Реферат: Our Radiant Planet Depletion Of The Ozone
Our Radiant Planet- Depletion Of The Ozone Layer Essay, Research Paper
Our Radiant Planet- Depletion of the Ozone LayerOzone 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 the same effect as changes in the terrestrial webs mentioned above.Ecosystems may be further disturbed by effects of UV radiation on animals, especially in vulnerable, early stages of life such as larvae or eggs. Scientific research has only begun to scratch the surface on the impacts of UV-B radiation, but what is known is cause for concern. Despite the ever increasing list of negative UVB effects, ozone depleting chemicals are continually released into our atmosphere. Despite the availability of safer alternatives, technologies which are only slightly safer than the ones which they replace continue to be promoted. Despite the wisdom of the global science we still drag our feet. How far will the burning go? It is already deep into our seas and forests, and deep into our skin. We need to act now, and protect our planet. Our radiant earth. BibliographyThe Electric LibraryEncarta 95Ozone Depletion book at www.now.edu.au/arts/sts/sberer/h.htmlBeder, Sharon The hole story, 6/1992 ISBN SydneyH.S Johnston, Atmospheric Ozone, Annu.Rev London 1994J.M Wallace and P.V Hobbs, Atmospheric Science, and introductory survey, Academic Press USA 1993