The Americas are the lands of the Western hemisphere or New
World, consisting of the continents of North America and South
America with their associated islands and regions. The Americas
cover 8.3% of the Earth's total surface area (28.4% of its land
area) and contain about 14% of the human population (about 900
million people). The Americas may instead be referred to as
America; however, America may be ambiguous, as it can refer
either to the entire landmass or to the United States of
America. South America broke off from the west of the
supercontinent Gondwanaland around 135 million years ago (Ma),
forming its own continent. Starting around 15 Ma, the collision
of the Caribbean Plate and the Pacific Plate resulted in a
series of volcanoes along the border that created a number of
islands. The gaps in the archipelago of Central America filled
in with material eroded off North America and South America,
plus new land created by continued volcanism. By 3 Ma, the
continents of North America and South America we