The document summarizes 3 important Earth cycles: the water cycle, which involves the evaporation, condensation, precipitation, transpiration, and runoff of water; the carbon cycle, through which carbon dioxide is absorbed by plants through photosynthesis and released through respiration and burning fossil fuels; and the nitrogen cycle, where nitrogen gas in the atmosphere is converted into usable forms by bacteria in the soil and plants to build proteins, and then returned to the soil after death.

2. The water cycle

5. The Carbon Cycle

8. The Nitrogen Cycle