The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about 106,460,000 km2 (41,100,000 sq mi). It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe and Asia from the "New World" of the Americas in the European perception of the World. Scientific explorations of the Atlantic include the Challenger expedition, the German Meteor expedition, Columbia University's Lamont–Doherty Earth Observatory and the United States Navy Hydrographic Office.