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The origin, history and role of water in the evolution of the inner Solar System
Theo Murphy meeting organised by Professor Monica Grady CBE, Professor Sara Russell and Professor Chris Ballentine
Water is fundamental to life. This meeting will explore how the Earth and its planetary neighbours obtained their water, how abundant it is, and its distribution in both pre-planetary and early planetary times. It will bring together Earth and planetary scientists, astrophysicists and chemists to learn from each other about the history of water on our planet and its role in creating the conditions that support life.
Biographies and abstracts are available below, together with the schedule of talks. Alternatively you can download the draft programme (PDF). Recorded audio of the presentations will be available on this page after the event has taken place, and meeting papers will be published in a future issue of Philosophical Transactions A.
Attending this event
This is a residential conference, which allows for increased discussion and networking. It is free to register, however participants need to cover their accommodation and catering costs.
Enquiries: Contact the events team
Schedule
| 09:05 - 09:30 |
The origin of inner solar system water
Midplane temperatures at ~1 AU in the solar protoplanetary disk were probably too warm for planetesimals to have accreted water-ice. In the classical picture, the terrestrial planets acquired their volatiles when planetesimals that formed in the outer asteroid belt (3-4 AU) were scattered into the terrestrial planet region. However, two recent models suggest that the volatile-rich asteroids formed in the outer Solar System and are the remnants of a population of planetesimals that were scattered into the inner Solar System by the radial migration of the giant planets. The H isotopes of water are predicted to show a strong radial gradient due to mixing between D-rich interstellar water and water that re-equilibrated with H2 in the hot inner Solar System. The D/H of meteoritic water suggests that at most ~7-10% of it is interstellar in origin, and that the meteorites formed sunward of the formation locations of Saturn’s moons (~3-7 AU in the migration scenarios). The N isotopic compositions of meteorites are also consistent with this. The O isotopic compositions of water in outer Solar System objects are predicted to exhibit large mass independent anomalies due to formation by UV photodissociation of CO in the interstellar medium and/or outer Solar System. While meteoritic water is significantly different from the solar composition, like most known solar materials, it is far less anomalous than some predictions, again pointing to an origin in the inner Solar System. 
Dr Conel Alexander, Carnegie Institute for Science, USA
Dr Conel Alexander, Carnegie Institute for Science, USAConel Alexander is a geochemist at the Carnegie Institution of Washington. He specializes in the study of primitive chondritic meteorites, particularly what they can tell us about conditions and processes in the very early stages of Solar System formation. The focus of his most recent work has been the origin(s) of organic matter and water in chondrites, and how they can be used to test dynamical models of planet formation and migration. |
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| 09:30 - 10:00 |
Evaluating the significance of comets in relation to the Earth’s water budget – the perspective from the Rosetta space mission
The water that exists at the surface of the Earth, both today, and through most of geological history, ultimately had to come from somewhere. In principle, it could have arisen from a process whereby volatiles that were included into the planet at the time of its formation subsequently migrated to the surface during degassing. Alternatively, the water could have been added from external sources some time after the major planet-building process was complete. In either case, the constraint has to be that the surface was stable enough to allow (liquid) water to accumulate; in other words, the crust had to have solidified and cooled down from whatever state it was in at the time of accretion (since during this era, conditions at the surface were such that water of whatever provenance was largely lost to space). So, in simplistic terms, the water on Earth either came from below (inside), or above (outside). Or perhaps, more likely, it came from a combination of sources. The Rosetta space mission to 67P/Churyumov-Gerasimenko had, as one of its goals, to try and assess the relevance of cometary water to the overall budget on Earth. We will review the extent to which it was successful in this regard, and consider the role of comets in the delivery of water to Earth. 
