BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:After the Moon - Stephen J. Mojzsis\, Research Centre for Astronom
 y and Earth Sciences (CsFK)\, Hungarian Academy of Sciences
DTSTART:20231017T110000Z
DTEND:20231017T120000Z
UID:TALK206584@talks.cam.ac.uk
CONTACT:Dr Rachael Rhodes
DESCRIPTION:The inner solar system experienced bombardment from late accre
 tion of leftover planetesimals\, comets and asteroids in the first several
  hundred million years of the Solar System. The sources and tempo of this 
 bombardment are debated. Radiometric dating of achondrite meteorites recor
 d differentiation and formation of crusts by ca. 3 Myr into Solar System h
 istory. Superimposed on this early history are later impact-induced U-Pb a
 nd Pb-Pb ages that wane by ca. 4.45 Gyr ago. Younger ages are confined to 
 40-39Ar geochronology\, which is relatively susceptible to thermal resetti
 ng\, and describe an age continuum from ca. 4.48 Gyr ago extending in a lo
 ng tail to 3.0 Gyr ago with occasional impact events as recently as 250 My
 r ago. The decline in late accretion intensity was well underway before Ea
 rth\, 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 coupling models of giant 
 planet migration with time-integrated ages compiled from different radioge
 nic systems for meteorites\, and lunar\, martian and terrestrial rocks. I 
 show that if giant planet migration commenced at ca. 4.49 Gyr ago\, it led
  to an intense ~30 Myr influx of comets to the inner solar system capable 
 of continually renewing planetary crusts until ca. 4.45 Gyr ago. This age 
 comports with planetary Pb\, Xe and Nd isotopic values extrapolated to pri
 mordial compositions which yield separation times for terrestrial silicate
  reservoirs. Concurrent bombardment continues to affect the inner solar sy
 stem as a smooth (monotonic) decline in impactor flux. I end with a descri
 ption of the dynamical basis of this late accretion scenario\, its thermal
  consequences to the crusts of the terrestrial planets and assess the like
 lihood that a persistent biosphere could be established on Earth (and Mars
 ) since ca. 130 Myr after solar system formation.
LOCATION:Department of Earth Sciences\, Tilley Lecture Theatre
END:VEVENT
END:VCALENDAR