CARBON IN EARTH Midterm Scientific Report of the Deep Carbon Observatory

CARBON IN EARTH
Quantities, Movements,
Forms, and Origins
Midterm Scientific Report of the
Deep Carbon Observatory
December 2014

Transcript

1. deepcarbon.net CARBON IN EARTH Quantities, Movements, Forms, and Origins Midterm Scientific Report of the Deep Carbon Observatory December 2014 DEEP CARBON OBSERVATORY deepcarbon.net
3. i CARBON IN EARTH Quantities, Movements, Forms, and Origins Midterm Scientific Report of the Deep Carbon Observatory CONTENTS Author Message ii Earth Materials Discoveries iii Decadal Goals iv Introduction 1 Quantities 3 Movements 6 Forms 10 Origins 14 The Next Five Years 17 Contributors to 21 Deep Carbon Science References 22
4. ii Casey McAdams Author Message Five years ago we began a decade of discovery in a new field of scientific exploration of carbon in Earth. The Deep Carbon Observatory (DCO) brings together scientists from many disciplines around the world to answer critical questions about Earth’s past, present, and future. Seeded with funding from the Alfred P. Sloan Foundation (New York), partnerships fostered under the banner of DCO have earned support from research sponsors in many nations, including the UK Natural Environment Research Council, Russian Ministry of Science and Education, European Research Council, the European Commission’s Marie Sklodowska Curie Research Program, US National Science Foundation, US Department of Energy, Natural Sciences and Engineering Research Council of Canada, Canadian Space Agency, Canada Research Chairs Program, Conseil Régional d’Ile de France, Deutsche Forschungsgemeinschaft, Japan Society for the Promotion of Science, Ministry of Education, Culture, Sports, Science, and Technology of Japan, and the Chinese Academy of Sciences, as well as the International Continental Scientific Drilling Program and the International Ocean Discovery Program. Key partners around the world also include leading academic institutions, commercial organizations, national geological surveys and professional societies concerned with geophysics, geochemistry, mineralogy, and microbiology. We look forward to strengthening our relationships with colleagues in Europe and North America, and further expanding the DCO Science Network within Asia, South America, Africa, and Australia. In this midterm scientific report, and with great help from many colleagues in DCO, we take a look back over five years of transfor- mative science taking place within a vibrant and growing research community. There is much to accomplish over the next five years, and we have outlined some key directions and opportunities for the next phase of DCO. It is with a sense of pride, achievement, and excitement that we share our work with you. Finally, DCO remains indebted to the Carnegie Institution of Washington for its enthusiastic support and nurturing of the program from its inception. Russell J. Hemley Co-Executive Director Deep Carbon Observatory Carnegie Institution of Washington
5. iii Diamond (C) Ultradeep diamonds from >670 km depth reveal the cycling of organic mat- ter to the lower mantle;3 lithospheric diamonds show the start of plate tec- tonics.4 Graphite (C) Graphite forms from carbon-rich flu- ids in both the deep crust and upper mantle, and can deliver carbon to deep Earth.5,  6,  7 Carbides (SiC, FeC, Fe3 C, Fe3 C7 ) Iron carbides are stable to Earth core conditions and may be a significant car- bon reservoir in Earth’s deep interior.8,  9 Carbonates [(Ca,Mg,Fe)CO3 ] The discovery of new dense carbon- ate structures suggests that the lower mantle may be more carbon-rich than previously thought.10 Carbo-silicates (Si-C-O)* Carbon can substitute for both silicon and oxygen in mantle silicates and pro- vide a previously unrecognized deep carbon reservoir.11,12 Silicates (trace C)* Common silicate minerals in Earth’s mantle may incorporate more than 1000 parts per million of carbon— enough to significantly increase Earth’s known carbon budget.13 Metals (Fe, Ni,...C) 2 x 1020 tons of carbon may reside in Earth’s core, and that carbon affects the distribution of other elements between mantle and core.8, 9, 14 Oxides (C-O) ‘Polymeric’ CO2 adopts a silica-like struc- ture15, 16 that is stable to the conditions of Earth’s lower mantle.17 Earth Materials Discoveries In 2009 DCO scientists tabulated known and unknown information about carbon in minerals, melts, and fluids throughout Earth’s interior, and outlined the considerable gaps in knowledge about each.1, 2 During the past five years, DCO scientists have made numerous discoveries about these carbon-bearing Earth materials. These material reservoirs are listed here, along with groups that are either new or received scant attention (marked by an asterisk). Sulfides (metal-S…C)* Sulfide minerals promote remarkably se- lective catalysis of organic molecules,18 and deep microbes use sulfide-sulfate redox energy.19 Melts (Si-O-C) Carbonate-rich melts pervade regions of Earth’s upper mantle, and these melts may lubricate tectonic plates, thereby facilitating their movement.20,  21,  22 Fluids (C-O-H-N)* The unusual character of hot car- bon-containing fluids promotes both diamond formation and organic synthe- sis23 and may even give rise to Earth’s distinctive atmosphere.24 Hydrocarbons (C-H) Unique isotopic measurements of meth- ane help to identify sources of Earth’s deep gas,25, 26, 27 and experiments iden- tify reactions leading to abiogenic hydrocarbons.28, 29 Clathrate hydrates (H2 O + CH4  + CO2 ) Gas hydrates are stable over a broad range of conditions in near-surface envi- ronments and remain a major potential energy source. 30 Complex organic molecules (C-H-O-N...) Hydrogen production by mineral reac- tions can drive the production of both abiotic and biotic organic molecules.31,  32 Microbes (C-H-O-N-P-S...) Subsurface microbial abundance varies regionally by factors of up to 100,000, and these sparse subsurface microbial ecosystems are characterized by low di- versity and slow metabolisms.33–38 Viruses (C-H-O-N-P-S...)* Genomic studies reveal a surprising abundance and diversity in a deep, subsurface viriosphere, and these deep-subsurface viruses propagate pri- marily by long-term incorporation into microbial genomes.39 Impetus for a Deep Carbon Observatory Carbon plays an unparalleled role in our lives. It is the element of life, providing the chemical backbone for all essential bio- molecules. Carbon-based fuels supply most of our energy, while small carbon-containing mole- cules in Earth’s atmosphere play a major role in our variable and uncertain climate. Yet in spite of carbon’s importance we remain largely ignorant of the physical, chemical, and biological behavior of carbon-bearing systems more than a few hundred meters be- neath our feet. We do not know how much carbon is stored in Earth’s interior, nor do we know the nature of those deep res- ervoirs. We do not know how carbon moves from one deep re- pository to another, nor do we know the extent to which carbon moves to and from Earth’s sur- face. We have only vague hints of an extensive deep microbial eco- system, which by some estimates rivals the total surface bio- mass. Accordingly, we propose to commence a decade-long, international, multidisciplinary research program that will fo- cus on the deep carbon cycle. (Proposal for the Deep Carbon Observatory, 2009) Robert M. Hazen Executive Director Deep Carbon Observatory Carnegie Institution of Washington
