The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian subcontinent; on the west by East Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean (or, depending on definition, by Antarctica). The ocean isnamed after the geographic location called India.
As one component of the interconnected global ocean, the Indian Ocean is delineated from the Atlantic Ocean by the 20° east meridian running south from Cape Agulhas, and from the Pacific by the meridian of 146°55' east. The northernmost extent of the Indian Ocean is approximately 30° north in the Persian Gulf. The Indian Ocean has asymmetriccirculation. This ocean is nearly 10,000 kilometers (6,200 mi) wide at the southern tips of Africa and Australia; its area is 73,556,000 square kilometers (28,350,000 sq mi), including the Red Sea and the Persian Gulf.
The ocean's volume is estimated to be 292,131,000 cubic kilometers (70,086,000 mi3). Small islands dot the continental rims. Island nations within the ocean are Madagascar, theworld's fourth largest island; Reunion Island; Comoros; Seychelles; Maldives; Mauritius; and Sri Lanka. The archipelago of Indonesia borders the ocean on the east.
The origin and evolution of the Indian Ocean is the most complicated of the three major oceans. Its formation is a consequence of the breakup, about 150 million years ago, of the southern supercontinent Gondwana (orGondwanaland); by the movement to the northeast of the Indian subcontinent (beginning about 125 million years ago), which began colliding with Eurasia about 50 million years ago; and by the western movement of Africa and separation of Australia from Antarctica some 53 million years ago. By 36 million years ago, the Indian Ocean had taken on its present configuration. Although it first opened some 125million years ago, almost all the Indian Ocean basin is less than 80 million years old.
The world's earliest civilizations in Mesopotamia (beginning with Sumer), ancient Egypt, and the Indian subcontinent (beginning with the Indus Valley civilization), which began along the valleys of the Tigris-Euphrates, Nile and Indus rivers respectively, all developed around the Indian Ocean.Civilizations soon arose in Persia (beginning with Elam) and later in Southeast Asia (beginning with Funan).
During Egypt's first dynasty (c. 3000 BC), sailors were sent out onto its waters, journeying to Punt, thought to be part of present-daySomalia. Returning ships brought gold and myrrh. The earliest known maritime trade between Mesopotamia and the Indus Valley (c. 2500 BC) was conducted along the IndianOcean. Phoenicians of the late 3rd millennium BC may have entered the area, but no settlements resulted.
The Indian Ocean is far calmer and thus opened to trade earlier than the Atlantic or PacificOceans. The powerful monsoons also meant ships could easily sail west early in the season, then wait a few months and return eastwards. This allowed Indonesian peoples to cross the Indian Ocean tosettle in Madagascar.
In the 2nd or 1st century BC, Eudoxus of Cyzicus was the first Greek to cross the Indian Ocean. Hippalus is said to have discovered the direct route from Arabia to India around this time. During the 1st and 2nd centuries AD intensive trade relations developed betweenRoman Egypt and the Tamil kingdoms of the Cheras, Cholas and Pandyas in Southern India. Like the Indonesianpeoples above, the western sailors used the monsoon to cross the ocean. The unknown author of the Periplus of the Erythraean Sea describes this route and the ports and trade goods along the coasts of Africa and India around AD 70.
From 1405 to 1433, Admiral Zheng He led large fleets of the Ming Dynasty on several voyages to the Western Ocean (Chinese name for the Indian Ocean) and reached the coastal...