Themes and Sessions


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Theme 02: Primitive Earth : From core to atmosphere

Co-ordinators:
Stephen Mojzsis (University of Colorado)
James Kasting (Pennsylvania State University)
Guillaume Caro (CRPG-CNRS)

Team members:
Janne Blichert-Toft (ENS-LYON), David Catling (University of Washington), Nicolas Dauphas (University of Chicago, USA), Caroline Fitoussi (ENS-Lyon), John Hernlund (UC-Berkeley), Diane Newman (California Institute of Technology), Nathan Sheldon (University of Michigan)

Theme 02 sessions:

02a: Redox Evolution of the Early Mantle, Oceans and Atmosphere
Convenors: David Catling, Bernie Wood
Keynote: Ariel Anbar (ASU)
Orals: Fri AM, Fri PM
Posters: Thu PM
What was the redox state of the early oceans and atmosphere and what was its relationship to biological evolution and geochemical evolution of the mantle and lithosphere? Issues of interest include: (i) Controls on redox through interactions between the atmosphere, ocean, solid Earth and biosphere. (ii) The connection between atmosphere/ocean redox and the environment of the early Earth, including climate and habitability. We welcome papers concerning evidence and models for the link between redox and the early evolution of the Earth system.
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02b: Geology, Age and Origin of the Oldest Terrestrial Rocks and Minerals
Convenors: Nicholas Arndt, Stephen Mojzsis, Janne Blichert-Toft
Keynote: Martin Van Kranendonk (G.S.W.A.)
Orals: Mon PM, Tue AM
Posters: Mon PM
What are the oldest terrestrial rocks and where are they found? What geochemical information do they convey about the timing of formation of crust, the kind of crust on the early Earth, and the nature of the mantle and surface zone? How do the compositions of the oldest rocks relate to the record contained in (older) Hadean detrital zircons?
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02c: The Faint Young Sun Revisited: The Message from Rocks and Climate Models
Convenors: James Kasting, Nicolas Dauphas, Nathan Sheldon
Keynote: Marc Chaussidon (CNRS)
Orals: Tue PM
Posters: Tue PM
What is the status of constraints imposed by model studies and geochemical analyses of ancient sediments for Archean surface temperatures? Can models and conflicting interpretations of isotopic and trace element data be reconciled? In particular, can past atmospheric carbon dioxide concentrations be determined from analysis of paleosols and banded iron-formations, and how secure are these interpretations? Also, was the early Earth hot, or do oxygen and silicon isotope measurements in cherts have alternative explanations?
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02d: Geochemical Evidence For, and Consequences of, Microbial Activity in the Archean Rock Record
Convenors: Kurt Konhauser, Yuichiro Ueno, Abigail Allwood, Sylvie Derenne
Keynote: Woodward Fischer (Caltech)
Orals: Tue PM
Posters: Tue PM
The record of geochemical changes induced by life is obvious and widely accepted in younger rocks (e.g. Proterozoic to Phanerozoic), but consensus breaks down for the Archean record. Why is this so? If the interpretation of the evolution of life from the rocks conforms more to a ‘non-uniformitarian’ perspective, how can the molecular biochemical record inform us of what we see in the oldest sediments?
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02e: Timing and Conditions of Core Formation in the Primitive Earth
Convenors: Caroline Fitoussi, Mathieu Touboul
Keynote: David Rubie (Univ. Bayreuth)
Orals: Wed AM
Posters: Tue PM
What is the geochemical record of core formation? When did Earth's core chemically "close"? How does this event affect the evolution of the mantle and crust? Core differentiation over the course of Earth’s accretion is essential to determine the bulk composition of our planet and relate it to the composition of planetary objects. It also provides invaluable information on related events such as the formation of the Moon. Constraints on the timing of core formation and composition of the core can be derived by isotope systematics. Other constraints on the physical conditions and processes of core formation result from experimental studies of siderophile element metal-silicate partitioning and theoretical modeling.