6. iv Decadal Goals The evolving goals of DCO’s four scientific communities guide the program’s scientific activities and adaptive vision for the growing field of carbon in Earth. The Deep Life community explores the evolutionary and functional diversity of Earth’s deep biosphere and its interaction with the carbon cycle. n Determine the processes that define the diversity and distribution of deep life as it relates to the carbon cycle n Determine the environmental limits of deep life n Determine the interactions between deep life and carbon cycling on Earth The Reservoirs and Fluxes community is dedicated to identifying the prin- cipal deep carbon reservoirs, determining the mechanisms and rates by which carbon moves among these reservoirs, and assessing the total carbon bud- get of Earth. n Establish continuous open-access monitoring of volcanic gas emissions n Determine the chemical forms and distribution of carbon in Earth’s deepest interior n Determine the seafloor carbon budget and global rates of carbon input into sub- duction zones n Estimate the net direction and magnitude of tectonic carbon fluxes from the man- tle and crust to the atmosphere n Develop a robust overarching global carbon cycle model through deep time, includ- ing the earliest Earth, and co-evolution of the geosphere and biosphere n Produce quantitative models of global carbon cycling at various scales, including the planetary scale (mantle convection), tectonic scale (subduction zone, orogeny, rift, volcano), and reservoir scale (core, mantle, crust, hydrosphere) The Deep Energy community is dedicated to quantifying the environmen- tal conditions and processes from the molecular to the global scale that control the volumes, rates of generation, and reactivity of organic compounds de- rived from deep carbon through geologic time. n Conduct field investigations to determine processes controlling the origin, rates of production, migration, and transformation of abiotic gases and organic species in Earth’s crust and mantle n Develop techniques to identify and characterize hydrocarbons and organic species from global fluid and solid samples across deep time (e.g., the Moho, Mars, and meteorites), including their compositions, structures, and isotopic characteristics that resolve the contributions of abiotic- versus biotic-controlled processes n Explore the nature of the organic molecule–mineral interface at crustal and upper mantle conditions n Determine the nature and extent of abiotic reaction rates and mechanisms leading to deep hydrocarbons, other organic compounds, and H2 synthesis n Integrate our understanding of the environmental conditions and processes that control the generation, transport, and reactivity of abiotic/biotic compounds lead- ing to transformative models of global carbon cycles through geologic time The Extreme Physics and Chemistry community seeks to achieve a trans- formative understanding of the physical and chemical behavior of carbon at extreme conditions, as found in the deep interiors of Earth and other planets. n Inventory possible carbon-bearing phases in Earth’s mantle and core n Achieve a fundamental understanding of carbon in Earth’s core n Characterize the physical and thermochemical properties of deep-Earth phases at relevant pressure and temperature conditions n Develop environmental chambers to access carbon-bearing samples in new regimes of pressure and temperature under controlled conditions (e.g., pH, fO2 ) and with increased sample volumes and enhanced sample analysis and recovery capabilities n Achieve a fundamental understanding of carbon bonding at conditions equivalent to the cores of Jovian planets n Implement an integrated carbon algorithm-software-hardware computational facili- ty for multiscale deep carbon simulations DCO Legacies DCO’s legacies will include an international community of deep carbon researchers who integrate geoscience, physics, chemistry, and biology; new in- strumentation to make mea- surements at high temperatures and pressures; insights into the distribution, nature, and depo- sition of energy resources; networks to detect fluxes of carbon-containing gases and fluids between Earth’s interi- or and the surface; open access publications and data for use by the global research community; a collaborative infrastructure viewed as a model for future research programs; and public interest in the birth of a new field of scientific exploration.
7. 1 Volcanoes provide a window to deep Earth, linking the mantle and atmosphere. By measuring outgassing from volcanic vents, DCO scientists evaluate this important piece of the global carbon cycle. A gas monitoring station on the summit of Mount Etna, Italy, is one of many stations providing data for DCO’s global volcanic monitoring network. Credit: Adrian Jones Introduction A new science is emerging for carbon, one of nature’s key elements — of life, of energy, of climate change. Despite its importance, we remain largely ignorant of carbon’s behavior throughout the planet. The carbon that is familiar to us — in the surface, atmosphere, and oceans —probably accounts for only a small fraction of Earth’s total abundance of this fundamental element. More than 90% of Earth’s carbon may be hidden deep within the planet and remains unexplored. We do not know the Quantities of that carbon and where it resides. We do not know its Movements from one repository to another or how it moves to the surface and back into the planet. We do not know the Forms of carbon at depth, ranging from the inorganic realm of minerals to organic constituents of the deep biosphere. Finally, these questions have implications for Origins — of life, Earth and the Solar System, and deep carbon itself. Launched in 2009 as a 10-year program, the Deep Carbon Observatory (DCO) is laying the groundwork for a new scien- tific discipline revolving around carbon. Under the auspices of DCO, scientists from over 40 countries are now studying this central element in diverse, innovative, and transdisci- plinary ways. Communities of scientists are focusing on the Reservoirs and Fluxes of carbon within Earth, the nature and extent of Deep Life, carbon-derived Deep Energy within the planet, and Extreme Physics and Chemistry of carbon.1, 2 Here we outline the significant discoveries fostered by DCO to date midway through this decadal quest to answer overarching questions about carbon in Earth. We also highlight plans for the next five years that will target new discoveries about car- bon in our planet and related extreme environments. Carbon in Earth, a landmark, open access volume of Reviews in Mineralogy and Geochemistry, is the first major col- lective publication of the Deep Carbon Observatory.1
8. 2 Next Generation Technologies Technological innovation goes hand in hand with cutting-edge scientif- ic discovery, and DCO made signif- icant commitments to developing novel instrumentation at its outset. For example, DCO is simultaneously pursuing two radically different ap- proaches for measuring rare, doubly substituted (or “clumped”) isotopo- logues of methane. One approach Next generation instruments developed by research teams at Caltech,25 MIT,26 and UCLA27 (clockwise from top left) address methane formation temperatures and sources. Credit: Caltech/Thermo Fisher; MIT/Aerodyne Research; UCLA/Nu Instruments involves mass spectrometry and the other involves absorption spectros- copy. Mass spectrometry and ab- sorption spectroscopy are based on different physical principles and each approach has distinct advan- tages and disadvantages. Recent in- strumentation breakthroughs by research groups at Caltech,25 MIT,26 and UCLA27 have positioned DCO to achieve a major decadal goal re- garding a deeper understanding of methane formation temperatures, sources, and provenance. Data from these instruments will enable re- searchers to test hypotheses about biotic versus abiotic origins of meth- ane. This new instrumentation rep- resents major steps in developing a new branch of isotope geochemistry.
