Throughout the world there are various types of pollution that interfere with the quality of life for all living creatures and with the natural functioning of the earth's ecological systems. Although some environmental pollution is a result of natural causes (such as methane emissions from cattle and toxic materials expelled from volcanoes), most pollution is caused by human activities.

Human Industrial Activities

In the United States, as is the case in most industrialized nations, the greatest source of pollution is the industrial community. According to the 2000 Toxics Release Inventory (TRI) of the U.S. Environmental Protection Agency (EPA), over 2.95 million metric tons (6.5 billion pounds) of toxic chemicals from about 2,000 industrial facilities are annually released into the environment, including nearly 45,360 metric tons (100 million pounds) of recognized carcinogens.

Early History

Human contamination of the earth's atmosphere has existed since humans first began to use fire for heating, cooking, and agriculture...