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02f: Primordial Differentiation and Destruction of Hadean Silicate Reservoirs
Convenors: Guillaume Caro, Vickie Bennett
Keynote: Geoff Davies (Australian National University)
Orals: Thu AM
Posters: Wed PM
Despite an abundance of new observations shedding light on the previously "dark age" of the Hadean, fundamental questions of early Earth processes remain. These include: What was the composition, volume and physical properties of the early crust? What was the role of early planetary events, including impacts and magma oceans in creating Hadean silicate reservoirs? Was plate tectonics possible in the Hadean and Archean, or are there other plausible mechanisms for recycling crust on a young Earth? How far forward into the geologic record do Hadean reservoirs persist and how much do the geochemical signatures of modern mantle reservoirs reflect Hadean events? This session welcomes contributions based on observations from the rock record, experimental data or numerical models that explore the inception and evolution of the silicate rock cycle on Earth
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02g: What was the Source of Earth’s Volatiles?
Convenors: Sean Raymond, Bernard Marty
Keynote: Kevin Zahnle (NASA ARC)
Orals: Wed PM
Posters: Wed PM
The origin of Earth's atmosphere and hydrosphere remains mysterious. What were the sources of volatiles to the Earth and at what time? Current models of the solar nebula suggest that temperatures at 1 AU radial distance were sufficiently high that only refractory iron and silicate minerals could condense; hence, Earth’s volatiles must have come from farther out. Asteroids, comets and interplanetary dust are potential sources of volatiles. Which of these sources dominated can be constrained by measurements of elemental and isotopic abundance ratios, as well as via dynamical models of the accretion process. The timing of volatile delivery is also an issue, as some models predict that significant amounts of volatiles could have been delivered well after the main accretion period. This session will look at volatile delivery from all of these different viewpoints.
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02h: Taphonomy and Geochemistry: Experiment and Observation in Understanding the Fossil Record of Early Life
Convenors: Tanja Bosak, Michael Tice, Jochen Brocks
Keynote: Jan DeLeeuw (NIOZ)
Orals: Thu PM
Posters: Wed PM
The interpretation of putative signs of life in the geologic record, recent and ancient, requires a thorough understanding of the mode of formation of fossils. How is morphological and chemical information preserved? This session invites contributions that address the problem of the preservation of putative signs of life in old rocks from a geochemical perspective.
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02i: The Evolving Early Earth Hydrosphere as a Geodynamic Tracer and Facilitator for Life: Constraints from the Supracrustal Rock Record
Convenors: Vincent van Hinsberg, Emilie Thomassot
Keynote: Kurt Konhauser (Univ. Alberta)
Orals: Mon AM
Posters: Mon PM
Supracrustal rocks in Archaean belts provide the best constraints on the physical and chemical conditions prevailing on the surface of the young Earth, and, more importantly, how these changed over time. This information is vital to understand the diversity of changes that took place in the early history of our planet, from changes in element reservoirs and fluxes, to the onset of plate tectonics, and the origins and evolution of life. This session focuses specifically on constraining the (trace) element composition of the Archaean (and Hadean) hydrosphere, both in its role as a tracer of Early Earth processes and as a facilitator for the development of life. We invite contributions using the full range of geochemical and geological tools to better understand this crucial time in our planet’s history.
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02j: Aqueous Environments Captured by Clay Mineral Deposits on the Early Earth and on Mars
Convenors: Joseph Michalski, Javier Cuadros
Keynote: Martin Kennedy (University of Adelaide)
Orals: Thu PM
Posters: Wed PM
Much of the early geologic record of Earth has been lost to plate tectonics, but on Mars, the ancient crust is relatively well preserved. In recent years, infrared spectroscopic data have shown that phyllosilicate minerals, especially smectite clays, are commonly observed where the ancient Martian crust is well exposed. This session aims to explore aqueous geologic processes that could explain the formation of phyllosilicates in extraterrestrial and ancient terrestrial environments. Studies focused on all aspects of geochemistry, mineralogy, modeling, and planetary remote sensing would be welcomed.
