Evolution Of Biosphere Research Articles

What does not kill Gaia makes her stronger: impacts of external perturbations on biosphere evolution

ABSTRACT Life on Earth has experienced numerous upheavals over its approximately 4 billion year history. In previous work, we have discussed how interruptions to stability lead, on average, to increases in habitability over time, a tendency we called entropic Gaia. Here, we continue this exploration, working with the Tangled Nature Model of co-evolution, to understand how the evolutionary history of life is shaped by periods of acute environmental stress. We find that while these periods of stress pose a risk of complete extinction, they also create opportunities for evolutionary exploration which would otherwise be impossible, leading to more populous and stable states among the survivors than in alternative histories without a stress period. We also study how the duration, repetition and number of refugia into which life escapes during the perturbation affects the final outcome. The model results are discussed in relation to both Earth history and the search for alien life.

Stochastic Character Mapping, Bayesian Model Selection, and Biosynthetic Pathways Shed New Light on the Evolution of Habitat Preference in Cyanobacteria.

Cyanobacteria are the only prokaryotes to have evolved oxygenic photosynthesis paving the way for complex life. Studying the evolution and ecological niche of cyanobacteria and their ancestors is crucial for understanding the intricate dynamics of biosphere evolution. These organisms frequently deal with environmental stressors such as salinity and drought, and they employ compatible solutes as a mechanism to cope with these challenges. Compatible solutes are small molecules that help maintain cellular osmotic balance in high salinity environments, such as marine waters. Their production plays a crucial role in salt tolerance, which, in turn, influences habitat preference. Among the five known compatible solutes produced by cyanobacteria (sucrose, trehalose, glucosylglycerol, glucosylglycerate, and glycine betaine), their synthesis varies between individual strains. In this study, we work in a Bayesian stochastic mapping framework, integrating multiple sources of information about compatible solute biosynthesis in order to predict the ancestral habitat preference of Cyanobacteria. Through extensive model selection analyses and statistical tests for correlation, we identify glucosylglycerol and glucosylglycerate as the most significantly correlated with habitat preference, while trehalose exhibits the weakest correlation. Additionally, glucosylglycerol, glucosylglycerate, and glycine betaine show high loss/gain rate ratios, indicating their potential role in adaptability, while sucrose and trehalose are less likely to be lost due to their additional cellular functions. Contrary to previous findings, our analyses predict that the last common ancestor of Cyanobacteria (living at around 3180 Ma) had a 97% probability of a high salinity habitat preference and was likely able to synthesise glucosylglycerol and glucosylglycerate. Nevertheless, cyanobacteria likely colonized low-salinity environments shortly after their origin, with an 89% probability of the first cyanobacterium with low-salinity habitat preference arising prior to the Great Oxygenation Event (2460 Ma). Stochastic mapping analyses provide evidence of cyanobacteria inhabiting early marine habitats, aiding in the interpretation of the geological record. Our age estimate of ~2590 Ma for the divergence of two major cyanobacterial clades (Macro- and Microcyanobacteria) suggests that these were likely significant contributors to primary productivity in marine habitats in the lead-up to the Great Oxygenation Event, and thus played a pivotal role in triggering the sudden increase in atmospheric oxygen.

Co-evolution of early Earth environments and microbial life.

Two records of Earth history capture the evolution of life and its co-evolving ecosystems with interpretable fidelity: the geobiological and geochemical traces preserved in rocks and the evolutionary histories captured within genomes. The earliest vestiges of life are recognized mostly in isotopic fingerprints of specific microbial metabolisms, whereas fossils and organic biomarkers become important later. Molecular biology provides lineages that can be overlayed on geologic and geochemical records of evolving life. All these data lie within a framework of biospheric evolution that is primarily characterized by the transition from an oxygen-poor to an oxygen-rich world. In this Review, we explore the history of microbial life on Earth and the degree to which it shaped, and was shaped by, fundamental transitions in the chemical properties of the oceans, continents and atmosphere. We examine the diversity and evolution of early metabolic processes, their couplings with biogeochemical cycles and their links to the oxygenation of the early biosphere. We discuss the distinction between the beginnings of metabolisms and their subsequent proliferation and their capacity to shape surface environments on a planetary scale. The evolution of microbial life and its ecological impacts directly mirror the Earth's chemical and physical evolution through cause-and-effect relationships.

