The Volatile Legacy of the Early Earth

Lead Research Organisation: University of Bristol
Department Name: Earth Sciences

Abstract

In response to the NERC Theme Action (TA) we propose a consortium among scientists at seven UK institutions and with three international partners centred on the 'The Volatile Legacy of the Early Earth'. Earth's habitability is strongly linked to its inventory and cycling of volatiles, which today are coupled to plate tectonics, but we still have little notion as to how our planet found itself in this near-ideal 'Goldilocks' state where the volatile mix is 'just right'. Was it simply a matter of being at the right solar distance with the right supply of volatiles? Or were the details of the chemistry and dynamics of early accretion and differentiation crucial to the eventual outcome? Such questions are of critical importance for understanding our own planets development, and given the burgeoning field of exo-planet discovery, they gain extra piquancy for gauging the probability of life elsewhere. In this proposal we investigate how the early evolution of volatiles on Earth set the stage for habitability.

Planets grow by collisions and these violent events may lead to loss of the volatiles carried within the impacting bodies. We will explore with numerical modeling the conditions under which the volatiles are retained or lost in planetesimal collisions. We will also assess the likelihood that volatiles were delivered to Earth 'late', namely after the maelstrom of major collisions was finished and the planet was largely constructed, by studying the element S and notably its geochemical twin, Se. We will constrain the process of loss to the core and the isotopic signature imparted by this process. We will further use isotopic measurements as finger-prints of the origin of modern Se, and will find out whether it corresponds to any known meteorite type, or if it was possibly delivered by comets. The Moon provides further clues to the origin of the Earth, and Interrogating the significance of the recently refined volatile inventory of the Moon requires new experiments under appropriate conditions.

The energy generated by planetary collisions inevitably results in large-scale melting. The solubility and chemical nature of volatiles within a magma ocean controls whether or not gases are carried into the interior of the planet or left in the atmosphere. Volatiles retained in the magma ocean may become part of a deep mantle volatile cycle or become permanently sequestered in deep reservoirs. We will redress this issue with a series of experiments that simulate conditions of the early magma ocean. We will further investigate the stability of phases in the lower mantle that can potentially hold volatile elements if delivered to great depths by solubility in a convecting magma ocean. Using seismic and modeling techniques, we will assess if any remnants of such stored volatiles are currently 'visible' in the deepest mantle. The influence of the core on volatile budgets is potentially great because of its size, but volatile solubility is poorly known. We will examine the solubility of hydrogen, carbon and nitrogen in liquid metal at high pressures and temperatures.

In this consortium we will also create a cohort of PhD students and supervisors who work as part of a large team to piece together the evidence for Earth's volatile evolution using inclusions trapped in diamonds. These may be the key 'space-time' capsules that can link experimental and theoretical work on early Earth evolution to present-day volatile budgets and fluxes in the deep Earth.

The questions raised in this proposal are complex and require a wide range of information in order to provide meaningful answers. It is our goal to establish a much-improved understanding of how Earth initially became a habitable planet, and to build a solid foundation on which further UK research can continue to lead the way in this exciting field. This will be the ultimate legacy of this consortium, and through links to other consortia, of the entire Theme Action.

Planned Impact

The initial conditions for the formation of Earth have made it the habitable planet that it is. Understanding how volatile elements like water and carbon were delivered to the inner planets of our solar system is a key piece of the puzzle that links astrophysics to geology. Volatile elements are obviously why we have life on Earth, but also why we have plate tectonics and volcanism. A less obvious consequence of water and other volatile elements is the formation of precious minerals and economically valuable ore bodies. For these reasons our 'impact plan' is focused on the role of the early Earth in economic geology. We target two sets of end users - the general public and the mining industry in its widest sense.

Beneficiaries

Outreach and education: educators; school children; general public
Industry: mining companies; local, regional and national government that may benefit from economic geology and enhanced exploration practices; the mineral exploration community, including surveyors, geophysicists, geologists and engineers.

