Sulfur (S) the 10th most abundant element in the universe, is a brittle yellow, tasteless and odorless non-metallic element. It plays a critical role in both climate and in health of various ecosystems. Majority of Earth's sulfur is stored underground in rocks, minerals and buried deep within ocean sediments.

The sulfur cycle contains both atmospheric and terrestrial (land) processes. Within the terrestrial portion the cycle begins with the weathering of Rocks, releasing the stored sulfur. The sulfur then comes into contact with air where it is converted into sulfate SO4.

The sulfate is taken up by plants and microorganisms and is converted into organic forms (amino acid, Allicin, Penicillin etc). Animals then consume these organic forms through food they eat.

As organisms die and decompose, some of the sulfur is again released as sulfate and some enters the tissues of microorganisms.There are also a variety of natural sources that emit sulfur directly into atmosphere such as, volcanic eruptions, wetlands and evaporation of water.

Sulfur eventually settles back into the Earth or comes down within rain fall. Sulfur also enters oceans through lakes and streams. A portion of ocean's sulfur is emitted back to land through waves (sea spray). The remaining sulfur is lost into the oceans depth combining with iron to form Ferrous Sulfide which is responsible for the black color of most marine sediments.

Since the industrial revolution one third of the sulfur that reaches the atmosphere and 90% of sulfur-dioxide is because of human activities such as burning fossil fuels and processing of metals. This produces chemicals in the atmosphere which then fall as Acid Rain, causing a variety of damage to both natural and man-made environment.