Еволюційна система біосфери: діалектичний підхід

The dialectics of evolution is that the development of various systems, complication is determined by several principles, which themselves are similar to emergent systems based on opposite but dialectically complementary categories and concepts. A new concept of evolution of the biosphere as an integral system of its successive states united by development trends is proposed. The structure of the biosphere is considered as a fractal system with the ecosystem as its elementary unit. The next fractal levels are biogeomes and biospheromerons. The fractal structure corresponds to the principle of emergence. The proposed concept of biosphere evolution is based on general naturalistic principles and categories of dialectics, such as states and interstates, continuity and discreteness, reproducibility and uniqueness, the hypothesis of information channels or trends, the concept of biosphere organisation in a specific evolutionary space-time. In general, the evolutionary history of the biosphere is a metameric picture of changing states and interstates. A complex system of continuums is the most important feature of the biosphere’s organisation in space-time. Continuity of the first kind can be observed when there is a continuum of indistinguishability within a continuing state: during a long geological time, there were no cardinal changes in the structure of biosphere elements and connections between them. At the same time, the development of an integral biosphere system occurs in a continuum of the second kind: given the continuity of life, the differences between the early and subsequent states are very significant and obvious in the biosphere. Moreover, these differences are associated with complication, development, which is, in fact, evolution. The states of the biosphere in certain periods are connected by trends, which form an evolutionary system. Continuing states, when the system remains self-identical for a long period, are replaced by new states through interstates. Thus, a specific type of continuum, the metameric continuum, is formed. The taxonomic, ecomorphic, symbiotic, and ecosystem trends are identified and considered as the main ones in the evolution of the biosphere. The Vernadsky–Margalef hypothesis of the origin of life and biosphere in the form of protoecosystems is considered and supported.

Authigenic clay mineral constraints on spatiotemporal evolution of restricted, evaporitic conditions during deposition of the Ediacaran Doushantuo Formation

The carbonate-rich shelf facies of the Ediacaran Doushantuo Formation (South China) have produced a broad array of microfossil and isotope proxy records which underpin much of our understanding of environmental change and biospheric evolution during this key time period. Recent reports of locally abundant authigenic, Mg-rich saponite clay in the Yangtze Gorges Area hint at potentially widespread evaporitic conditions in a lagoonal setting. Despite the implications for interpretation of proxy records and the environmental setting of early metazoans, the spatiotemporal extent of restricted, evaporitic conditions across the Yangtze Block remains largely unexplored. Here we use mineralogical and petrographic techniques to document the spatial and stratigraphic distribution of authigenic clay minerals across seven sites, representing a transect from shallow proximal shelf to deep basinal settings. Our results demonstrate the widespread and persistent occurrence of authigenic saponite in proximal shelf settings, whereas talc is identified at more distal shelf sites, consistent with Mg-clay authigenesis in an evaporitic lagoon with spatially variable detrital aluminosilicate input. Slope and basinal sites contain no Mg-clays and are instead characterized by abundant authigenic illite, consistent with an open marine setting. Stratigraphically, illite was found in the basal cap carbonate and uppermost Doushantuo Formation, with Mg-clays only present in the interval in-between, suggesting gradual development of an extensive carbonate rimmed lagoon over the Yangtze shelf that restricted seawater exchange, followed by stronger marine influence due to erosion of the carbonate rim and subsequent marine transgression. We conclude that restricted, evaporitic conditions were much more expansive than previously assumed, potentially providing favorable conditions for the Doushantuo Biota. Further, the widespread presence of authigenic clays across the shelf supports the case for enhanced reverse weathering before the advent of biosilicification.