Delivery of Benefit

Teaching resources: for children at two key stages (7-9 yrs and 14-15 yrs) delivered through Bristol's 'Your planet Earth' education series. A suite of teaching tools that explain how Earth processes have led to the formation of key economic mineral resources such as copper, diamonds, and gold will be developed. This will highlight the finite nature of natural resources and encourage more responsible use.
Exhibits at science fairs: posters, animations and hands-on exhibits will be developed. This will not only show how mineral resources are formed and how their existence is a consequence of Earth evolution, but also highlight where common minerals in household products come from.
Exploiting existing collaborations with the mining industry: for example, BHP-Billiton has recently awarded Bristol a 5-year project to work on porphyry copper. Synergy with such projects can be used to better explore more fundamental questions of ore formation and precious metal genesis.

Workshop on Earth formation and economic geology: Speakers from industry and academia will be invited, with structured discussion sessions to encourage collaborations. This will be facilitated through key project partners who have extensive industry expertise.
Development of broader engagement with the natural resources industry: The impact plan will be used to help develop a broader Bristol-based project that will be funding through a NERC accelerator grant. Industry interaction through research and workshops will help develop stronger ties through secondment programmes for young researchers (i.e., PDRAs and PhD students) to spend some time at a company, and vice versa where industry scientists spend time at the University.

Publications

10 25 50
 
Title Work with artist Matthew C. Wilson 
Description Along the lines of the theme of the consortium, Matthew and I formulated a project based on the concept of habitable other Earth's. We conducted experiments to simulate to the interior of an Earth-twin exoplanet saturated in carbonic acid. The starting mix was based on a model for the composition of the 'rocky' part of the Earth, known as 'pyrolite'. Pyrolite is a useful model for the composition of the Earth at depths of hundreds of kilometres. As such, this composition allows us to explore, through high pressure and high temperature experiments, the interior of an Earth-like exoplanet. In contrast to the Earth, however, we modified this pyrolite model so that it was saturated in carbonic acid. Carbonic acid is formed by the reaction of H2O with CO2 (water with carbon dioxide). On the surface of the Earth, water dissolves small amounts of carbon dioxide; surface water is very weak carbonic acid. Industrially elevated atmospheric carbon dioxide levels increase water acidity, which has severe effects on marine ecosystems. We are literally acidifying the planet we live on. Our model exoplanet explores an extreme outcome of this: an Earth-like planet catastrophically altered by millennia of industrialisation, and saturated in carbonic acid. The starting mix was prepared by combining powdered oxides, hydroxides and carbonates of various elements. Small amounts of this mix were packed into platinum capsules which were then welded shut. Experiments were performed using a piston-cylinder apparatus at pressures of 2 GPa (approximately 20,000 times atmospheric pressure, equivalent to a depth of approximately 65 km). One experiment was run at 1000 degrees C, and one at 1400 degrees C, both for 48 hours to allow reaction to occur. These temperatures were chosen to investigate 'normal' or 'stable' regions of a planet saturated in carbonic acid, and regions where heating resulted in melting and production of magma, respectively. We saw some really interesting things when we observed the recovered samples using a scanning electron microscope. The lower temperature experiments contain the same combination of minerals we would expect to find at equivalent depth in the Earth, although in a more oxidised form. Pressure promotes formation of carbonic acid. However, at high pressure and temperature this acid oxidises rocks; it literally pumps extra oxygen into the minerals. In some ways this is similar to the use of carbonic acid as a restorative gas (i.e. what you told me about James Watt and his invalid son). The higher temperature experiment has a combination of 'rock' and magma (liquid rock); the conditions we used provide a snapshot of a volcanic process where heat and carbonic acid cause the planet to melt. Once again, carbonic acid has oxidised the material. The magma is quenched to glass imperfectly, so that we capture small crystals starting to form, and bubbles of carbon dioxide forming. Textures suggest that this magma had a very unusual composition; carbonic acid was fully dissolved in the melt, but was slowly released as carbon dioxide and then water as the magma crystallised. In our hypothetic exoplanet, carbon dioxide and water and forced together deep within the planet to form a highly concentrated acid. However, this acid oxidises the planet, in the same way that iron rusts on the surface of the Earth. Volcanic activity on our exoplanet returns carbonic acid to the surface as both water and carbon dioxide, also producing unusual carbonatite volcanoes, similar to Ol Doinyo Lengai in Tanzania (https://en.wikipedia.org/wiki/Ol_Doinyo_Lengai). 
Type Of Art Artwork 
Year Produced 2019 
Impact -vdrome film "Geological evidences"; this platform provides give high profile to short films; curators include the Tate Modern's film curator: https://www.vdrome.org/matthew-c-wilson -exhibition as part of the Amsterdam Art weekend (21-24 November 2019); exhibition of a series of infused aluminum prints "Factitious Earths": https://www.matthewcwilson.com/work/factitious-earths -Talk and presentation, follwoed by discussion and reception event, in collaboration with the Talbot Rice Gallery, Edinburgh by Matthew C. Wilson and Geoff Bromiley: Geological evidences (https://www.matthewcwilson.com/film-video). 
 
