1. Slide 1 The Earth is differentiated How and When did this occur? Two Sets of Constraints: Physical Mechanisms and Chemical Signatures

2. Slide 2 Useful Isotope Systems Parent nuclide 182Hf 146Sm 147Sm 176Lu 187Re 232Th 235U 238U Daughter nuclide 182W 142Nd 143Nd 176Hf 187Os 208Pb 207Pb 206Pb Half-life 9 Ma 103 Ma 106 Ga 35.9 Ga 42.2 Ga 14.01 Ga 0.7038 Ga 4.468 Ga Tracer ratio (daughter/stable) 182 W/ 184 W 142 Nd/ 144 Nd 143 Nd/ 144 Nd 176 Hf/ 177 Hf 187 Os/ 188 Os 208 Pb/ 204 Pb 207 Pb/ 204 Pb 206 Pb/ 204 Pb

3. Slide 3 Oxygen  -Notation 18 O/ 16 O sample - 18 O/ 16 O SMOW  18 O = 18 O/ 16 O SMOW X 1000 A scaled deviation from a standard SMOW: Standard Mean Ocean Water abundance 16 O99.76% 17 O0.037% 18 O0.200%

4. Slide 4 Sulfur  -Notation 33 S/ 32 S sample - 33 S/ 32 S CDT  33 S = 33 S/ 32 S CDT X 1000 A scaled deviation from a standard CDT: Canyon Diablo Troilite abundance 32 S95% 33 S0.75% 34 S4.2% 36 S0.017%

5. Slide 5 Mass-Dependent Fractionation Wiechert et al (2001) Science 294: 345

6. Slide 6 Short Lived Isotopes: Early Solar System Gilmore (2002) Science

7. Slide 7 LEW86010; silicate differentiation reference (4558 ± 0.5 Ma) Core segregation (4556 ± 1 Ma) Silicate differentiation (4526 ± 21 Ma) ALH84001 (4500 ± 130 Ma) Gov. Valad. (1370 ± 20 Ma) Lafayette (1320 ± 50 Ma) Y000593 (1310 ± 30 Ma) NWA998 (1290 ± 50 Ma) Nakhla (1260 ± 70 Ma) Dhofar 019 (575 ± 7 Ma) DaG 476 (474 ± 11 Ma) Y980459 (290 ± 40 Ma) QUE94201 (327 ± 10 Ma) NWA1195 (348 ± 19 Ma) NWA1056 (185 ± 11 Ma) LEW88516 (178 ± 9 Ma) ALH77005 (177 ± 6 Ma) EET79001B (173 ± 3 Ma) Y793605 (173 ± 14 Ma) EET79001A (173 ± 10 Ma) NWA856 (170 ± 19 Ma) LA1 (170 ± 7 Ma) Zagami (169 ± 7 Ma) Shergotty (165 ± 11 Ma) Chassigny (1362 ± 62) 174 ± 2 Ma 1327 ± 39 Ma 332 ± 9 Ma Carbonates ALH84001 (3929 ± 37 Ma) Salts shergottites (0-175 Ma) Iddingsite nakhlites (633 ± 23 Ma) Borg & Drake 010002000300040004657 Age (Ma) CAI (solar system formation reference) (4567 ± 0.6 Ma) Ages of Dated Martian Events

8. Slide 8 Observations/Inferences: Rocky inner, icy outer solar system Asteroid differentiation temperatures heliocentrically distributed Gross zonal structure within asteroid belt preserved The Moon had a magma ocean The solar photosphere has a composition very similar to CI carbonaceous chondrites Heat source concentrated near Sun? or Longer times to accrete object farther from the sun (less Al heating)? 26

9. Slide 9 Heat Sources: Solar/Magnetic Induction heating (but T-Tauri: Polar Flows) Short-lived radioisotopes ( 26 Al 0.73 Ma half life: must accrete fast) Long-lived radioisotopes (U, Th, K) (slow, only for larger bodies) Large impacts (only for larger bodies: between Moon and Mars-sized) Potential energy of core formation (larger bodies: 6300 km radius: 2300°C rise, Resonant tidal heating (Only moons: Moon?, Titan, Io, Europa) 3000 km radius: 600°C rise)

10. Slide 10 Timing of Core formation

11. Slide 11 Two Possible Mechanisms to Separate Metal from Silicate Porous FlowImmiscible Liquids and Deformation

12. Slide 12 Dihedral (wetting) Angle Theory The Dihedral Angle Theta is a force balance between interfacial energies

13. Slide 13 Sulfide Melt in an Olivine Matrix Most Fe-Ni-S melts do not form interconnected melt channels

14. Slide 14 0 Depth km Pressure GPa 500 750 250 15 22.5 0 7.5 Pressure GPa after Carlson, 1994 No Crystal Settling Perovskite Settling Low Mg/Si Dunite High Mg/Si Liquid 15 22.5 0 7.5 Crystal Cummulates t Quench Crust Quench Crust Magma Ocean Crystallization Cummulates should give a chemical signature

15. Slide 15 Lower Mantle Solidus d u s ( u p p e r b o u n d ) CoreT Multianvil Peridotite Solidus Olivine shock melting M a g n e s i o w ü s t i t e m e l t i n g Zerr et al (98), Holland & Ahrens (97) Diamond Anvil Peridotite Solidus

16. Slide 16 Samples Recording Planetary Differentiation

17. Slide 17 Pallasites: Asteroid Core-Mantle Boundary Brenham

18. Slide 18 Old Lunar Highland Crust

19. Slide 19 An Oblique Collision between the proto- Earth and a Mars-sized impactor 4.2 minutes 8.4 minutes12.5 minutes Kipp and Melosh (86), Tonks and Melosh (93)