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Formation of the Ozone Layer

One billion years ago, early aquatic organisms called blue-green algae began using energy from the Sun to split molecules of H2O and CO2 and recombine them into organic compounds and molecular oxygen (O2).This solar energyconversion process is known as photosynthesis.Some of the photosynthetically created oxygen combined with organic carbon to recreate CO2 molecules.The remaining oxygen accumulated in the atmosphere, touching off a massive ecological disaster with respect to early existing anaerobic organisms.As oxygen in the atmosphere increased, CO2 decreased.

High in the atmosphere, some oxygen (O2) molecules absorbed energy from the Sun's ultraviolet (UV) rays and split to form single oxygen atoms.These atoms combined (27k jpeg) with remaining oxygen (O2) to form ozone (O3) molecules, which are very effective at absorbing UV rays.The thin layer of ozone that surrounds Earth acts as a shield, protecting the planet from irradiation by UV light.

The amount of ozone required to shield Earth from biologically lethal UV radiation, wavelengths from 200 to 300 nanometers (nm), is believed to have been in existence 600 million years ago.At this time, the oxygen level was approximately 10% of its present atmospheric concentration.Prior to this period, life was restricted to the ocean.The presence of ozone enabled organisms to develop and live on the land.Ozone played a significant role in the evolution of life on Earth, and allows life as we presently know it to exist.

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Last updated: Sep 09, 2009 02:24 PM ET