Description We have come to a new understanding on the behaviour on the bonding behaviour of carbon at high pressures, adding to work on the role of subduction in the Earth's carbon budget. One of the key, deep carbon phase is diamond and PhD-student work from the consortium has illustrated the pitfalls in trying to date these objects. Another PhD student presented new evidence that 'super-deep' diamonds likely form from volatile rich melts of carbonated, subducted crust. Indeed the production of these melts appears to form a barrier to deeper subduction of carbon. Our work on the high pressure speciation of CO3 has also been published, with important implications for the grand scale carbon cycle on Earth. The volatile budget during subduction has also been studied using the novel fractionation of Mo isotopes. This indicates that the slab is flushed with fluids, released from underlying serpentine and this process has a major control on global fluxes of some elements. We have also examined the volatile budget of the Moon through experimental partitioning of halogens with appropriately reduced melts. Our experiments and modelling help confirm that the Moon's interior is still depleted in volatiles compared to Earth, but particularly in Cl relative to F and H2O.
Exploitation Route Through published outputs
Sectors Environment

Other

 
Description A significant thread of work from this consortium has been into studying diamonds. Software developed for this work is being developed for commercialisation to gem companies. This has generated significant interest and companies have provided feedback to an initial package to drive further changes. The work on Mo fluxes has relevance for economic deposits. Although this has not led to current new research, our findings have been presented to the mining industry through regular meetings as part of on-going collaborations with BHP. During the course of the project, significant improvements were made to a windowless internally heated pressure vessel (IHPV) used to perform high pressure/temperature 'in situ' x-ray investigations using a synchrotron source at ESRF as part of the fluid speciation study in WP 2-1. This apparatus is now commercially available from CNRS Institut NEEL in Grenoble. Development of capability for Cl isotope analysis (development of protocols and standards) at the NERC Edinburgh Ion Microprobe Facility increases capacity in sample analyses at this UK national facility. This is a benefit for both academic and non-academic users of the facility, and other international facilities through knowledge exchange. We have made our methods and standards freely available to all future users of the Edinburgh facility.
First Year Of Impact 2017
Sector Chemicals,Digital/Communication/Information Technologies (including Software)
Impact Types Economic

 
Description DIAMOND beamtime Apatite as a probe to redox state in magma (XAS)
Amount £24,000 (GBP)
Funding ID SP12876 
Organisation Diamond Light Source 
Sector Private
Country United Kingdom
Start  
 
Description IMF Approved Project - Cl isotopes in lunar glasses
Amount £24,000 (GBP)
Organisation Natural Environment Research Council 
Department NERC Ion Micro-Probe Facility
Sector Academic/University
Country United Kingdom
Start 05/2017 
End 12/2017
 
