Rob Rye

Life associated with a 2.76 Ga ephemeral pond?: evidence from Mount Roe #2 paleosol

Dark sericitic material at and near the top of the 2.765 +/- 0.01 Ga Mount Roe #2 paleosol in Western Australia contains 0.05-0.10 wt% organic carbon with delta 13C values between -33% and -51% PDB (Peedee belemnite). Such negative isotopic values strongly indicate that methanotrophs once inhabited this material. The textures and the chemical composition of the dark sericitic material indicate that the methanotrophs lived in or at the edges of ephemeral ponds, that these ponds became desiccated, and that heavy rains transported the material to its present sites. The discovery of methanotrophs associated with the Mount Roe #2 paleosol may extend their geologic record on land by at least 1.5 b.y. Methanotrophy in this setting is consistent with the notion that atmospheric methane levels were > or = 20 (mu)atm during the Late Archean. The radiative forcing due to such high atmospheric methane levels could have compensated for the faint younger sun and helped to prevent massive glaciation during the Late Archean.

Evidence for low or no oxygen in the late Archean atmosphere from the ∼2.76 Ga Mt. Roe #2 paleosol, Western Australia: Part 3†

Abstract This paper is a contribution to the ongoing controversy regarding the evolution of atmospheric oxygen. The history of the oxidation state of paleosols can help to resolve the controversy, because the distribution of redox-sensitive elements in soils has been strongly influenced by the oxygen content of the ambient atmosphere, particularly before the advent of the higher land plants. The distribution of the major and minor elements in a section through the 2.76 Ga Mt. Roe #2 paleosol seems to have been unaffected by the presence of oxygen, and indicates that this soil developed under an atmosphere that contained very little or no oxygen.

Evidence in pre–2.2 Ga paleosols for the early evolution of atmospheric oxygen and terrestrial biota: Comment and Reply

The major points of disagreement between Holland and Rye and Ohmoto concern (1) the behavior of ferric iron. (2) the mechanisms of Fe loss. (3) the identification of real paleosols, and (4) the ages of some paleosols.

High precision mass spectrometric analysis of isotopic abundance ratios in nitrous oxide by direct injection of N2O

Abstract This paper presents the technical and theoretical background of a technique for directly determining the nitrogen and oxygen isotopic composition of N2O by measuring simultaneously the m/z 44, 45, and 46 beam intensities on a gas source ratio mass spectrometer. Mass interferences are caused by any CO2 contaminant as CO2 has the same molecular masses as N2O. Any small amount of CO2 remaining in the sample can be corrected for by measuring the ratio of m/z 12 to 14 or m/z 12 to 44 ratio in the sample. Under certain source conditions, NO2 is produced in the ion source, causing a mass interference at m/z 46. NO2 production in the source can be corrected for by establishing an NO2 slope correction factor through measuring the ratio of m/z 46 to 44 in the sample at various ion source pressures. The production of NO2 can be totally eliminated by increasing the draw-out voltage in the source to a value similar to that used for hydrogen isotope analysis. Experiments were carried out on both a Finnigan MAT251 and a Finnigan MAT252. Delta values for oxygen and nitrogen isotope abundances were obtained with an internal precision of better than 0.08 permil and 0.02 permil, respectively, on samples as small as 3 μmol on both instruments.