Organic matter in the ocean is depleted in 13C by ~20‰ relative to the (arbitrarily chosen) standard, carbon from fossil (extinct) marine Belemnite

carbonates in the Pee Dee formation in South Carolina (the PDB standard). By definition, the isotopic value of the standard relative to itself is 0‰ . Mantel carbon, emitted from volcanoes, has an isotopic value of ca. −5‰. Hence, to obtain such a mantel carbon isotopic value requires mixing 4 mass equivalents of carbonate with one mass equivalent of organic carbon. This basic notion provides the basis for estimating the oxidation state of the planetary surface (from a practical purpose, the atmosphere, as a very small fraction of the free find more oxygen is dissolved in the ocean or is found in crustal rocks). The notional concept is that as more organic carbon is buried oxygen concentrations in the atmosphere increase. On geological time scales, the burial of organic carbon removes the lighter isotope, 12C, in the inorganic phase, from the ocean/atmosphere system, leaving behind inorganic carbon that is increasingly enriched in 13C. Hence, on

geological time scales, increased net oxidation of the Earth’s surface can quantitatively be related to increased 13C content of inorganic carbon buried in the rock record as carbonates. The geochemical record of carbon isotopes over geological time, while clearly not perfect, is extensive and clearly reveals the pattern www.selleckchem.com/products/3-deazaneplanocin-a-dznep.html of burial of reducing equivalents over the past 3.5 billion years. The results strongly suggest that organic carbon was extensively buried for 200 million years around the time of the GOE, and subsequently around 700 Ma (million years ago), and 350 Ma. Burial of organic matter on geological time scales is not trivial. Although until approximately 400 Ma, all primary production

on Earth was confined to aquatic ecosystems (by far the oceans), and the residence time of marine sediments is relatively short—on order of ca. 200–300 million years. The sediments are largely subducted into the upper mantel where they are heated and the resulting gases emitted via volcanism back to the atmosphere. Pyruvate dehydrogenase Indeed on geological time scales this is the source of CO2 in Earth’s atmosphere. This so-called Wilson cycle [named after the late Canadian geophysicist, Tuozo Wilson (1966)] constrains oxidation of the atmosphere to small levels of oxygen, on order of ca. 1% PAL. To escape this constraint, organic carbon must be removed from the cycle. One mechanism is the uplift of marine sediments onto continental cratons, where it can be stored for billions of years. Indeed, subduction of marine crust along active continental margins leads to the formation of stable sedimentary rocks (as shales and mudstones) uplifted onto land and hence removed from the Wilson cycle. This process is driven by plate tectonics. Earth is the only planet in our solar system with active plate tectonics.