Continents and oceans: a quick world tour

Seven continents, five oceans

A continent is a large, continuous stretch of land. The usual count gives seven: Asia, Africa, North America, South America, Antarctica, Europe and Australia. Around them lie five connected oceans: the Pacific, the Atlantic, the Indian, the Southern and the Arctic. The Pacific is the largest and deepest, with whales and tuna; the Atlantic is one of the busiest routes for ships and a rich fishing ground; the Indian Ocean is warm, full of life and has carried trade for thousands of years; the Southern Ocean circles Antarctica, with its penguins and seals; and the Arctic, the smallest and shallowest, is covered with sea ice and home to polar bears and walruses.

Why the oceans matter

Salt water covers about 71% of the Earth’s surface, which is why astronauts called it the blue planet, and the oceans hold about 97% of all its water. Microscopic plankton, which make food from sunlight and carbon dioxide, supply nearly half of the oxygen in the air we breathe. The oceans also steady the climate: they absorb heat, release it slowly and add moisture to the air, which becomes clouds and rain. Life in them ranges from plankton to the blue whale, the largest mammal, over 30 m long. The ocean floor is not flat either; it has mountains, valleys and plains, just like the land.

Currents, trenches and reefs

Ocean water is always moving. Currents flow like giant rivers: warm ones carry water from the Equator towards the poles, and cold ones carry water from the poles towards the Equator. The warm Gulf Stream crosses the Atlantic to Western Europe and keeps places like the United Kingdom milder than other lands lying at a similar latitude. The deepest parts of the seafloor are V-shaped trenches. In the Mariana Trench, the Challenger Deep goes more than 11,000 m down, in freezing, dark, crushing water where living things make food from chemicals. Reefs, ridges near the surface often built by corals, are among the richest ecosystems on Earth. The Great Barrier Reef off Australia stretches over 2,000 km.

Seas, gulfs, bays, straits and canals

Geographers name smaller water bodies by their shape. A sea, like the Arabian Sea, is partly enclosed by land but joined to an ocean. A gulf, like the Persian Gulf, reaches deep into the land, while a bay, like the Bay of Bengal, the largest bay in the world, is smaller and wider. A strait, like the Strait of Malacca, is a narrow channel joining two seas or oceans, and a canal is dug by people: the Suez Canal, opened in 1869, links the Red Sea and the Mediterranean.

Landforms on every continent

On land, the main landforms are mountains, plateaus and plains, along with deserts, which get less than 25 cm of rain a year and can be hot or cold. Every continent has its own famous examples: the Tibetan Plateau and the Gobi Desert in Asia, the European Plain and the Alps in Europe, the Sahara and the Nile in Africa, the Andes and the Amazon in South America, the Rocky Mountains and the Great Lakes in North America, and the Great Australian Desert. The largest desert of all is icy Antarctica. The full tour is in the Chapter 1 notes; for maps see mapping the Earth, and every question is answered in the NCERT solutions.