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 hydrogen sulfide in the atmosphere. Microorganisms play a crucial role in converting these forms of sulfur, allowing it to be used by plants and animals. In the sulfur 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. Eventually, sulfur is returned to the atmosphere through decomposition and other processes, completing the cycle.