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02k: Astrobiology and Extreme Terrestrial Environments
Convenors: Jan Jehlicka, Howell G M Edwards
Keynote: Aharon Oren (The Hebrew University of Jerusalem )
Orals: Mon PM
Posters: Mon PM
The search for signs of extant or extinct life elsewhere in the Solar System is informed by relevant studies carried-out in extreme environments on Earth. The understanding of the survival strategies adopted by biological organisms in deep oceanic subsurfaces, hot springs and deserts and the ways in which geological niches can be adapted for biological colonisation can provide information that is important for astrobiological planetary exploration . It is proposed to address geochemical aspects of these extreme environments including results obtained using microbiological, spectroscopic and isotopic techniques several of which have been included in planned planetary probes using remote robotic vehicles. This session focus on areas as prebiotic chemical evolution, biosignatures, and the roles played by mineralization in the preservation of biosignatures and biomarkers of extant and relict life.
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Theme 02 related sessions:

01a: The Disc Epoch: Sources and Compositions of Early Solar System Materials
Convenors: Jérome Aléon, Ko Hashizume
Keynote: Sylvie Derenne (Univ. Paris)
Orals: Mon AM
Posters: Mon PM
Planets and planetesimals form from a batch of diverse materials from different sources, characterized by their mineralogical, chemical and isotopic compositions. Such materials include (1) old interstellar gas and dust available at the onset of solar system formation : from circumstellar grains to molecular cloud materials reaching the presolar dense core phase and (2) young materials formed in the earliest stages of solar system formation : the class 0 stage, the protosolar collapse or the various environments in the earliest solar protoplanetary disk (jet, midplane, photosphere…). These materials are commonly found in primitive meteorites and comets, however their origins and astrophysical conditions of formation often remain unclear, in spite of their importance to unravel the physics and chemistry of the earliest solar system. The goal of this session is to bring together cosmochemists and astrochemists/physicists to present an up-to-date summary of these primordial materials (presolar grains, organics, CAIs, ferromagnesian silicates, amorphous or non-stoechiometric dust grains, water etc.) and to discuss their possible formation in the context of the most recent understanding of low mass star formation.
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01b: From Gas and Dust to Planetesimals: Processes and Timescales
Convenors: Fred Ciesla, Ed Young
Keynote: Audrey Bouvier (Arizona State University)
Orals: Thu PM, Fri AM
Posters: Thu PM
Meteorites provide a record of the complex processes that controlled how our solar system formed and evolved. The chemical and isotopic variation seen in these bodies provide insights into the ranges of environments in which planetary materials were processed, while radiometric ages inform us about the timing of this processing. Despite this wealth of data, we are still working to understand how solid materials in the solar nebula aggregated together to form planetesimals. The goal for this session is to gain new insights into the formation of these objects by discussing the latest cosmochemical data in the context of models for the formation of planetesimals.
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01c: From Planetesimals to Planets
Convenors: Ghylaine Quitté, Frederic Moynier
Keynote: David Stevenson (Caltech)
Orals: Mon PM
Posters: Mon PM
Accretion and differentiation are the main processes leading to the present structure and composition of planets. This session will focus on recent advances in understanding the timescales and physical processes prevailing during these events in planetesimals and planets. We aim at a better comprehension of runaway growth, the role of impacts in the early solar system, planetary heating processes, element partitioning, core formation and mantle melting including crust formation. We welcome contributions in the fields of cosmochemistry and planetary geochemistry (radiogenic and stable isotopes, trace elements) in experimental petrology, modelisation (heating models, metal segregation models), dynamical calculations, and astronomical observations to try and reconcile the various perspectives.
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01d: Mars and the Moon: New Discoveries from Sample Science to Recent Missions
Convenors: Anne Peslier, Tomas Magna, Carsten Münker
Keynote: Zach Sharp (University of New Mexico)
Orals: Fri AM, Fri PM
Posters: Thu PM
This session brings together researchers whose work aims to understand the formation, differentiation, magmatism, surface processes, and atmospheric compositions of Mars and the Moon. Of particular interest are the following ongoing debates: Do the interiors of these planets contain significant amounts of water and other volatiles to alter our current models of planetary formation and evolution, such as the formation of the Moon by a giant impact of a Mars-size body into proto-Earth, and the origin of Mars and Moon volcanism? Is or was water present on their surfaces? What are the chronology and processes active prior, during, and after crystallization of their magma oceans? We welcome analytical or experimental developments, analyses of Apollo samples and lunar and martian meteorites, petrology and geochemistry studies, impact shock research, modeling studies from micrometer to planetary scales, and results from remote-sensing or surface missions. Contributions are especially encouraged that combine the different approaches.
