SUPPLEMENTARY INFORMATION

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1 Supplementary Table Iron Meteorite Evidence for Early Formation and Catastrophic Disruption of Protoplanets Jijin Yang 1, Joseph I. Goldstein 1 & Edward, R. D. Scott 2 1 Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003, USA. 2 Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 96822, USA. Nature manuscript Table S1. Bulk P content of IVA irons Meteorite Name Wt.%P Ref. Obernkirchen Jamestown La Grange Bishop Canyon Gibeon Seneca Township Altonah Bushman Land Steinbach Duchesne References 1. Buchwald, V. F. Handbook of Iron Meteorites. Their History, Distribution, Composition and Structure. Berkeley and Los Angeles, CA, University of California Press, (1975). 1

2 2. Moren, A. E. & Goldstein, J. I Cooling rates of group IVA iron meteorites determined from a ternary Fe-Ni-P model. Earth Planet. Sci. Lett. 43, (1979). 3. Rasmussen, K. L., Ulff-Moller, F. & Haack, H. The thermal evolution of IVA iron meteorites: Evidence form metallographic cooling rates. Geochim. Cosmochim. Acta. 59, (1995). 2

3 Supplementary Notes Iron Meteorite Evidence for Early Formation and Catastrophic Disruption of Protoplanets Jijin Yang 1, Joseph I. Goldstein 1 & Edward, R. D. Scott 2 1 Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003, USA. 2 Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 96822, USA. Nature manuscript Errors in the cooling rate measurements A. Nucleation of the Widmanstätten pattern For the IVA irons, the P content is low (see Supplementary Table) and the nucleation of the Widmanstätten pattern occurs by the reaction γ α 2 + γ α + γ (ref. 1) where γ is taenite and α is kamacite. The nucleation temperature is the martensite start temperature at which α 2 (martensite) first forms. However, it has been suggested that the diverse metallographic cooling rates of IVA irons are an artefact arising from a totally different nucleation mechanism 2. This proposal envisages that all the IVA irons had identical cooling rates appropriate for samples of a mantled core and that the Widmanstätten pattern nucleated simultaneously throughout the IVA core following impact-induced seismic waves 2. This process can be simulated with the metallographic cooling rate program by assuming that the Widmanstätten pattern nucleates according to the traditional reaction, γ α + γ. 3

4 In order to test the potential effect of impact-induced kamacite nucleation we chose three nucleation temperatures, 973, 948 and 883 K and four IVA irons, Obernkirchen, Bishop Canyon, Seneca Township, and Duchesne, which span the range of Ni and P contents in the IVA meteorites (see Table 1 and Supplementary Table). Each IVA iron becomes saturated in P at a different temperature due to its unique bulk Ni and P content. The Ni concentrations at the α kamacite/γ-taenite phase boundaries are different in each meteorite during the cooling process until the meteorite becomes saturated in P. The procedure used in this paper to determine the compositions of α kamacite/γ-teanite phase boundaries was applied previously to the IIIAB irons 3. We measured the cooling rate for the four meteorites using the Wood method 4 for each assumed kamacite nucleation temperature. Figure S1 shows the cooling rates as a function of Ni content in the four meteorites assuming impact-induced kamacite nucleation at 973 K. Similar results are obtained for nucleation at 948 and 883 K. The cooling rate range for the four meteorites is more than a factor of 10 for all three nucleation temperatures, and the scatter on the Wood diagram is increased. The cooling rate range is less than the cooling rate range measured in this study (Table 1), but still much too large for a mantle-insulated metallic core, which would have a uniform cooling rate. Clearly, the impact nucleation mechanism 2 does not eliminate the systematic decrease in cooling rate with increasing Ni and cannot produce uniform cooling rates for IVA irons. 100,000 Cooling rate (K/Myr) 10,000 1, Ni content (wt.%)

