Origins

Millions of years ago all of the land on the Earth formed one giant continent. Eventually that continent started breaking apart as the plates underneath the land started to move in different directions. This movement formed the continents that exist today. About 170 million years ago the plate underneath the Pacific Ocean and the plate under the continent of South America began to collide, forcing the land on the continent upward.

At the same time, magma from inside the Earth began to well up through the Earth in the form of volcanoes. This activity increased from about 15 to about 6 million years ago and helped to form the Andes. The Andes are part of the Pacific region known as the ring of fire because of its many volcanoes. Many of the highest Andean peaks are volcanoes, some of which are still active. Earthquakes are common in the region as well.

Physical features and climate

The Andes are not a single line of mountains. In most places they are divided into distinct eastern and western ranges. In Bolivia and Peru, the land between these ranges is a high plateau called the Altiplano. This fairly flat area is about 500 miles (800 kilometers) long and 80 miles (130 kilometers) wide. The waters of the Altiplano drain into Lake Titicaca. At 12,500 feet (3,810 meters) above sea level, Titicaca is the world's highest lake that can be navigated by large boats.

Many Andean peaks are higher than any mountains in North America. The tallest are in the south, near the border between Chile and Argentina. At 22,831 feet (6,959 meters), Argentina's Mount Aconcagua is the highest mountain anywhere in the world outside Asia.

The climate of the Andes varies according to factors such as location and altitude. In general, the temperature increases from south to north. But even within one section of the mountains—for example, the Andes of Peru and Ecuador—temperatures can range from tropical on the lowest slopes to frigid on the highest peaks. Precipitation also varies widely. A long stretch of the narrow coastal region west of the Andes receives very little rainfall. The desert of northern Chile is one of the driest places in the world. On the eastern side of the mountains, however, rainfall is generally heavy. The highest peaks are covered with snow throughout the year.

Plants and animals

Like the climate, the plant and animal life of the Andes varies with altitude. Some plants and animals can live at any height, and others can live only at certain levels. Lush tropical forests can be found at lower elevations of some parts of the Andes. At higher levels there is grassland. Above 13,000 feet (4,000 meters), only a few types of plants can resist the cold temperatures. Above 16,000 feet (4,877 meters), vegetation is almost absent.

Pumas and other South American cats rarely live above 13,000 feet (4,000 meters), but white-tailed mice live all the way up to 17,000 feet (5,180 meters). Llamas, guanacos, alpacas, and vicuñas, which are South American relatives of the camel, generally live on the Altiplano at elevations between 11,200 (3,400 meters) and 12,800 feet (3,900 meters). The Andean condor, a vulture that is one of the world's largest flying birds, can soar above even the tallest mountains.

People

Humans first settled in the Andes more than 10,000 years ago. Indian peoples such as the Inca established cities in high valleys and built roads through mountain passes. People with at least some Indian ancestors still form the bulk of the population in the Andean region. Many of them speak Indian languages such as Aymara or Quechua. The northern Andes are more heavily populated than the southern Andes.

Economy

Farming is difficult in the Andes because of the rough terrain, poor soils, and irregular rainfall. Nevertheless, most of the people of the mountains are involved in agriculture. Most crops are grown for use within the region, but some—including coffee, tobacco, and cotton—are exported. The potato was first grown in the Andes. The raising of sheep, goats, llamas, and alpacas is widespread, especially in Peru and Bolivia.

Despite the importance of agriculture, increasing numbers of people have become involved in mining, industry, and commerce. The Andean region is one of the world's richest sources of minerals. Copper, iron ore, tin, lead, zinc, silver, gold, platinum, and emeralds are all produced in the Andes. Extensive deposits of oil are found along the entire eastern side of the mountains. Sheep and alpaca wool are processed for export. Some Indian peoples engage in ceramics and weaving.

Study and exploration

Before the Spanish conquest in the1530s, the Indians had developed a thorough knowledge of the Andes. Early Spanish exploration of the mountains consisted of raids of Indian cities.

The first European studies of the region were conducted in the late 16th century. By the mid–19th century South American countries started sponsoring research in the area. Eventually most of the research focused on developing the economies of the Andean countries through establishing mining operations and building railways.