Asia (// or //) is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and comprises 30% of its land area. With approximately 4.3 billion people, it hosts 60% of the world's current human population. Asia has a high growth rate in the modern era. For instance, during the 20th century, Asia's population nearly quadrupled.
Asia is defined as comprising the eastwards four-fifths of Eurasia. It is located to the east of the Suez Canal, the Ural River, and the Ural Mountains, and south of the Caucasus Mountains (or the Kuma–Manych Depression) and the Caspian and Black Seas. It is bounded on the east by the Pacific Ocean, on the south by the Indian Ocean and on the north by the Arctic Ocean.
Given its size and diversity, Asia – a toponym dating back to classical antiquity – "is more a cultural concept" incorporating diverse regions and peoples than a homogeneous physical entity. Asia differs very widely among and within its regions with regard to ethnic groups, cultures, environments, economics, historical ties and government systems.
The original distinction between Europe and Asia was made by the ancient Greeks. They used the Aegean Sea, the Dardanelles, the Sea of Marmara, the Bosporus, the Black Sea, the Kerch Strait, and the Sea of Azov as the border between Asia and Europe. The Nile was often used as the border between Asia and Africa (then called Libya), although some Greek geographers suggested the Red Sea would form a better boundary. Darius' canal between the Nile and the Red Sea introduced considerable variation in opinion. Under the Roman Empire, the Don River emptying into the Black Sea was the western border of Asia. It was the northernmost navigable point of the European shore. In the 15th century the Red Sea became established as the boundary between Africa and Asia, replacing the Nile. As exploration developed, the border between Asia and Europe had to be redefined, as the borders of the time did not extend to the arctic.