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03a: Experimental Constraints on the Origin and Evolution of Earth’s Early Mantle and Core
Convenors: James Badro, Mike Walter
Keynote: Bernie Wood (University of Oxford)
Orals: Tue AM
Posters: Mon PM
Much of Earth’s internal physical and chemical structure was founded during the first 100 million years of its evolution. The Earth’s core segregated from the mantle, probably over a period of time and in a number of metal segregation events. The chemistry of the core, including its siderophile and light element inventory was largely established during these events, and can shed insights into the core forming processes. The mantle also may have undergone repeated melting and internal differentiation as the core segregated and the mantle crystallized. The possibility of an early deep, dense melt layer may hold the key to several geochemical and isotopic conundrums. Experiments at extreme conditions are required to understand melting behavior, element partitioning, density relations and physical properties of core and mantle materials. We solicit contributions from experimental petrology and geochemistry for this session dedicated to enhancing our understanding of this fascinating time in Earth’s history.
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03b: Estimating the Deep Mantle Water Budget from Geochemistry, Geophysics, and Geodynamical Modelling
Convenor: Bruno Reynard
Keynote: Hikaru Iwamori (Tokyo Institute of Technology)
Orals: Thu AM
Posters: Wed PM
Evaluating the water budget in the deep Earth involves various methods ranging from isotope geochemistry and experimental petrology, to seismology, electromagnetic studies and geodynamics. A top priority is to accurately constrain the amount of water re-cycled into the mantle via subduction of crust and lithosphere. We welcome contributions relating to a range of problems including the chemical and isotopic budget of subducted material, the water content and volume of lavas emitted at volcanic arcs, the experimental constraints on phase relations, water fractionation and migration, the effect of water on seismic and other geophysical observables of the mantle, and physical and numerical modelling of mass transfer during subduction down to the transition zone and lower mantle. Integration of these different approaches should help place tighter constrains on water recycling to the deep mantle.
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03c: Mantle Redox and the Deep Carbon Cycle
Convenors: Yingwei Fei, Dan Frost, Bob Luth
Keynote: Hugh O'Neill (Australian National University)
Orals: Tue AM, Tue PM
Posters: Tue PM
The oxidation state of the mantle is strongly associated with the speciation of volatile components, which in turn can influence magma genesis and metasomatic processes. Carbon is one of the main volatile elements for which redox conditions plays a major role, exemplified by the existence of oxidised carbonate minerals and melts and reduced graphite and diamond in the mantle. The oxygen fugacity of the mantle remains controversial, however, and its variation in different tectonic environments has come under continuous scrutiny particularly due to the advent of new methods for redox measurements. The cycling of carbon through the earth is also poorly understood both in the depth and extent to which carbon is subducted and the depth at which melting commences in carbon-bearing mantle. We seek contributions that examine the redox state of mantle rocks and magmas in addition to those which explore the speciation or cycling of carbon through the interior. Estimates of the carbon budget of mantle reservoirs and the stability and formation mechanisms of carbon-bearing phases, such as diamond, are of particular interest. Through a synthesis of disciplines we hope to develop the understanding of the mechanisms that have governed, influenced or been influenced by the redox state of planetary mantles throughout history and the cycling of carbon through the interior.
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04a: Chemical Geodynamics: 25 Years of Mantle Components
Convenors: Al Hofmann, Francis Albarède, Matthew Jackson, Thorsten Becker
Keynote: Stan Hart (Woods Hole Oceanographic Institution)
Orals: Mon AM, Mon PM
Posters: Mon PM
In the 25 years since the publication of the landmark paper on chemical geodynamics by Zindler and Hart, more species have been proposed for the mantle zoo, but the relationship of this geochemical zoo to the geodynamics and petrology of the mantle remains a subject of lively debate. We invite contributions that investigate the creation, existence and sampling of mantle components and their geodynamic interpretation throughout the thermo-chemical history of the Earth's mantle.
