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CATEGORIES:Department of Earth Sciences Seminars (downtown)
SUMMARY:After the Moon - Stephen J. Mojzsis\, Research Cen
 tre for Astronomy and Earth Sciences (CsFK)\, Hung
 arian Academy of Sciences
DTSTART;TZID=Europe/London:20231017T120000
DTEND;TZID=Europe/London:20231017T130000
UID:TALK206584AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/206584
DESCRIPTION:The inner solar system experienced bombardment fro
 m late accretion of leftover planetesimals\, comet
 s and asteroids in the first several hundred milli
 on years of the Solar System. The sources and temp
 o of this bombardment are debated. Radiometric dat
 ing of achondrite meteorites record differentiatio
 n and formation of crusts by ca. 3 Myr into Solar 
 System history. Superimposed on this early history
  are later impact-induced U-Pb and Pb-Pb ages that
  wane by ca. 4.45 Gyr ago. Younger ages are confin
 ed to 40-39Ar geochronology\, which is relatively 
 susceptible to thermal resetting\, and describe an
  age continuum from ca. 4.48 Gyr ago extending in 
 a long tail to 3.0 Gyr ago with occasional impact 
 events as recently as 250 Myr ago. The decline in 
 late accretion intensity was well underway before 
 Earth\, Moon and Mars could have last experienced 
 wholesale crustal melting as defined by the oldest
  zircon U-Pb ages around 4.4 Gyr ago. Here I track
  the dynamical profile of late accretion flux by c
 oupling models of giant planet migration with time
 -integrated ages compiled from different radiogeni
 c systems for meteorites\, and lunar\, martian and
  terrestrial rocks. I show that if giant planet mi
 gration commenced at ca. 4.49 Gyr ago\, it led to 
 an intense ~30 Myr influx of comets to the inner s
 olar system capable of continually renewing planet
 ary crusts until ca. 4.45 Gyr ago. This age compor
 ts with planetary Pb\, Xe and Nd isotopic values e
 xtrapolated to primordial compositions which yield
  separation times for terrestrial silicate reservo
 irs. Concurrent bombardment continues to affect th
 e inner solar system as a smooth (monotonic) decli
 ne in impactor flux. I end with a description of t
 he dynamical basis of this late accretion scenario
 \, its thermal consequences to the crusts of the t
 errestrial planets and assess the likelihood that 
 a persistent biosphere could be established on Ear
 th (and Mars) since ca. 130 Myr after solar system
  formation.
LOCATION:Department of Earth Sciences\, Tilley Lecture Thea
 tre
CONTACT:Dr Rachael Rhodes
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