Global warming
The earth’s surface is warmed by the sun and radiates heat back into space. Gases such as carbon dioxide, nitrogen oxides, methane and CFCs in the atmosphere trap some of this heat, and warm the lower atmosphere. The atmosphere radiates heat back to earth. This is called the `greenhouse effect’, and without it the earth would be so cold that life could not exist. But many scientists fear that the huge amounts of these `greenhouse gases’ released into the atmosphere by industrial process and burning fossil fuels are warming the earth so much that they will eventually upset the world’s climate, and cause sea –levels to rise.
The ozone layer
Ozone is a form of oxygen in which the molecule is made up of three atoms, rather than the usual two. It forms in the stratosphere. Ultraviolet (UV) radiation from the sun splits oxygen molecules into free oxygen atoms. Each oxygen atom joins an oxygen molecule to form ozone. UV radiation also splits ozone molecules. So ozone is constantly forming, splitting reforming. The UV radiation absorbed by this process cannot reach earth. UV radiation causes sunburn, skin cancer and eye problems, and affects plant growth.
• Apartheid: the policy of racial segregation practiced in South Africa till the 1990’s.
• Brain washing: the technique of changing a person’s ideas, beliefs and attitudes by force.
• Catchments Rea: area from which water is collected by a river and its tributaries.
Volcanoes
A volcano is any kind of natural opening, or fissure, in the earth’s crust through which hot molten rock (called lava), ash, steam, gas and other material is spewed. The heat comes from within the earth’s mantle. The world is also used to describe the cone of lava and ash that builds up around the opening. The shape depends on the type of eruption. Volcanic activity may take place under the sea as well as on land, and sometimes creates new land.
A geyser is an opening in the earth which, form time to time, shoots a fountain of boiling water high into the air. The water at the bottom of the geyser boils before that at the top.