<P> The Black Death, one of the most devastating pandemics in human history, is thought to have originated in the arid plains of central Asia, where it then travelled along the Silk Road . </P> <P> The Russian Empire began to expand into Asia from the 17th century, and would eventually take control of all of Siberia and most of Central Asia by the end of the 19th century . The Ottoman Empire controlled Anatolia, most of the Middle East, North Africa and the Balkans from the mid 16th century onwards . In the 17th century, the Manchu conquered China and established the Qing dynasty . The Islamic Mughal Empire and the Hindu Maratha Empire controlled much of India in the 16th and 18th centuries respectively . </P> <P> Asia is the largest continent on Earth . It covers 8.8% of the Earth's total surface area (or 30% of its land area), and has the largest coastline, at 62,800 kilometres (39,022 mi). Asia is generally defined as comprising the eastern four - fifths of Eurasia . It is located to the east of the Suez Canal 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 . Asia is subdivided into 48 countries, three of them (Russia, Kazakhstan and Turkey) having part of their land in Europe . </P> <P> Asia has extremely diverse climates and geographic features . Climates range from arctic and subarctic in Siberia to tropical in southern India and Southeast Asia . It is moist across southeast sections, and dry across much of the interior . Some of the largest daily temperature ranges on Earth occur in western sections of Asia . The monsoon circulation dominates across southern and eastern sections, due to the presence of the Himalayas forcing the formation of a thermal low which draws in moisture during the summer . Southwestern sections of the continent are hot . Siberia is one of the coldest places in the Northern Hemisphere, and can act as a source of arctic air masses for North America . The most active place on Earth for tropical cyclone activity lies northeast of the Philippines and south of Japan . The Gobi Desert is in Mongolia and the Arabian Desert stretches across much of the Middle East . The Yangtze River in China is the longest river in the continent . The Himalayas between Nepal and China is the tallest mountain range in the world . Tropical rainforests stretch across much of southern Asia and coniferous and deciduous forests lie farther north . </P>

How many countries are there in asian continent