The world's second-largest and second-most-populous continent. At about 30.2 million sq km (11.7 million sq mi) including adjacent islands, it covers six percent of Earth's total surface area and 20.4 percent 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 has 54 fully recognized sovereign states (or 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 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 ethnicity, cultures and languages. In the late 19th century European countries colonized most of Africa. Most modern states in Africa originate from a process of decolonization in the 20th century.