The sulfur cycle is the natural process by which sulfur moves through the environment, including the atmosphere, soil, and living organisms. Sulfur exists in various forms, such as sulfates in water and organic compounds in plants and animals. Microorganisms play a crucial role in converting these forms of sulfur, allowing it to be used by different life forms. In the cycle, sulfur is released into the atmosphere through volcanic eruptions and human activities, like burning fossil fuels. It then returns to the earth through precipitation, where it can be absorbed by plants or transformed by bacteria into forms usable by other organisms, completing the cycle.