Professor Ian Wright, Open University, UK
Professor Ian Wright, Open University, UKIan Wright has spent his career studying the volatile constituents of extraterrestrial materials. This has either been in the laboratory, with the analysis of meteorites, various samples of the Moon and Mars, cometary dust, etc., or through off-world investigations involving space missions. His most recent efforts have been associated with the Rosetta space mission, which, in November 2014, placed analytical instruments on board the Philae lander, onto the surface of comet 67P/Churyumov-Gerasimenko. In searching for a new challenge (i.e. one without a 20-year lead-in) he has been focussing his attention on the Moon. With water being water wherever it exists in the Universe, Ian attempts to distinguish reservoirs and elucidate processes by measuring differences in stable isotopic compositions of different water-containing components. |
| 11:00 - 11:30 |
The search for surviving direct samples of early Solar System water
We have become increasingly aware of the fundamental importance of water, and aqueous alteration, on primitive solar-system bodies. All classes of astromaterials studied show some degree of interaction with aqueous fluids. Nevertheless, we are still lacking fundamental information such as the location and timing of the aqueous alteration and the detailed nature of the aqueous fluids. Halite crystals in two meteorite regolith breccias were found to contain aqueous fluid inclusions (brines) trapped ~4.5 BYBP. Heating/freezing studies of the aqueous fluid inclusions in these halites demonstrated that they were trapped near 25°C. The initial results of our O and H isotopic measurements on these brine inclusions can be explained by a simple model mixing asteroidal and cometary water. We have been analysing solids and organics trapped alongside the brines in the halites by FTIR, C-XANES, SXRD and Raman, as clues to the origin of the water. The organics show thermal effects that span the entire range witnessed by organics in all chondrite types. Since we identified water-soluble aromatics, including partially halogenated methanol, in some of the halite, we suspected amino acids were also present, but have thus far found that levels of amino acids were undetectable (which is very interesting). We have also been locating aqueous fluid inclusions in other astromaterials, principally carbonates in CI and CM chondrites. Although we have advanced slowly towards detailed analysis of these ancient brines, since they require techniques right at or just beyond current analytical capabilities, their eventual full characterisation will completely open the window on the origin and activity of early solar system water. 
Dr Michael Zolensky, NASA Johnson Space Center, USA
Dr Michael Zolensky, NASA Johnson Space Center, USAAfter obtaining a PhD in Mineralogy and Geochemistry at the Pennsylvania State University, Dr Zolensky came to NASA's Johnson Space Center as an expert in microparticle analysis. He has led or participated in successful meteorite recovery expeditions on four continents and developed techniques for characterization of meteoroid and space debris impact features on spacecraft. Dr Zolensky also led the effort to characterize the impact record of the LDEF satellite and developed new techniques for the analysis of astromaterials, characterization of the chemical weathering record of asteroids, and primitive mineralogy of comets. He served on the science teams of the Stardust and Hayabusa Missions, the first missions to return samples from a comet and an asteroid. He is currently leading an effort to locate and characterize aqueous fluid inclusions in meteorites. |
| 11:30 - 12:00 | Professor Monica Grady, Open University, UK |
| 13:30 - 14:00 |
What do recent orbital and rover observations tell us about the history of water flow and stability at the martian surface?
Mars provides the only other evidence aside from Earth of the significant flow of water at a planetary surface. Four decades of orbital observations have revealed a rich record of erosional and depositional landforms that are inferred to have formed by fluvial processes. The ever increasing resolution of image and topographic datasets has provided significant confidence in our interpretation of past aqueous processes, in particular through comparison with Earth analogues. Moreover, the discovery in orbital images of sedimentary rock deposits exhumed at the martian surface clearly demonstrates, from their preserved morphology, deposition in ancient river and deltaic systems. These results provide vital information to reconstruct past climatic conditions on Mars and the evolution of palaeoclimates. Furthermore, they inform us about the potential for rocks on Mars to contain a record of ancient microbial life. Despite these advances, numerous questions remain about the timing, magnitude and duration of water activity on Mars and the sequence of events in the evolution of water flow at the martian surface. In this talk, I will review the latest findings from both orbital and rover (eg. Mars Science Laboratory Curiosity rover) investigations, and consider the current questions and controversies. I will conclude by highlighting the major questions that need to be addressed about the evolution of liquid water at the martian surface. 
