Modern Earth Research Articles

Earth Sciences in the secondary education of Bulgaria

About 50 years ago, the study of geology has been removed from the curricula of the Bulgarian secondary education system. The young generations have to receive from the Geography textbooks (centred more on Human Geography) only unsystematic knowledge about some physical geographical features related to geological processes and structures, as the generalized Earth’s shape and structure, volcanoes, earthquakes, the geomorphology, and the elementary knowledge of plate tectonics as the basic paradigm of modern Earth sciences. Even basic knowledge of minerals, crystals and symmetry, rocks, and fossils was evicted not to speak about the sedimentation, igneous and metamorphic rocks, formations, and processes. With the present paper a short review of the secondary (high school) education in European and American schools is made. On its basis together with the rich experience in former textbooks of Geography and Geology (before 1970), suggestions are made for the replacement of the curricula and textbooks of Geography for the 8th to 10th classes (grades) by curricula and textbooks of Earth Sciences based on the modern knowledge of the Planet Earth System.

Detectability of biosignatures in warm, water-rich atmospheres

Warm rocky exoplanets within the habitable zone of Sun-like stars are favoured targets for current and future missions. Theory indicates these planets could be wet at formation and remain habitable long enough for life to develop. However, it is unclear to what extent an early ocean on such worlds could influence the response of potential biosignatures. In this work we test the climate-chemistry response, maintenance, and detectability of biosignatures in warm, water-rich atmospheres with Earth biomass fluxes within the framework of the planned LIFE mission. We used the coupled climate-chemistry column model 1D-TERRA to simulate the composition of planetary atmospheres at different distances from the Sun, assuming Earth's planetary parameters and evolution. We increased the incoming instellation by up to 50 percent in steps of 10 percent, corresponding to orbits of 1.00 to 0.82 AU. Simulations were performed with and without modern Earth’s biomass fluxes at the surface. Theoretical emission spectra of all simulations were produced using the GARLIC radiative transfer model. LIFEsim was then used to add noise to and simulate observations of these spectra to assess how biotic and abiotic atmospheres of Earth-like planets can be distinguished. Increasing instellation leads to surface water vapour pressures rising from 0.01 bar (1.31<!PCT!>, S = 1.0) to 0.61 bar (34.72<!PCT!>, S = 1.5). In the biotic scenarios, the ozone layer survives because hydrogen oxide reactions with nitrogen oxides prevent the net ozone chemical sink from increasing. Methane is strongly reduced for instellations that are 20<!PCT!> higher than that of the Earth due to the increased hydrogen oxide abundances and UV fluxes. Synthetic observations with LIFEsim, assuming a 2.0 m aperture and resolving power of a R = 50, show that ozone signatures at 9.6 mu m reliably point to Earth-like biosphere surface fluxes of O$_2$ only for systems within 10 parsecs. The differences in atmospheric temperature structures due to differing H$_2$O profiles also enable observations at 15.0 mu m to reliably identify planets with a CH$_4$ surface flux equal to that of Earth's biosphere. Increasing the aperture to 3.5 m and increasing instrument throughput to 15<!PCT!> increases this range to 22.5 pc.

Evolution of gas envelopes and outgassed atmospheres of rocky planets that formed via pebble accretion

In this work, we present results of numerical simulations of the formation and early evolution of rocky planets through pebble accretion, with an emphasis on hydrogen envelope longevity and the composition of the outgassed atmosphere. We modelled planets with a range in mass from 0.1 to 5 Earth masses that orbit between 0.7 and 1.7 AU. The composition of the outgassed atmosphere was calculated with the partial pressure of free oxygen fit to geophysical models of magma ocean self-oxidation. The combined X-ray and UV (XUV) radiation-powered photoevaporation is considered as the main driver of atmospheric escape. We modelled planets that remain below the pebble isolation mass and hence accrete tenuous envelopes only. We considered slow, medium, or fast initial stellar rotation for the temporal evolution of the XUV flux. The loss of the envelope is a key event that allows the magma ocean to crystallise and outgas its bulk volatiles. The atmospheric composition of the majority of our simulated planets is dominated by CO2. Our planets accrete a total of 11.6 Earth oceans of water, the majority of which enters the core. The hydrospheres of planets lighter than the Earth reach several times the mass of the Earth’s modern oceans, while the hydrospheres of planets ranging from 1 to 3.5 Earth masses are comparable to those of our planet. However, planets of 4–5 Earth masses have smaller hydrospheres due to the trapping of volatiles in their massive mantles. Overall, our simulations demonstrate that hydrogen envelopes are easily lost from rocky planets and that this envelope loss triggers the most primordial partitioning of volatiles between the solid mantle and the atmosphere.

