Genre: Information/Explanation

The environment has four major components : the air , the land , the water and the living organisms which inhabit it . Scientists have given special names for each by creating words based on Greek vocabulary . The first component of the environment is called the atmosphere . The atmosphere contains gases such as nitrogen , oxygen and a small amount of carbon dioxide . The next category of the environment is where all the water is found . It is called the hydrosphere . Bodies of water such as lakes , streams and the oceans form the hydrosphere . The lithosphere is the rock crust of the Earth . The entire planet is covered by the lithosphere , even though most of it has a layer of water on top called the oceans . The last category of the environment is what makes the Earth unique : the biosphere . The biosphere is where all life is found . The Atmosphere Although it is almost entirely invisible , the atmosphere is the easiest part of the Earth's environment to study . Most of the hydrosphere and the lithosphere are difficult to access and remain largely unexplored . The atmosphere , however , has very few mysteries . Just about every cubic metre of it has been observed by scientists or satellites . Johnny's Fact File No. 40 Some Greek words and their meanings " atmo " means vapour or air " hydro " means water " litho " means rock or stone " bios " means life Composition of the Air Over 200 years ago , the French scientist Antoine Lavoisier measured the chemical composition of air . Since the gases which make up the atmosphere are invisible , the best way to visualize them is by expressing them as percentages and by using a pie chart . It is important to note that oxygen gas , whose chemical symbol is 0 2 , is not the main component of air and that carbon dioxide , C0 2 , represents much less than one percent . You can see the apparatus Lavoisier used to measure the atmosphere at the Musée des arts et Métiers in Paris Ultraviolet Radiation and Heat Even though it is invisible , the atmosphere is very important for life on this planet . First of all , the atmosphere protects the surface from too much ultraviolet radiation . Ultraviolet radiation , or UV radiation , is a type of energy from the sun which , in high doses , can be dangerous for living organisms . UV radiation is responsible for giving people sun burns . Too much of it causes skin cancer . The atmosphere protects the Earth's surface in two ways . The first way is that gases in the atmosphere are capable of absorbing certain types of radiation , like a sponge absorbs water . The second way is by reflecting radiation in the same way that a mirror reflects light . As a result , very little UV radiation from the Sun ever gets to the Earth's surface . Heat , another type of energy , is absorbed or reflected by the gases in the atmosphere . Some of the heat from the Sun is reflected by the atmosphere so that the Earth does not get too hot . At night , the atmosphere prevents the Earth's heat from escaping into space . As a result , the surface does not get too cold at night .