underwater). Submerged: To be under water. Ridge: A high pointed area near the top of a mountain (can be underwater). Evaporation: The process by which liquid changes into steam or vapor. Indented: (Of an edge or a surface) an indented edge is not even, because parts of it are missing or have been cut away. Migratory: The movement every year of large numbers of birds or animals from one place to another. Brackish: Containing salt and tasting of it in an unpleasant way (less salty than seawater, more salty than freshwater). Surface run-off: Water from rain, melting snow, or other sources that flows over land and is part of the water cycle.
Overall Chapter Summary
This chapter explores the major water bodies on Earth, highlighting their characteristics, importance, and environmental challenges.
Self Study
