Ge/Ay133 When and how did the cores of terrestrial planets form?

Estimated core sizes of the terrestrial planets. Two end member hypotheses for core formation:

Estimated core sizes of the terrestrial planets. Two end member hypotheses for core formation: For homogeneous accretion, when does the onset of differentiation occur?

How might we distinguish these, and their timing? Step 1: Know your geochemical affinities!

Highly siderophile elements in the mantle: Late veneer…

…or high pressure chemistry?

Step 2: Know how to measure isotopes very well!

Absolute Pb-Pb dating error bars getting down to ~1 Myr!

182 Hf 182 W 9

Once you have ages, can look for short-lived excesses: Hf/W ideal because Hf is a lithophile, whereas W is a siderophile, and  1/2 = 9 Myr. 180 Hf/ 184 W

Yin et al. (2002)Kleine et al. (2002)

Size dependence? What about earth-moon?

Geochemical partitioning is sensitive to the depth at which silicates last “see” Fe/Ni metal. The atmosphere is also strongly affected by core formation, and its timing.

Equilibrium Gas Abundances in Silicate Magmas SiO 2 + 2Fe 3 O 4 → 3Fe 2 SiO SiO 2 + 2Fe + O 2 → Fe 2 SiO 4

Might the exogenous delivery of organics to the early Earth been important? Equilibrium Gas Abundances in Silicate Magmas SiO 2 + 2Fe 3 O 4 → 3Fe 2 SiO Quartz Fayalite Magnetite (QFM) SiO 2 + 2Fe + O 2 → Fe 2 SiO 4 Quartz Iron Fayalite (QFI)

Giant impacts & the Earth-Moon System: 1. Temperature behavior R. Canup 2004, Icarus 168, 433 (and the slides that follow)

Where does material go, & what is its composition?

A `typical’ Moon forming event & simulation summary:

Temperature evolution:

Where does the iron/silicate go?