Description Moray endowment fund: Cl in lunar glasses
Amount £1,808 (GBP)
Organisation University of Edinburgh 
Sector Academic/University
Country United Kingdom
Start 05/2016 
End 06/2017
 
Description The Moon's enigmatic chlorine fingerprint and the origin of Earth's water
Amount £192,333 (GBP)
Funding ID RPG-2021-015 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2021 
End 10/2024
 
Title Data from Drewitt et al EPSL 2019 
Description This deposit contains reduced x-ray diffraction and Raman spectra from the paper by Drewitt et al. (2019) "The fate of carbonate in oceanic crust subducted into earth's lower mantle". 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Description Buildings Habitable Worlds annual meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact Invited talk given by PDRA Nicci Potts "The lunar interior as a reservoir for volatile material" at consortium meeting, with invited international scientists, in Tenerife, Sept 2018
Year(s) Of Engagement Activity 2017
 
Description Europlanet Science Congress 2020 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I gave a presentation on results, and published a short abstract, highlighting the main findings of our work on lunar volatiles, at the prestigious Europlanet Science Congress, 21 September-9 October 2020 (https://www.epsc2020.eu/home.html), which was run in 2020 as a fully online event. Over 1000 planetary scientists participated in this meeting.
Year(s) Of Engagement Activity 2020
 
Description Gave Public Lecture at Geology Society of London 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The Public Lectures are presented in Burlington House, London with an afternoon and evening sitting to attract different audiences (afternoon to attract schools and evening to attract professionals). Both talks were given to a near full auditorium of ~100 people.
Year(s) Of Engagement Activity 2019
URL https://www.geolsoc.org.uk/gslpubliclectures19
 
Description Habitable planet consortium meeting, Edinburgh 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Policymakers/politicians
Results and Impact I co-organised (with Dr Linda Kirstein) a meeting of all members of the related NERC consortium (Deep Volatiles) In Sept, in Edinburgh. Representatives from NERC were present during the meeting. We also hosted a group of Chinese Geoscience researchers employed on a similar consortium funded in China, and discussed plans (both consortia) for future work and grant applications. As part of the meeting we also organised 3 field trips, including a 2 day pre-meeting fieldtrip for our Chinese visitors.
Year(s) Of Engagement Activity 2018
 
Description Invited talk at Scottish Planetary Science Research Network Meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact Invited talk for Nicci Potts, the postdoc currently employed on this grant, who spoke about work conducted to date, the purpose of the project, and the intent of the wider consortium, so an audience of scientists from across Scotland who work on all aspects of planetary sciences. The purpose of the meeting was to highlight potential for future grant applications. Dr Geoff Bromiley then spoke about work previously conducted on core formation in the Earth, and Tetsuya Komabayashi spoke about work on the voaltile element content of Earth's core.
Year(s) Of Engagement Activity 2017
 
Description Invited talk at joint Habitable planet China meeting, Nanjong, China 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact Consortium meeting held in China to engage with Scientists from across China interested in the role of volatiles in planetary interiors. I gave a talk highlighting the work being conducted as part of this award, and also mentioned previous work on visualising core formation in the deep early Earth.
Year(s) Of Engagement Activity 2016
 
Description Invited talk, PVG joint meeting between Edinburgh and St Andrews Universities 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Other audiences
Results and Impact Invited 15 minute talk entitled "core formation in the early solar system: is everything we know about terrestrial geochemistry wrong?"
Year(s) Of Engagement Activity 2018
 
Description PhS student talk at NERC consortium meeting in Tenerife 2017 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact PhD student gave talk "Water in the early solar system: effect of oxygen fugacity on water speciation and partitioning." NERC Deep Volatiles Programme, Tenerife, Spain, September 10, 2017.
Year(s) Of Engagement Activity 2017