You may have heard of the ozone shield. You may remember that it protects the Earth’s surface from most of the most harmful ultraviolet radiation. Where did the ozone layer come from? How important is the ozone layer? Do other planets have ozone layers? These are a few questions that may arise.

The ozone layer was a critical component to the evolution of life on Earth. Life on Earth is possible and first developed without an ozone layer. But, when the ozone layer did develop, the prospects for more advanced life flourished, especially on the land surface. The Earth’s atmosphere did not originally have a significant ozone layer. Ozone is made of three oxygen molecules thus it would be critical for the atmosphere to have large amounts of oxygen for it to develop to a significant extent. Ozone develops from the bonding of 3 oxygen atoms in the presence of nearly unfiltered solar radiation high in the atmosphere. Normally oxygen exists as 2 oxygen atoms that are merged but high in the atmosphere, the energy from intense solar radiation can help bond three oxygen atoms together. Ozone is a very strong absorber of UV radiation. Originally, the atmosphere had very little oxygen and thus an ozone layer could not form. Early life lived primarily if not exclusively in the ocean. Underneath several feet of water is equivalent to having a sun block from harmful UV radiation. With no ozone layer, UV radiation bombarded the Earth. Early ocean life could escape this harmful radiation by existing underwater. How did the ozone layer eventually develop?

The photosynthesis process uses carbon dioxide and energy to produce sugar and oxygen. It is the photosynthetic process that ignited the development of an atmosphere rich in oxygen. It did not occur overnight. To transform the atmosphere from oxygen poor to oxygen rich took a substantial amount of time. Once oxygen is emitted into the atmosphere, much of it stays for a significant amount of time. Oxygen is a stable relatively heavy gas that can remain in the atmosphere for long periods of time. Once the atmosphere was richer in oxygen, the ozone layer could begin to develop. As the ozone layer developed, this is one major factor that made land habitation possible. At one time the landmasses of Earth were barren from life and much of life lived in the ocean. With the bombardment of UV radiation over, life began to gradually establish itself on land over a substantial length of time through the evolution process. It can not be emphasized enough how important the ozone layer is for life on land.

For an ozone layer to develop, a planet would need to be oxygen rich with enough gravity to hold the atmosphere to the planet. The planets in our solar system, besides Earth, are relatively oxygen poor. One reason for this may be that photosynthetic life needs to develop in order for an atmosphere to have a large amount of oxygen. The more oxygen a planet has, then the greater potential it has to have an ozone layer.