X-Ray Emission of Nearby Low-mass and Sunlike Stars with Directly Imageable Habitable Zones

Stellar X-ray and UV radiation can significantly affect the survival, composition, and long-term evolution of the atmospheres of planets in or near their host star’s habitable zone (HZ). Especially interesting are planetary systems in the solar neighborhood that may host temperate and potentially habitable surface conditions, which may be analyzed by future ground- and space-based direct-imaging surveys for signatures of habitability and life. To advance our understanding of the radiation environment in these systems, we leverage ∼3 Ms of XMM-Newton and Chandra observations in order to measure three fundamental stellar properties at X-ray energies for 57 nearby FGKM stellar systems: the shape of the stellar X-ray spectrum, the luminosity, and the timescales over which the stars vary (e.g., due to flares). These systems possess HZs that will be directly imageable to next-generation telescopes such as the Habitable Worlds Observatory and ground-based Extremely Large Telescopes. We identify 29 stellar systems with L X/L bol ratios similar to (or less than) that of the Sun; any potential planets in the HZs of these stars therefore reside in present-day X-ray radiation environments similar to (or less hostile than) modern Earth, though a broader set of these targets could host habitable planets. An additional 19 stellar systems have been observed with the Swift X-ray Telescope; in total, only ∼30% of potential direct imaging target stars has been observed with XMM-Newton, Chandra, or Swift. The data products from this work (X-ray light curves and spectra) are available via a public Zenodo repository (doi:10.5281/zenodo.11490574).

High‐Dimensional Covariance Estimation From a Small Number of Samples

AbstractWe synthesize knowledge from numerical weather prediction, inverse theory, and statistics to address the problem of estimating a high‐dimensional covariance matrix from a small number of samples. This problem is fundamental in statistics, machine learning/artificial intelligence, and in modern Earth science. We create several new adaptive methods for high‐dimensional covariance estimation, but one method, which we call Noise‐Informed Covariance Estimation (NICE), stands out because it has three important properties: (a) NICE is conceptually simple and computationally efficient; (b) NICE guarantees symmetric positive semi‐definite covariance estimates; and (c) NICE is largely tuning‐free. We illustrate the use of NICE on a large set of Earth science–inspired numerical examples, including cycling data assimilation, inversion of geophysical field data, and training of feed‐forward neural networks with time‐averaged data from a chaotic dynamical system. Our theory, heuristics and numerical tests suggest that NICE may indeed be a viable option for high‐dimensional covariance estimation in many Earth science problems.

Latent magmatism beneath the Korean Peninsula caused by asthenosphere upwelling

Volatiles such as helium and carbon dioxide provide insights into geological processes spanning from the Earth’s deep interior to its surface. Integration with geophysical data providing enhanced vertical resolution with a wider horizontal range better elucidates the mantle dynamics and its interactions with the crust. Here we present geochemistry of volatiles dissolved in fluid samples from fault-related springs, thermal spa waters, and groundwaters across the Korean Peninsula. These were examined in conjunction with existing geophysical information. Remarkably, there is a strong spatial correlation between helium isotopes and S-wave velocity, suggesting the influence of mantle upwelling on both geochemical and geophysical parameters. Furthermore, the computed helium flux is comparable to that of volcanic regions, implying partial melting induced by mantle upwelling due to edge-driven convection beneath the Korean Peninsula. Therefore, these findings suggest that mantle-derived volatiles can be released diffusely over large areas through faults in the modern Earth’s intraplate environment.

Sediment subduction in Hadean revealed by machine learning

Due to the scarcity of rock samples, the Hadean Era predating 4 billion years ago (Ga) poses challenges in understanding geological processes like subaerial weathering and plate tectonics that are critical for the evolution of life. The Jack Hills zircon from Western Australia, the primary Hadean samples available, offer valuable insights into magma sources and tectonic genesis through trace element signatures. However, a consensus on these signatures has not been reached. To address this, we developed a machine learning classifier capable of deciphering the geochemical fingerprints of zircon. This allowed us to identify the oldest detrital zircon originating from sedimentary-derived "S-type" granites. Our results indicate the presence of S-type granites as early as 4.24 Ga, persisting throughout the Hadean into the Archean. Examining global detrital zircon across Earth's history reveals consistent supercontinent-like cycles from the present back to the Hadean. These findings suggest that a significant amount of Hadean continental crust was exposed, weathered into sediments, and incorporated into the magma sources of Jack Hills zircon. Only the early operation of both subaerial weathering and plate subduction can account for the prevalence of S-type granites we observe. Additionally, the periodic evolution of S-type granite proportions implies that subduction-driven tectonic cycles were active during the Hadean, at least around 4.2 Ga. The evidence thus points toward an early Earth resembling the modern Earth in terms of active tectonics and habitable surface conditions. This suggests the potential for life to originate in environments like warm ponds rather than extreme hydrothermal settings.

