Earthquakes and global warming
Earthquakes produce shock waves that cause damage. There are two types of seismic wave - p-waves and s-waves. Seismometers can detect these waves and provide evidence of the Earth’s structure.
The ozone layer reduces the amount of ultraviolet light from the Sun that reaches the Earth’s surface. Exposure to ultraviolet radiation can lead to sunburn and skin cancer, but sunblocks can reduce this damage.
Increased energy use and deforestation raise the amount of carbon dioxide in the atmosphere. This leads to global warming.
The Earth’s crust and upper mantle are broken up into huge tectonic plates. Where these meet, the Earth’s crust becomes unstable and earthquakes and volcanic eruptions occur.
Earthquakes cause damage to buildings, and often lead to loss of life. It is difficult to predict exactly when an earthquake might happen and how bad it will be, even in places that are known for having earthquakes.
Earthquakes produce shock waves. These travel through the Earth and can be detected using a device called a seismometer.
There are two types of seismic wave.
|Type of wave||longitudinal||transverse|
|What can they travel through?||solids and liquids||solids only|
P-waves are longitudinal waves like sound waves, and s-waves are transverse waves like light waves
Ultraviolet radiation is found naturally in sunlight. Exposure to ultraviolet radiation can cause:
We cannot see or feel ultraviolet radiation, but our skin responds to it by turning darker. This happens in an attempt to reduce the amount of ultraviolet radiation that reaches deeper skin tissues.
Darker skins absorb more ultraviolet light, so less ultraviolet radiation reaches the deeper tissues. This is important because ultraviolet radiation can cause normal cells to become cancerous.
Sunblocks can reduce the damage caused by ultraviolet radiation. They contain chemicals that absorb a lot of the radiation and prevent it from reaching our skin. They may also contain chemicals that reflect some of the radiation away from the skin.
Manufacturers of sunblocks make products with different sun protection factors:
If, for example, you would get sunburnt after ten minutes in the sun, with Factor 5 applied you could stay in the sun for 50 minutes - or for 1500 minutes with Factor 150 applied. But the real time is usually lower, because some of the sunblock gets absorbed by the skin, and some gets rubbed off.
Dust from volcanoes reflects heat radiation from the Sun, leading to cooling. But dust from factories reflects heat radiation from cities, stopping it from escaping. This leads to warming in urban areas.
Carbon dioxide is a greenhouse gas. It absorbs heat energy that is radiated from the Earth’s surface and prevents it from escaping into space. This keeps the Earth warmer than it would otherwise be. But human activities are increasing the amount of carbon dioxide in the atmosphere. This increases the greenhouse effect and leads to global warming.
Human activities leading to global warming include:
Most of the energy we use comes from burning fossil fuels. These release carbon dioxide when they burn. So the increasing use of energy is leading to increasing amounts of carbon dioxide in the atmosphere.
When land is cleared for timber and farms, there are fewer trees to remove carbon dioxide from the atmosphere by photosynthesis. Also, if the fallen trees are burned or left to rot, additional carbon dioxide is released into the atmosphere.
A knowledge of how seismic waves travel through the Earth provides us with evidence of the Earth’s structure. Remember that:
The speed of p-waves and s-waves increases as they travel deeper into the mantle. They travel through the Earth in curved paths, but they change direction suddenly when they pass through the boundary between substances in different states. The diagrams show what happens when p-waves and s-waves pass through the Earth:
S-waves cannot pass through the liquid outer core, but p-waves can. When p-waves pass from solid to liquid, then from liquid to solid, there are sudden changes in direction.
Ozone (O3) absorbs ultraviolet radiation. The ozone layer is the part of the upper atmosphere where ozone is found in the highest concentrations. The ozone there absorbs ultraviolet radiation, preventing most of it from reaching the ground. This is important because ultraviolet radiation can lead to skin cancer.
Chlorofluorocarbons, or CFCs, are chemicals that were once used widely in insulating foam and aerosol spray-cans. They release reactive chlorine atoms in the upper atmosphere. These break down ozone and damage the ozone layer. CFCs have now been almost completely replaced by chemicals that do not destroy ozone.