5 Fig. S1. Cooling rates of four IVA iron meteorites assuming impact-induced kamacite nucleation at 973 K. Error bars are 2σ uncertainty factors. B. Experimental errors in the Ni content of the kamacite-taenite phase boundaries The cooling rate measurements for some IVA irons are sensitive to the Ni content of the α/(α + γ) phase boundary in the Fe-Ni-P system used in the metallographic cooling rate model 5. It was suggested therefore that the diverse cooling rates of IVA irons were a result of using inappropriate α/(α + γ) phase boundaries in the computer model 2, 6. In order to determine the effect of the uncertainty of the kamacite α/(α + γ) phase boundary on the cooling rates of the IVA irons, the α/(α + γ) phase boundaries in the Fe- Ni-P system were adjusted within the error limits of the experimentally determined Ni content of the binary α/(α + γ) phase boundary 7, 8 and of the P saturated ternary α/(α + γ) phase boundary 8, 9, 10. The same approach was used in the study of the potential cooling rate errors of the IIIAB irons 3. Combinations of plausible binary and ternary α/(α + γ) phase boundaries were substituted in the cooling rate simulation program. In addition, the α/(α + γ) boundaries for both low Ni and high Ni irons that were adopted to minimize the cooling rate variation in group IVA (ref. 5) were substituted in the cooling rate model. The Ni-P contents of two meteorites, Steinbach with a high Ni and P content and Gibeon with a low Ni and P content, were used for the calculations (see Table 1 for Ni content and Supplementary Table for P content). The calculations showed that the measured cooling rate for the high Ni IVA (Steinbach) is not sensitive to the Ni and P content of the α/(α + γ) phase boundary, while the cooling rate for the low Ni member (Gibeon) is sensitive to the Ni and P content of the α/(α + γ) phase boundary. The errors in the cooling rate measurement increase dramatically in this procedure as the measured data no longer follow a single calculated cooling rate curve on the Wood plot but cross one or more calculated cooling rate curves. Nevertheless, even if using these various trial α/(α + γ) phase boundaries, we still obtain highly diverse cooling rates for the low Ni-P Gibeon and the high Ni-P Steinbach. For 5

6 example, the calculated cooling rate is 1100 K/Myr for Gibeon and 150 K/Myr for Steinbach when we use the α/(α + γ) phase boundaries for low Ni and high Ni meteorites that were proposed to minimize the IVA cooling rate range 5. Our calculated cooling rates are 1500 and 150 K/Myr respectively (see Table 1). As in the study of the IIIAB irons 3, we find that manipulation of the Ni-P contents of the α/(α + γ) phase boundaries 2, cannot produce uniform cooling rates for the IVA irons.. References 1. Yang, J. & Goldstein, J. I. The formation mechanism of the Widmanstätten structure in meteorites, Meteorit. Planet. Sci. 40, (2005). 2. Wasson, J. T. & Richardson, J. W. Fractionation trends among IVA iron meteorites: contrast with IIIAB trends. Geochim. Cosmochim. Acta 65, (2001). 3. Yang, J. & Goldstein, J. I. Metallographic cooling rates of the IIIAB iron meteorites. Geochim. Cosmochim. Acta 70, (2006). 4. Wood, J. A. The cooling rates and parent bodies of several iron meteorites. Icarus 3, (1964). 5. Willis, J. & Wasson, J.T. Cooling rates of group IVA iron meteorites. Earth and Planet. Science Lett. 40, (1978). 6. Wasson, J. T., Matsunami, Y. & Rubin, A. E. Silica and pyroxene in IVA irons; possible formation of the IVA magma by impact melting and reduction of L-LLchondrite materials followed by crystallization and cooling. Geochim. Cosmochim. Acta 70, (2006). 7. Goldstein, J. I. and Ogilvie, R. E. A re-evaluation of the iron-rich portion of the Fe-Ni system. Transactions of the Metallurgical Society of AIME. 233, (1965). 6

7 8. Romig, A. D. & Goldstein, J. I. Determination of the Fe-Ni and Fe-Ni-P phase diagrams at low temperatures (700 to 300 o C). Metall. Trans. 11A, (1980). 9. Romig, A. D. & Goldstein, J. I. Low temperature phase equilibrium in the Fe-Ni and Fe-Ni-P Systems: Application to the thermal history of metallic phases in meteorites. Geochim. Cosmochim. Acta 45, (1981). 10. Doan, A. S. & Goldstein, J. I. The ternary phase diagram, Fe-Ni-P. Metall. Trans. 1, (1970). 7