Our Radiant Planet- Depletion of the Ozone Layer

Ozone is a relatively unstable form of molecular oxygen containing three oxygen
atoms produced when upper-atmosphere oxygen molecules are split by ultra violet
light. Stratospheric ozone is found in a broad band, extending generally from 15
to 35km above the earth. Although the ozone layer is surprisingly thin, it acts
as a protective shield to the earth, as it filters out most of the harmful solar
ultraviolet radiation (in particular UV-B) that would otherwise reach our
planets surface.

Humans have damaged the ozone layer by adding molecules containing chlorine
and/or bromine that lead to ozone destruction. The largest group among these are
chloroflurocarbons (CFC's). At ground level, these molecules are very stable
and have many uses in industrial and domestic applications, such as in spray
cans, industrial solvents, degreasing compounds, and cooling in fridges. However
when released into the stratosphere, such molecules can be broken down by
energetic light rays (UV-C radiation) in a reaction that liberates an atom of
chlorine, which destroys ozone by oxidising with the Ozone molecules, forming
Cl-O and Oxygen. One atom of chlorine can destroy 10,000 ozone molecules! Atoms
containing bromine, nitrous oxide, and hydrogen oxide radicals are also
primarily dangerous. As a result, the Ozone in the stratosphere has been reduced
to such an extent that ozone holes are appearing around the globe, in particular
one over Antarctica that in 1995 measured 8.2 million square miles. This
depletion has allowed more dangerous UV-B radiation to reach the earths surface.

So what effects will ozone depletion have on us? Although, at present, the
ozone layer blocks out most of the damaging UVB radiation received from the Sun,
a small amount slips by, damaging out skin in the form of sunburns and suntans.
UVB radiation is strongly absorbed in the skin and in the outer layers of the
eye. Human skin has developed various defence mechanisms against the damaging
effects of UV radiation. The skin adapts to increased UV exposure by thickening
its outer layer and by developing pigmentation that serves to shade the more
vulnerable and deeper residing dividing cells. Overly damaged cells will
normally self destruct through a process called apoptosis, and if this fails,
the immune system should get rid of any resulting aberrant cells. It is when
these natural safeguards fail or are overcome by UVB that real trouble can ensue.
The most well known impacts on human health from exposure to UV radiation are
skin aging, sunburning and skin cancer, although recent research has expanded
the list to include eye damage such as cataracts and the suppression of the
body's immunes system to both infectious disease and chemical sensitivities.
Sunburning is caused by UVB exposure. It causes a reddening of the skin and
over time can cause a dramatic aging effect on the skin. The three types of skin
cancers induced by UV radiation are basal cell, squamous cell and melanoma.
Basal cells and squamous cell cancers, also called non-melanomas are caused by
UVB irradiation, and account for 93% of skin cancers. They can be easily removed
and are rarely fatal. The rarest cancer caused by UVB is melanoma and is the
most deadly. It spreads quickly to the blood, lymphatic system and other organs.
The damage caused by UV radiation to the eyes ranges from acute sunblindness to
chronic damage such as cataracts and eye tumours. The principal form of
chronic damage linked to UV radiation is cataracts. Exposure to UVB has been
shown to suppress a portion of the human immune system important as the skin's
defence against infectious agents such as bacteria, viruses and chemicals. The
impact of UVB on human disease works in three levels. One is the increase in
activation of viruses, the second is the decrease in the immune system to
respond to viral and bacterial infection, and the third is the decrease in
tolerance to chemical exposure.

So what about the ecosystem? All animals and plants that are exposed to the Sun,
though well shielded by the ozone layer, have developed ways to cope with the
UVB radiation the reaches the earths surface, but again when their tolerance
levels are overcome many species may be clearly limited in their growth. In
addition to these direct growth effects, there may occur more subtle changes
such in plants with delays in flowering and shift in leaf distribution, causing
dramatic shifts in plant populations and in biodiversity. Depletion of plants
that serve as a sink for carbon dioxide could lead to major problems and
enhance climate change, and changes in food web could have a domino effect that
could affect mankind. Similar processes can occur in the marine ecosystem,
decreasing populations of phytoplankton in the worlds oceans. Disruption of the
marine food webs will have