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04b: New Insights into Mantle and Crustal Processes from High Temperature Stable Isotope Techniques
Convenors: Bruce Watson, Anat Shahar, Craig Lundstrom
Keynote: Frank Richter (University of Chicago)
Orals: Tue AM
Posters: Mon PM
In recent years, improvements in analytical capabilities have enabled the observations of stable isotope fractionation in magmatic systems and under mantle pressure and temperature conditions. Multiple isotope systems are beginning to show variable extents of fractionation, apparently controlled by different processes. This session aims at bringing together investigations of kinetic and equilibrium fractionation processes, from natural, theoretical and experimental studies.
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04d: Influence of Volatiles on Mantle and Magma Processes
Convenors: Rajdeep Dasgupta, Alison Shaw, Dan Frost
Keynote: Hans Keppler (Universität Bayreuth)
Orals: Thu AM, Thu PM
Posters: Wed PM
Volatile elements such as hydrogen, carbon, sulfur, chlorine, and fluorine in the Earth's mantle play a key role in controlling the dynamics and differentiation of the planet, as well as in facilitating elemental exchange between the mantle and its exospheric reservoirs. These elements, stored in various forms and concentrations, are known to have significant effects on the loci of partial melting and on physical and chemical properties of magma including viscosity, density, conductivity, diffusivity, oxidation state and elemental compositions. The presence of hydrogen is also known to influence the physical properties of minerals; whereas the presence of volatile-bearing partial melts likely have considerable influence on convective processes in the mantle. This session seeks to highlight recent advances in geochemical, geophysical, and petrologic constraints on the involvement of volatiles on mantle processes including melting, element fractionation, redox reactions, mantle flow, and element transport. We encourage contributions from any discipline, that cover some aspect of volatile cycling in the Earth's interior based on: (1) natural observations of lavas, xenoliths, melt inclusions or fluids, (2) laboratory experiments, and (3) theoretical calculations and geodynamic modeling.
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05a: The Origin of Planetary Crusts
Convenors: Audrey Bouvier, James Day
Keynote: Hilary Downes (University College, London)
Orals: Wed AM
Posters: Tue PM
Crust-forming processes on fully differentiated planetary bodies in the Solar System appear to have created largely ‘basaltic’ compositions unlike terrestrial continental crust. Felsic and evolved compositions have been suggested for some partially differentiated asteroidal bodies, as well as for Mars and for minor components of the lunar crust. Refined understanding on the processes of planetary differentiation may shed light on the formation of early terrestrial crust, possible hidden reservoirs, and what conditions are necessary for the formation of evolved felsic crust. Contributions with emphasis on comparative planetology are particularly encouraged.
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05c: Continent Formation through Time
Convenors: Steve Parman, Peter Clift, Steven Shirey, Martin Van Kranendonk
Keynote: Chris Hawkesworth (St. Andrews)
Orals: Thu AM, Thu PM
Posters: Wed PM
Although processes associated with plate tectonics (subduction, arc volcanism, and island arc accretion) are generally accepted as controlling crust-generation during post-Archean times, it is still not clear how early in Earth’s history plate tectonics operated or whether continent formation occurred by fundamentally different processes. What role did slab melting, melting during crustal thickening, and large plumes play in making continents in the past, and what insights can be gained from modern examples of such processes? How has the composition of continental crust and its building blocks changed with time? We invite contributions using a variety of approaches (field observation; petrologic, geochronologic and isotopic study; numerical and experimental modeling; etc.) to address these problems.
