Ozone Layer - What is the Ozone Layer?

Ozone is a naturally occurring gas found in the atmosphere where it absorbs most of the sun's ultraviolet light - invisible rays which are harmful to both plant and animal life.

Ozone is found throughout the atmosphere including at ground level, but is mostly (about 90%) found in a band called the ozone layer at about 15 - 30 km above the Earth's surface, in the stratosphere, the height at which larger aircraft fly.  It is not really a “layer” at all but one of many gases found in the stratosphere.  

The ozone layer is essential for life - until it was formed, about a billion years ago, the only life on Earth was at the bottom of the ocean.  It is thought that single celled organisms released oxygen through photosynthesis.