The+Earth

The Earth, man's home, is a planet. It moves around the sun in a regular orbit, as do the eight other planets in the solar system. Each of the solar planets has special characteristics, some of which are well known to both scientists and the public in general. Saturn, for example, is surrounded by a set of rings, and Jupiter is famous as the largest planet in the solar system. The Earth also has special characteristics, and these are important to man. It is the only planet known to have the right temperature and the right atmosphere to support the kind of life man knows. (See also Planets.) The Earth's special characteristics make possible the kinds of environments and natural resources in which plants and man and other animals can survive. This fact is so important to man that he has developed a special science called ecology, which deals with the dependence of all living things upon one another and upon their environments. Ecologists try to find out how the Earth's environments can be preserved so that living things will continue to survive on the planet. Some scientists believe that millions of planets in the Milky Way, the galaxy that contains the Earth, may be able to support life. But no one can predict the forms that such life might take. An indication of just how difficult such a prediction might be is illustrated by the vast variety of life forms on Earth. Many millions of kinds of plants and animals have developed on the Earth. They range in size from microscopic plants and animals to giant trees and mammoth whales. Distinct types of plants or animals may be common in many parts of the world or may be limited to a small area. Some kinds thrive under conditions that are deadly for others. So some persons suggest that forms of life quite different from those known on Earth might possibly survive on planets with conditions that are far different from conditions on Earth.