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07b: Trace Elements at the Intersection of Biological and Geochemical Evolution
Convenors: Aubrey Zerkle, Stefan Lalonde
Keynote: Christopher Dupont (J. Craig Venter Institute)
Orals: Tue AM
Posters: Mon PM
Biology exerts a profound metabolic influence over the cycling of trace elements at the Earth's surface. At the same time, some trace elements constitute essential nutrients that drive primary biogeochemical cycles, giving rise to a complex interplay between biological and geochemical evolution. Such feedbacks would have been particularly important on the early Earth, when changes in the redox state of the oceans and atmosphere impacted global nutrient cycles and the course of biological evolution. In order to better understand these relationships, new trace element studies of ancient sediments, as well as new experiments and modern field studies in trace element biogeochemistry, are required. This session invites submissions exploring the co-evolution of the biology and geochemistry of trace elements, especially as it pertains to the use and cycling of trace elements by microorganisms, the evolution of microbial metabolisms, the trace nutrient status of natural waters, and the interplay of these forces through deep geological time.
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08d: Biotic/abiotic Nucleation and Early Life
Convenors: Karim Benzerara, Andreas Kappler, Kurt Konhauser
Keynote: Christophe Dupraz (University of Connecticut)
Orals: Tue AM
Posters: Mon PM
Life forms a wide diversity of minerals offering potential biosignatures that can be preserved in the geological record. The formation pathways of intracellular magnetites by bacteria or of emblematic objects such as stromatolites or Banded Iron Formations by diverse microbes have for example received a particular attention from the community over the last years. There is however still a lot of work needed on biominerals to understand 1. how life impacts mineral nucleation, 2. how it controls the buildup of complex structures such as stromatolites, 3. what biomolecules are involved in biomineralization processes and 4. how mineral nucleation and growth in modern systems compare with biomineralization in early environments. Contributions from geobiologists, mineralogists and geochemists on Early life or modern biomineralizing analogue systems and presenting microscopy, spectroscopy and isotopy data are as well as mechanistic or physiological studies are welcome.
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18a: Advances in Resolution and Accuracy of in situ Determination of Isotope Ratios
Convenors: Anders Meibom, Jan Kosler
Keynote: Takafumi Hirata (Kyoto University)
Orals: Mon AM, Mon PM
Posters: Mon PM
The coupling of multi-collector instruments with laser ablation/plasma or secondary ionisation sources has given rise to a wealth of new opportunities for in situ isotope ratio determination. New technologies have enhanced a wide range of capabilities from high spatial resolution with high ion-yields on in SIMS to minimisation of fractionation on larger sample sizes for high precision ratio measurement using femto second lasers. Additionally, a welcome resurgence of custom built instruments addresses novel frontiers of challenging measurements.
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19h: High Pressure Behavior from Impacts to Interiors
Convenors: Nico de Koker, Kanani Lee
Keynote: Burkhard Militzer (University of California, Berkeley)
Orals: Fri PM
Posters: Thu PM
The behavior of materials at high pressure is important for understanding the origins and evolution of planets, the dynamics and structure of Earth's interior, and impact processes. High pressure presents unique challenges because it is difficult to replicate in the laboratory. Over the last decade ab initio theory has grown to be a powerful complement to the experimental approach. Theory is not limited by extreme conditions and serves as a source of additional insight into the fundamental origins of physical behavior. Theory has made important contributions to our understanding of phase transitions, including the discovery of the post-perovskite phase, insulator-metal transitions, spin transitions such as the high-spin to low-spin transition in transition metal oxides, and in elucidating the role of core electrons in high pressure chemistry. We welcome contributions focused on any aspect of high pressure behavior from any of the wide range of ab initio and semi-empirical theoretical techniques that have been applied in this regime.
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Scope of theme:
Little is known of the "Primitive Earth". The prevailing archetypes for the first 800 million years of Earth history subsequent to the formation of the Moon include core closure, the establishment of crust, and acquisition of an atmosphere, hydrosphere and biosphere by various physical and chemical mechanisms. Several models have postulated the establishment of a primordial mafic/ultramafic crust and the absence of considerable continents, and a dry hot (or even cold) sterile world before about 4 Ga. These contrast with the view of large-scale differentiation, subsequent continental growth, efficient recycling and generally habitable conditions very early in Earth history. This Theme invites contributions that report on progress in our understanding of the early (bio)geochemical evolution of the Earth based on model studies and observations.