The Amazon basin
The Amazon basis is a vast area in South-America that is drained by the Amazon river and its tributaries. It has a surface of 4,5 million km2. It is the lower part of a watershed that is bordered by the Andes in the west, the Guyana Highlands in the north, the Atlantic Ocean in the East and the Brazilian Highlands in the south. The Amazon basis is covered by the famous Amazon rainforest.
Geology
The Amazon basin has a remarkable geological history. The Brazilian Highlands and the Guyana Highlands are extremely old and were formed during the Precambrian, a period between 2000 million years and 600 million years ago. The rivers that carried water from these mountains flowed into the Pacific Ocean. This remained unchanged during the largest part of prehistory. This changed when the Andes mountains rose above the sea, about 60 million year ago. The Amazon basis became a vast inland sea, which gradually became a massive swampy, freshwater lake. Sea animals became trapped and had to adapt to the freshwater conditions. In the freshwater of the Amazon river live a number of stingrays while stingrays are usually seawater animals. About 10 million years ago, the waters broke the sandstone to the west near Óbidos in Para. Since then, the Amazon became a river that flows eastward.
Population
The Amazon basin is not heavily populated. The total number of inhabitants is about 26 million of which 11 million live on the Brazilian side. The largest cities are Manaus (1.4 million inhabitants), Belém (1 million inhabitants) and Iquitos (400 thousand inhabitants). Most people in the Amazon region live off fishing and small scale agriculture.
See also
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