Noble Gas Partitioning Into The Earth's Outer Core? Ab Initio Calculations On Noble Gas Partitioning Between Silicate and Liquid Iron

Lead Research Organisation: University College London
Department Name: Earth Sciences

Abstract

Rocks from some oceanic islands, such as Iceland and Hawaii, show an unusual geochemical signature with the ratio of isotopes of helium (3He/4He) being very high. Because 3He cannot be produced from radioactive decay, all the 3He must have originated from the accreting solar system. This suggests that the source of these rocks comes from material within a deep isolated primordial reservoir that has been trapped within the Earth throughout its history and has not been affected by subsequent mantle mixing and dynamics. For many years, scientists have been "searching" for these primordial reservoirs and have come up with a number of potential locations, such as regions close to the core-mantle boundary (Large Low Shear Velocity Provinces - LLSVPs, and Ultra Low Velocity Zones - ULVZs) and even isolated zones higher up in the mantle (Bridgmanite Enriched Ancient Mantle Structures - BEAMS). But all these suggestions have their problems. However, one deep reservoir that has received relatively little attention is the Earth's liquid outer core. To establish whether the outer core could, indeed, host noble gases, such as helium, requires knowledge of the partitioning of noble gases between the silicate mantle and the liquid iron alloy outer core. In this proposal we will calculate the necessary partition coefficients in order to determine whether or not the sources of primitive noble gases are consistent with an outer core reservoir.

Our results will directly influence our understanding of the origin, scale and survival of mantle heterogeneities, and the intrinsic link to mantle convection and core- mantle exchange. These are some of the biggest issues for understanding the evolution of the Earth from its accretion to present day.

Planned Impact

1. Who will benefit:
The knowledge arising from this research will lead to a better understanding of the core-mantle segregation and evolution, and provide constraints on the whereabouts of the noble gas reservoirs. This fundamental knowledge will primarily interest academics concerned with the evolution of the Earth - geochemists and geophysicists in particular. The applied knowledge resulting from this project will benefit metallurgists and material scientists. The general public have an enduring interest in the evolution of the Earth and the planets in our solar system. The media are also keen to report results which have broad public appeal.

2. How will they benefit:
Geochemists and geophysicists will gain deeper insight into core-mantle segregation, which, in turn, may well have implications for our understanding of processes occurring in the mantle. This research will lead to constraints on the partitioning behaviour of noble gases between the mantle and core. Material scientists will benefit from the new data on partitioning of noble gases at high pressures and temperatures. Even though the end users of this type of knowledge are dominantly academics, the results have great media appeal because of human curiosity concerning the Earth on which we live.

3. What will be done:
Training: One PDRA will gain expertise in simulation methods; this is an area which has been identified as having a national shortfall of trained researchers.

General public:
(i) We will set up a social media presence with information disseminated via Facebook, Instagram, Twitter, etc.. These will give up-to-date background information about the Earth's deep interior together with highlights from our research here at UCL and links, with easy accessible explanation, to high quality research elsewhere.

(ii) We will be able to continue and extend our work on Box Office Blunders (http://www.ucl.ac.uk/EarthSci/impact/bob/index.html), an impact initiative we set up several years ago, and which we will develop to include movie blockbusters concerning the whole earth.

(iii) We will continue to run our series of Rocks and Minerals workshops for children in Key Stage 3, Years 3 and 4 (ages 7-9) to meet their curriculum needs via the statutory requirement: compare and group together different kinds of rocks on the basis of their appearance and simple physical properties. The children will have a guided hands-on experience, learning also about the Earth as a whole through discussion and questions at the end of each session.

(iv) The London GeoBus
The London based GeoBus is run out of UCL and we will continue to provide innovative material based on current research outcomes. In this particular case we will make an activity for primary school children about Helium. Helium is, of course, the gas in balloons and so is of great interest to children. We believe we can design and deliver an activity based on the life of a Helium atom, beginning either as U or Th decay or in the sun (depending on which isotope), and may in the end float out into space. Or perhaps based on where does the helium on my balloon come from, and where does it go?

4. Milestones/measures of success
Key outputs will be publications in scientific journals and presentation of the work at international and national conferences. Possible exit-jobs of the PDRAs include work in academia, industrial materials research, computing and mathematical modeling (including the business and financial sectors) as well as scientific administration and journalism.

Publications

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