Sustained increases in atmospheric oxygen and marine productivity in the Neoproterozoic and Palaeozoic eras

A geologically rapid Neoproterozoic oxygenation event is commonly linked to the appearance of marine animal groups in the fossil record. However, there is still debate about what evidence from the sedimentary geochemical record—if any—provides strong support for a persistent shift in surface oxygen immediately preceding the rise of animals. We present statistical learning analyses of a large dataset of geochemical data and associated geological context from the Neoproterozoic and Palaeozoic sedimentary record and then use Earth system modelling to link trends in redox-sensitive trace metal and organic carbon concentrations to the oxygenation of Earth’s oceans and atmosphere. We do not find evidence for the wholesale oxygenation of Earth’s oceans in the late Neoproterozoic era. We do, however, reconstruct a moderate long-term increase in atmospheric oxygen and marine productivity. These changes to the Earth system would have increased dissolved oxygen and food supply in shallow-water habitats during the broad interval of geologic time in which the major animal groups first radiated. This approach provides some of the most direct evidence for potential physiological drivers of the Cambrian radiation, while highlighting the importance of later Palaeozoic oxygenation in the evolution of the modern Earth system.

Open-ended versus bounded evolution: Mineral evolution as a case study.

To what extent are naturally evolving systems limited in their potential diversity (i.e. "bounded") versus unrestricted ("open-ended")? Minerals provide a quantitative model evolving system, with well-documented increases in mineral diversity through multiple stages of planetary evolution over billions of years. A recent framework that unifies behaviors of both biotic and abiotic evolving systems posits that all such systems are characterized by combinatorial richness subject to selection. In the case of minerals, combinatorial richness derives from the possible combinations of chemical elements coupled with permutations of their formulas' coefficients. Observed mineral species, which are selected for persistence through deep time, represent a miniscule fraction of all possible element configurations. Furthermore, this model predicts that as planetary systems evolve, stable minerals become an ever-smaller fraction of the "possibility space." A postulate is that "functional information," defined as the negative log2 of that fraction, must increase as a system evolves. We have tested this hypothesis for minerals by estimating the fraction of all possible chemical formulas observed from one stage of mineral evolution to the next, based on numbers of different essential elements and the maximum chemical formula complexity at each of nine chronological stages of mineral evolution. We find a monotonic increase in mineral functional information through these nine stages-a result consistent with the hypothesis. Furthermore, analysis of the chemical formulas of minerals demonstrates that the modern Earth may be approaching the maximum limit of functional information for natural mineral systems-a result demonstrating that mineral evolution is not open-ended.

A non-methanogenic archaeon within the order Methanocellales

Serpentinization, a geochemical process found on modern and ancient Earth, provides an ultra-reducing environment that can support microbial methanogenesis and acetogenesis. Several groups of archaea, such as the order Methanocellales, are characterized by their ability to produce methane. Here, we generate metagenomic sequences from serpentinized springs in The Cedars, California, and construct a circularized metagenome-assembled genome of a Methanocellales archaeon, termed Met12, that lacks essential methanogenesis genes. The genome includes genes for an acetyl-CoA pathway, but lacks genes encoding methanogenesis enzymes such as methyl-coenzyme M reductase, heterodisulfide reductases and hydrogenases. In situ transcriptomic analyses reveal high expression of a multi-heme c-type cytochrome, and heterologous expression of this protein in a model bacterium demonstrates that it is capable of accepting electrons. Our results suggest that Met12, within the order Methanocellales, is not a methanogen but a CO2-reducing, electron-fueled acetogen without electron bifurcation.

