Chapter 2 — Oceans and Continents

Almost three-fourths of Earth's surface is covered by water. Because of this, the Earth appears mostly blue when seen from outer space, which is why early astronauts lovingly called it the 'blue planet.'

The five oceans are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Arctic Ocean, and the Southern (or Antarctic) Ocean. The Pacific Ocean is the largest, followed by the Atlantic. The Indian Ocean is the third largest, the Southern Ocean is the fourth, and the Arctic Ocean is the smallest.

Although oceans are shown with boundaries on maps, those lines are just conventions — the natural world does not follow such boundaries. Seawater constantly flows across different oceans, and many plant and animal species can be found across multiple oceans, so the five oceans are all naturally interconnected.

The water in oceans is seawater, which is salty and unfit for consumption by most land animals, including humans. Freshwater — the kind suitable for drinking — makes up only a very small proportion of the planet's water and is found in glaciers, rivers, lakes, the atmosphere, and underground.

Marine means related to or found in the oceans and seas. Marine flora refers to the plant life of the ocean — this includes tiny plants called algae and all kinds of seaweeds. Marine fauna refers to animal life — thousands of species of colourful fish, dolphins, whales, and countless mysterious deep-sea creatures.

Continents can be counted in several ways — anywhere between four and seven, depending on whether neighbouring landmasses like Europe and Asia or North and South America are counted as one or two. In practice, the list of seven continents is most widely used: Africa, Antarctica, Asia, Australia, Europe, North America, and South America.

An island is a smaller piece of land surrounded by water on all sides. India has more than 1,300 small islands. Two major island groups are the Andaman and Nicobar Islands in the Bay of Bengal and the Lakshadweep Islands in the Arabian Sea. Greenland is the largest island in the world.

A tsunami is a huge and powerful wave generally caused by a strong earthquake or a volcanic eruption at the bottom of the ocean. Tsunamis can travel thousands of kilometres and submerge coastal areas, causing widespread damage. They are rare but very destructive.

On 26 December 2004, a powerful tsunami caused by an earthquake in Indonesia struck India and 13 other countries around the Indian Ocean. More than two lakh people lost their lives. In India, the Andaman and Nicobar Islands and the coasts of Tamil Nadu and Kerala were severely affected.

The Indian Ocean Tsunami Warning System is a collaborative early warning network to which many countries, including India, contribute. It helps detect tsunamis before they hit a coast so that measures can be taken to protect lives and property. India also has its own National Disaster Management Authority to handle all kinds of disasters.

Oceans play a crucial role in regulating the Earth's climate. They send moisture into the atmosphere, which falls as rain on the continents. For example, the monsoon rains that India receives every summer originate in the ocean. Without such rains, agriculture and all life would suffer. However, oceans can also give rise to storms such as cyclones, which can cause widespread damage to coastal regions.

More than half of the world's oxygen is produced by the flora (plant life) of the oceans — mainly algae and seaweeds. Because of this enormous contribution to the air we breathe, oceans are called 'the planet's lungs.' The United Nations has designated June 8 as World Oceans Day to highlight the ocean's role as a major source of oxygen, food, and medicine.

Scientific studies show that oceans are polluted by human activity — several million tonnes of plastic waste are thrown into the oceans every year, choking marine life. Overfishing (excessive fishing) is another cause for the decline of marine life. The chapter states it is our collective responsibility to protect oceans for the future of the planet and of humanity.

Since 1981, the Indian Antarctica Programme has been exploring Antarctica. In 1983, India established its first scientific base station there, called 'Dakshin Gangotri.' Two more bases were established later. About 40 teams of Indian scientists have conducted research there, especially on the evolution of climate and environment.

Yes, the NCERT PDF is completely free to download on cbseprepmaster.com. No sign-up or account is required — just open the page and download or read the chapter directly.