9. 3 Quantities How Much Carbon Does Earth Contain, and Where Is It? The amounts and locations of carbon in Earth are paramount questions for DCO. To address them, one must also understand how the abundance of carbon in its different oxidation states varies with depth within the planet. Also, carbon cannot be considered in isolation; it is a component within complex chemical systems—fluids, melts, and solids —that compose Earth’s interior. Indeed, DCO’s study of Earth’s carbon is revealing a great deal about other elements and materials at depth, including the water we drink and the air we breathe. The different physical and chemical properties of the mantle and core affect carbon storage in different ways, and point to significant, unexpected reservoirs of carbon. This emerging understanding is crucial for investigating a host of problems, ranging from energy resources, geological hazards, and the evolution of Earth and life, to estimates of the extent of the biosphere deep below the surface. Extent and Sources of Deep Gas The clumping of carbon and hydrogen isotopes in hydrocar- bon molecules contains important information on the source of hydrocarbons. DCO scientists have developed and implement- ed new methodologies for the analysis of clumped isotopes in methane. These far-reaching advances could impact a variety of disciplines. For example, mass spectrometric and laser spec- troscopy measurements of methane will allow researchers to distinguish between geological and biological sources of methane in the atmosphere, hydrosphere, and interior of the planet.25 – 27 These measurements will lead to improved understanding of the biogeochemistry of methane in the environment, and extending the measurements to larger carbon-containing molecules is ex- pected to lead to the identification of unique signatures of life. This question of deep gas is intimately connected with the extent of oxidation of Earth’s interior—a major question in geoscience. DCO scientists discovered that carbon plays an important role in controlling the oxidation state of Earth’s mantle.40 Studying samples of basalts from mid-ocean ridg- es, DCO researchers found that the pristine mantle is more reduced — contains less oxygen or more hydrogen — than pre- viously thought. On the other hand, experimental studies show that the mantle underlying Earth’s oldest continents is consid- erably more oxidized than previously thought; carbon that re- sides there is oxidized to form CO2  , which is incorporated into melts and rises to the surface.41 Volcanic glasses, such as the one show- cased on the 14 June 2013 cover of Science, reveal a link between Earth’s oxi- dation state and the deep carbon cycle.40 The featured DCO research investigated this connection using analyses of volcanic glass formed from lava erupting on the seafloor. Credit: AAAS / Glenn Macpher- son, Tim Gooding, Elizabeth Cottrell
10. 4 Diamonds Reveal What’s Within Natural diamonds are not only stunningly beautiful, they are also essential for unraveling secrets of Earth’s deep interior. Ultradeep diamonds from 400 to 670 km below the surface (Earth’s transition zone) trap pieces of the surrounding rock at that depth. These tiny inclusions thus give researchers a sample of the planet’s interior that is far beyond the reach of drilling from the surface. Measurements of inclusions in ultradeep diamonds from Brazil reveal the transition zone might have as much water as all the world’s oceans put together, with local “wet spots” deep within Earth.42 Specifically, the water content of the mantle is about 1% by weight, which agrees with estimates from electromagnetic remote sensing. This discovery has transformed our view of the amount of water and other volatiles in the mantle —and our understanding of the deep water/hydrogen cycle. Similarly, by studying an inclusion of olivine (Mg, Fe)2 SiO4 in a diamond, DCO scientists directly measured the com-position of the surrounding rock and identified the precise mantle depth at which the diamond formed.43 These results exemplify what carbon (as diamond) can tell us about the deep Earth. The extent of rich informa- tion available from detailed study of diamond is only now being recognized,44 such as finding that a single diamond can form in two growth stages, one billion years apart.45 Measurements of the nitrogen impurities of other diamond samples provide evidence for multiple formation events in the mantle.46 How Much Is Alive? DCO embarked on a broad program of sampling the bio- sphere to depths of many kilometers in the crust. If we know the extent of the deep biosphere, we can better understand how much carbon is stored in Earth as well as the hidden richness of the biosphere. Researchers have begun to quan- tify the abundance of microbes in the crust,37, 38, 47 and have refined estimates of microbial abundance in the seafloor by one order of magnitude compared to what was previously thought. An influential study provides the most accurate es- timate to date of the microbial biomass in the global subsea- floor; it refines our knowledge of the distribution of microbial life in the subseafloor­­ — estimates that significantly improve our understanding of deep life. The new measurements show that populations of subseafloor microbes can vary by at least 100,000 times regionally, and improve estimates of total glob- al abundance.38 The water content of ringwoodite, included in a diamond from Brazil, indi- cates Earth’s mantle transition zone may contain an ocean of water.42 • • • Ultradeep diamonds such as these from Brazil provide detailed information on the deep carbon cycle. Credit: Steven Shirey Analysis of the minerals trapped in diamonds, such as the red garnet shown here, provide valuable clues to processes in Earth’s ancient mantle. Credit: Steven Richardson
11. 5 Unexpected Reservoirs of Carbon Discoveries by DCO scientists point to the existence of places where significant carbon can be held within Earth — from miner- alogical to regional scales. Carbonates, which are common min- erals found at Earth’s surface, are potential carriers of carbon into Earth’s mantle, and thus play an important role in the global deep carbon cycle. One of these, magnesite, is a major carbon host in Earth’s mid-lower mantle.48 Carbonates that contain iron undergo an electronic high- to low-spin transition that stabilizes the mate- rial in the deep lower mantle.49, 50 This discovery complements other research indicating that magnesite could be a deep carbon reservoir.50 The abundance of carbon-bearing materi- al at depth may be masked by reactions near the surface that produce zeolite minerals, which disguise the initial origin of the rocks.51 Moreover, very recent findings suggest that carbon dissolved in grain boundaries and defects of known minerals could be a significant carbon reservoir.11, 13, 52 Novel minerals and rocks consisting of pure carbon and ox- ygen may exist at depth. One of these, a high-pressure “poly- meric” form of CO2 , was synthesized in the laboratory several years ago. This unusual material, an ultrahigh-pressure form of dry ice, has been shown to be stable at conditions of Earth’s lower mantle, which is the largest region by volume in the planet.17 Related novel carbonates form at these conditions as well.10 Moving deeper still, carbon is one of the candidate light elements of Earth’s core. However, estimates of carbon abun- dance in the core differ by more than an order of magnitude. Recent studies have put bounds on the amount of carbon in the core, and show the presence of carbon at depth could have a significant effect on how other elements are distributed between the core and mantle.8, 14 Scientific drilling expeditions at sea and on land afford opportunities to examine the subsurface biosphere, collecting samples from several kilometers below the surface. These deep-sea cores were obtained from Integrated Ocean Drilling Program Expedi- tion 330 to the Louisville Seamount Trail. Credit: Jason Sylvan
