piles of bones on the soil surface, leading to localized enrichment of the soil below. Redox conditions in wetland soils Nutrient cycling in lakes and freshwater wetlands depends heavily on redox conditions. Under a few millimeters of water heterotrophic bacteria metabolize and consume oxygen. They therefore deplete the soil of oxygen and create the need for anaerobic respiration. Some anaerobic microbial processes include denitrification, sulfate reduction and methanogenesis and are responsible for the release of N2 (nitrogen), H2S (hydrogen sulfide) and CH4 (methane). Other anaerobic microbial processes are linked to changes in the oxidation state of iron and manganese. As a result of anaerobic decomposition, the soil stores large amounts of organic carbon because the soil carbon sponge stays intact. The redox potential describes which way chemical reactions will proceed in oxygen deficient soils and controls the nutrient cycling in flooded systems. Redox potential, or reduction potential, is used to express the likelihood of an environment to receive electrons and therefore become reduced. For example, if a system already has plenty of electrons (anoxic, organic-rich shale) it is reduced. In a system, it will likely donate electrons to a part that has a low concentration of electrons, or an oxidized environment, to equilibrate to the chemical gradient. An oxidized environment has high redox potential, whereas a reduced environment has a low redox potential. The redox potential is controlled by the oxidation state of the chemical species, pH and the amount of oxygen (O2) there is in the system. The oxidizing environment accepts electrons because of the presence of O2, which acts as an electron acceptor: O2 + 4 e- + 4 H+ <=>> 2 H2O This equation will tend to move to the right in acidic conditions. Higher redox potentials are found at lower pH levels. Bacteria, heterotrophic organisms, consume oxygen while decomposing organic material. This depletes the soils of oxygen, thus increasing the redox potential. At high redox potential, the oxidized form of iron, ferric iron (Fe3+), will be deposited commonly as hematite. In low redox conditions, decomposition rates decrease and the deposition of ferrous iron (Fe2+) increase. By using analytical geochemical tools such as X-ray fluorescence (XRF) or inductively coupled mass spectrometry (ICP-MS) the two forms of Fe (Fe2+ and Fe3+) can be measured in ancient rocks therefore determining the redox potential for ancient soils. Such a study was done on Permian through Triassic rocks (300–200 million years