How and when did the ozone layer form?

Question

Cora Andrews · Accepted Answer

The conventional answer is "it formed by the Chapman mechanism", which implies that the layer was created when the atmospheric concentration of oxygen was sufficient.

The highly reactive single oxygen atoms attack molecular oxygen that is in contact with a third non-reacting agent. Because ozone is unstable and will revert to oxygen by a reverse process, the ozone layer is the result of an equilibrium between the splitting, the formation of the ozone, and its decay back to oxygen. This theory, known as the Chapman mechanism, was put forth by British scientist Sydney Chapman in 1930. This suggests that once plants emerged and photosynthesis began, the ozone layer progressively increased in proportion to the rise in atmospheric oxygen concentration. Political pressure to lower CFC production prompted a reexamination of the Chapman hypothesis in the 1980s. Some contend that the flaw, which is that the energy in an ultra-violet quantum is insufficient to break the bond, at least in the accepted mechanism, is one that Chapman could not have known in 1930 because quantum mechanical calculations had not been sufficiently developed. This issue has gained importance because there are those who believe that CFCs interfere with the Chapman Mechanism and could lower ozone concentration. The current position on this matter is unclear.

Nathan Abbe · Answer

undefined The ozone layer formed gradually over millions of years through the accumulation of ozone molecules in the Earth's stratosphere. It began to form approximately 600 million years ago, as oxygen levels in the atmosphere increased due to photosynthetic activity by early microorganisms. The ozone layer reached its current state around 300 million years ago, providing a protective barrier against harmful ultraviolet radiation from the sun.

Evan Abrahamson · Answer

undefined The ozone layer formed approximately 2.4 billion years ago, during the Great Oxidation Event. This event occurred when photosynthetic organisms, such as cyanobacteria, began producing oxygen through photosynthesis at a rate greater than it could be consumed by geological processes. As oxygen levels in the atmosphere increased, some of it was converted into ozone (O3) through photochemical reactions involving ultraviolet (UV) light. The formation of the ozone layer was crucial for the development of life on Earth as it absorbed and blocked most of the Sun's harmful ultraviolet radiation, allowing for the evolution of complex life forms.