Research Investigation 2, Task 3
Genesis of iron oxide minerals

The Fe³⁺/Fe²⁺ redox couple is one of the most important ones in the solar system, given the relatively high abundance of Fe, and the fact that the interior of the terrestrial planets is largely Fe²⁺ while the surfaces of Earth and Mars have extensive ferric oxide/hydroxide minerals. The pathways by which Fe²⁺ is oxidized in biologic and abiologic systems have been studied in detail in isolated systems, but a broad geochemical model that accounts for current or past conditions on Mars or in the early Earth has yet to be fully developed, particularly for cases where Fe²⁺ oxidation occurs through biological catalysis. Finally, the kinetic and equilibrium O and Fe isotope fingerprints of iron oxidation that may be left in the rock record are poorly known for ferric oxide/hydroxides and magnetite.

Our work in Task 3 will include:

• Determining the O and Fe isotope fractionations during ferrihydrite, goethite, hematite, and magnetite formation, under equilibrium and kinetic conditions. Such information is important for interpreting iron oxide deposits in nature.
  Lead Investigator: Clark Johnson (UW-Madison)

• Investigation of biologic Fe²⁺ oxidation under low-pH conditions, but in the absence of pyrite, using L. ferrooxidans, L. thermoferrooxidans, and A. brierleyi, over a range of temperatures and pH. This line of inquiry provides an important contrast to studies of biologic Fe²⁺ during pyrite oxidation, which has been extensively studied.
  Lead Investigator: Eric Roden (UW-Madison)