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Supplementary methods, results, figures, and tables.

We have performed experiments at 1.5 GPa over the temperature range 1400-2100°C to determine the partitioning of lithophile elements (U, Th, Eu, Sm, Nd, Zr, La, Ce, Yb) between sulfide liquid, low-S metals and silicate melt. The data demonstrate pronounced increases in partitioning of all the lithophile elements into sulfide at very low FeO contents (10 in some cases. Similarly DSm may be > 2 under the same conditions of low silicate FeO. This strong partitioning behaviour is found only be important in S-rich metals, however because the observed effect of low FeO on partitioning is uniquely confined to metallic melts close to stoichiometric FeS in composition. The results and the effects of FeS content of the metal and FeO content (or activity) of the silicate may be understood in terms of exchange reactions such as: UO2+2FeS=2FeO+US2 silicate sulfide silicate sulfide High concentrations of FeS (in metal) and low FeO contents of the silicate melts drive the reaction to the right, favouring high US2 in the sulfide and hence high DU. The effect is, we find, enhanced by the high solubility of S in the silicate (up to 11 wt%) at low FeO contents. This S content greatly reduces the activity coefficient of FeO in the silicate melt, enhancing the displacement of the reaction to the right. For sulfide-silicate partitioning at 1.5GPa and 1400°C we obtain DNd/DSm of about 1.4 and DTh ∼ 0.1DU. With increasing temperature the differences between these geochemically similar element pairs decreases such that, at 2100°C DNd/DSm is 1.0 and DTh/DU is about 0.3. We used these results, together with DU and DSm to model addition of a putative Mercury-like component (with FeS core) to early Earth. We find that the 1400o results could lead to a significant (∼11ppm) 142Nd anomaly in silicate Earth and add >8 ppb U to the core, but lead to an unreasonably high Th/U of silicate Earth (4.54). Based on the 2100°C results the 142Nd anomaly would be 0 but addition of the sulfur-rich body could add up to 10 ppb of U to the core, generating, when the accompanying 21 ppb Th is also considered, ∼3 TW of the energy required for the geodynamo. In this case, the Th/U ratio of silicate Earth would approximate 4.3, within the range of some estimates.

We have developed a method for the manufacture of polycrystalline olivine capsules, suitable as containers for olivine-saturated melts in near-liquidus experiments. The aim was to avoid some of the problems found in 1 atmosphere gas-mixing experiments, notably iron loss from silicate melts to Pt wire loops and reaction between noble metal loops and sulfide liquids. Use of olivine capsules of fixed Mg/Fe enables the Mg# of the coexisting melt to be controlled and doping of the capsule with minor elements of interest enables partition coefficients to be determined at measureable concentrations. Capsules with olivine compositions ranging from Fo.70 to F0.90 have been manufactured and found to remain impermeable to basaltic melts for extended periods. in the case of magnesian compositions (∼Fo90), we found that several cycles of heating and cooling from (1250°C to 1550°C) were needed to enhance grain growth and reduce permeability to an acceptable level. in contrast, our iron-rich composition (Fo70) functioned well after a single cycle of heating from 800 to 1350°C.

We have performed an experimental and modeling study of the partial melting behavior of the HED parent body and of the fractional crystallization of liquids derived from its mantle. We estimated the mantle composition by assuming chondritic ratios of refractory lithophile elements, adjusting the Mg# and core size to match the density and moment of inertia of Vesta, and the compositions of Mg-rich olivines found in diogenites. The liquidus of a mantle with Mg# (=100*(Mg/(Mg+Fe))) 80 is ~1625oC and, under equilibrium conditions the melt crystallises olivine alone until it is joined by orthopyroxene at 1350oC. We synthesized melt from our 1350oC experiment and simulated its fractional crystallization path. Orthopyroxene crystallizes until it is replaced by pigeonite at 1200oC. Liquids become eucritic and crystal assemblages resemble diogenites below 1250oC. MELTS correctly predicts the olivine liquidus but overestimates the orthopyroxene liquidus by ~70oC. Predicted melt compositions are in reasonable agreement with those generated experimentally. We used MELTS to determine that the range of mantle compositions that can produce eucritic liquids and diogenitic solids in a magma ocean model is Mg# 75-80 (with chondritic ratios of refractory elements). A mantle with Mg# ~ 70 can produce eucrites and diogenites through sequential partial melting., Comment: 13 pages, 3 figures, Published in MAPS

The concept of Late Veneer has been introduced by the geochemical community to explain the abundance of highly siderophile elements in the Earth's mantle and their chondritic proportions relative to each other. However, in the complex scenario of Earth accretion, involving both planetesimal bombardment and giant impacts from chondritic and differentiated projectiles, it is not obvious what the "Late Veneer" actually corresponds to. In fact, the process of differentiation of the Earth was probably intermittent and there was presumably no well-defined transition between an earlier phase where all metal sunk into the core and a later phase in which the core was a closed entity separated from the mantle. In addition, the modellers of Earth accretion have introduced the concept of "Late Accretion", which refers to the material accreted by our planet after the Moon-forming event. Characterising Late Veneer, Late Accretion and the relationship between the two is the major goal of this chapter., Comment: In press as a review chapter of the AGU Monograph "The Early Earth", J. Badro and M. Walter Eds

Early version of paper for PNAS.