Matter Cycle #1: Nitrogen Cycle http://www.lenntech.com/nitrogen-cycle.htm
The Nitrogen Cycle Interactive Game http://www.ext.vt.edu/resources/4h/virtualfarm/flash_mov/nitrogencycleintro.swf
Matter Cycle #2: Phosphorus Cycle http://www.lenntech.com/phosphorus-cycle.htm
Matter Cycle #3: The Carbon Cycle http://www.windows.ucar.edu/tour/link=/earth/Water/co2_cycle.html
Matter Cycle #4: The Sulfur Cycle http://www.lenntech.com/sulphur-cycle.htm
Matter Cycles and Polution http://www.lenntech.com/matter-cycles-pollution.htm
Global warming site http://www.marshall.org/pdf/materials/391.pdf
http://www.epa.gov/climatechange/