The Americas, or America, are lands in the Western Hemisphere that are also known as the New World. Comprising the continents of North America and South America, 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 strongly 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 .. …