Siliciclastic input controlling carbonate deposition on a low-angle ramp system: New insight from the Upper Triassic Luning Formation (Western-Central Nevada)

Although more than one century has passed since the first studies, knowledge about the Upper Triassic shallow-water carbonates from the Panthalassa Ocean remains lower than their Tethyan counterparts. Characterising these sedimentary rocks represents a unique way to deepen our understanding of the biosphere's evolution and recovery after the major Permian–Triassic biological crisis. The Triassic Luning Formation in Western–Central Nevada is a crucial sedimentary succession due to its considerable thickness and areal extent. Among the three members forming the Luning Formation, the present study has only described the upper one in detail due to the minor areal distribution of the Lower Member and the pure siliciclastic nature of the middle Member. All accessible localities in this region, 21 in total, have been extensively sampled for facies and micropalaeontological analyses, including conodonts and poorly preserved foraminifera, leading to new insights about the depositional conditions and exact age of the Luning Formation's Upper Member. A depositional model is proposed for the first time, corresponding to a low-angle ramp with homogeneous bathymetric and hydrodynamic conditions subjected to frequent siliciclastic input from the continent. The regular terrigenous influx causes a significant cyclicity in this portion of the formation, comprising heterogeneously thick limestone beds. The environment-diagnostic fauna is characterised by pioneer organisms that regenerate carbonate production after the main break related to the pure siliciclastic Middle Member's deposition. Numerous conodont specimens indicate that the entire Upper Member is middle Norian in age. Identifying the observed organisms, tied to a reliable stratigraphic interval, allows comparing the Luning Formation with other Upper Triassic carbonates from the Panthalassa Ocean, now cropping out at different latitudes on the eastern and western coasts of the Pacific Ocean. Despite some faunal affinities, especially with carbonate build-ups developed at middle-palaeolatitudes, the Luning Formation differs from most other East Panthalassa carbonates because of its short palaeo-distance from the continent (i.e. the American craton), being deposited near the mainland coast instead of on an isolated volcanic arc.

The Emergence of Astrobiology: A Topic-Modeling Perspective.

Astrobiology is often defined as the study of the origin, evolution, distribution, and future of life on Earth and in the Universe. As a discipline that emerged in the past decades of the 20th century, its contours have not always been straightforward, resulting from the interweaving of several lines of research as early as the 1960s. By applying computational topic-modeling approaches to the complete full-text corpus of three flagship journals in the field, Origins of Life and Evolution of Biospheres (1968-2020), Astrobiology (2001-2020), and the International Journal of Astrobiology (2002-2020), we identify specific topics that characterize the early blossoming of the discipline. We also map their evolution through time, as emphasis changed between different readings of astrobiology, from an exobiology and origins-of-life perspective to a more space- and planetary-sciences view of the discipline.

SPIRITUAL AND MORAL VECTOR OF THE FUTURE CHOICE: TO A STRATEGY FOR SUFFICIENT DEVELOPMENT

The article considers a complex of global problems of modernity that pose a threat to the near future of mankind. It is noted that the end of the twentieth century was marked by the decline and extinction of environmental protests, the period of active struggle for the improvement of the Planet ended. The highest point of such protests can be considered the UN Conference on Environment and Development in Rio de Janeiro (Brazil) in 1992 at the level of heads of state and government. Everything that was said and adopted at the conference about environmental danger has not lost its relevance today, and in some areas the situation has become significantly aggravated and aggravated. This is especially true for industrial development, the careful conservation of natural nonrenewable resources, and the understanding of the fact that the restorative abilities of nature are not unlimited. In the last decade, the arms race again prevailed, samples of new equipment are being created on a fundamentally new technological basis, and environmental costs are not always taken into account. The dismantled Chernobyl nuclear power plant has stood as a menacing reminder of human recklessness for almost four decades. In the period of modern geopolitical squabbles, the struggle for resources has escalated to the limit, and the environmental factor becomes a bargaining chip, but humanity does not solve the problems of cleansing the natural environment for life and development. The first quarter of the XXI century in the world is characterized by global instability. There is exponential population growth, lack of natural resources and living space, environmental pollution, the emergence of previously unknown diseases such as Covid-19, the gap between rich and poor is widening, the vast majority of people lack financial resources, etc. In these emergency conditions points of growth of a new civilization are crystallizing, where the main challenge is clearly becoming a new vision of the role of the natural environment in the life of mankind. A strategy of sufficient development is proposed, where the paths of a new vector of social and economic prospects are outlined on the basis of its coordination with the laws of biosphere evolution, the patterns of conservation of natural ecosystems and the biosphere as a whole are revealed, the expediency of developing environmentally friendly technologies and establishing a new humanism as a necessary condition for achieving a secure future is indicated.