Early Earth “subduction”: short-lived, off-craton, shuffle tectonics, and no plate boundaries

Subduction is a key geodynamic feature on modern Earth that drives crustal chemical diversity, bridging the atmo-, hydro-, and lithosphere, but remains an enigmatic, unique planetary feature. Indisputable is the critical role of subduction in shaping Earth’s geomorphology and crustal dichotomy (ocean vs continental crust) and its impacts on long-term climate, making it arguably the most important process on present-day Earth across all geosciences. It is thus important to understand to what degree, or if at all, subduction was operational during the billions of years that led to our geological status quo.Here, we assess the feasibility of Archean subduction with a focus on early Earth geodynamics. We argue that convection-driven rifting, but not spreading, formed the first keels under the primordial crust, providing the necessary stability for crustal survival. These sections of crustal rejuvenation would counterintuitively forge the first stable proto-cratonic terranes, which later evolved into cratons. Hydrated upper crustal rocks were vital in generating early fluxed mantle melting and related volcanism, but also for partial melting in hydrated lower crustal sections within proto-cratons, giving rise to tonalite-trondhjemite granodiorites (TTGs). Both processes operated off- and on-craton, respectively, and required melting of hydrated crust and crustal convergence but are unrelated. Away from proto-cratonic regions of minor episodic divergence and rifting, relative motions were accommodated by convergence and shuffle tectonics, leading to Archean-style subduction in localised regions that were prone to destruction. This primitive form of subduction and crustal maturation has operated from the earliest Archean time in a plate-and-lid regime. Crucially, this ‘Archean subduction’ represents short-lived crustal shuffle-tectonics outside areas of today’s cratons with fluxed melting in upper mantle regions but does not resemble present-day Benioff-style subduction. The development of subduction akin to present-day processes towards the end of the Archean could plausibly have driven atmospheric oxygenation over a few hundred million years between ca. 2.8–2.3 Ga, with H-loss to space accompanied by atmospheric oxidation through subduction-related global volcanic SO2 emissions.

Biogenic Sulfur Gases as Biosignatures on Temperate Sub-Neptune Waterworlds

Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in the atmospheres of temperate sub-Neptune waterworlds for the first time. On Earth today, organic sulfur compounds produced by marine biota are rapidly destroyed by photochemical processes before they can accumulate to significant levels. Domagal-Goldman et al. suggest that detectable biogenic sulfur signatures could emerge in Archean-like atmospheres with higher biological production or low UV flux. In this study, we explore biogenic sulfur across a wide range of biological fluxes and stellar UV environments. Critically, the main photochemical sinks are absent on the nightside of tidally locked planets. To address this, we further perform experiments with a 3D general circulation model and a 2D photochemical model (VULCAN 2D) to simulate the global distribution of biogenic gases to investigate their terminator concentrations as seen via transmission spectroscopy. Our models indicate that biogenic sulfur gases can rise to potentially detectable levels on hydrogen-rich water worlds, but only for enhanced global biosulfur flux (≳20 times modern Earth’s flux). We find that it is challenging to identify DMS at 3.4 μm where it strongly overlaps with CH4, whereas it is more plausible to detect DMS and companion byproducts, ethylene (C2H4) and ethane (C2H6), in the mid-infrared between 9 and 13 μm.

Speciation controls on Ni adsorption to birnessite and organo-birnessite

Nickel (Ni) is an essential micronutrient for phytoplankton. Its importance to both the modern and ancient Earth system has encouraged development of Ni and its isotopes as biogeochemical tracers. To interpret these signatures however, understanding of how Ni and its isotopes are recorded in marine archives is required. Here we simulate different inorganic and organic Ni species in seawater and investigate their adsorption behaviours to variably crystalline phyllomanganates and organo-mineral phyllomanganate. We conduct pH adsorption edge experiments to determine the binding affinity of the different Ni species to the minerals and then perform desorption experiments to operationally define Ni bonding strength. We also use thermodynamic surface complexation modelling to constrain Ni adsorption mechanisms. From the adsorption edges and stability constants generated from our modelling, the binding affinity increases in the order of Ni-formate+ (aq) < NiCl+ (aq) < Ni2+ (aq). From the desorption experiments, desorption at pH 8 is non quantitative and increases in the opposite order of Ni-formate+ (aq) > NiCl+ (aq) ∼ Ni2+ (aq). For the organo-mineral however, Ni desorption at pH 8 is non quantitative and similar for all three experiments, and is significantly higher compared to the variably crystalline phyllomanganates. Although both our adsorption and desorption experiments were performed over 48 h, it is possible that desorption is somewhat slower than adsorption such that a longer desorption period may result in further Ni loss to solution and thus greater adsorption reversibility. Taken together however, the Ni-formate+ (aq) and Ni organo-birnessite desorption experiments suggest that Ni bonding strength is decreased by the presence of organic carbon, compared to NiCl+ (aq) and Ni2+ (aq). Because bonding strength governs equilibrium stable isotope fractionation, we use our experimental findings to suggest how Ni speciation in seawater might influence Ni isotope behaviour during adsorption to phyllomanganate. We find that our suggestions are consistent with isotopic measurements from natural sediments. Although the balance of Ni adsorption versus incorporation during uptake to phyllomanganates may play a greater part in explaining the variation in the Ni isotope composition in Mn-rich sediments, Ni speciation and the presence of organics might increase the range of δ60Ni values measured in natural settings.