Professor Sanjeev Gupta, Imperial College London, UK
Professor Sanjeev Gupta, Imperial College London, UKTrained as a field geologist, Sanjeev Gupta is interested in the evolution of earth and planetary surface environments and processes. He uses techniques and theory from geomorphology, sedimentology and stratigraphy to observe and learn about the evolution of modern and ancient sedimentary systems. His early work focussed on the role of active faults and folds on sediment routing systems, and the evolution of tectonically perturbed landscapes. He then switched to working on underwater landscapes exploring the morphology of the English Channel using sonar data to understand how Britain became an island. More recently he has become involved in planetary exploration with a focus on Mars. He is a Participating Scientist and Long Term Planner on NASA's Mars Science Laboratory Curiosity rover mission, where his role is to analyse ancient sedimentary rocks on Mars and determine if the Red Planet could ever have been habitable for life. He is also involved in the European ExoMars rover mission planned for 2018. |
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| 14:00 - 14:30 |
Water on Mars: what we have learnt from the mineralogy of Martian meteorites and the Martian surface
Mineralogical traces of ancient water on Mars have been shown through Near IR observations by orbiters, which reveal – in gaps through the Martian dust – clays and carbonate often associated with large impact craters, originating either through excavation of ancient altered crust or impact-induced hydrothermal activity. Clays have also been identified in fine-grained sedimentary terrains and are one of the targets for landers. In Gale Crater, the Curiosity Rover has studied such sediments and, in the first 1000 sols of the MSL mission, shown a secondary assemblage of clay and magnetite with later sulphate veins. These are the result of low temperature alteration of basaltic to trachybasalt material by brines. The Martian meteorites have preserved a record of short-lived, near-surface alteration producing oxidised, low temperature ≤150 oC, metastable carbonate and clay (ferric saponite) dominated assemblages. In contrast, a meteorite fragment of an impact regolith records the presence of higher temperature water-rock reaction. Much of the mineralogical record of water on Mars can be understood through the reaction of basaltic or moderately fractionated igneous assemblages with dilute, neutral pH, near surface fluids including groundwater. However, sulphate mineralogy at the MER Opportunity landing site suggests that sometimes more acidic, fluid activity occurred through evaporation of brines. A major unresolved question that the observations of Mars’ mineralogy raise is whether extensive chemical weathering took place on the ancient martian surface, perhaps associated with the presence of large standing bodies of water in impact craters, or whether water-rock reaction was a largely subsurface, closed system process. 
Professor John Bridges, University of Leicester, UK
Professor John Bridges, University of Leicester, UKThrough much of his career at the NHM, OU and since 2007, Space Research Centre, University of Leicester, studying planetary materials (e.g. martian meteorites, chondrite chondrites, Comet Wild2 Stardust mission, Hayabusa asteroidal samples) Professor Bridges has made the most detailed analyses of hydrothermal minerals in the martian meteorites, using electron microscopy and developing new synchrotron techniques. From this he has been able to make an accurate characterisation of the associated fluids e.g. T, pH, oxidation, composition, and thus constraining the nature of their associated crustal processes. Publishing the leading work in this field has led to Professor Bridge's participation in other projects and missions e.g. Mars Science Laboratory, ExoMars 2016, 2018, HiRISE, iMars, Beagle2, associated with major recent insights into crustal differentiation and associated water, and thus habitability, on Mars. |
| 15:30 - 16:00 |
Accretion processes and the implications for inner Solar System volatile budgets
The budgets of water, carbon and nitrogen in the Earth can be determined from comparisons with the noble gases. The concentrations of these are constrained by the age of the Earth and the budget of potassium and the resultant argon-40. However, the potassium budget is dependent on knowing the K/U ratio and the amount of uranium. Recent models of collisional stripping and volcanic losses of incompatible elements from accreting planetesimals and planetary embryos mean that the amount of water in the Earth’s interior is highly uncertain between one and ten ocean masses. What is clear however is that nitrogen is far more depleted than hydrogen in the combined silicate Earth, hydrosphere and atmosphere, than what is expected from a late veneer of accreted materials. Furthermore, cometary water is insignificant even though a major fraction of the heavy noble gases probably have such an origin. 