Identification of areas of interest for radiological impact assessments in an evolving landscape context

Regulations concerning potential future health impacts of the final disposal of radioactive wastes in geological disposal facilities are written in terms of annual dose to individuals who are representative of small groups living in the landscape in the vicinity of the repository site. As disposal programmes in Sweden and Finland have progressed towards licensing and construction, so too has detail describing the state and evolution of surface biosphere and the landscape around the proposed disposal sites increased. Simple and generic biosphere dose assessment models in early iterations have grown in complexity with increasing site-specific detail that aims to capture the radiologically significant features of the landscape into which future releases of radionuclides might credibly occur. Current dose assessment models used in support of license applications for disposal programmes in Sweden and Finland are highly complex and their application consequently lacks transparency. An alternative simpler approach to characterising landscape objects for dose assessment models would be beneficial in that it would offer an additional line of reasoning and would add clarity, thereby supporting the decision-making process of the regulatory authorities.In the context of coastal Fennoscandia, landscape change is relatively rapid and dramatic with post-glacial landrise transforming areas of the coastal seabed into terrestrial ecosystems over a period of a few thousand years, global sea level rise notwithstanding. The locations of the geosphere-biosphere interfaces for deep geologic disposal can be estimated with some precision but the nature of the receiving ecosystems at the time of the release is less certain.The approach described here provides a statistical quantification of key morphological characteristics of areas in the landscape where doses could arise, so as to better express uncertainties in dose modelling. The proposed method assumes that the variation in the morphology of potential release locations can be described by the variation in landscape objects seen in the landscape on a wider scale, providing a statistical description of the possible landscape objects, so allowing a more comprehensive range of potential future evolutions to be addressed.Our understanding of the evolution of the landscape, based on the kinds of terrain and ecosystem development models used by POSIVA in Finland and SKB in Sweden, suggests that objects identified in present-day maps can be used as analogues for a statistical characterisation of objects in the future landscape; objects identified in the observed topography and bathymetry can therefore serve as the basis for the statistical description of landscape dose objects over the period during which doses are likely to arise. Using digital elevation models around a disposal site in Finland, we show that the statistical descriptions of landscape dose objects at three times over a period of 10 kyear of the evolved landscape are sufficiently similar to establish the suitability of the approach.The aim of this statistical analysis is to supplement current methods for defining radiological assessment models so as to provide additional numerical support to both the simpler and more complex methods employed by implementors and regulators. The method has been developed in the context of the Swedish and Finnish regulatory review process and is referred to in the IAEA's revised BIOMASS methodology. We briefly address how the method might be applied in other landscape contexts.

Authigenic clay mineral evidence for restricted, evaporitic conditions during the emergence of the Ediacaran Doushantuo Biota

The Ediacaran Period witnessed major environmental change and an expansion of eukaryotic life following the Marinoan glaciation. The Doushantuo Formation of south China has furnished much of our understanding of Earth System and biosphere evolution during this period, but its depositional setting–marine or non-marine–is still debated. Here we conduct mineralogical, petrographic and geochemical analyses of samples from the lower Doushantuo Formation in order to determine the origin of saponite clay minerals which are abundant in this interval. We find that the morphology and distribution of the saponite clays suggest they are of pre-compaction, authigenic origin. We infer that the lower Doushantuo sediments were deposited in a restricted, mildly evaporitic lagoonal basin, offering additional constraints on the environmental setting into which metazoan life emerged. Further, our findings confirm that Ediacaran seawater favored reverse weathering, with marine clay formation likely representing an important sink for various elements during the Precambrian.

