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HIDDEN: Is the Earth’s core the hidden reservoir of noble gases?

About the project

In the project we employ atomistic simulations (i) to establish the presence or not of a hidden geochemical reservoir in the deep mantle that can store noble gases, (ii) to calculate the permeability of the core-mantle boundary throughout geological time with respect to noble gases, (iii) to determine the exchanges of noble gases between the mantle and the core during the core formation, and (iv) to give estimates of fluxes of noble gases through the Earth’s mantle throughout the geological time. 

Why noble gases? The noble gases bear in their isotopic ratios the traces of the Earth differentiation, degassing, and long-term geodynamic evolution. They have the particularity that each one of them has at least one stable non-radiogenic isotope and at least one radiogenic isotope. The non-radiogenic isotopes are residues, either of the Big Bang or of supernovas. They arrived on Earth during accretion and were in great part degassed from the mantle during the episodes of partial or total melting during the very early history of our planet. Whatever fraction remained was stored in (a) geochemical reservoir(s) inside the Earth. The non-radiogenic isotopes continuously escape to the atmosphere at a very slow rate via deep melts that eventually bring them to the surface. Their concentration in deep Earth reservoirs, therefore, decreases over geological time. In contrast, the radiogenic isotopes of noble gases are products of nuclear decay reactions from unstable parent isotopes, like 238U, 235U, or 232Th. These parent isotopes reside in the crust and mantle.

The concentration of radiogenic noble gas isotopes held in Earth’s interior reservoirs are therefore partially replenished over geological time. Therefore, when mixtures of non-radiogenic and radiogenic isotopes of the noble gases arrive at the surface, their ratios hold the key to deciphering the isolation and mixing of Earth’s internal reservoirs over the course of Earth’s history.

Objectives and computational techniques

In our project we employ a range of atomistic simulations to answer these fundamental questions related to the history of our planet. 

(i) We start with first-principles molecular dynamics simulations. In this method the atoms are allowed to move at finite difference in configurational space under the action of interatomic forces, which are computed using quantum mechanics, i.e. density-functional theory. The advantage is that the results are highly accurate, as the forces are correctly calculated. The main disadvantage is the low tractability of such calculations, as we are limited to systems that typically contain a few hundred atoms in a periodically repeated cubic simulation box and the simulation lasts for a few dozen thousand steps. 

(ii) In a second step we use the results of the first principles simulations to build interatomic potentials using machine learning techniques. So far, we employ the GAP/QUIP and the Vasp6 codes but are planning to diversify the use of such software. 

(iii) Furthermore, we employ thermodynamic integration associated with molecular dynamics to compute free energies and chemical potentials of the noble gases in the silicate and iron-based melts; theoretical vibrational spectroscopy to look for signature of volatiles in silicate melts and to construct phase stability relations; nudge elastic band simulations to estimate diffusion and the associated energy barriers.

The computations are done on the Fram, Betzy, and Saga supercomputers of the Norwegian Research Infrastructure Services (NRIS), and on the LUMI supercomputer of the European Network of Supercomputer Centers. 

Financing

The full name of the project is; 'HIDDEN: Is the Earth’s core the hidden reservoir of noble gases?'. The project is financed from The Research Council of Norway (NFR) in the  FRINATEK-grant programme with the NFR project number 325567.

The project period is from 2021 with an end in 2025.

Cooperation and access to HPC capacity

HIDDEN benefits of access on two clusters of High-performance computing (HPC) computation resources, which are the Norwegian Research Infrastructure Services (NRIS), and the European Network of Supercomputer Centers.

Publications

  • Ozgurel, Ozge & Caracas, Razvan (2023). The magma ocean was a huge helium reservoir in the early Earth. Geochemical Perspectives Letters. ISSN 2410-339X. 25, p. 46–50. doi: 10.7185/geochemlet.2314. Full text in Research Archive
  • Charnoz, Sébastien; Falco, Aurélien; Tremblin, Pascal; Sossi, Paolo; Caracas, Razvan & Lagage, Pierre-Olivier (2023). The effect of a small amount of hydrogen in the atmosphere of ultrahot magma-ocean planets: Atmospheric composition and escape. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 674. doi: 10.1051/0004-6361/202245763. Full text in Research Archive
  • Farsang, Stefan; Caracas, Razvan; Adachi, Takuji B.M.; Schnyder, Cédric & Zajacz, Zoltán (2023). S ·<inf>3</inf>radicals and the S·<sup>2</sup><inf>4</inf>polysulfide ion in lazurite, haöyne, and synthetic ultramarine blue revealed by resonance Raman spectroscopy. American Mineralogist. ISSN 0003-004X. 108(12), p. 2234–2243. doi: 10.2138/am-2022-8655.

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Published Oct. 5, 2022 2:03 PM - Last modified July 3, 2023 11:35 AM

Contact

Razvan Caracas, Researcher and Project Leader

Participants

Detailed list of participants