Ozone
by Chris Archer
Ozone makes up only a tiny fraction of the Earth's
atmosphere. In fact if all the ozone were to be brought down to ground
level, the layer of pure ozone would be only 3.5mm thick. However,
atmospheric ozone levels have important consequences for the plants
and animals on Earth. Ozone close to the Earth's surface is a harmful
pollutant which can cause damage to lung tissue and some plants, whereas
stratospheric ozone provides a shield, absorbing harmful ultraviolet
radiation from the sun. By about 600 million years ago the amount
of ozone in the atmosphere was sufficient to shield Earth from biologically
lethal UV radiation. This allowed the evolution of organisms which
could live on land.
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