Impact of terrestrial biosphere on the atmospheric CO<sub>2</sub> concentration across Termination V

Abstract. Among the 100 kyr climatic cycles of the Late Pleistocene, Termination V (TV, ∼ 433–404 kyr BP), the fifth last deglaciation, stands out for its minimum in astronomical forcing associated paradoxically with maxima in sea level, Antarctic temperature and atmospheric CO2 concentration. However, the driving mechanisms explaining TV remain only partially understood. For instance, climate models cannot fully represent the atmospheric CO2 variation observed in paleoclimate data. Aside from essential oceanic circulation processes, there is increasing evidence that terrestrial biosphere may have played a key role in the global carbon cycle. This study proposes a three-step integrated approach, combining regional and global vegetation records with modelling results, to unveil the evolution of terrestrial biosphere and its contribution to the carbon cycle during TV. First, we provide a new high-resolution (∼ 700 years) deep-sea pollen record from the Gulf of Cádiz (site U1386, 36∘49.680′ N; 7∘45.320′ W) for TV, which shows a moderate expansion of the Mediterranean forest. We then construct the first global forest pollen database for this period. Our compilation features distinct evolutions for different types of forest, highlighting a strong development of temperate and boreal forest which might have delayed the atmospheric CO2 increase during TV. Finally, the direct comparison of global simulated forests (iLOVECLIM model) to our pollen database reveals overall consistent temperate and boreal forest evolutions despite model biases, thereby supporting the hypothesis of a significant CO2 sequestration by middle and high-latitude forests of the Northern Hemisphere shortly after the onset of TV.

Gaia as Solaris: An Alternative Default Evolutionary Trajectory.

Now that we know that Earth-like planets are ubiquitous in the universe, as well as that most of them are much older than the Earth, it is justified to ask to what extent evolutionary outcomes on other such planets are similar, or indeed commensurable, to the outcomes we perceive around us. In order to assess the degree of specialty or mediocrity of our trajectory of biospheric evolution, we need to take into account recent advances in theoretical astrobiology, in particular (i) establishing the history of habitable planets' formation in the Galaxy, and (ii) understanding the crucial importance of "Gaian" feedback loops and temporal windows for the interaction of early life with its physical environment. Hereby we consider an alternative macroevolutionary pathway that may result in tight functional integration of all sub-planetary ecosystems, eventually giving rise to a true superorganism at the biospheric level. The blueprint for a possible outcome of this scenario has been masterfully provided by the great Polish novelist Stanisław Lem in his 1961 novel Solaris. In fact, Solaris offers such a persuasive and powerful case for an "extremely strong" Gaia hypothesis that it is, arguably, high time to investigate it in a discursive astrobiological and philosophical context. In addition to novel predictions in the domain of potentially detectable biosignatures, some additional cognitive and heuristic benefits of studying such extreme cases of functional integration are briefly discussed.

An introduction to the Great Ordovician Biodiversification Event: insights from the Tafilalt Biota, Morocco

Abstract The exquisitely preserved, diverse and abundant fossil assemblages yielded by the ‘echinoderm meadows’ of the Tafilalt region of the eastern Anti-Atlas represent a new Konservat-Lagerstätte, one of the few exceptionally preserved Late Ordovician open-marine faunas found globally, giving us an insight into the radiation of life during the later phases of the Great Ordovician Biodiversification Event (GOBE) in high-latitude peri-Gondwana. The GOBE resulted in an unprecedented increase in the diversity of families, classes and orders, at the fastest rate of the entire Phanerozoic and represents one of the most significant events in the evolution of the marine biosphere, preceding the end-Ordovician mass extinction. Nine different phyla and several soft-bodied problematica are represented in the Tafilalt, including several notable echinoderm Lagerstätten. This volume is the culmination of over 20 years of research by several international teams and integrates a series of contributions that look at diverse aspects of the biota, including the stratigraphic distribution of the faunas, depositional environments, systematic palaeontology, preservation, palaeobiogeography and the nature and impact of the international fossil trade on these exceptionally preserved fossil faunas.

