Speakers Club: Professor Alex Halliday

Event Date: 

Thursday, October 27, 2016 - 2:00pm

Event Location: 

  • Webb 1100

Professor Alex Halliday from the University of Oxford will give our Speakers Club talk on Thursday, October 27. 

Title: The Origin of the Earth and Moon 


The Earth, like other terrestrial planets, is thought to have formed from and been modified by progressive accretion of other smaller planetary objects. Isotopic ages and dynamic models provided evidence that the Moon formed late - more than 30 million years and probably about 100 million years after the start of the Solar System, consistent with a late Giant Impact between an Earth that was roughly >50% formed and a Mars-sized impactor sometimes called "Theia", which added most of the remaining mass.  The amount of energy imparted would be significant and some have suggested that Earth could not have acquired and retained its current volatiles until after the Moon formed, adding support to the idea of a subsequent "late veneer".  However, there are problems with this Giant Impact model as there are with explaining Earth's volatiles with a late veneer.  In particular, most of the Moon is derived from Theia in the simulations whereas the isotopic compositions of many elements provide evidence that most  of the atoms came from Earth.  As such we do not yet have a consistent model of how the Moon formed.  In addition Earth's volatiles have hydrogen / nitrogen / carbon ratios that are distinct from those expected from volatile rich veneers.  The overall patterns of noble gases and major volatiles make more sense as a series of additions punctuated by major differential losses to space.  Indeed there are new arguments that most of Earth’s inventory of volatile elements actually predated the Giant Impact.