The Americas, or America, also known as the New World, are the combined continental landmasses of North America and South America, in the Western Hemisphere. Along with their associated islands, they cover 8.3% of the Earth's total surface area (28.4% of its land area). The topography is dominated by the American Cordillera, a long chain of mountains that run the length of the west coast. The flatter eastern side of the Americas is dominated by large river basins, such as the Amazon, Mississippi, and La Plata. Extending 14,000 km (8,699 mi) in a north-south orientation, the climate and ecology varies widely across the Americas, from arctic tundra of Northern Canada, Greenland, and Alaska, to the tropical rain forests in Central America and South America.
Humans first settled the Americas from Asia between 40,000 BCE and 15,000 BCE. A second migration of Na-Dene speakers followed later from Asia. The subsequent migration of the Inuit into the neoarctic around 3500 BCE completed what is generally regarded as the settlement by the Indigenous peoples of the Americas. The first European discovery of and settlement in the Americas was by the Norse explorer Leif Ericson. However the colonization never became permanent and was later abandoned. The voyages of Christopher Columbus from 1492 to 1502 resulted in permanent contact with European (and subsequently, other Old World) powers, which led to the Columbian exchange. Diseases introduced from Europe and Africa devastated the Indigenous peoples, and the European powers colonised the Americas.