12. 6 Deep C storage Volcanoes C outgassing Deep carbon melting C subduction C ingassing Community Initiatives An important aspect of DCO’s near- and long-term contribu- tion to the scientific community is the potential to form focused groups of researchers with common goals. Within the Res- ervoirs and Fluxes community, for example, the DECADE (DEep CArbon DEgassing) initiative co- alesced around a common goal of increasing volcanic emissions monitoring throughout the world, and ensuring catalogu- ing of global volcanic emissions data in cutting-edge, openly ac- cessible data repositories. Simi- larly, the Census of Deep Life, headed up by members of the Deep Life community, is bring- ing together microbiologists from around the world in an ef- fort to characterize Earth’s deep biosphere. Groups like these flourish across DCO and exem- plify the open and collaborative spirit we continue to nurture. The deep carbon cycle includes ingas- sing, storage, and outgassing of carbon in Earth, as depicted in this schematic.21 Credit: Adapted from MSA / Rajdeep Dasgupta Atmosphere Crust Mantle Core Movements What Is the Nature of the Deep Carbon Cycle? We shift focus now from reservoirs to the fluxes of carbon, both within the planet and to and from Earth’s surface and interior. Carbon moves in fluids sequestered naturally in Earth, but it is also released in various ways. The global, “whole-Earth” flux of carbon has major implications for energy and the environment. DCO researchers have identified large apparent discrepancies between intake and release of carbon on both this global scale as well as regional scales. Recent advances resolving the origin of the apparent discrepancies are leading to a new understanding of the global cycle and epicycles. Carbon-rich Melts and Gases DCO has embarked on an ambitious program to monitor car- bon emissions from volcanoes on Earth. So far, scientists have discovered that the total of known volcanic CO2 emissions is twice what was previously thought.53 This significant outgas- sing connects deep carbon to the air we breathe. Moreover, and underappreciated until now, emission of carbon through nominally “inactive” volcanic vents rivals that of active volca- noes. In addition, there can be significant amounts of diffuse
13. 7 outgassing of carbon-bearing gases from tectonic regions. The findings provide a much broader view to assess the extent of carbon-based greenhouse gases than previously recognized. In addition, this interaction between fluids in the crust and degas- sing carbon connects the biosphere to deep Earth. Ultimately, untangling this connection requires multidisciplinary science. Melting of rock at depth and its subsequent upwelling toward the surface is the principal means by which heat is released from within the planet, and by which its component material is transported. Mantle melting at mid-ocean ridges is dictated both by chemical composition and by temperature­ —features that can now be linked to seismic signatures. New findings are emerging about the important roles CO2 and H2 O may play.54, 55 Carbon emitted in volcanically active regions is a key to un- derstanding the reservoirs and fluxes of deep carbon, and in particular whether that carbon comes from the upper or lower mantle. A comprehensive investigation of the CO2 content of the Icelandic mantle, for example, overlaps with previous estimates from the upper mantle, even though Iceland bears the fingerprint of the lower mantle, thereby showing how the source of carbon can be pinpointed.56 DCO researchers have discovered that carbonate-rich melts pervade regions of Earth’s upper mantle — observations that revolutionize our understanding of mantle melting beneath mid-ocean ridges.20, 21 These melts react progressively with the mantle as they rise, eventually becoming mid-ocean ridge ba- salts. If true, all CO2 degassed at ridges originated from carbon- ate-rich magma, a hypothesis that explains recent evidence for deeper melting beneath ridges.22 This melt may also lubricate tectonic plates and facilitate their movement. Indeed, carbon has a remarkable effect on the properties of melts formed from silicate rocks.20 At high concentrations, these melts produce carbonatites causing unusually explosive volcanic eruptions. DCO scientists have discovered that the unique character of these eruptions also arises in part from volatiles such as H2 O. Diamonds Track Earth Dynamics Studies of diamond play a key role in monitoring Earth’s internal dynamics.3, 4, 41, 42, 57 DCO scientists discovered that diamond morphology shows how the rocks that contain them move from mantle to surface,57 and additional studies of the inclusions of diamonds reveal the beginning of plate tectonics, pinpointing the start of colliding continents on the planet.4 Moreover, measurements of the isotopes 12C and 13C and of the mineral inclusions reveal the remarkable signature of material transport from the surface through the mantle to below 670 km, and then back to the surface again — where Known volcanic emissions of carbon dioxide are two times greater than previously thought.53 • • • DCO researchers investigate explosive carbon-rich volcanic eruptions around the world, including those of Ol Doinyo Lengai in Tanzania, Africa, shown here. Studies of this volcano clarify how water and carbon control the nature of its unusual eruptions.20 Credit: Maarten de Moor
14. 8 these diamonds are studied in the laboratory.3 The inclusions initially crystallized as single minerals that could form only at these depths within Earth. However, the isotopic variations of carbon from these ultradeep diamonds are most consistent with an origin in the organic component, providing direct evidence for a deep carbon cycle from surface to the deep lower mantle.3 Carbon and Plate Tectonics The abundance of mantle carbon influences plate tectonics and the global deep carbon cycle in other ways.58 –60 Depo- sition of metastable graphite in crustal fluids may facilitate plate boundary subduction of carbon-rich material in Earth.5 Further, recent research shows that graphite forms readily from carbonates during subduction.6, 7 DCO researchers discovered that oxygen levels control carbon movement in the mantle and allow carbon to remain mobile in active subduction zones.61 Carbonate mineral dissolution plays a key role in the release of CO2 from subduction zones to volcanoes.58 Additionally, studies of subduction zone processes in volcanic rocks from the vol- canoes of southern Chile found remarkably sharp variations in melt chemistry over distances of only a few kilometers. This variation greatly affects the release of volatiles during eruption and the severity of volcanic hazard.62 Looking back in time, scientists see that these considerations lead to new findings about Earth’s ancient carbon cycle, includ- ing the beginning of plate tectonics4 and the planet’s first ice age.63 Earth’s growing continents became an increasingly large sink for carbon present in the early atmosphere. Moreover, deep carbon research on Earth informs us about other plan- ets64, 65 and the Moon.66 For example, an ancient carbon cycle on Mars could have involved methane, which has a stronger greenhouse effect than CO2 . Challenging the prevailing view, Martian volcanic degassing could have produced a thinner at- mosphere, yet one more capable of warming the planet.65 Returning to energy resources on Earth, at a time when the hydrocarbon industry is shifting toward nontraditional fuels such as shale gas, we need spatially- and time-resolved atmospheric data to assess the before and after of regional and local energy operations. DCO is creating the necessary databases to address this challenge and is developing new methods to measure outgassing.67 Methane clathrate deposits in continental shelves and permafrosts form potentially the largest accessible energy resources on Earth, but exploiting Fluid-mediated reactions in subduction zones can release significant amounts of carbon, which is later degassed at arc volcanoes.55 A photomicrograph of vari- ous crystals from a quartz vein analyzed for this DCO study appeared on the May 2014 cover of Nature Geoscience. Credit: Nature Publishing Group / Jay J. Ague Using Earth as a model system, DCO researchers are exploring geologic pro- cesses relevant on other planetary bodies, such as Mars. Credit: NASA/JPL/ Malin Space Science Systems; NASA
