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SUMMARY:The Earth’s Inner Core Nucleation Paradox - Professor Dario Alf
 è\, UCL
DTSTART:20251203T143000Z
DTEND:20251203T153000Z
UID:TALK232753@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:The Earth’s solid inner core plays a fundamental role in det
 ermining the past and present properties and dynamics of the Earth’s\nde
 ep interior. Inner core growth powers the geodynamo\, producing the protec
 tive global magnetic field\, and provides a record\nof core evolution span
 ning geological timescales. However\, the origins of the inner core remain
  enigmatic. Traditional core\nevolution models assume that the inner core 
 formed when the core first cooled to its the melting temperature\, but thi
 s neglects\nthe physical requirement that liquids must be supercooled to b
 elow their melting point before freezing. Prior estimates from\nmineral ph
 ysics calculations of the supercooling δT required to homogeneously nucle
 ate the inner core from candidate binary\nalloys exceed constraints of δT
  ≲ 400 K inferred from geophysical observations\, while a plausible scen
 ario for heterogeneous\nnucleation has yet to be identified. Here we consi
 der a different possibility\, that atomic-scale compositional fluctuations
  can\nincrease the local melting temperature\, and hence supercooling\, av
 ailable for homogeneous nucleation. Using molecular\ndynamic simulations o
 f Fe-O alloys we find that compositional fluctuations producing O-depleted
  regions are too rare to aid\nnucleation\, while O-enriched regions can re
 duce the undercooling by ∼50 K (δT ∼ 700 K) for a bulk concentration 
 of 20 mol%O\nor ∼400 K (δT ∼ 300 K) for a bulk concentration of 30 mo
 l% O. While these results do not explain the nucleation of Earth’s\ninne
 r core\, they do show that compositional fluctuations can aid the process 
 of homogeneous nucleation.
LOCATION:Unilever Lecture Theatre\, Yusuf Hamied Department of Chemistry
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