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Oxygen cycle: The cycle that describes the movement of oxygen within and between its three main reservoirs on Earth: the atmosphere, biosphere (zone in which all living things are found) and lithosphere (solid portion of the Earth in which no water is found).
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