15. 9 them for energy use presents major technological and environmental challenges. DCO scientists are involved in studies of the movements of vast methane hydrate fields.68 DCO scientists are also playing a leading role in efforts to understand the geochemistry of geologic carbon sequestration, a significant challenge in mitigating the effects of atmospheric CO2 .69 DCO Global Field Studies In their 10-year quest to clarify the role of deep carbon in Earth’s past, present, and future, DCO scien- tists journey to some of the most remote and scientifically valuable places on the planet. From estab- lishing global volcano monitoring systems to collecting sediment, rocks, and gases from Earth’s vast seafloor, DCO researchers apply innovative techniques and technol- ogies to find surface clues about car- bon contained deep inside Earth. In 2014, the entire community came together to assemble a compre- hensive picture of the scope and geographic diversity of DCO field- work. Our website hosts resources allowing DCO scientists to evaluate the portfolio of field studies from a global perspective, including an interactive map, shown below, and information about ongoing work at more than 150 field sites. Coordinat- ing field activities and data analysis across the four DCO communities over the remaining five years of the program is a high priority and will promote innovative science that crosses traditional disciplinary boundaries. Earth’s subduction zones host a rich variety of organic carbon species that could spark the formation of diamonds and perhaps become food for microbial life. This finding may hold the key to understanding the origins of life itself.23
16. 10 Forms What Forms of Carbon Exist Within Earth? Novel carbon structures and chemical reactions are being documented observationally, experimentally, and theoreti- cally. Structurally, electronically, and chemically, carbon can mimic other elements in the periodic table. This diversity of carbon forms also touches on biological diversity at depth. Observations over the past five years have led to remark- able findings, and surprising correlations are emerging. DCO science has updated the once-prevailing view that carbon in deep fluids is mostly oxidized; it is now thought that reduced forms of carbon are potentially more common than oxi- dized forms in deep Earth. Further, the study of new forms of carbon materials is leading to discoveries in physics and advanced technology. DCO’s 2014 Early Career Scientist Workshop in Costa Rica featured two days of immersive field trips, including a visit to Póas volcano. Credit: Katie Pratt and Carlos José Ramirez Umaña This diagram depicts a remarkable framework, or “polymeric” structure, of CO2 determined by DCO scientists.15, 16 The structure is stable under the high temperature and pressure conditions of Earth’s lower mantle, thus representing a potential reservoir of deep carbon.17 Credit: PNAS /Mario Santoro
17. 11 Novel Structures Two teams have determined the structure of a remarkable polymeric form of CO2 , finding that the structure is that of the cristobalite form of SiO2 , in which the coordination of the car- bon atom by oxygen goes from two to four.15, 16 The detailed determination of the crystal structure of this silica-like CO2 , to- gether with the determination of its stability range,17 opens vast new possibilities for carbon storage at high pressure. Such pos- sibilities are even more likely with the demonstration of CO2 - SiO2 solid solution, forming cristobalite-type mixed polymeric structures.70 The discovery that carbon can substitute for silicon in certain ceramics11 suggests the existence of related structures in the planet as well as prospects for the creation of new mate- rials based on this unusual substitution. Moreover, carbon, ox- ygen, and silicon can all potentially substitute for each other in mineral structures at mantle conditions,12 in striking contrast to the rules that govern Earth’s surface mineralogy. Other novel forms of carbon are being found at depth. Clues obtained by DCO scientists hint at the enigmatic origin of car- bonados, an unusual polycrystalline form of carbon,71 and this work shows that altogether new structures form at high pressures.72-75 In conditions of planetary interiors, methane re- acts to form heavy hydrocarbons.29, 76 Research has uncovered the fundamental thermodynamic and kinetic basis for these reactions.77 Using new neutron scattering techniques devel- oped with support from DCO, scientists have determined the high-pressure structures of methane clathrates,28 a major po- tential energy resource,30 and another group has identified new silica-based clathrates containing hydrocarbons.78 Also, new transitions in methane itself have been discovered.79 By tracking carbon isotopes through chemical reactions in the lab, DCO researchers found signatures of the role of metal car- bides never seen at the surface­ — a feature previously attribut- ed to subducted organic carbon.80 Finally, DCO researchers have found that at the atomic level carbon can be stored in “defect sites” in mantle minerals — a discovery that provides a mechanism for trapping much more carbon within this re- gion of the planet than previously assumed.52, 81 Discoveries are being made in solid-state physics that could lead to the creation of new carbon-based devices for advanced technology. For example, DCO researchers have found that the electronic properties of defects in diamond could be used in quantum computing.82 Polymers of carbon and sulfur formed under pressure make up a new class of superconduc- tors.83 Amorphous carbon forms a novel crystalline material at high pressure,84 and compression of benzene leads to novel diamond nanothreads.85 DCO Early Career Scientists A new generation of scientists trained with support from DCO is tackling diverse and important sci- entific challenges. As one of its legacies, DCO aims to foster the pro- fessional development of these di- verse young scientists as the means to promote international and in- terdisciplinary collaboration and to lay the foundation for the fu- ture of deep carbon science. The first step in building a network of DCO Early Career Scientists was to host a workshop organized ex- clusively by and for this communi- ty. In February 2014, 40 postdocs, grad students, and newly appoint- ed assistant professors came to- gether at the University of Costa Rica in San José. The workshop, con- vened by an Early Career Scientist Committee, included two days of presentations and two days in the field visiting nearby Turrialba and Póas volcanoes. The major goal of this workshop was to bring togeth- er scientists at similar points in their career and encourage both interna- tional and cross-disciplinary collabo- ration. In July 2014, DCO continued to expand the community of ear- ly career scientists with a Summer School at Yellowstone National Park, USA. The Summer School mod- el featured a small faculty of senior DCO scientists, connecting near- ly 40 early career scientists through classroom lectures and field activ- ities. After many participants at both events expressed a strong de- sire to meet again, the young scien- tists organized sessions and events for the 2014 AGU Fall Meeting, and developed a successful proposal to support a second DCO Early Career Scientist Workshop.
