Davies, CJ;
Pozzo, M;
Alfè, D;
(2018)
Assessing the Inner Core Nucleation Paradox with Atomic-Scale Simulations.
Earth and Planetary Science Letters
, 507
pp. 1-9.
10.1016/j.epsl.2018.11.019.
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Abstract
We investigate the conditions required to freeze liquid iron and iron alloys near the centre of Earth's core. It is usually assumed that inner core growth begins once the ambient core temperature falls below the melting temperature of the iron alloy at Earth's centre; however, additional (under)cooling is required to overcome the energy barrier associated with creating a solid–liquid interface. Predictions based on Classical Nucleation Theory (CNT) have estimated a required undercooling of ∼1000 K, which cannot be reconciled with predicted core cooling rates of ∼100 K Gyr−1. This apparent contradiction has been called the ‘inner core nucleation paradox’. Here we address three major uncertainties in the application of CNT to inner core nucleation using atomic-scale simulations. First, we simulate freezing in Fe and Fe–O liquids at core conditions to self-consistently constrain all parameters required by the CNT equations. Second, we test the basic validity of CNT by directly calculating the waiting time to observe freezing events in Fe and Fe–O liquids. Third, we investigate the influence of wave-like forcings applied to the atomic simulations, which have been suggested as a means to significantly reduce the energy barrier. Our results are consistent with CNT in the computationally accessible parameter regime, though error estimates on the waiting time can reach 50% of the measurement at the largest undercooling temperatures. Using CNT to extrapolate to inner core conditions yields estimated undercooling of K for the pure iron system and K for the Fe–O system. Forcings corresponding to large pressure variations of GPa reduce these values by ∼100 K. While our undercooling estimates are significantly lower than previous estimates they are not low enough to resolve the inner core nucleation paradox.
| Type: | Article |
|---|---|
| Title: | Assessing the Inner Core Nucleation Paradox with Atomic-Scale Simulations |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1016/j.epsl.2018.11.019 |
| Publisher version: | https://doi.org/10.1016/j.epsl.2018.11.019 |
| Language: | English |
| Additional information: | This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ |
| Keywords: | Earth core, inner core freezing, atomic-scale simulations, homogeneous nucleation, classical nucleation theory |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10061645 |
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