BIOGEOCHEMICAL CYCLES OF CARBON AND SULFUR ON EARLY EARTH (AND ON MARS

The physical and chemicalinteractions between the atmosphere, hydrosphere,geosphere and biosphere can be examined forelements such as carbon (C) and sulfur (S) that haveplayed central roles for both life and the environment.The compounds of C are highly important, not onlyas organic matter, but also as atmospheric greenhousegases, pH buffers in seawater, oxidation-reductionbuffers virtually everywhere, and key magmaticconstituents affecting plutonism and volcanism. Sassumes important roles as an oxidation-reductionpartner with C and Fe in biological systems, as a keyconstituent in magmas and volcanic gases, and as amajor influence upon pH in certain environments.These multiple roles of C and S interact across anetwork of elemental reservoirs interconnected byphysical, chemical and biological processes. Thesenetworks are termed