The co-evolutionary approach to nature-based solutions: A conceptual framework

The concept of NbS bridges between researchers and practitioners who search for innovative solutions to a wide range of societal problems and challenges, mostly related to ecological issues. Our conceptual paper aims at grounding the concept in theorizing NbS as a variant of ‘co-evolutionary technology’ CET, informed by ecological and institutional economics, and contextualized in recent Anthropocene research. This results in a new definition of NbS. NbS mediate between technosphere and biosphere evolution. We formulate four principles of CET, with the pivot of CET meeting both human needs and enhancing biospheric evolutionary potential, which feeds back on CET in co-creative design. The paper introduces core theoretical concepts, such as distributed agency and affordances, and proceeds in detailing CET along the standard tripartite view of technology, that is, design, production and use. We conclude in arguing that CET are inherently ethical since their design requires equal recognition of various human and non-human actors, both in terms of functions and ways of world-making.

Pacific ocean mega ecotone of Northern Eruasia as the belt of the origin of the modern continental biosphere

The Pacific Ocean margin of Eurasia includes the age row (at the geologic time scale) of geoecotone objects which can be imagined by certain nodal stages of the evolutionary trajectory of exogenous landscape genesis in the continental biosphere. The reported strategy of scientific research is aimed at the establishment of zonal-regional and local regularities of landscape organization of insular and marginal-continental land in different morphotectonic and macroclimatic sectors of the Pacific Ocean mega-ecotone of Northern Eurasia, which is considered as a natural laboratory for studying the modern stage of development of the geographical envelope The empirical statistical models of the island-arc stage of continental biosphere development in the North-West Pacific have been created by the example of experimental test ground of the active Mendeleev volcano on the Kunashir Island (the South Kuril Ridge). It was shown that on this initial stage local geomorphological and hydro-edaphic conditions created the centers of origin of diverse phytocoenological structures. An exceptionally high percentage of green mass in the structure of production results in the acceleration of the biological cycle as a factor of stability of forest community under unfavorable conditions of “cold” oceanicity. Geothermal energy induces rearrangement of the plant cover towards the increase in its flora- and phytocoenotic diversity to the detriment of biomass formation rate. The “climatically unjustified” but sufficiently stable sub-boreal forest ecosystems were formed, as well as the early stages of buffer forest communities. The multidimensional empirical-statistical modeling of landscape connections in the marginal-continental sector of the Pacific Ocean mega ecotone has been performed based on an experimental site in the Lower By-Amur Region. The ecology of the boreal-forest landscape of the continental margin characterizes the mature stage of evolution of the continental biosphere. The regularities and causal mechanisms of the formation of buffer forest communities typical of ecotone systems have been represented more integrally. Forests of this phenomenal buffer flora are distinguished by extremely high parameters of structural and functional development and have reached the state approaching the evolutionary climax. The previously advanced concepts of the Pacific ecotone of Northern Eurasia as a focus of evolutionary processes in the continental biosphere have been confirmed.

