August 03, 2010

SETI Talks Archive: seti.org/talks

Lunar evidence of Late Heavy Bombardment has been interpreted to suggest that large-body impacting declined rapidly after about 3.8 Ga and that by 3.5 Ga the terrestrial bombardment rate was not much greater than the impact rates of today. In 1986 and 1989 Dr. Lowe and colleagues described four major layers of spherical particles in the 3.22-3.55 Ga Barberton greenstone belt (BGB), South Africa, ranging from 3,472 to 3,243 Ma, and interpreted them to represent the products of large terrestrial impacts of bolides 20-50 km in diameter. Since describing and interpreting these early impact layers, they have identified at least three additional thick layers of spherules in the Barberton belt that likely represent deposits of large impacts, and two new layers that display some geological features associated with impacts. Large impact layers have been identified to date in most of the major sedimentary units in the BGB. Intervening sections are composed largely of volcanic rocks where the record of impact events is unlikely to be preserved: it seems likely that other large impacts occurred during this period without leaving a record. These layers suggest that Earth continued to be bombarded by large extraterrestrial objects late into the Archean, at least until 3.2 Ga. The large sizes possible for these objects means that, while none was probably a sterilizing impact, many may have severely heated the oceans and atmosphere, boiled off the upper layer of seawater. The 3.8-3.2 Ga development of the Earth's surface environment and life may have been constrained largely by the continuing flux of large impactors. Only as that flux declined in the Late Archean were stable surface systems established within which non-thermophilic organisms and a stable geodynamic system could develop and evolve.

1. Dale Cruikshank: Outer Solar System Ices
2. Adrian Brown: Poles of Mars
3. Bruce Damer: Simulating Life's Origin
4. Laurance Doyle: Mongolian and other Historic Solar Eclipses
5. Daniel Rasky: Augustine Commission - The Way Forward on US Manned Spaceflight
6. Sergei Dubovsky: Observing String Multiverse with Astrophysical Black Holes
7. Conny Aerts - Asteroseismology
8. Carol Stoker - Phoenix Mission and Habitability
9. ames Benford - Interstellar Beacons
10. Brad Bailey - Life in Basaltic Glass in the oceanic basins
11. Nancy McKeown: Mawrth Vallis, Mars
12. Bob Pappalardo: Europa Jupiter Orbiter
13. David Jewitt:- Solar System Primordial Ice Reservoirs
14. Harry Jones: Starship Life Support
15. Jeff Moore: Mysteries on Titan
16. Farid Salama: Interstellar Clouds
17. Mark Showalter: Marine Biodiversity
18. Jen Blank: ChemCam on Mars Science Lab Rover
19. Pete Worden, Pavel Podvig, Will Marshall: Nuclear Weapons and Space Weapons
20. Samantha Blair: Interstellar Medium Interference
21. Jon Jenkins: Kepler Worlds
22. Dan Lubin: Maunder Minimum
23. Monika Kress: Habitable Planets
24. Intersection of Physics and Biology - Jan Liphardt
25. Mark Marley: Atmospheres of Brown Dwarfs and Exoplanets
26. Sarah Church: Polarized Cosmic Microwave Background
27. Peter Jenniskens: Hayabusa Reentry
28. Don Lowe: Late Heavy Bombardment
29. Mark Krumholz: Star Formation Rate
30. Heather Knutson: Exoplanet Atmospheres
31. David Des Marais: Exploring Mars for Habitable Environments
32. Ralph Lorenz: Titan Unveiled
33. REU Students Review 2010
34. Nick Kanas: Psychology of Spaceflight
35. Rus Belikov: Beyond Kepler - Imaging Exo-Earths
36. Bill Colson: Free Electron Laser Communications
37. David Korsmeyer: NASA Future Human Missions
38. Pascal Lee: Haughton-Mars Project
39. Chris McKay: Titan - Past, Present, Future
40. Nathalie Cabrol: Lakes on Mars
41. Margarita Marinova: Martian Dichotomy
42. Ellen Howell: Radar videos of asteroids

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