North America is a continent in the Earth's northern hemisphere and (chiefly) western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the south and west by the North Pacific Ocean; South America lies to the southeast. It covers an area of about 24,709,000 square kilometers (9,540,000 sq mi), about 4.8% of the planet's surface or about 16.5% of its land area. As of July 2007, its population was estimated at nearly 524 million people. It is the third-largest continent in area, following Asia and Africa, and is fourth in population after Asia, Africa, and Europe. North America and South America are collectively known as the Americas. Scientists have several theories as to the origins of the early human population of North America. The indigenous peoples of North America themselves have many creation myths, by which they assert that they have been present on the land since its creation. Before contact with Europeans, the natives of North America were divided into many different polities, from small bands of a few families to large empires. They lived in several "culture areas", which roughly correspond to geographic and biological zones and give a good indication of the main lifeway or occupation of the people who lived there (e.g. the Bison hunters of the Great Plains, or the farmers of Mesoamerica). Native groups can also be classified by their language family (e.g. Athapascan or Uto-Aztecan). It is important to note that peoples with similar languages did not always share the same material culture, nor were they always allies. Scientists believe that the Inuit people of the high Arctic came to North America much later than other native groups, as evidenced by the disappearance of Dorset culture artifacts from the archaeological record, and their replacement by the Thule people.
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