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34848828112
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methods, and supplemental data are available as supporting material on Science
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Materials, methods, and supplemental data are available as supporting material on Science Online.
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Online
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Materials1
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23
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34848904580
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A. J. Kaufman et al., Science 317, 1900 (2007).
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24
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34848867098
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reference. Here, the reference is average crust (16). This normalization compensates for variable dilution by carbonate sedimentation and facilitates visualization of authigenic enrichment.
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reference. Here, the reference is average crust (16). This normalization compensates for variable dilution by carbonate sedimentation and facilitates visualization of authigenic enrichment.
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25
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34748927293
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Mo/TOC slopes are probably now steeper than they were at the time of deposition, because organic carbon is preferentially lost during catagenesis
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Mo/TOC slopes are probably now steeper than they were at the time of deposition, because organic carbon is preferentially lost during catagenesis.
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27
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34848836850
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This dissolution time assumes that a detrital pyrite crystal is exposed on all sides to water in equilibrium with O2 at pH > 5 and temperature < 70°C. The weathering rate is only slightly sensitive to temperature but roughly doubles if pH increases to a typical marine value of ∼8.3. These rates are lower limits because they neglect the rate-enhancing effects of crystal defects and microbial activity
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2 at pH > 5 and temperature < 70°C. The weathering rate is only slightly sensitive to temperature but roughly doubles if pH increases to a typical marine value of ∼8.3. These rates are lower limits because they neglect the rate-enhancing effects of crystal defects and microbial activity.
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The duration of S1 is difficult to estimate but is <16 million years based on the uncertainty in the Re/Os isochron. Assuming a typical average shale accumulation rate of ∼2.5 m/million years, the duration is ∼11 million years. These estimates are consistent with accumulation rates determined from prior geochronology of sampled units (20, 21).
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The duration of S1 is difficult to estimate but is <16 million years based on the uncertainty in the Re/Os isochron. Assuming a typical average shale accumulation rate of ∼2.5 m/million years, the duration is ∼11 million years. These estimates are consistent with accumulation rates determined from prior geochronology of sampled units (20, 21).
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34848901870
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This rate assumes pH, 5 and PCO2 ∼ 20 PAL. Higher P O2 would be required if CO2 were higher, because feldspar weathering rate is a strong function of pH
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2 were higher, because feldspar weathering rate is a strong function of pH.
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31
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2S appears in sediment porewaters.
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2S appears in sediment porewaters.
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4344682885
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J. L. Hannah, A. Bekker, H. J. Stein, R. J. Markey, H. D. Holland, Earth Planet. Sci. Lett. 225, 43 (2004).
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Hannah, J.L.1
Bekker, A.2
Stein, H.J.3
Markey, R.J.4
Holland, H.D.5
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34848880660
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2S concentrations, so delivery of Mo to sediments can be affected by changes in primary production, sulfate availability, or the vigor of bacterial sulfate reduction.
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2S concentrations, so delivery of Mo to sediments can be affected by changes in primary production, sulfate availability, or the vigor of bacterial sulfate reduction.
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We interpret this stratigraphic shift as indicating a change in environmental oxygenation with time. It is alternatively possible that the shift records sediments accumulating at different water depths in a redox-stratified water column. In either case, the Mo and Re enrichments are evidence of oxidative weathering ∼2.5 Ga
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We interpret this stratigraphic shift as indicating a change in environmental oxygenation with time. It is alternatively possible that the shift records sediments accumulating at different water depths in a redox-stratified water column. In either case, the Mo and Re enrichments are evidence of oxidative weathering ∼2.5 Ga.
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2+.
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2+.
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39
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34848867712
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O2.
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O2.
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41
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34848877143
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The authors thank A. H. Knoll for inspiration and encouragement; B. Runnegar and R. Grymes for launching the Astrobiology Drilling Program; B. Blumberg for supporting the Mission to Early Earth Focus Group of the NASA Astrobiology Institute; and J. Farquhar, R. Raiswell, D. Johnston, A. Bekker, T. Algeo, J. Kasting, and J. Hannah for helpful discussions. Two anonymous reviewers helped improve the manuscript. J. S. R. Dunlop, L. C. Bonser, M. van Kranendonk, A. Hickman, and the Geological Survey of Western Australia assisted with core recovery. Funding was provided by the NASA Astrobiology Institute and the NSF Geobiology and Low Temperature Geochemistry program.
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The authors thank A. H. Knoll for inspiration and encouragement; B. Runnegar and R. Grymes for launching the Astrobiology Drilling Program; B. Blumberg for supporting the Mission to Early Earth Focus Group of the NASA Astrobiology Institute; and J. Farquhar, R. Raiswell, D. Johnston, A. Bekker, T. Algeo, J. Kasting, and J. Hannah for helpful discussions. Two anonymous reviewers helped improve the manuscript. J. S. R. Dunlop, L. C. Bonser, M. van Kranendonk, A. Hickman, and the Geological Survey of Western Australia assisted with core recovery. Funding was provided by the NASA Astrobiology Institute and the NSF Geobiology and Low Temperature Geochemistry program.
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