When we look at a globe or a photograph of Earth taken from space, the most widespread colour visible is blue. This is because most of the Earth's surface is covered with water — almost three-fourths (¾) of the surface, or roughly 71%.

This overwhelming presence of water led early astronauts to lovingly call the Earth the "Blue Planet". Jules Verne, the great French author, captured the ocean's significance in 1870: "The ocean is everything. It covers seven-tenths of the terrestrial globe... The globe began with the ocean, so to speak, and who knows if it will not end with it."

Land covers a little over one-fourth (¼) of the globe (approximately 29%). The brown colour visible in Earth photographs represents land. Both oceans and continents play a vital role in shaping the Earth's climate, and they affect all aspects of life — all plants, animals, and human beings.

🌊 Don't Miss Out — Indian Navy Motto

Image 1 — The Indian Navy emblem with the motto Sam noh Varunah (Source: NCERT)

The emblem of the Indian Navy contains the motto Sam noh Varunah (pronounced 'Śham no Varuṇah'), which means "Be auspicious to us, O Varuna." This is an invocation to Varuṇa, a Vedic deity associated with the oceans, the sky, and water in general. This reflects India's ancient maritime heritage and deep cultural connection with the sea.

Oceans and continents are not distributed equally between the Northern and Southern Hemispheres. This unequal distribution has profound effects on climate, biodiversity, and human civilisation.

Fig. 2.2 — Maps of the Earth as seen from above the North Pole (left) and above the South Pole (right). The circular lines are parallels of latitude and the radiating lines are meridians of longitude. (Source: NCERT)

The smaller extensions of oceans have various names: Sea, Bay, Gulf, Strait, Channel, etc. Importantly, all oceans are connected with one another — they form one continuous global ocean. The divisions between them are merely conventions drawn on maps, not physical barriers. Seawater constantly flows across different oceans.

On the world map (Fig. 2.3), we can observe five oceans. While we name them separately, it must be remembered that they are not truly separate — the lines dividing them are conventions only.

Fig. 2.3 — A world map showing the five oceans, their conventional boundaries, and the continents. This map uses the six-continent model (reflecting Eurasia as one continent). (Source: NCERT)

India's civilisational relationship with the sea is ancient and profound. The Indian Navy's motto "Sam noh Varunah" is drawn from the Taittirīya Upaniṣhad (a Vedic text). Varuṇa is one of the oldest Vedic deities — the god of the cosmic waters, the sky, and moral order (ṛta).

Oceans support a breathtaking diversity of life, from the sun-lit surface to the dark, mysterious depths. Each zone of the ocean has its own unique life forms.

Marine Flora includes tiny plants called algae and all kinds of seaweeds. Algae are critical because they produce more than half of the world's oxygen through photosynthesis, making oceans literally "the planet's lungs."

Marine Fauna consists of thousands of species of colourful fish, dolphins, whales (including the sperm whale — the largest toothed predator on Earth), sharks, sea turtles, emperor penguins, starfish, sea anemones, coral reef organisms, and countless mysterious deep-sea creatures.

Coral reefs, sometimes called the "rainforests of the sea," are home to about 25% of all marine species despite covering less than 1% of the ocean floor.

While oceans are the source of life and rainfall, they also give rise to some of nature's most destructive events.

A continent is a large continuous expanse of land. Counting the number of continents is not as simple as it might seem — depending on our approach, we can count anywhere from four to seven continents. Here is why:

• North America and South America are generally considered two continents; but if viewed as a single landmass, they can be treated as one (America).
• Europe and Asia form a single physical landmass. Geologists often call this Eurasia. However, for historical and cultural reasons (their very different civilisational trajectories), they are usually treated as two continents.
• Africa and Eurasia are generally regarded as two continents, but sometimes as one (especially in older geographic traditions).

Count of Continents table — showing 4, 5, 6, and 7 continent models in alphabetical order. The 7-continent model is most widely used. (Source: NCERT)

Based on the seven-continent model, here is the ranking of continents by size (area):

When we combine Europe and Asia as Eurasia, it becomes by far the largest single landmass on Earth, dwarfing all other continents in size.

An island is a piece of land that is surrounded by water on all sides. Unlike continents (which are also surrounded by water), islands are much smaller. There are lakhs of islands on the planet, of very different sizes.

Don't Miss Out — Key facts about Greenland, India's islands, and the Indian Antarctica Programme (Source: NCERT)

Oceans and continents are vital parts of the environment and affect most aspects of life, even if we do not always notice it. Their importance cannot be overstated:

Don't Miss Out — Indian Ocean boundaries and India's two ocean arms (Source: NCERT)

India occupies a uniquely strategic position in the Indian Ocean — the only ocean named after a country. India's peninsular landmass juts into the Indian Ocean, giving it access to both arms of the ocean:

• Arabian Sea — to the west of India (part of the Indian Ocean)
• Bay of Bengal — to the east of India (part of the Indian Ocean)
• Indian Ocean — to the south of India

The limits of the Indian Ocean are: Asia to the north, Africa to the west, Australia to the east, and the Southern Ocean in the south.