The ozone layer is a thin layer of ozone in the Earths atmosphere that protects us from harmful UV rays. It is found primarily in the stratosphere, which is the second layer of Earths atmosphere, between the top of the troposphere and about 50 kilometers (31 miles) altitude. The stratospheres ozone layer is uneven, and thinner near the poles. The amount of ozone in the Earths atmosphere is declining steadily, and scientists have linked the use of chemicals such as chlorofluorocarbons (CFCs) to ozone depletion.