Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093 Proceedings of the National Academy of Science in USA (2010), V107 (47), pp20213–20218, doi: 10.1073/pnas.1014399107 Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars R. Shaheen, A. Abramian, J. Horn, G. Dominguez, R. Sullivan, and Mark H. Thiemens Shorted text: The life on Mars debate centers around the source of the globular, micrometer-sized mineral ALH84001 meteorite carbonates; consequently, ident. of Martian processes to form carbonates is critical. A earth and likely martian carbonate formation process is reported (terrestrial aerosol carbonates; 17O excess; 0.4–3.9‰). The unique O-isotopic composition describes the atmos. heterog. chem. reaction on aerosol surfaces. Lab exp. define the transfer of O3 isotopic anomaly to carbonates via H2O2 formation (O3 reacts with surface adsorbed water). This chem. react. scenario provides an explanation for the isotopically anomalous carbonates production. The anomalous H2O2 formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir (producing MIF secondary mineral evaporites). The formation of H2O2 via heterogeneous chemistry on aerosol surfaces reveals an oxidative process in understanding ozone and oxygen chemistry (Mars & Earth).