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Proterozoic Ocean Chemistry and Evolution: A Bioinorganic Bridge?
Recent data imply that for much of the Proterozoic Eon, Earth's oceans were moderately oxic at the surface and sulfidic at depth, and biologically important trace metals would have been scarce in most marine environments. Expand
A Whiff of Oxygen Before the Great Oxidation Event?
High-resolution chemostratigraphy reveals an episode of enrichment of the redox-sensitive transition metals molybdenum and rhenium in the late Archean Mount McRae Shale in Western Australia, pointing to the presence of small amounts of O2 in the environment more than 50 million years before the start of the Great Oxidation Event. Expand
Tracing the stepwise oxygenation of the Proterozoic ocean
A new perspective on ocean oxygenation is presented based on the authigenic accumulation of the redox-sensitive transition element molybdenum in sulphidic black shales, which reflects a greatly expanded oceanic reservoir due to oxygenation of the deep ocean and corresponding decrease in sulphide conditions in the sediments and water column. Expand
Natural fractionation of 238U/235U
Abstract The isotopic composition of U in nature is generally assumed to be invariant. Here, we report variations of the 238 U/ 235 U isotope ratio in natural samples (basalts, granites, seawater,… Expand
Natural mass-dependent variations in the isotopic composition of molybdenum
We present the first observations of natural mass-dependent fractionation of the isotopic composition of molybdenum (Mo), using multi-collector inductively coupled plasma mass spectrometry.… Expand
Late Archean Biospheric Oxygenation and Atmospheric Evolution
The correlation of the time-series sulfur isotope signals in northwestern Australia with equivalent strata from South Africa suggests that changes in the exogenic sulfur cycle recorded in marine sediments were global in scope and were linked to atmospheric evolution. Expand
A photochemical model of the martian atmosphere.
Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Expand
Iron isotopes in hot springs along the Juan de Fuca Ridge
We present Fe isotope data for high temperature hydrothermal fluids, sulfides, and basalts from the Juan de Fuca Ridge, USGS basalt standard BCR-2 and the Canyon Diablo iron meteorite. The Fe… Expand
Molybdenum Stable Isotopes: Observations, Interpretations and Directions
- A. Anbar
- 1 May 2004
The unusual chemistry of molybdenum (Mo) makes this trace element interesting to both geochemists and biochemists. Geochemically, Mo is relatively unreactive in oxygenated, aqueous solutions, and… Expand
Response to Comment on "Molybdenum Isotope Evidence for Widespread Anoxia in Mid-Proterozoic Oceans"
New molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid-Proterozoic compared to the present-day ocean, suggesting oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years. Expand