How did the Earth get its ozone layer?

The earth got its ozone layer from the oxygen present in its atmosphere. Ultraviolet rays from the Sun photolyze oxygen molecules (O2), to yield two oxygen atoms. A single oxygen atom can react with an oxygen molecule (O2) to yield ozone (O3). read more

The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth's atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometers (12 to 19 mi) above Earth, although its thickness varies seasonally and geographically. read more

A layer of ozone gas acts as a shield encircling Earth, and exists between 9.3 (15 kilometers) to 18.6 miles (30 kilometers) above its surface. As one might suspect, the ozone layer is filled with ozone, also known as [math]O_3[/math] [math] [/math] or trioxygen. read more