Bolreal ecotone of the East-European Plain: Empirical statistical modeling

The solution of multipurpose tasks of ecological forecasting may depend to a great extent on the results of system analysis of nature-territorial structures, which are most sensitive to external effects including anthropogenic. The scientific search in this direction focuses more and more attention on the natural boundaries – both individual and complex, where the most significant natural or anthropogenic shifts in the structure and function of geo(eco)systems are observed. Considering one or another natural boundary as a vector (connection, cascade, para-dynamical, etc.) landscape system with a clearly defined spatial polarization of its different properties, we obtain a "fast-flowing" model of state response and resistance of geo(eco)systems to the action of certain ecological factors. The study of the structural-functional organization of natural ecosystems at the geographical ecotones is also of scientific and methodical importance, which is common with geo-ecology and, in addition, most important for regional and local landscape-ecological forecasts. Geographical ecotones are the most sensitive (and, in this sense, the least stable) fragments of natural-territorial mosaic. The boreal biogeographic ecotone of the Volga River basin is described as an example for considering the theoretical and scientific-methodical problems of geographical zonality: the fundamental ecological-geographical conception at the present-day stage of biosphere evolution associated with the global anthropogenic impact on the climate. A conception on regional bioclimatic system, characterizing climate-genic exo-dynamic characteristics of soil-vegetation "core" of natural com-plexes is presented. It can survey as a scientific-methodological base of paleogeographical reconstructions and landscape-ecological forecasts. Climate nishes of the phytocoenological and soil’ units are the elements of bioclimatic system and the forms of display of soil-vegatation cover’ hydrothermal stability during the changing climate. Zonal boundaries are considered as modern spatial analogs of the future landscape changes in time. The work dwells on the basic "trigger" mechanisms of zonal boundary formation at the interaction of background climatic signals and their refraction by local (mainly lithe-genic) factors.

Thermochronologic perspectives on the deep-time evolution of the deep biosphere

The Earth's deep biosphere hosts some of its most ancient chemolithotrophic lineages. The history of habitation in this environment is thus of interest for understanding the origin and evolution of life. The oldest rocks on Earth, formed about 4 billion years ago, are in continental cratons that have experienced complex histories due to burial and exhumation. Isolated fracture-hosted fluids in these cratons may have residence times older than a billion years, but understanding the history of their microbial communities requires assessing the evolution of habitable conditions. Here, we present a thermochronological perspective on the habitability of Precambrian cratons through time. We show that rocks now in the upper few kilometers of cratons have been uninhabitable (>∼122 °C) for most of their lifetime or have experienced high-temperature episodes, such that the longest record of habitability does not stretch much beyond a billion years. In several cratons, habitable conditions date back only 50 to 300 million years, in agreement with dated biosignatures. The thermochronologic approach outlined here provides context for prospecting and interpreting the little-explored geologic record of the deep biosphere of Earth's cratons, when and where microbial communities may have thrived, and candidate areas for the oldest records of chemolithotrophic microbes.

Hexagonal magnetite in Algoma-type banded iron formations of the ca. 2.52 Ga Baizhiyan Formation, North China: Evidence for a green rust precursor?

Abstract Banded iron formations (BIFs) are iron-rich marine chemical sedimentary rocks, and their mineralogy and geochemistry can be used to gain insights into ancient ocean chemistry and biospheric evolution. Magnetite is the major iron-bearing mineral in many BIFs (particularly in the Archean) and is variably interpreted to be of primary, early diagenetic, or metamorphic origin. Different genetic interpretations for magnetite lead to divergent pictures of the Precambrian Earth system and its evolutionary models through time. The Baizhiyan Formation of the Neoarchean Wutai Group (Shanxi, North China) features magnetite-bearing, Algoma-type BIFs deposited ca. 2.52 Ga, in the lead-up to a major period of global iron formation deposition in the Paleoproterozoic. Abundant magnetite crystals found in the silica-rich bands of these BIFs show euhedral, hexagonal morphology. We suggest that this hexagonal magnetite likely represents pseudomorphs after green rust, a mixed-valence iron hydroxy-salt formed in the water column. The rare earth element composition of the BIFs shows negligible to slightly positive Ce anomalies (CeSN/CeSN* = 1.03 ± 0.07), which is characteristic of a dominantly anoxic water column. The presence of positive Eu anomalies (EuSN/EuSN* <3.9) suggests a substantial influence from proximal hydrothermal fluids. The co-occurrence of siderite layers associated with the magnetite-bearing strata may indicate iron cycling associated with ferruginous bottom seawater conditions. Geochemical signatures of the Baizhiyan BIFs are consistent with the interpretation that the magnetite was transformed from metastable green rust. This green rust could have formed via several processes, including the partial oxidation of Fe(II) by molecular oxygen/photoferrotrophs, the reaction of settling ferrihydrite with Fe(II)-rich hydrothermal fluids under anoxic conditions, or local dissimilatory iron reduction. In all cases, the contribution of primary green rust to BIF formation requires iron redox cycling, and similar pseudomorphs in the form of hexagonal magnetite may be more common in the geological record. Our findings support the models in which green rust was an important primary constituent of the Precambrian iron cycle, and the potential interactions of green rust with other elements (e.g., phosphorus) should be taken into consideration when reconstructing Precambrian biogeochemical cycles.

