The Volatile Legacy of the Early Earth

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Geosciences

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 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.
 
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 The project aims to determine the volatile content (i.e. the abundance of water, CO2, Cl and F) in the interior of the Moon. The Moon formed following collision of a Mars-size body with the newly formed Earth more then 4 billion years ago. However, although Earth has been extensively modified by geological processes, the Moon has remained largely intact since formation. Therefore, the Moon can provide insight into the early Earth-Moon system. The fundamental question we are seeking to answer is how and when water was delivered to the Earth. Water sustains life on Earth but also has a strong control on planetary processes. Understanding how Earth has evolved through time, how it first formed, why it is able to sustain complex life, and how life first arose all depends on knowing when Earth acquired its water. This remains largely unknown. However, the presence of water (and other volatiles) in lunar rocks suggests that at least some water may have been present in the Earth when it first formed.

In this project we developed a new experimental method for determining how water (H), Cl and F behave during lunar magmatic processes. Experiments were performed to determine how H, Cl and F are distributed between mineral phases (deep interior lunar rocks) and melt (magma that would be erupted to form mare basalts on the surface of the Moon). This is the first study of its kind, and involved considerable development of high pressure techniques to perform experiments under the reducing (low fO2) conditions of the lunar interior. The key findings of our work are as follows: (1) counter to predictions we find that reducing conditions (fO2) have little influence on H partitioning between minerals and melts. It contrast to previous work, H remains incorporated in mineral and melt structures as OH, with only a small proportion present as H2. This means that 'water' behaves in the Moon in a very similar way as it would in the Earth. (2) In fact, H, Cl and F partitioning in the Moon's interior are remarkably similar to their behavior in Earth's interior. This means that we can use our considerable knowledge on these elements to model what happened in the early Moon. In particular, we can use to contrast behaviour or F and Cl to understand how these elements are concentrated in lunar rocks. (3) Our data can be used to reinterpret F, Cl and H concentrations in samples returned from the Apollo lunar missions. We are able to model the 'volatile' content of the lunar interior using our data, and obtain a result which is consistent with other estimates using different techniques. This resolves some important dependencies between previous studies. (4) However, we then took this a step further. We developed a model to explain how F, Cl and H were distributed between different parts of the lunar interior as it slowly cooled after formation. This solidification of the Moon's magma ocean resulted in variations in the ratios F/Cl and F/H within the lunar interior; importantly, later remelting in the Moon does not destroy these signatures; this means that lunar rocks retain ratios of volatile elements which reflect initial formation and cooling of the Moon. In fact, this explains observed ratios in many lunar samples, and importantly, implies that the interior of the Moon could be a lot more volatile rich than previously suggested. In fact, our model is consistent with a Moon that contains as much water as the interior of the present day Earth, strongly implying that all Earth's water was delivered as the Earth first formed.

This study re-emphasises the importance of Moon-forming processes in modifying the volatile budget and distribution of volatile elements in the Moon. To provide further insight into these processes we have conducted an initial study into the effect of high temperature magmatic processes on Cl isotopes. Cl has 2 isotopes; proportions of these are a useful indicator of how easily volatile elements are lost at high temperatures. Importantly, the Moon's ratio of 35Cl/37Cl is unique in the inner solar system, suggesting that some process occurred on the Moon which did not occur elsewhere. we have performed initial high temperature degassing experiments to constrain this process. Initial results cast doubt on simple explanations of volatile loss from the early Moon, again, with implications for what the presence of 'water' in lunar rocks actually means.



