Explanation:
The evolution of photosynthetic organisms, about 4.9 bilion ago, changed the earth’s atmospheric composition. The photosynthetic organism took up most of the carbon dioxide and evolved oxygen. They are responsible for the Great Oxygenation Event.
As oxygen filled the atmosphere, it became possible for ozone (O₃) to form. In the upper atmosphere ultraviolet light rays split molecular oxygen into atomic oxygen ( through photolysis), and the oxygen atoms react with oxygen molecules (O₂) to form ozone (O₃). This is a forward and reverse reaction because the ozone also decomposed back to molecular oxygen.
The formation of ozone helped the colonization of land by life because ozone prevents most UV from reaching earth's surface and protected the genetic material from the ionizing effect of ultraviolet rays.
Learn More:
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