1. 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

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

5. 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): 466- 469 MAY 26 2005. 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 2006. ?

6. Pre-4000 Ma thermal events? 4300 Ma core age

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

8. Hadean Zircons and the LHB relative quiet?

9. Results JH992FC02_31 JH992FC16_8-10

10. Modeled lunar Accretionary mass flux Gomes et al., 2005

11. 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?

12. Beartooth Mountains Map from Mueller et al., 1992

13. Beartooth Mountains