Professor Alex Halliday FRS, Vice President (Physical Secretary), the Royal Society
Professor Alex Halliday FRS, Vice President (Physical Secretary), the Royal SocietyProfessor Alex Halliday has been Head of the Mathematical, Physical and Life Sciences Division at Oxford University since October 2007. Before coming to Oxford, he spent twelve years as a professor at the University of Michigan and then six years in Switzerland, where he was Head of the Department of Earth Sciences at the ETH in Zürich. In 2004 he took up the Chair of Geochemistry at Oxford, where his research involves the use of isotopic methods to study Earth and planetary processes. Professor Halliday is a former President of the Geochemical Society and of the European Association for Geochemistry. He has experience with a range of top science boards and advisory panels including those of the Natural Environment Research Council, the Natural History Museum London, the Max Planck Society, the Royal Society and the American Geophysical Union. An enthusiast for technological innovation, most of Professor Halliday's recent research is in developing and using new mass spectrometry techniques to shed light on the origin and early development of the solar system and recent earth processes, such as continental erosion and climate. However, he has also been engaged in other studies, such as the mechanisms of volcanic eruptions, and the formation of mineral and hydrocarbon deposits. Professor Halliday's scientific accomplishments have been recognised with awards including the Murchison Medal of the Geological Society, the Bowen Award of the American Geophysical Union and the Urey Medal of the European Association of Geochemistry. He was elected a Fellow of the Royal Society in 2000. |
| 16:00 - 16:30 |
Origin and delivery of water to the forming inner solar system
The origin of water in the planetary bodies of the inner solar system is fundamental to the potential and practical viability for the sustenance of life, as well as for the development of observable geophysical phenomena such as atmospheric composition, surface volcanism and plate tectonics. While important observations on the origins of water in the inner solar system have been obtained from primitive carbonaceous chondrites, the systematics of H2O in these objects is often dominated by gas-ice-water-rock interactions at low temperatures where isotopic fractionations can be large and dominated by non-equilibrium processes. Our recent work on H2O has focused on differentiated solar system objects, as exemplified not only by the Earth and Mars, but also achondrites (e.g. 4 Vesta) and the Moon, where volcanism has provided a record of the abundance and isotopic composition of H2O preserved in volcanic glasses, melt inclusions and magmatic minerals. The age of water delivery to these various objects ranges widely, from ~8 Myr after CAIs to the formation age of the Moon 50-90 Myr after CAIs (i.e. 4560 – 4470 Ma). Mars, Earth, Moon and Vesta display a wide range of volatile-element depletion in their geochemistry, for example displaying a range of K/Th ratios from 360 (Moon) to 1000 (Vesta) to 5500 (Earth, Mars). Yet the abundance of H2O in primitive magmas from these bodies, and the relative abundances of S/H2O, F/H2O and Cl/H2O, appear to be rather similar to each other and to the Earth. This similarity extends to the D/H ratio which is solidly within the range of carbonaceous chondrites, as are the isotopic compositions of nitrogen and carbon (but not oxygen). The systematics of H2O and other similarly volatile elements thus provides evidence for the presence of a ubiquitous and homogenous chondritic volatile reservoir in the inner solar system very shortly after the first planetary embryos began to form, and extending for nearly 100 Myr afterward. Cosmochemical and dynamical scenarios consistent with these observations will be discussed. 