Atmospheric Chemistry of Secondary and Hybrid Atmospheres of Super Earths and Sub-Neptunes

The atmospheres of small exoplanets likely derive from a combination of geochemical outgassing and primordial gases left over from formation. Secondary atmospheres, such as those of Earth, Mars, and Venus, are sourced by outgassing. Persistent outgassing into long-lived, primordial, hydrogen–helium envelopes produces hybrid atmospheres of which there are no examples in the solar system. We construct a unified theoretical framework for calculating the outgassing chemistry of both secondary and hybrid atmospheres, where the input parameters are the surface pressure, oxidation, and sulfidation states of the mantle, as well as the primordial atmospheric hydrogen, helium, and nitrogen content. Nonideal gases (quantified by the fugacity coefficient) and nonideal mixing of gaseous components (quantified by the activity coefficient) are considered. Both secondary and hybrid atmospheres exhibit a rich diversity of chemistries, including hydrogen-dominated atmospheres. The abundance ratio of carbon dioxide to carbon monoxide serves as a powerful diagnostic for the oxygen fugacity of the mantle, which may conceivably be constrained by James Webb Space Telescope spectra in the near future. Methane-dominated atmospheres are difficult to produce and require specific conditions: atmospheric surface pressures exceeding ∼10 bar, a reduced (poorly oxidized) mantle, and diminished magma temperatures (compared to modern Earth). Future work should include photochemistry in these calculations and clarify the general role of atmospheric escape. Exoplanet science should quantify the relationship between the mass and oxygen fugacity for a sample of super Earths and sub-Neptunes; such an empirical relationship already exists for solar system bodies.

Onset of double subduction controls plate motion reorganisation

Face-to-face double subduction systems, in which two oceanic plates subduct toward each other, are essential elements of plate tectonics. Two subduction zones in such systems are typically uneven in age and their spatially and temporally variable dynamics remain enigmatic. Here, with 2D numerical modelling, we demonstrate that the onset of the younger subduction zone strongly changes the dynamics of the older subduction zone. The waxing younger subduction may gradually absorb plate convergence from the older one, resulting in older subduction waning featured by the dramatic decrease in subduction rate and trench retreat. The dynamical transformation of subduction predominance alters the intraplate stress and mantle flow, regulating the relative motion among the three different plates. The process of waxing and waning of subduction zones controls plate motion reorganisation, providing a reference to interpret the past, present, and future evolution of several key double subduction regions found on the modern Earth.

An Analytic Theory of Near-Surface Relative Humidity over Land

Abstract There is no simple explanation for the spatial structure of near-surface relative humidity over land. We present a diagnostic theory for zonally and temporally averaged near-surface relative humidity (RH) over land based on energy budgets of an atmospheric column in radiative–convective equilibrium. The theory analytically relates RH to the surface evaporative fraction (EF), has no calibrated parameters, and is quantitatively accurate when compared with RH from a reanalysis, and with cloud-permitting simulations over an idealized land surface. The theory is used to answer two basic questions. First, why is RH never especially low (e.g., 1%)? The theory shows that established lower bounds on EF over land and ocean are equivalent to lower bounds on RH that preclude particularly low values, at least for conditions typical of the modern Earth. Second, why is the latitudinal profile of RH over land shaped like the letter W, when both specific humidity and saturation specific humidity essentially decline monotonically from the equator to the poles? The theory predicts that the latitudinal profile of RH should look more like that of water stored in the soil (which also exhibits a W-shaped profile) than in the air (which does not).

