P2 - RADIATION AND LIFE

The ultraviolet radiation in sunlight can cause skin cancer, which can kill. Melanin, a brown pigment in the skin, provides some protection from UV radiation. Human skin absorbs sunlight to make vitamin D. This nutrient strengthens bones and muscles. It also boosts the immune system. Recent research suggests that vitamin D can prevent the growth an spread of some cancers. Darker skin makes it harder for the body to make vitamin D. So in none sunny regions of the world there is an advantage in having fair skin.

THE OZONE LAYER - The atmosphere is a mixture of gases, including oxygen. In the upper atmosphere some of the oxygen is in the form of ozone, it makes an ozone layer. The ozone layer is good at absorbing UV radiation. When UV radiation is absorbed its energy can break ozone molecules to make oxygen molecules and free atoms of oxygen or break oxygen molecules to make free atoms of oxygen. These chemical changes are reversible. Life on earth depends on the ozone layer absorbing UV radiation.

THE ELECTROMAGNETIC SPECTRUM (Least photon energy to most)

Radio - Microwave - infrared - visible - UV - X Ray - Gamma

All radiation has a source that emits it. Then it has a journey, it spreads out or radiates. Some radiation at the end of its journey causes chemical changes and the back of your eye. This radiation is visible light. Some materials, like air, are good at transmitting light. For all examples there is a source, a journey and a detector. The detector must absorb radiation for it to work.

IONISING RADIATON - Sources of gamma radiation, x-rays and UV radiation pack a lot of energy into each photon ( a packet of radiation). So absorbs get a lot of energy from each photon. These photons have a strong local effect- they can ionize. Gamma radiation, x-rays and UV radiation are all called IONIZING RADIATON. Visible infrared, microwave and radio radiation are all NON IONIZING - their main effect is warming. The lower the photon energy the smaller the heating effect.

MICROWAVE OVENS - In a MO, microwave radiation transfers energy to absorbing materials. Molecules of water, fat and sugar are good absorbers of microwave radiation. MW make these molecules vibrate. Food containing them gets hot. Other particles, like the particles in glass or pottery take very little energy from the radiation. The heating effect of non ionizing radiation on an absorbing material always depends on its intensity (the energy that arrives every second) and its duration ( the exposure time).

SAFETY FEATURES - Exposure to sufficient microwave radiation could cook you. The oven door has a metal grid to reflect the radiation back inside the oven. Also a hidden switch prevents ovens from operating with the door open.

MOBILE PHONES - Mobile phones uses microwave radiation. They receive MW from a nearby phone mast and send MW back. Patterns in the radiation carry information. When you make a call, the fairly thick bones of your scull absorb some of the radiation. But some of this reaches your brain and slightly warms it, vigorous physical exercise has a greater heating effect. Distance from a radiation source is important. The intensity of MW decreases with distance, because the energy spreads out as it travels.

PHONE MASTS - People have concerns about the radiation from phone masts. Fortunately, PM are designed so their radiating beam is shaped like the beam of light from a lighthouse. If you stand directly under one, its radiation is much weaker than the radiation from you phone.

X-RAY SAFETY - X-rays were discovered in the 1890's. They soon caught on as a useful medical tool but they are a form of ionizing radiation. X-ray photons can ionize molecules in you body. This can disrupt the chemistry of the body cells, and cause cancer. 2 Scientists carried out a survey on a large number of women and their children, they discovered a correlation between X-ray exposure of mothers during pregnancy and cancers in their children, resulting in more cautious use of X-rays.

PAST TEMPERATURES - Weather stations have been keeping temperature records for over a century. Climate scientists study these records. They also study natures own records, going back thousand of years. These include growth rings in trees, ocean sediments and air trapped in ancient ice. There is a clear pattern - the earths average temperature has been increasing since 1800.

CORROLATION WITH CO2 - Most scientists think that CO2 in the atmosphere is causing the earths av temperature to rise.

• Global temps and CO2 levels have both increase recently
• There is evidence from the distant past that temp and CO2 level change together
• Scientist know how CO2 in the atmosphere warms the earth
• Computer climate models show that global temps are related to CO2 levels

GREENHOUSE GASES - Tiny amounts of a few gases in the atmosphere make all the difference. Carbon dioxide, methane and water vapour absorb some of the earths infrared radiation. They are called green house gases.

THE CARBON CYCLE - The earths crust, oceans, atmosphere and living organisms all contain carbon. Carbon atoms are used over and over again in natural processes. The carbon cycle describes stores of carbon and processes that move carbon.

CO2 IN THE ATMOSPHERE - 100 of millions years ago the amount of CO2 in the atmosphere was much higher than today. Green plants made use of CO2 and released oxygen, this made life possible for animals. Eventually lots of carbon was locked up underground in the form of fossil fuels, as well as carbonaceous rocks such as limestone and chalk.

HUMAN ACTIVITIES AND CARBON - Most things that people need require energy. But when ever fossil fuels - oil, gas and coal - are burnt, they increase the amount of CO2 in the atmosphere. Methane, another GHG, is produced by grazing animals and from rise paddies. Although methane is the more effective GHG, CO2 produced by human activities has a bigger effect. This is because the amount of CO2 is so huge. This is why there is talk of reducing carbon emissions.

EFFECTS OF CLIMATE CHANGES - Global warming is expected to produce a variety of effects in different parts of the world. To evaluate a risk, you need to consider both the chances of something happening and the consequences if it does. The risk associated with GW are enormous. Climate models predict that winters will become wetter and summers dryer across all of the UK.We are already seeing its effects:-

• Mountain glaciers are retreating everywhere
• Some polar regions are warming at a rate 2 to 3 times the global average
• Many parts of the world are experiencing extreme weather eg. high winds, heavy rains or heat waves and draughts

POSSIBLE EFFECTS ON PEOPLE - Human societies depend on stable climates. Climate change may cause problems for :-

• Food and water resources
• Coastal populations and industry affected by rising sea levels
• Insurance companies and other financial services
• Human health (malaria will spread if mosquitoes can breed in more places)

REDUCING THE AMOUNT OF CO2- Perhaps you will take action yourself, now and in the future. You could-

• Turn the heating down
• Use a car less
• Have fewer holidays involving air travel
• Use energy from non-fossil fuel sources
• Recycle paper, glass, tin, cardboard and plastic
• Insulate your house
• Buy an energy efficient car
• Buy local food
• Share transport
• Use more public transport
• Plant more tree