Africa is the world's second-largest and second-most-populous continent. At about 30.3 million km² (11.7 million square miles) including adjacent islands, it covers six per cent of Earth's total surface area and 20.4 per cent of its total land area. With 1.1 billion people as of 2013, it accounts for about 15% of the world's human population. The continent is surrounded by the Mediterranean Sea to the north, both the Suez Canal and the Red Sea along the Sinai Peninsula to the northeast, the Indian Ocean to the southeast, and the Atlantic Ocean to the west. The continent includes Madagascar and various archipelagos. It contains 54 fully recognized sovereign states (countries), nine territories and two de facto independent states with limited or no recognition. Africa's population is the youngest amongst all the continents; the median age in 2012 was 19.7, when the worldwide median age was 30.4. Algeria is Africa's largest country by area, and Nigeria by population. Africa, particularly central Eastern Africa, is widely accepted as the place of origin of humans and the Hominidae clade (great apes), as evidenced by the discovery of the earliest hominids and their ancestors, as well as later ones that have been dated to around seven million years ago, including Sahelanthropus tchadensis, Australopithecus africanus, A. afarensis, Homo erectus, H. habilis and H. ergaster – with the earliest Homo sapiens (modern human) found in Ethiopia being dated to circa 200,000 years ago. Africa straddles the equator and encompasses numerous climate areas; it is the only continent to stretch from the northern temperate to southern temperate zones. Africa hosts a large diversity of ethnicities, cultures and languages. In the late 19th century European countries colonized most of Africa. Most present states in Africa originate from a process of decolonization in the 20th century.