Life, as recorded in almost every corner of the oceans and continents, has evolved to take advantage of chemical gradients. Organisms, both big and small, utilize reduction–oxidation (redox) reactions to gain the energy required to live and grow. Although aerobic respiration (using O2) is the most popular form, other modes of respiration use oxygen alternatives and drive additional element cycles (for example, nitrogen, sulfur, and metals such as iron and manganese). These alternative metabolisms, and especially those cycling sulfur, helped shape Earth's long history and much of the world we see today. Sulfur is a fundamental constituent in macroscopic and microscopic worlds alike and is a key oxidant in the anaerobic biosphere. By reconstructing the distribution of sulfur metabolisms throughout the marine realm, we can better understand the role that sulfur plays in marine biogeochemical cycling and Earth-surface processes.

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