1. Developed a new experimental technique for equilibrating mixtures of crystals and melts under the extreme pressure-temperature conditions of earth's deep interior, under very reducing, but volatile-rich conditions. 2. Determined, for the first time, H, C, F and Cl mineral-melt partition coefficients relevant to the events which gave rise to magmatism on the Moon. 3. Using this data, we are currently preparing 2 manuscripts. In the first, we show that 'water' contents in the lunar interior, based on the presence of OH in lunar glasses and lavas, have been significantly overestimated. It is likely that the lunar mantle is much more deficient in 'water' than currently believed. This is more consistent with the canonical theory for how the Moon formed. In a second paper, based on follow on funding, we demonstrate the Cl isotope systematics can be used to constrain volatile degassing of the early Moon. The extent of degassing is consistent with low lunar volatile contents, and explains isotopic differences between the Moon and Earth. In a final paper, based on work we are currently performing, we show that substantial quantities of both C and H can be stored in the interiors of terrestrial planets under very reducing conditions. This has major implications for ouir understanding of atmospheric evolution, and for Earth's carbon cycle
Exploitation Route Our methods can easily be applied to other studies of how volatiles behave under deep planetary conditions, particularly in the Moon, Mars, Venus and the early Earth. Cl isotope work has involved considerable technique development at the NERC Edinburgh Ion Microprobe Facility; we have prepared standards which are freely available to the wider community, facilitating a range of future studies in diverse research areas.

Our work on H partition is immediately relevant to modelling processes in the early Earth, and in other bodies in the inner solar system (Mars, Venus, Mercury, Vesta etc); this has important implications for understanding the behaviour and effects of water. Importantly, the key finding is of interest in understanding the nature of the early Earth, so will be of wide interest. This work has just been submitted for publication (we ended up changing plans and producing one large, single higher impact paper).
Sectors Energy,Environment

 
Description Development of Cl isotope analysis at the NERC Edinburgh Ion Microprobe Facility increases capacity in sample analyses. This could be of use to non-academic users. We have made our methods and standards freely available to all future users.
First Year Of Impact 2019
Sector Chemicals,Environment,Pharmaceuticals and Medical Biotechnology
Impact Types Economic

 
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 06/2017 
End 12/2017
 
Description IMF approved project: H partitioning in NAMS
Amount £7,000 (GBP)
Organisation Natural Environment Research Council 
Department NERC Ion Micro-Probe Facility
Sector Academic/University
Country United Kingdom
Start 06/2016 
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 06/2016 
End 06/2017
 
Description Principal's career development PhD students joint with Geosciences funding
Amount £109,500 (GBP)
Organisation University of Edinburgh 
Sector Academic/University
Country United Kingdom
Start 09/2016 
End 09/2019
 
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 Doors Open Day 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact I led the involvement of the Cockburn Geological Museum (housed in the Grant Institute, School of GeoSciences, University of Edinburgh) in teh annual Edinburgh Doors Open Day public engagement event. Nearly 200 people visited the museum during the day (26th Sept 2015). I manned a stall during the event which included a introduction to how the Earth and Moon formed, and birth of our solar system. Most visitors were school-aged, although we also engaged with a number of adults regarding current scientific theories and the work we are conducting at Edinburgh as part of the NERC Habitable Planet funding. I also managed tours of the Ion Microprobe facility.
Year(s) Of Engagement Activity 2015
 
Description Fall Agu 2015 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presented initial findings from WP1_4 as part of a poster presentation at the Fall American Geophysical Union meeting in SanFrancisco in Dec 2015. Poster was then used as a discussion point in engaging with interested potential future collaborators and advertising our NERC Habitable Planet consortium.
Year(s) Of Engagement Activity 2015
 
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
 
Description PhS student talk at joint PVG research meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact "Water in the early solar system: a study of terrestrial, lunar, and Martian mantle melting." Edinburgh & St Andrews PVG Convention, Edinburgh, Scotland, March 5, 2018
Year(s) Of Engagement Activity 2018
 
Description SPERO meeting 2017, PhD student poster presentation 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact PhD student gave poster presentation: "Effects of oxygen fugacity on water speciation and partitioning in terrestrial planets." Inaugural Meeting of Scottish Planetary Research Network (SPERO), Edinburgh, Scotland, February 22, 2017.
Year(s) Of Engagement Activity 2017
 
Description Talk and participation at young researcher meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Talk given by PDRA Nicci Potts at young researcher networking meeting, associated with the NERC consortium, In Oxford, October 2016
Year(s) Of Engagement Activity 2016
 
Description VMSG conference, St Andrews, January 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Prepared and presented a poster highlighting work constraining the influence of fO2 on volatile element partitioning in the early Earth-Moon system.
Year(s) Of Engagement Activity 2019