Spectrum of Light: We do not see all types of light (or electromagnetic waves in physics). Different types of light have different energies. Energy of visible light lies somewhere in between.
Some types of light have less energy than visible light. We cannot see Infra Red Light. We can feel them through our skin. It feels like heat. This is why it feels hotter when we step out in direct sunlight. We use microwave for communication. It is used in mobile, TV and most other wireless communications. It is also used in cooking food in a microwave oven.
Some types of light are more energetic. X-Ray is so energetic that it can penetrate our body. It fails to pass through bones. This is used for developing X-Ray films. Doctors used them to see whether we have broken any bones. High energy electromagnetic waves can be harmful to health. A very small amount of X-Ray light is used to perform X-Ray. The sun produces negligible amount of X-Ray.
The sun produces lots of Ultra Violet light (or just UV). Ultra Violet light is also more energetic than visible light. It is harmful for living beings. It causes skin cancer and damages eyes. Fortunately there is a layer of Ozone gas above the surface of earth which blocks most of Ultra Violet light from reaching the earth.
Ozone Layer
Ozone is an elder brother of Oxygen. An oxygen molecule is made up of two oxygen atoms. Ozone molecule is made up of three atoms of oxygen. Ozone and Oxygen together absorb Ultra Violet Light. Ozone absorbs UV and converts into Oxygen. Oxygen absorbs UV and converts into Ozone. Together they form a cyclic reaction. This reaction is called Chapman Cycle. This process keeps absorbing Ultra Violet from the sunlight.
Ozone layer was discovered by French scientists Charles Fabry and Henri Buisson in 1913. The process by which Ozone layer blocks Ultra Violet light was explained by British scientist Sydney Chapman in 1930 (Hence the name, Chapman Cycle). In 1985 three scientists working in England found that there was a hole in Ozone layer! This hole was located over Antarctica. The hole was growing. They also found the chemical responsible for the hole – ChloroFlouroCarbons (CFCs).
CFCs were in common use at that time. They were used in Refrigerators. They were also used as solvents in many industrial applications. When CFCs reach upper atmosphere, they produce Chlorine. The Chlorine reacts immediately with Ozone. This depletes ozone in upper atmosphere. This disturbs the Chapman cycle. Atmosphere is not able to block Ultra Violet light.
This was scary news. It represented an immediate danger to humanity. Until then, the hole was above Antarctica. Not many people live in Antarctica. However, the spread of ozone hole over populated regions would have caused an epidemic of Skin Cancer.
Countries of the world reacted immediately. Montreal Protocol was signed in 1987. It banned use of CFCs and other chemicals which could cause depletion of Ozone layer. This treaty was ratified by all countries in the world. Such rapid international cooperation is rare in history, especially in the field of Climate Science.
It worked! In 2001, it was found that the size of the hole was constant for past few years. In 2016, it has been observed that the hole is now healing slowly and becoming smaller. The process of closing of hole is very slow. CFCs which have already been produced can stay in atmosphere for 60 to 70 years. Scientists are hoping that the hole will be closed completely by 2070.
Some Bad News
Ozone is good for us when it is high above the earth. It blocks Ultra Violet Rays. Ozone on earth surface is bad. It is harmful for health. It has a major role in pollution in many cities. It contributed to the smog which enveloped Delhi last year.
The sun is not the only source of Ultra Violet light. It is also produced in Electric Arc Welding. We should not look directly at the point where welding is being done. That is harmful for eyes. People who work in welding should wear protective glasses. Full sleeves clothes are also essential for reducing risk of skin cancer.
Stephen Montzka works at NOAA in Colorado. NOAA stands for National Oceanic and Atmospheric Administration. It is an American Government scientific agency. He keeps a watch on the level of different chemicals in atmosphere. He has been doing this for past 27 years. This year he found that the level of CFCs has increased suddenly. He looked at various possible reasons for the rise. He was left with only one possible explanation. Someone somewhere is producing CFCs. He published his research in May edition of journal Nature. Scientists are trying to solve the mystery. They are optimistic that they will soon find the source of emission and stop it. There should be no lasting damage.
Wolves of Chernobyl
Chernobyl is located in Ukraine. Earlier it was part of the Soviet Union. There was a nuclear power plant at Chernobyl. It exploded in 1986. It was not certain how much radioactive material had leaked. No one knew how much harm it will inflict. As a precaution an exclusion zone was created. No one was allowed to live there. This zone was centred at the site of accident and had a diameter of 30 kilometres.
As human activity has ceased, the region has automatically become a natural reserve. Wildlife has flourished. Grey wolves have specially prospered. With increase in population many wolves are wandering out of the region. Some scientists are worried that these wolves may have mutant genes. Mutant genes are a side effect of radioactivity. They think that these genes may spread into larger population. Other scientists are not too worried. They point out that there is no evidence that harmful mutations are taking place and spreading.
Flourishing of wildlife at Chernobyl proves one thing for sure. Radiations may be harmful for forests and wild animals. However human beings are more hazardous than after effects of nuclear radiations.