Dr Erik Hauri, Carnegie Institution of Washington, USA
Dr Erik Hauri, Carnegie Institution of Washington, USAErik H. Hauri is a Staff Scientist in Geochemistry in the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. He received a BS degree in Marine Geosciences at the University of Miami and a PhD in Geoscience from the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. He is currently the Chair of the Reservoirs and Fluxes Community of the Deep Carbon Observatory, an international decadal programme focused on the Earth’s deep carbon cycle. His current research focuses on the volatile cycles of the Earth, Moon and Mars, the nature of magma migration and eruption, the thermal and chemical evolution of the Earth’s interior, and the fundamental chemical behaviour of water, carbon and other volatiles under the pressure–temperature conditions of planetary interiors. |
| 17:00 - 18:00 | Poster session |
| 09:00 - 09:30 |
Remotely distinguishing and mapping endogenic water on the Moon
Water and/or hydroxyl detected remotely on the lunar surface may originate from several sources: 1) comets and other exogenous debris; 2) solar-wind implantation; 3) the lunar interior. While each of these sources are interesting in their own right, distinguishing among them is critical for testing hypotheses for the origin and evolution of the Moon and our solar system. Existing spacecraft observations are not of high enough spatial and spectral resolution to uniquely characterise the bonding energies of the hydroxyl molecules that have been detected. Nevertheless, the spatial distribution and associations of H, OH-, or H2O with specific lunar lithologies provide some insight into the origin of hydrous materials. Further inferences can be made on the basis of laboratory measurements and computational models that have been developed to constrain the production of solar wind hydroxyl and the migration and stability of any OH- or H2O molecules on the surface. The current understanding, limitations, and future outlook for mapping and characterising water and hydroxyl on the lunar surface will be discussed. 
Dr Rachel Klima, Johns Hopkins University Applied Physics Laboratory, USA
Dr Rachel Klima, Johns Hopkins University Applied Physics Laboratory, USARachel Klima is a planetary geologist at the Johns Hopkins University Applied Physics Laboratory (APL). She obtained her undergraduate degree in Geophysical Sciences at the University of Chicago, and her PhD in Planetary Geology at Brown University, where she studied the relationship between crystal structure and the reflectance spectra of rock-forming minerals to improve methods for remote geochemical analysis of the Moon and asteroids. Rachel’s research interests center on using reflectance spectroscopy to understand the thermal evolution of airless bodies in the solar system. During graduate school and a postdoc at Brown, she was involved with the Dawn mission to the asteroids Vesta and Ceres as well as the Moon Mineralogy Mapper. At APL, she has continued her laboratory and lunar research and is working on the MESSENGER mission to Mercury and on the newly approved Europa mission. |
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| 09:30 - 10:00 |
History of water and other volatiles in the Moon and implications for the evolution of the inner Solar System
Recent sample studies have demonstrated that the lunar interior likely contains appreciable quantities of water, although estimates for the bulk-water content of the Moon vary considerably. The origin and evolution of this water remain unresolved with a range of possibilities, including retention of primordial water to a later addition of water following the crystallisation of the putative Lunar Magma Ocean. In addition to water, recent investigations focussing on other volatiles (e.g., C, N, Cl), have brought about a paradigm shift in our understanding of the history of lunar volatiles and their wider implications for volatiles in the inner Solar System. We have been investigating the volatile inventory of the Moon through laboratory analyses of lunar samples. Our main target has been measuring volatiles, such as OH, F and Cl, in apatite using NanoSIMS. These studies are complemented by bulk analyses of lunar samples for their C, N and noble gas signatures using stepped-combustion. Some highlights from our work carried out on lunar apatite include the revelation of significant effects of degassing on the initial magmatic H- and Cl-isotopic compositions, and the possibility of a common source of water in the Earth-Moon system. Whilst the dominant source for lunar water appears to be carbonaceous chondrite-type material, it is becoming apparent that the Moon may have received volatiles from multiple sources at different stages of its geological history. Unravelling this history will require further study of existing lunar samples, but also ‘new’ samples from regions of the Moon not sampled previously. 