Modern analogs for ammonia flux from terrestrial hydrothermal features to the Archean atmosphere

The isotopic composition of nitrogen in the rock record provides valuable evidence of reactive nitrogen sources and processing on early Earth, but the wide range of δ15N values (− 10.2 to + 50.4‰) leads to ambiguity in defining the early Precambrian nitrogen cycle. The high δ15N values have been explained by large fractionation associated with the onset of nitrification and/or fractionation produced by ammonia-ammonium equilibrium and water–air flux in alkaline paleolakes. Previous flux sensitivity studies in modern water bodies report alkaline pH is not a prerequisite and temperature can be the dominate parameter driving water–air flux. Here, I use the chemical and physical components of 1022 modern hydrothermal features to provide evidence that water–air NH3 flux produced a significant source of fixed nitrogen to early Earth’s atmosphere and biosphere. With regard to the modeled average NH3 flux (2.1 kg N m−2 year−1) and outlier removed average flux (1.2 kg N m−2 year−1), the Archean Earth’s surface would need to be 0.0092, and 0.017% terrestrial hydrothermal features, respectively, for the flux to match the annual amount of N produced by biogenic fixation on modern Earth. Water–air NH3 flux from terrestrial hydrothermal features may have played a significant role in supplying bioavailable nitrogen to early life.

Halogen Cycling in the Solid Earth

Each of the halogens constrains a different aspect of volatile cycling in the solid Earth. F is moderately incompatible in the mantle and has a low mobility at Earth's surface, meaning that it is preferentially retained in the mantle and continental crust. In contrast, Cl, Br, and I are strongly incompatible and highly soluble. Chloride is the dominant anion in seawater and many geofluids and a major component of evaporite minerals. Br and I are essential for life and significantly incorporated into organic matter that accumulates in marine sediments. Surficial fluids circulated into continental and oceanic crust incorporate surface-derived halogens into alteration minerals. As a result, subducting slabs and arc lavas are weakly enriched in F and strongly enriched in Cl, Br, and I. Subduction has maintained mantle Cl and Br concentrations at relatively constant levels since Earth's early differentiation, but mantle I/Cl has decreased over time. ▪Halogen abundances on the early Earth were affected by I partitioning into Earth's core and possible loss of hydrophilic Cl, Br, and I in an early formed ocean.▪Halogens are powerful tracers of subduction zone processes on the modern Earth, with Cl, Br, and I having a dominantly subducted origin in Earth's mantle.▪The deep subduction cycles of Cl, Br, and I are more similar to that of H2O than they are to F, but the geochemical cycle of each halogen differs in detail.▪Halogen abundance ratios and stable isotope ratios vary systematically in Earth's surface reservoirs, meaning that halogens are powerful tracers of geological fluids and melts.

Retrievals Applied to a Decision Tree Framework Can Characterize Earthlike Exoplanet Analogs

Exoplanet characterization missions planned for the future will soon enable searches for life beyond our solar system. Critical to the search will be the development of life detection strategies that can search for biosignatures while maintaining observational efficiency. In this work, we adopted a newly developed biosignature decision tree strategy for remote characterization of Earthlike exoplanets. The decision tree offers a step-by-step roadmap for detecting exoplanet biosignatures and excluding false positives, based on Earth’s biosphere and its evolution over time. We followed the pathways for characterizing a modern-Earth-like planet and an Archean-Earth-like planet and evaluated the observational trades associated with coronagraph bandpass combinations of designs consistent with the Habitable Worlds Observatory precursor studies. With retrieval analyses of each bandpass (or combination), we demonstrate the utility of the decision tree and evaluate the uncertainty on a suite of biosignature chemical species and habitability indicators (i.e., the gas abundances of H2O, O2, O3, CH4, and CO2). Notably for modern Earth, less than an order of magnitude spread in the 1σ uncertainties was achieved for the abundances of H2O and O2, planetary surface pressure, and atmospheric temperature, with three strategically placed bandpasses (two in the visible and one in the near-infrared). For the Archean, CH4 and H2O were detectable in the visible with a single bandpass.

Per-capita change rates of the Phanerozoic Earth-life system exhibited Zipf distributions

The Zipf distribution is widespread in physical and biological systems on the modern Earth; whether such distributions existed in the ancient Earth-life system, however, remains understudied. Here I demonstrate that per-capita change rates (PCCRs) of the atmospheric CO2 level, global average temperature, genus richness, and body size during the Phanerozoic exhibited Zipf distributions. Statistical analyses, including the goodness-of-fit test, likelihood-ratio test, and complementary cumulative distribution function (CCDF), support these Zipf distributions. Moreover, correlation analyses show that these environmental variables and biological metrics are correlated while their PCCRs are not, suggesting that Zipf distributions in PCCRs are unlikely to directly connect to each other; instead, there probably existed a set of common but unknown factors responsible for these systematic Zipf distributions in PCCRs. The results in this study offer new perspectives on the evolutionary patterns of the ancient Earth-life system.