Workshop report: Exploring deep oceanic crust off Hawai`i

Abstract. For more than half a century, exploring a complete sequence of the oceanic crust from the seafloor through the Mohorovičić discontinuity (Moho) and into the uppermost mantle has been one of the most challenging missions of scientific ocean drilling. Such a scientific and technological achievement would provide humankind with profound insights into the largest realm of our planet and expand our fundamental understanding of Earth's deep interior and its geodynamic behavior. The formation of new oceanic crust at mid-ocean ridges and its subsequent aging over millions of years, leading to subduction, arc volcanism, and recycling of some components into the mantle, comprise the dominant geological cycle of matter and energy on Earth. Although previous scientific ocean drilling has cored some drill holes into old (> 110 Ma) and young (< 20 Ma) ocean crust, our sampling remains relatively shallow (< 2 km into intact crust) and unrepresentative of average oceanic crust. To date, no hole penetrates more than 100 m into intact average-aged oceanic crust that records the long-term history of seawater–basalt exchange (60 to 90 Myr). In addition, the nature, extent, and evolution of the deep subseafloor biosphere within oceanic crust remains poorly unknown. To address these fundamentally significant scientific issues, an international workshop “Exploring Deep Oceanic Crust off Hawai`i” brought together 106 scientists and engineers from 16 countries that represented the entire spectrum of disciplines, including petrologists, geophysicists, geochemists, microbiologists, geodynamic modelers, and drilling/logging engineers. The aim of the workshop was to develop a full International Ocean Discovery Program (IODP) proposal to drill a 2.5 km deep hole into oceanic crust on the North Arch off Hawai`i with the drilling research vessel Chikyu. This drill hole would provide samples down to cumulate gabbros of mature (∼ 80 Ma) oceanic crust formed at a half spreading rate of ∼ 3.5 cm a−1. A Moho reflection has been observed at ∼ 5.5 km below the seafloor at this site, and the workshop concluded that the proposed 2.5 km deep scientific drilling on the North Arch off Hawai`i would provide an essential “pilot hole” to inform the design of future mantle drilling.

Cooperative Equilibrium in Biosphere Evolution: Reconciling Competition and Cooperation in Evolutionary Ecology.

As our understanding of biological evolution continues to deepen, tension still surrounds the relationship between competition and cooperation in the evolution of the biosphere, with rival viewpoints often associated with the Red Queen and Black Queen hypotheses respectively. This essay seeks to reconcile these viewpoints by integrating observations of some general trends in biosphere evolution with concepts from game theory. It is here argued that biodiversity and ecological cooperation are intimately related, and that both tend to cyclically increase over biological history; this is likely due to the greater relative stability of cooperation over competition as a means of long-term conflict resolution within ecosystems. By integrating this view of the biosphere with existing models such as Niche Game Theory, it may be argued that competition and cooperation in ecosystems coexist at equilibria which shift preferentially towards increasing cooperation over biological history. This potentially points to a state of "cooperative equilibrium" as a limit or endpoint in long-term biosphere evolution, such that Black Queen and Red Queen behavior dominate different phases in an evolutionary movement towards optimal cooperative stability in ecological networks. This concept, if accepted, may also bear implications for developing future mathematical models in evolutionary biology, as well as for resolving the perennial debate regarding the relative roles of conflict and harmony in nature.