Dr Mahesh Anand, Open University, UK
Dr Mahesh Anand, Open University, UKDr Anand is a Planetary Scientist with over 10 years of research experience in working with Apollo lunar samples and meteorites (lunar, martian, HEDs etc.). His primary interest lies in understanding the origin and evolution of planetary bodies in the inner Solar System through mineralogical, petrological, geochemical and isotopic analysis of extra-terrestrial samples in Earth-based laboratories using state-of-the art analytical instrumentation. Currently, his research is primarily focussed on understanding the abundance, distribution, and source(s) of water (H, OH, H2O) and other volatiles (e.g., C, N, Cl, F) in the lunar interior through lunar sample studies. |
| 11:00 - 11:30 |
Hydrogen isotope ratios in the inner Solar System
Based on meteorite measurements, the ratio of hydrogen (1H) to deuterium (2H or D) differs for each type of rocky body in the inner Solar System. In astrophysical environments water is D-rich, but exchange with D-poor H2 gas can decrease the D/H ratio. Thus, water close to the Sun, where higher temperatures drive ion exchange, has low D/H ratios relative to water further away from the Sun, where colder temperatures mean ion exchange is sluggish. Therefore, a meteorites D/H ratio can indicate how and where its parent body formed in the Solar System. For example, could Earth have formed from carbonaceous chondrites? However, hydrogens volatility and incompatibility in silicate melts means that separate water and hydrogen reservoirs can form on the same planetary bodies (e.g., surface vs. interior), with processes such as evaporation, sublimation, atmospheric stripping, impact shock events, aqueous alteration and plate tectonic recycling (on Earth) all affecting the D/H ratio of different reservoirs and/or individual meteorites over geological time. For example, water on the surface of Mars and Earth appears to be more D-rich than water from the interior of these planets. Therefore, if D/H ratios are to tell us anything about the Solar System’s formation it is important to unravel the processes each meteorite has experienced, and how these processes are likely to have affected the D/H ratio. 
Dr Lydia Hallis, University of Glasgow, UK
Dr Lydia Hallis, University of Glasgow, UKDr Lydia Hallis is a Marie Curie Fellow at the University of Glasgow studying how the volatile element content of the Martian interior, surface and atmosphere changed over geological time. Her research involves sub-microscopic mineralogical analyses, as well as measurements of the hydrogen isotope content and abundance of water, chlorine and fluorine in hydrous phases in Martian meteorites of differing ages. Before moving to Glasgow Lydia spent 4 years as a NASA Astrobiology Fellow at the University of Hawaii, where she studied the mineralogy and chemistry of Martian meteorites and terrestrial rocks. |
| 11:30 - 12:00 |
Global water cycle and the coevolution of Earth’s interior and surface environment
The bulk Earth composition contains only less than 1% of water, but this trace amount of water can affect the long-term evolution of the Earth in a number of different ways. The foremost issue is the occurrence of plate tectonics, which governs almost all aspects of the Earth system, and the presence of water could both promote and prevent the operation of plate tectonics, depending on where water resides. Global water cycle, which circulates surface water into the deep mantle and back to the surface again, is thus suggested to have played a critical role in the Earth history. In this contribution, we first review the present-day water cycle and discuss its uncertainty as well as its secular variation. The evolution of mantle dynamics and surface environment are linked through global water cycle, and we explore a range of co-evolutionary scenarios to take into account various uncertainties. We survey relevant geological and geochemical observations to distinguish between different possibilities. The initiation of plate tectonics in the early Earth is suggested to be possible with abundant surface water and dry mantle, and the gradual introduction of water into the mantle by subduction could potentially explain a major geological transition from the Archean to the Proterozoic and even the uprise of oxygen in the early Proterozoic. 
