Earth's atmosphere is made of layers. The troposphere is closest to the ground. It reaches about six miles above the Earth. The stratosphere is the next layer. It stretches from about six miles to about thirty miles above the earth. In the stratosphere, ozone is good. When found in the troposphere, it is bad. Good ozone is made naturally in the stratosphere. It protects all life on earth. Ozone absorbs most of the harmful UV rays from the sun. UV rays have negative effects on humans, plants, and animals.

Wind is moving air. Warm air rises. Cold, dense air rushes in to take its place. This causes wind. This helps to keep the climate zones in balance. No one place can keep on getting hotter or colder.

There is water all around us in the air. This state of water is called water vapor. When liquid water gets warm enough, it becomes a gas. This is called evaporation. You can't see water vapor, but sometimes you can feel it. If there is a lot of water vapor in the air on a hot day, you might feel sticky. People say it is humid. The warmer the air is, the more water vapor it can hold.