Why Earth Supports Life

There are three major reasons why Earth is uniquely suited for life:

1. Earth is part of the "habitable zone", which is an area around the Sun in which it is not too hot or too cold. The idea that our planet formed in a part of the solar system that is not too hot or too cold is called the "Goldilocks Principle."

2. Earth's atmosphere contains gases such as nitrogen and oxygen that are essential for life. Also, gasses in Earth's atmosphere, such as water vapor, carbon dioxide, methane and nitrous oxide, trap heat in the atmosphere and prevent it from escaping into space. As a result, the Earth is warm enough to sustain life. The trapping of heat within Earth's atmosphere is called "the Greenhouse Effect."

3. The third major reason is the presence of liquid water. Earth has liquid water, in part, because of the atmosphere and its "Goldilocks" position. It would be difficult for life as we know it to form without liquid water.