Professor Jun Korenga, Yale University, USA
Professor Jun Korenga, Yale University, USAJun Korenaga studies the evolution of the Earth using an array of theoretical and observational methods. He is known particularly for his hypothesis of slower plate tectonics on the young Earth, which challenges a prevailing belief in earth sciences. The hypothesis could resolve long-standing conflicts between geophysics and geochemistry, and supporting evidence has been emerging, including the petrological reconstruction of Earth's cooling history and the atmospheric abundance of radiogenic xenon isotopes. As a self-described "freestyle" geophysicist, he traverses multiple disciplines at will and works on the pressure points of the Earth system. He uses computational fluid dynamics to construct the scaling of mantle convection, while formulating inverse problems to bring statistical rigor to global geochemistry. He is also keen on quantifying laboratory constraints on rock mechanics using Markov chain Monte Carlo, and he sometimes goes out to sea to probe the origin of massive submarine volcanism. |
| 13:30 - 14:00 |
Born wet: how the Earth gained and lost water during formation
The formation of the Earth is now understood as a rapid transition from dust and gas to planetesimals, followed by a more protracted period of gravitationally-driven growth through planetary embryos the size of Mars, and finally to a completed planet. In tracing water through this process we find increasing evidence that while each heating stage involves the loss of water, none are sufficient to dry the planetary material. Internal heat of planetesimals by short-lived radioisotopes likely lead to some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. In contrast, the giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. On an Earth-sized planet a magma ocean would solidify to produce dense near-surface solids that contain the bulk of the interior water, held in the solid state. During gravitationally-driven overturn these solids sink deeper into the mantle and dewater. This event would have the potential to partially melt the upper mantle and to produce a damp asthenosphere. The transition from magma ocean to modern-day plate tectonics is very poorly understood. The earliest part of this transition, however, was likely dominated by an enormous flux of extra-terrestrial bodies. The surface of the Hadean Earth was likely widely reprocessed by impacts through mixing and melting, and the earliest atmosphere would have been highly altered by this process. 
Professor Lindy Elkins-Tanton, Arizona State University, USA
Professor Lindy Elkins-Tanton, Arizona State University, USALindy Elkins-Tanton is the director of the School of Earth and Space Exploration at Arizona State University. Her research is on the formation of terrestrial planets, and the relationships between Earth and life on Earth, particularly examining the role of volcanism. Elkins-Tanton received her B.S. and M.S. from MIT in 1987, and then spent eight years working in business, with five years spent writing business plans for young high-tech ventures. She then returned to MIT for a Ph.D. Elkins-Tanton spent five years as a researcher at Brown University, followed by five years on MIT faculty, culminating as Associate Professor of Geology, before accepting the directorship of the Department of Terrestrial Magnetism at the Carnegie Institution for Science. In 2014 she moved to the directorship at Arizona State University. |
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| 14:00 - 14:30 |
Relating the record preserved by the terrestrial noble gases to the processes controlling the accretion of water to Earth
The presence of solar nebular gases in the earliest stages of terrestrial planet accretion provide a starting point for considering the origin of volatiles and water on and in Earth. Nevertheless, Earth likely accreted most of its mass in the absence of solar nebular gases. Planetary volatile acquisition after nebular dispersion is sourced from volatiles trapped within accreting meteoritic or cometary material, surviving on accreting planetisimals, or as part of a later veneer of similar material associated with the late heavy bombardment ending at ca3.8Ga. Noble gases provide a view on these processes. The extreme deficit of terrestrial Xe isotopes derived from 129I and 244Pu has been used to argue for complete planetary loss of all gaseous species until closure to loss at ca100Myr after Solar Nebular formation. This closure ages appears to be the same for the Earth’s interior and atmosphere and points to a process capable of efficiently removing volatiles, including water, from the whole early planet. Such a loss process would point to a ‘dry’ accretion. Complete loss of early planetary volatiles is supported by the shielded isotopes of Ne, Ar and Kr within the Earth’s mantle (He and Xe cannot distinguish between sources) which are dominated by a meteoritic volatile source, albeit with a subducted atmosphere overprint. Whether or not some part of the Earth’s deep mantle, sampled by mantle plumes, preserves a remnant of Solar Nebular volatiles remains uncertain. There are no viable processes to link the noble gases in the Earth’s mantle alone to the Earth’s atmosphere. The Earth’s atmosphere requires a Solar-like noble gas component; one that has either mixed with earth interior meteoritic gases or mass fractionated to form the composition seen today. The most likely delivery of these Solar-like noble gases are cometary material. Although noble gas concentrations within cometary material are poorly defined, calculations suggest that the amount of cometary material to have supplied the atmosphere noble gases may provide an insignificant amount of water to Earth. Earth’s surface water is then most likely meteoritic (consistent with hydrogen and nitrogen isotopes) and delivered late to the Earth (>100Ma), most likely in the late heavy bombardment. 
