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

2. 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

3. Solar/Magnetic Induction heating (but T-Tauri: Polar Flows)
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,
3000 km radius: 600°C rise)
Resonant tidal heating
(Only moons: Moon?, Titan, Io, Europa)

4. Timing of Core formation

5. Two Possible Mechanisms to Separate Metal from Silicate
Porous Flow
Immiscible Liquids and Deformation

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

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

8. Samples Recording Planetary Differentiation

9. Pallasites: Asteroid Core-Mantle Boundary
Brenham

10. Old Lunar Highland Crust

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

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

13. Lower Mantle Solidus Pressure (GPa) 2000 T e m p r a t u ( K ) 3000
Diamond Anvil Peridotite Solidus
Pressure (GPa)
2000 T e m p r a t u ( K )
3000
4000
5000 20 40 80
120
CMB M n l A d i b s o
Olivine
shock meltin g n g e l t i m e ü s t i t w e s i o g n n d )
Core T M a o u r b p p e s ( u d u
Multianvil Peridotite Solidus
Zerr et al (98), Holland & Ahrens (97)

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

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

16. Oxygen d-Notation
A scaled deviation from a standard
18O/16Osample - 18O/16OSMOW
d18O =
X 1000
18O/16OSMOW
SMOW: Standard Mean Ocean Water
abundance
16O 99.76%
17O 0.037%
18O 0.200%

17. Sulfur d-Notation
A scaled deviation from a standard
33S/32Ssample - 33S/32SCDT
d33S =
X 1000
33S/32SCDT
CDT: Canyon Diablo Troilite
abundance
32S 95%
33S 0.75%
34S 4.2%
36S 0.017%

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