Hadean zircons are the only dated material on Earth to have gone through the LHB (also found elsewhere besides Western Australia; more every year!) Five grains chosen for ultra-high resolution depth-profile analysis based on concordant ages (no significant Pb-loss in whole grain) Goal: Elucidate a cryptic record of thermal events affecting the crust before the rock record Depth profile analysis

A word about sample preparation (1) (2) (3)

Hadean Zircons and the LHB AFTER: Gomes R, Levison HF, Tsiganis K, Morbidelli, A Origin of the cataclysmic late heavy bombardment period of the terrestrial planets Nature 435 (7041): MAY APPEARING IN: Trail D, Mojzsis SJ, Harrison TM, Levison HF Do Hadean zircons retain a record of the Late Heavy Bombardment on Earth? LPSC XXXVII ?

Pre-4000 Ma thermal events? 4300 Ma core age

Pre-4000 Ma thermal events? 4200 Ma core age JH992FC02_31

Hadean Zircons and the LHB relative quiet?

Results JH992FC02_31 JH992FC16_8-10

Modeled lunar Accretionary mass flux Gomes et al., 2005

Future work Establish origin of 3.9 Ga overgrowths  Diffusion related?  Exogenic vs. Endogenic Profile tens of Hadean zircons  Are ~3.9 Ga zones common?  Will older >3.9 Ga rims be discovered? Impact related? Can Hadean zircons resolve individual impact events? Do Lunar zircons retain multiple growth episodes?

Beartooth Mountains Map from Mueller et al., 1992

Beartooth Mountains