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Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact

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Science  29 Jan 2016:
Vol. 351, Issue 6272, pp. 493-496
DOI: 10.1126/science.aad0525
  • Fig. 1 Oxygen isotope mass balance diagram.

    (A) Contours of Δ′17OMoon − Δ′17OEarth in parts per milliion versus fractional differences in Theia content of the bulk silicate Moon and Earth and Δ′17OTheia − Δ′17Oproto-Earth . The contour interval is 2 ppm. The pink region indicates that the contour intervals are consistent with the Δ′17OMoon − Δ′17OEarth reported by Herwartz et al. (21). The yellow region encompasses the contours consistent with our data ±2 SE. Corresponding values for δTheia are shown at right. One set of δTheia values applies if the fraction of the present-day bulk silicate Earth composed of Theia is 0.1, whereas the values in parentheses apply where the fraction of Theia in present-day Earth is 0.5. For comparison, the ranges in Theia contents of the Moon and Earth for four simulated Moon-forming impact scenarios are shown as dashed horizontal lines. The models include the “canonical” model requiring no subsequent angular momentum loss by Canup (2008; Canup08), the hit-and-run model of Reufer et al. (2012; RMBW012), and the high angular momentum scenarios, including Cuk & Stewart (2012; C&S012) and Canup (2012; Canup012). (B) The cumulative probability for Δ′17OTheia – Δ′17Oproto-Earth in per mil based on simulations in this study. Three cases are shown: those with late accreted mass to Earth <5%, those with late accreted mass <1%, and all simulations.

  • Fig. 2 Plot of Δ′17O versus δ′18O for lunar and terrestrial samples by using a fractionation line with β = 0.528 passing through San Carlos olivine as the reference.

    Only the powders of lunar samples are plotted. The gray region indicates the regions accessible through mass fractionation starting from SC olivine. Different fractionation laws are labeled with their defining β values. Error bars depict 2 SE for each measurement. Points lying inside of the gray region are consistent with simple one-stage, mass-dependent isotope fractionation relative to SC olivine, implying that they represent a single oxygen reservoir.

  • Fig. 3 A simulation of the oxygen isotopic evolution of the terrestrial planets and last giant (Moon-forming) impactor, Theia.

    The Δ′17O values of the growing Venus-like (green), Earth-like (blue), and Mars-like (red) planets are shown as a function of time as well as the value for the Theia-like impactor (black). (A) The case in which the water oxygen reservoir has Δ′17O = 3‰. (B) The case in which water Δ′17O = 100‰.

  • Table 1 Summary of oxygen isotope data for lunar and terrestrial samples.

    Delta values are in logarithmic form as defined in the text.

    Sampleδ′17Oδ′18OΔ′17O
    Lunar basalt
                Average (n = 8)3.0045.691–0.001
                Standard deviation0.0900.1720.005
                Standard error0.0320.0610.002
    Lunar basalt-fused beads
                Average (n = 4)2.9405.5720.000
                Standard deviation0.1330.2450.006
                Standard error0.0670.1230.003
    Lunar troctolite
                Average (n = 2)3.1786.050–0.016
                Standard deviation0.0090.0260.005
                Standard error0.0070.0190.003
    San Carlos olivine
                Average (n = 17)2.7115.1340.000
                Standard deviation0.0720.1340.005
                Standard error0.0170.0330.001
    Mauna Loa olivine
                Average (n = 4)2.7365.189–0.004
                Standard deviation0.0900.1700.001
                Standard error0.0450.0850.001
    Mauna Loa whole-rock samples
                Average (n = 5)2.7965.298–0.002
                Standard deviation0.0310.0630.003
                Standard error0.0140.0280.001
    San Carlos spinel
                Average (n = 2)2.1714.1040.004
                Standard deviation0.1350.2850.015
                Standard error0.0960.2020.011
    Bushveld anorthosite
                Average (n = 2)3.5226.694–0.012
                Standard deviation0.0020.0020.001
                Standard error0.0010.0020.000
    Gore Mountain garnet
                Average (n = 2)3.1746.020–0.004
                Standard deviation0.0170.0260.003
                Standard error0.0120.0190.002

Supplementary Materials

  • Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact

    Edward D. Young, Issaku E. Kohl, Paul H. Warren, David C. Rubie, Seth A. Jacobson, Alessandro Morbidelli

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    • Materials and Methods
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    • Tables S1 to S4
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