18. 12 Water and Carbon Understanding the nature of carbon in deep Earth requires improved knowledge of its most important solvent, H2 O, under these conditions. A team of DCO scientists developed a new model for water that permits computation of the uptake and transport of carbon by aqueous fluids at high pressure.86 The model complements the first direct measurements of the form of carbonate ion in hot, high-pressure aqueous fluids exist- ing at depth.87 This theoretical advance is based on the first accurate determination of dielectric properties of water under extreme pressures and temperatures.88, 89 Their work has the potential to revolutionize our understanding of the geochem- istry of fluids in Earth’s mantle in diverse ways, providing an explanation for why Earth has a unique, nitrogen-rich atmosphere24 in contrast to other planets, and how diamond forms within the planet.23, 90 Further, DCO scientists continue to investigate the intriguing properties of pure water under pres- sure, including the puzzling transitions from low- to high-den- sity water forms.91 Volcanism on Earth Volcanism on Mars and Venus Previously observed differences in the ratio of atmospheric nitrogen to noble gas- es (argon, krypton, neon, and xenon) on Earth, Mars, and Venus were explained by DCO scientists through the use of a novel deep Earth water model. Their calcula- tions point to subduction zone plate tectonics as the differentiating factor leading to Earth’s distinctive and habitable atmosphere.24 Credit: Nature Geoscience Populations of subseafloor microbes can vary by five orders of magnitude regionally.38 • • •
19. 13 Life at Depth Subsurface environments, both marine and continental, represent the largest habitat on Earth for microbial life. Scientists have identified the important role of pressure as a driving force in the distribution, activity, and survival of microbial life throughout Earth’s history.92 An important part of the global sulfur cycle is the subseafloor microbial conversion of sulfate. To estimate how much sulfate is turned over by microorganisms throughout the planet, DCO researchers used an artificial neural network and a vast accumulation of data collected over more than four decades by international drilling programs. They found that sulfate- starved microbes in fact control turnover.19 Furthermore, DCO scientists found that these reactions can occur at temperatures that could support primitive life (i.e., in the absence of photosynthesis).93 Recent discoveries are leading to numerous other insights about the deep biosphere.33–39, 94–96 For example, in addition to microbes, the deep biosphere may contain a wealth of vi- ruses — a “deep viriosphere.”39 In another finding, examination of subseafloor microbial populations33, 34 reveals surprisingly similar microbes in disparate places around the world,35 and new statistical methods enable researchers to visualize micro- bial diversity.97 DCO microbiologists also conducted laboratory experiments in a remarkable study of directed evolution of microbes at tens of kilobar pressures.98 Deep life discoveries are not restricted to microbes; new species of deep nematodes dramatically expand the known metazoan biosphere. 99 Scientific drilling in continental and marine settings provides samples for in- vestigations that address a wide range of DCO’s decadal goals, including the extent and diversity of the deep bio- sphere. A continental scientific drilling site in Sweden is shown above and the drilling vessel, JOIDES Resolution, below. Credit: Tom Kieft (top); Internation- al Ocean Discovery Program (IODP) and William Crawford
20. 14 Origins What Can Deep Carbon Tell Us About Origins? Studies of deep carbon address profound questions of the origins of carbon and carbon-bearing forms, including prebiotic systems and life itself. Carbon atoms are born in stars and are released in exploding supernovae. These atoms’ subsequent movements and modifications are revealed in part by diverse carbon-rich meteorites and planetary materials. Thus, DCO scientists use carbon from meteorites, Moon rocks, and planetary atmospheres as historical tracers to record events from the depths of space and time. Early Earth Examining the role of carbon in Earth through time provides an important window on the evolution of our planet. It is now apparent that both the atmosphere and near-surface reser- voirs of early Earth were rich in carbon. Key to understanding how the planet evolved since then is the coupling of the deep water and carbon cycles.101 Complementing studies of carbon elsewhere in the solar system,64–66 DCO is providing new infor- mation about the modulation and redistribution of the initial, planet-scale carbon budget set by accretion through various differentiation processes. During the first few tens of millions of years of Earth’s history, carbon partitioned strongly into the core, making the core the largest terrestrial reservoir of carbon. The flux of carbon being ingassed versus outgassed potentially varied greatly throughout Earth’s history.21 New discoveries in mineralogy provide fossil evidence for early life,102 and reveal the existence of more than 400 mineral species that were pres- ent on Earth when life began.1, 100 The work also constrains the composition of Earth’s atmosphere at the birth of life. 63, 103 Workshops DCO’s commitment to community building is exemplified by the broad spectrum of workshops taking place as part of the initiative. Success- ful workshops from the first half of the program focused on challeng- es and breakthroughs in deep car- bon science. Examples include the 2012 Serpentine Days Workshop (Porquerolles Island, France) and the 2013 Kazan Workshop on Abi- otic Hydrocarbons (Kazan Federal University, Russia). Others focused on building cross-disciplinary con- nections, such as the 2014 New Gen- eration Technology in Deep Carbon Science Workshop (Rice University, USA) and the 2014 DCO Data Sci- ence Day (Rensselaer Polytechnic Institute, USA). Each DCO Communi- ty also holds regular meetings and workshops, at which early career and veteran scientists present new findings alongside cross-community colleagues. These workshops bring together often-unlikely collabora- tors, and the resulting community of deep carbon scientists will con- tinue to grow as one of DCO’s cru- cial legacies. The number of carbon-bearing mineral species on Earth has grown from an esti- mated 35 when life began to more than 400 known carbon minerals today. 1, 100 • • •
21. 15 2.6-Billion-Year-Old Water In a landmark study, DCO scientists discovered deep pockets of water isolated from the surface at 2 –3 km depth for close to the last 2.6 billion years.104 This discovery in the Canadian Shield of saline fluid, rich in H2 , CH4 , 4He, and N2 , tells us a great deal about environments for the ancient deep biosphere. The fluids may represent the most extreme ancient continental environment yet observed in which life can survive, sustained by products of water-rock interaction in a setting cut off from sunlight. This interaction between rocks and water may also be a key factor in determining the history of Earth and other planets in the Solar System, and thus shed light on the possible existence of life beyond our own planet. For example, subsurface microbial life could have survived long after the surface of Mars lost its water and became sterile. These remarkable findings build on previous work by members of this team who found microbial communities at similar depths in a South African gold mine, living off dissolved hydrogen in water tens of millions of years old. Dissolved hydrogen and methane in water erupting from fractured rocks fuel the deep biosphere. These gases, such as those found at Soudan Mine, Minnesota, USA, may be trapped underground for billions of years, providing clues about the origins of life on Earth.104 Credit: Jon Telling The world’s oldest water, isolated for 2.6 billion years in fractures 2–3 km deep in the Canadian Shield, may represent the most ancient extreme environment in which life can survive.104
