The sulfur cycle involves both atmospheric and terrestrial processes with sulfur first being released into the atmosphere and environment by weathering rocks before coming into contact with air and getting converted into sulfate, which is taken up by plants and microorganisms before moving up the food chain. Once organisms expire, they will release the sulfate back into the environment where it will reenter the atmosphere, rain down into the ocean and combine with iron in the water to form ferrous sulfide and finally transform back into marine sediment. Ferrous sulfide is responsible for the black and brown color of marine sediment.
The amount of sulfur that enters the atmosphere in the sulfur cycle has exponentially increased throughout the years as a result of human activity. By burning fossil fuels as an energy source, human beings are increasing the amount of sulfide that enters the system. In fact, human beings are responsible for approximately one-third of all of the sulfide that enters the atmosphere via the sulfur cycle.
An increase of sulfur or sulfur dioxide in the atmosphere will cause more ultraviolet rays to be absorbed. This causes the greenhouse effect, which has been speculated as the main cause of global warming.