Professor Chris Ballentine, University of Oxford, UK
Professor Chris Ballentine, University of Oxford, UKChris Ballentine started his geochemistry career in Cambridge. His work focusses on developing and applying the noble gas isotope tool to advance our knowledge of different Earth systems. His interests include understanding how the Earth gained its volatile inventory and the processes controlling terrestrial reservoir interaction and evolution over time. He has also made significant discoveries in our understanding of the processes controlling the origin, migration and interaction of subsurface water, hydrocarbons and magmatic fluids in a variety of continental settings. His career has taken him to Switzerland (Paul Scherrer Institute and ETH Zurich); the US (University of Michigan), back to the UK (Manchester) and most recently to Oxford as the Chair of Geochemistry. Chris has been involved in organising and building the governance and structure of the European Association of Geochemistry (EAG) and the European Goldschmidt conferences since 2007: chairing Davos 2009; as the EAG Goldschmidt officer for Prague 2011; co-convenor for Florence in 2013; and EAG President (2014-2014). |
| 15:30 - 16:00 |
Water on Earth – extending our knowledge of the deep hydrosphere and implications for subsurface life
Geochemists have long relied on fluid inclusions, microscopic time capsules of fluid and gas encased in host rocks and fracture minerals, to access preserved samples of ore-forming fluids, metamorphic fluids, and remnants of the ancient atmosphere and hydrosphere. Until recently, groundwaters were thought to reflect only much younger periods of water-rock interaction (WRI) and Earth history, due to dilution with large volumes of yournger fluids recharging from surface (terrestrial) or mixing from the over-lying oceans. The earliest periods of Earth’s fluid history were largely thought to have been overprinted by mixing, and/or geochemically reset, at least on a macroscopic scale. Global investigations in the world’s oldest rocks have recently revealed groundwaters flowing at rates > L/min from fractures at km depth in Precambrian cratons. Rich in reduced dissolved gases such as CH4 and H2, these fracture waters have been shown to host extant microbial communities of chemolithoautotrophs dominated by H2-utilising sulfate reducers and, in some cases, methanogens. With mean residence times ranging from Ma to Ga at some sites, and in the latter case, geochemical components of Archean provenance, not only do these groundwaters provide unprecedented samples for investigation of the Earth’s ancient hydrosphere and atmosphere, they are opening up new lines of exploration of the history and biodiversity of extant life in the Earth’s subsurface. 
Professor Barbara Sherwood Lollar, University of Toronto, Canada
Professor Barbara Sherwood Lollar, University of Toronto, CanadaDr Barbara Sherwood Lollar FRSC is a University Professor in Earth Sciences at the University of Toronto. She is Research Chair in Isotopes of the Earth and Environment, Director of the Stable Isotope Laboratory, Past-President of the Geochemical Society and 2015 elected a Fellow of the American Geophysical Union. Sherwood Lollar has published extensively on stable isotope geochemistry and hydrogeology, the fate of fluids and gases such as CO2, CH4 and H2 in ancient fracture waters in the Earth’s crust, and the role of deep subsurface microbial populations in carbon cycling. She has been a recipient of, most recently, the 2012 Eni Award for Protection of the Environment, 2012 Geological Society of America Geomicrobiology and Geobiology Prize, and Natural Sciences and Engineering Research Council Polanyi Research Award – one of Canada’s top prizes for research. |
| 16:00 - 17:00 | Panel discussion - future directions |