22. 16 Fueling the Deep Biosphere Geologic hydrogen production has long been thought to fuel deep ecosystems. A critical reaction is “serpentinization,” which is also associated with the weathering and hydration of mantle rock. Laboratory studies by DCO scientists found that the rate of this reaction can be increased by an order of magnitude using aluminum oxide as a catalyst. This discovery could unlock understanding of the origins of life as well as show the way toward commercial hydrogen production for fuels or fuel cells.31 Deep microbial niches based on serpentinization byproducts mediate elemental fluxes in the hydrated oceanic mantle. The “microhydrogarnets” that form are widespread in oceanic crust and constitute a prebiotic environment of prime interest for studying the emergence of the first microbial cells on Earth.32 Cold seeps are spectacular ecosystems on the deep seafloor with an unexpectedly large biomass and diversity of animals and microbes. Researchers discovered that methane fuels these deep ecosystems, and a substantial fraction of the methane comes from sources of carbon buried kilometers under the seafloor.36 DCO scientists carefully examined metabolic rates per cell in ancient seafloors, suggesting that the microbial communities studied may be living at the minimum energy flux needed for prokaryotic cells to subsist, and that the total available energy flux ultimately controls deep biosphere community size.37 Hydrocarbon Origins Reactions among minerals and organic compounds in hydrothermal environments play critical roles in Earth’s deep carbon cycle, providing energy for the deep biosphere. A DCO team found that a common sulfide mineral, ZnS, cleanly catalyzes a fundamental chemical reaction —the making and breaking of a C-H bond.18 This discovery shows how the mineral surface affects hydrocarbon generation in marine hydrothermal systems such as black smokers, an environment proposed for the origins of life. These and other studies of the generation of hydrocarbons by mineral reactions are bridging the gap between organic and inorganic chemistry, potentially linking nucleotide and polypeptide formation, and eventually life within the mineral world. Aluminum oxide increases the produc- tion of hydrogen by the serpentinization reaction, an important source of energy for the deep biosphere, by an order of magnitude.31 This micrograph shows a snapshot of the serpentinization reaction as aqueous fluids come into contact with the mineral olivine (yellow). The reaction releases life-sus- taining chemical energy in the form of molecular hydrogen. Credit: Bernard Evans
23. 17 Global field work conducted by DCO scientists continues to expand knowledge of Earth’s carbon cycle. Sampling of gases, waters, and microorganisms in this crater lake, Dziani Dzaha, in the Mayotte Archipelago off the coast of Madagascar provides insights into biogeochemical connections. Credit: Magali Ader and Sébastien Turay The Next Five Years At this halfway mark in the DCO program, it is important to report significant successes from our first five years and evaluate the progress toward our decadal goals in order to plan for the remainder of the decade-long program. DCO scientists contin- ue paving the way for ever more exciting work, and, through a range of cross-disciplinary initiatives, they will continue to address some of the most important questions in science. New science opportunities include the following: Earth’s Carbon Budget. DCO has created a worldwide community of scientists who work together according to a well- defined plan, linking strands of research that complement one another and that otherwise would have been conducted out of sync. The problem of Earth’s carbon budget is truly a global one, and it needs to be tackled at the appropriate scale that includes the continued development of new experimental techniques.13 Abiogenic Carbon. The unambiguous differentiation of abiot- ic from biotic organic compounds remains a decadal challenge for DCO. Success will depend heavily on continued break- throughs in “clumped isotope” measurement technology and the quantification of the global sources, sinks, and fluxes of reduced carbon—especially methane—coupled with those of hydrogen. The link between reduced carbon compounds and hydrogen is key to elevating our understanding of the global carbon cycle, which lies at the intersection of all four DCO communities. Deep Carbon and Deep Time. The deep time data infrastructure, including new fundamental models along with vast data and modeling resources in an open-access platform, could be a major breakthrough in how the global scientific community tackles new scientific questions. This effort is building a new virtual scientific instrument, available to all, that will be an engine of discovery about Earth’s changing geosphere and biosphere through deep time. The envisioned statistical and visualization features will make this tool set an absolutely new and transformative advance.
24. 18 Deep Biosphere. One of the most important discoveries of DCO’s second half will involve major advances in what limits microbial life in the deep subsurface. Current and future projects, Deep mines serve as important field locations for deep carbon science. For example, DCO scientists discovered nematodes (roundworms) living 0.9 to 3.6 km under-ground in water- containing fractures located within the Driefontein gold mine, South Africa, shown here.97 Credit: T.C. Onstott Research on the forms of carbon under extreme temperatures and pressures has implications for materials science and technology. This diamond nanothread is an example of a newly discovered form of carbon that remains stable under am- bient conditions.85 Credit: Enshi Xu living systems as a whole is another decadal challenge. Such sys- tematic exploration of life’s adaptations to extremes remains an unexplored frontier. Application and extension of experimental and theoretical tools developed in molecular biology, biophys- ics, and drug discovery research could lead to breakthroughs in understanding the form and function of organisms and ecosys- tems in the deep biosphere as well as potentially elsewhere in the cosmos. Origins of Life. DCO is poised to address diverse questions about how Earth’s biosphere evolved through time, including the origins of life. New insights stem from developments in the study of mineral evolution and mineral diversity at Earth’s dynamic exosphere. A potential breakthrough would be discovery of vestiges of deep life in very ancient fluids from stable cratons and other geologically representative environments discussed above. New Carbon-based Materials. New discoveries of the phys- ics and chemistry of carbon under extreme conditions raise the possibility of creating altogether new carbon and carbon-rich materials with extraordinary properties for a range of new tech- nologies (e.g., superconductors, sensors, thermoelectrics, and high-strength components). Satellite Observations of Carbon Emissions. DCO is embracing the prospects of a new high-resolution CO2 -mon- itoring satellite with high-resolution imaging down to 500 m—a capability that would complement existing global missions like OCO-2. Such a satellite could be pointed at an with major involvement of DCO researchers, are systemat- ically examining the influences of factors such as temperature and energy on the presence and activity of microbial life in situ. This research will help establish the limits of geolog- ical detectability of life, which then provide unique and unprecedented constraints for the limits of life. Extreme Biophysics. Deter- mining biophysical effects of extreme environments on bio- molecular structures as well as
25. 19 active volcano when it erupts. Measuring volcanic emissions of CO2 from space will open the door to fully quantifying point sources of carbon in the atmosphere needed to under- stand natural versus anthropogenic fluxes and their impacts on climate. Missions Beyond Earth. An important new opportunity is the ongoing Rosetta mission, which sniffs out gases released by comet 67P/CG, 500 mil- lion   km from Earth. Results will constrain origins of water, carbon, and other volatile ele- ments on terrestrial planets— exploration at its purest level. DCO scientists are associated with groups who built and are in charge of the mass spectro- meters on board the spacecraft. The origin of the carbon in this comet and related bodies is a first-order cosmological problem. Nature of Extrasolar Carbon. The recognition that plan- ets are commonplace in the cosmos, including some with car- bon-rich compositions, opens up new prospects for DCO where its techniques, methodologies, and expertise could be applied to the nature of carbon well beyond our Solar System (perhaps ul- timately leading to a “Deep Space Carbon Observatory”). New Physics of Ultradense Carbon Materials. New facil- ities and instruments now exist for exploring matter at pres- sure-temperature conditions orders of magnitude more extreme than current approaches permit, and creating cold, highly com- pressed solids to hot, dense matter of stellar interiors. A recent landmark study at the National Ignition Facility at Lawrence Livermore National Laboratory demonstrated this new research tool with highly accurate measurements of the compression of diamond at 50 megabars of pressure.105 In addition to addressing the above science questions, DCO will expand its program in the following ways: Build the DCO Science Network. Our mission is to bring together a diverse group of scientists to tackle the big ques- tions of deep carbon science in novel ways. Over the next five years DCO will continue to grow our already far-reaching community through a variety of activities, including work- shops and conferences on cutting-edge scientific questions Satellites such as the Orbiting Carbon Observatory-2 (OCO-2), shown here, provide new opportunities for studies of carbon in Earth, such as measurements from space of carbon dioxide from volcanic emissions and outgassing of the oceans. Credit: JPL/NASA
