North America

I

Introduction

North America, third-largest of the seven continents, including Canada (the second-largest country in area in the world), the United States (4th largest), and Mexico (13th largest). The continental shelf also includes Greenland (the largest island); the large archipelago of Arctic islands; the island of Newfoundland; Nova Scotia; and the small French overseas department of St Pierre and Miquelon. With more than 380 million inhabitants (1994 estimate), North America is the 4th most populous continent; the United States ranks 4th and Mexico 11th in population among the world's countries. Canada and the United States have technologically developed early modern economies, and Mexico, although less technologically developed than its neighbours, contains some of the world's greatest deposits of petroleum and natural gas.

Together with Central America, the West Indies, and South America, North America makes up what is sometimes known as the western hemisphere of the Earth. North America is sometimes defined to include Central America and the West Indies, which are treated separately in this encyclopedia (although in History articles, Mexico is included in Central America). The name America is derived from that of the Italian navigator Amerigo Vespucci, who may have visited the mainland of North America in 1497 and 1498.

II

The Natural Environment

North America is roughly wedge shaped, with its broadest expanse in the north. Most of its bulk is in the middle latitudes, with a considerable northern section in the Arctic and a narrow part around the tropic of Cancer. The continent sprawls east-west across some 176° of longitude, from about longitude 12° west at Nordost Rundingen (North-east Foreland) in north-eastern Greenland to about longitude 172° east at the western extremity of Attu Island, Alaska. Its northern-southern extent is some 69°, from about latitude 83° north at Cape Morris Jesup in eastern Greenland (the most northerly point of land in the world) to about latitude 14° north in southern Mexico. North America is bordered on the north by the Arctic Ocean; on the east by the Atlantic Ocean; on the south by the Gulf of Mexico, Central America, and the Pacific Ocean; and on the west by the Pacific Ocean. The area of the continent is approximately 23.5 million sq km (9.1 million sq mi).

The outline of North America is exceedingly irregular; some extensive coastal reaches are relatively smooth, but by and large the coastline is broken and embayed, with many prominent offshore islands. The continent has three enormous coastal indentations—Hudson Bay in the north-east, the Gulf of Mexico in the south-east, and the Gulf of Alaska in the north-west. There are many small islands near the eastern and western coasts, but the most prominent islands are in the far north.

A

Geological History

According to a widely accepted theory, almost all of North America is situated on the North American plate, an enormous platform considered to be one of about a dozen major units constituting the structural mosaic of the Earth's crust. It is thought that North America was once joined to modern-day Europe and Africa and that it began to break away about 170 million years ago, in the Jurassic period, with the process of continental drift (the motor of plate tectonics) accelerating about 95 million years ago, in the Cretaceous period. As North America drifted west at a rate of about 1.25 cm (0.5 in) per year, the plate underlying the Pacific Ocean is believed to have thrust under the North American plate, thereby causing widespread early folding, evident today in a series of high mountains along the western coast. As the Atlantic Ocean widened, it caused extensive faulting along the eastern coast, resulting in the creation of mountains and offshore islands.

B

Physiographic Regions

North America can be divided into five major physiographic regions. The eastern half of Canada, as well as most of Greenland and sections of Minnesota, Wisconsin, Michigan, and New York in the United States, are part of the Canadian Shield (or Laurentian Plateau), which is a plateau region underlain by ancient crystalline rocks. The region has poor soil, and dense forests cover much of its southern part. A second region is made up of a coastal plain in most of the eastern United States and Mexico. In the United States the coastal plain is bordered on the west by a third region, comprising a relatively narrow cordillera of mountains and hills, notably the rounded Appalachian Mountains. A fourth region consists of the central portion of the continent, from southern Canada to south-western Texas, which encompasses an extensive lowland that has experienced alternating periods of submergence beneath the sea and uplift, with the result that it is deeply covered with layers of sedimentary rock. It is not an uninterrupted flatland, but includes much undulating and even hilly terrain, such as the Ozark Plateau. The western portion is made up of the Great Plains, which slope upwards to the foot of the Rocky Mountains.

The fifth, and westernmost, region of North America, taking in most of Mexico, is an active zone of mountain building; its recent geological history is dominated by crustal movements and volcanic activity. Adjacent to the Great Plains in the United States and Canada are the Rocky Mountains, which are geologically related to the Sierra Madre Oriental range of Mexico. To the west is an area of scattered basins and high plateaux, including the Interior Plateau of British Columbia in Canada, the Colorado Plateau and the Great Basin of the United States, and the vast central plateau of Mexico. Along the Pacific coast are a number of lofty mountain systems, extending from the Alaska Range to the Sierra Madre Occidental and Sierra Madre del Sur of Mexico. In between are such ranges as the Coast Mountains of British Columbia and the Cascade Range, the Coast Ranges, and the Sierra Nevada of the United States. Interspersed are some low-lying areas, notably the fertile Central Valley of California. The highest point in North America, Mount McKinley, or Denali (6,194 m/20,320 ft), is situated in the Alaska Range, and the lowest point, 86 m (282 ft) below sea level, is in Death Valley, California, a part of the Great Basin.