26. 20 and methods, global field studies, and collaborative research endeavors. We are also committed to supporting enhanced diversity among deep carbon scientists, as well as early career scientists who represent the future of this new field and a primary legacy of DCO. Develop Data Infrastructure. DCO scientists have already begun the process of creating an extensive deep carbon data infrastructure. Through both internal database development and partnerships with existing data management systems, DCO scientists will create a comprehensive deep carbon data infrastructure within the DCO Data Portal. Models & Visualization. Developing new ways to visu- alize complex datasets in the context of deep Earth through deep time represents another important legacy of DCO. We have begun the process of creating a four-dimensional planetary carbon circulation model. The research and de- velopment process for such a model is necessarily highly in- terdisciplinary, and will unite geobiologists, geochemists, and geodynamicists, as well as data scientists and engineers, in developing creative ways to visualize deep Earth data. The DCO Science Network One of the major legacies of DCO is a pioneering network of scientists in the new and transdisciplinary field of deep carbon science. From the outset, DCO has brought to- gether people with diverse skillsets to tackle cutting-edge scientif- ic questions in novel and produc- tive ways. To solidify, promote, and grow this network of deep carbon scientists, we developed the DCO Community Portal, an online sys- tem composed of user profiles, community resources, and collabo- rative tools. Members of the DCO Science Network can also access the DCO Data Portal, where deep car- bon and data scientists are build- ing a comprehensive suite of data analysis tools and legacy databas- es. Combined with vibrant public webpages reporting recent com- munity news, relevant science high- lights, events, and “deeper views,” external perspectives on hot top- ics in deep carbon science, the DCO website forms a focal point for the DCO Science Network. We encour- age graduate students, postdocs, faculty and research scientists, in- dustry representatives, artists, jour- nalists, and others interested in the field of deep carbon science to join the DCO Science Network and sub- mit their profile information at deepcarbon.net/join. New visualization techniques help clarify the forms and inter- actions of carbon under deep planetary interior conditions, such as carbonate-bearing aque- ous fluids shown here.88 Credit: Ding Pan
27. 21 Contributors to Deep Carbon Science Scientists from throughout the world are contributors to an ever-growing collection of hundreds of journal articles, books, and other scientific publications resulting from DCO-related research focused on deep carbon science (catalogued at deepcarbon.net). The first major collective publication of DCO, Carbon in Earth,1 integrates a vast body of research in physics, chemistry, biology, and Earth and space sciences. The chapters in this volume synthe- size the current state of knowledge about deep carbon, and outline unanswered questions guiding DCO for the remainder of the decade and beyond. Chapter 1. Why deep carbon? Robert M. Hazen and Craig M. Schiffries Chapter 2. Carbon mineralogy and crystal chemistry. Robert M. Hazen, Robert T. Downs, Adrian P. Jones, and Linda Kah Chapter 3. Structure, bonding, and mineralogy of carbon at extreme conditions. Artem R. Oganov, Russell J. Hemley, Robert M. Hazen, and Adrian P. Jones Chapter 4. Carbon mineral evolution. Robert M. Hazen, Robert T. Downs, Linda Kah, and Dimitri Sverjensky Chapter 5. The chemistry of carbon in aqueous fluids at crustal and upper-mantle conditions: experimental and theoretical constraints. Craig E. Manning, Everett L. Shock, and Dimitri A. Sverjensky Chapter 6. Primordial origins of Earth’s carbon. Bernard Marty, Conel M. O’D. Alexander, and Sean N. Raymond Chapter 7. Ingassing, storage, and outgassing of terrestrial carbon through geologic time. Rajdeep Dasgupta Chapter 8. Carbon in the core: its influence on the properties of core and mantle. Bernard J. Wood, Jie Li, and Anat Shahar Chapter 9. Carbon in silicate melts. Huaiwei Ni and Hans Keppler Chapter 10. Carbonate melts and carbonatites. Adrian P. Jones, Matthew Genge, Laura Carmody Chapter 11. Deep carbon emissions from volcanoes. Michael R. Burton, Georgina M. Sawyer, and Domenico Granieri Chapter 12. Diamonds and the geology of mantle carbon. Steven B. Shirey, Pierre Cartigny, Daniel J. Frost, Shantanu Keshav, Fabrizio Nestola, Paolo Nimis, D. Graham Pearson, Nikolai V. Sobolev, and Michael J. Walter Chapter 13. Nanoprobes for deep carbon. Wendy L. Mao and Eglantine Boulard Chapter 14. On the origins of deep hydrocarbons. Mark A. Sephton and Robert M. Hazen Chapter 15. Laboratory simulations of abiotic hydrocarbon formation in Earth’s deep subsurface. Thomas M. McCollom Chapter 16. Hydrocarbon behavior at nanoscale interfaces. David R. Cole, Salim Ok, Alberto Striolo, and Anh Phan Chapter 17. Nature and extent of the deep biosphere. Frederick S. Colwell and Steven D’Hondt Chapter 18. Serpentinization, carbon, and deep life. Matthew O. Schrenk, William J. Brazelton, and Susan Q. Lang Chapter 19. High-pressure biochemistry and biophysics. Filip Meersman, Isabelle Daniel, Douglas H. Bartlett, Roland Winter, Rachael Hazael, and Paul F. McMillan Chapter 20. The deep viriosphere: assessing the viral impact on microbial community dynamics in the deep subsurface. Rika E. Anderson, William J. Brazelton, and John A. Baross Carbon in Earth Reviews in Mineralogy and Geochemistry, Volume 75 Robert M. Hazen, Adrian P. Jones, and John A. Baross, editors Published in March 2013 as an Open Access volume, 698 pages “Carbon in Earth is an outgrowth of the Deep Carbon Observatory (DCO), a 10-year interna- tional research effort dedicated to achieving transformational understanding of the chemical and biological roles of carbon in Earth. Hundreds of researchers from 6 continents, including all 51 coauthors of this volume, are now engaged in the DCO effort. This volume serves as a benchmark for our present understanding of Earth’s carbon — both what we know and what we have yet to learn. Ultimately, the goal is to produce a second, companion volume to mark the progress of this decadal initiative.”1
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36. SECRETARIAT GEOPHYSICAL LABORATORY CARNEGIE INSTITUTION OF WASHINGTON 5251 BROAD BRANCH ROAD, NW WASHINGTON, DC 20015-1305 DEEP CARBON OBSERVATORY deepcarbon.net About the cover: The serpentinization process, a reaction between water and rock, is crucial for deep microbial ecosystems. The reaction releases life-sustaining chemical energy in the form of molecular hydrogen and, in the process, modifies surrounding minerals. A false color scanning electron micrograph illustrates this reciprocal relationship between the geosphere and biosphere, where hydrogarnets are shown in blue, poly- hedral serpentine in green, iron oxides in red, and relics of biofilm in yellow. Credit: Daniele Brunelli / Bénédicte Ménez (Università di Modena e Reggio Emilia / IPGP) 32 About the Deep Carbon Observatory Logo C is the chemical symbol for carbon. The cropped area of the C represents the estimated 10% of the carbon at Earth’s surface and in the oceans, atmosphere, and upper crust. The keyhole symbolizes DCO’s quest to unlock the secrets of deep carbon. The red area represents the remaining 90% of carbon contained in Earth’s lower crust, mantle, and core.1