Department of Earth and Planetary Science

A long-term cooling trend through the Ordovician Period, from 487 to 443 Ma, is recorded by oxygen isotope data. Tropical ocean basins in the Early Ordovician were hot, which led to low oxygen concentrations in the surface ocean due to the temperature dependence of oxygen solubility. Elevated temperatures also increased metabolic demands such that hot shallow water environments had limited animal diversity as recorded by microbially dominated carbonates. As the oceans cooled through the Ordovician, animal biodiversity increased, leading to the Great Ordovician Biodiversification Event. The protracted nature of the cooling suggests that it was the product of progressive changes in tectonic boundary conditions. Low-latitude arc-continent collisions through this period may have increased global weatherability and decreased atmospheric CO2 levels. Additionally, decreasing continental arc magmatism could have lowered CO2 outgassing fluxes. The Ordovician long-term cooling trend culminated with the development of a large south polar ice sheet on Gondwana. The timescale of major ice growth and decay over the final 2 Myr of the Ordovician is consistent with Pleistocene-like glacial cycles driven by orbital forcing. The short duration of large-scale glaciation indicates a high sensitivity of ice volume to temperature with a strongly nonlinear response, providing a valuable analog for Neogene and future climate change. ▪ Oxygen isotope data record progressive and protracted cooling through the Ordovician leading up to the onset of Hirnantian glaciation. ▪ The gradual cooling trend is mirrored by an Ordovician radiation in biological diversity, consistent with temperature-dependent oxygen solubility and metabolism as a primary control. ▪ Long-term cooling occurred in concert with low-latitude arc-continent collisions and an increase in global weatherability. Although CO2 outgassing may have also decreased with an Ordovician decrease in continental arc length, in the modern, CO2 outgassing is variable along both continental and island arcs, leaving the relationship between continental arc length and climate uncertain. ▪ Evidence for significant ice growth is limited to less than 2 Myr of the Hirnantian Stage, suggesting a high sensitivity of ice growth to pCO2 and temperature. ▪ Independent estimates for ice volume, area, and sea level change during the Hirnantian glacial maximum are internally consistent and comparable to those of the Last Glacial Maximum.

The ice giant planets Uranus and Neptune are assumed to contain large amounts of planetary ices such as water, methane, and ammonia. The properties of mixtures of such ices at the extreme pressures and temperatures of planetary interiors are not yet well understood. Ab initio computer simulations have predicted that a number of ices exhibit a hydrogen superionic state and a doubly superionic state. Since the latter state has not yet been generated with experiments, we outline here two possible pathways for reaching and detecting such a state with dynamic compression experiments. We suggest X-ray diffraction as the principal tool for detecting when the material becomes doubly superionic and the sublattice of one of the heavy nuclei melts. That would require a temperature of (Formula presented.) 3500 K and pressures greater than (Formula presented.) 200 GPa for H (Formula presented.) NO (Formula presented.), which we use as an example material here. Such conditions can be reached with experiments that employ an initial shock that is followed by a ramp compression wave. Alternatively, one may use triple-shock compression because a single shock does not yield sufficiently high densities.

Ultramafic-hosted seafloor massive sulfide deposits have been reported in present-day oceanic settings for nearly thirty years. However, the development of comprehensive genetic models that account for deep-seated hydrothermal processes is largely hindered by the limited availability of seafloor observations and their reliance on large-scale geophysical studies. The Platta nappe (Swiss Alps) preserves a Jurassic hydrothermal system (the Marmorera-Cotschen Hydrothermal System; MCHS), where Cu-Fe-Co-Zn-Ni mineralization is associated with Fe-Ca silicates (ilvaite, hydrogarnet, and diopside). Petrographic analyses and thermodynamic modeling indicate that Fe-Ca metasomatism occurred between 300 and 360 °C and at low fO2 (from FMQ −6 to +1), likely coeval with early-stage serpentinization. The composition of Fe-Ca silicates (Co, Ni, and REE contents, measured by in-situ LA-ICP-MS) indicates fluid-rock interaction from an ultramafic-dominated system to an open-system, involving fluids derived from both mafic and ultramafic rocks. Mineralogical and geochemical signatures of Fe-Ca silicates in the MCHS do not support genetic relationships with common rodingitization. Our results highlight that Fe-Ca metasomatism may be a widespread deep-seated alteration along mafic–ultramafic rock contacts or in mantle rocks modified through melt-rock interaction accompanying mantle exhumation.

Molecular hydrogen (H2) is found in a variety of settings on and in the Earth from low-temperature sediments to hydrothermal vents, and is actively being considered as an energy resource for the transition to a green energy future. The hydrogen isotopic composition of H2, given as D/H ratios or δD, varies in nature by hundreds of per mil from ∼−800 ‰ in hydrothermal and sedimentary systems to ∼+450 ‰ in the stratosphere. This range reflects a variety of processes, including kinetic isotope effects associated with formation and destruction and equilibration with water, the latter proceeding at fast (order year) timescales at low temperatures (<100 °C). At isotopic equilibrium, the D/H fractionation factor between liquid water and hydrogen (DαH2O(l)-H2(g)) is a function of temperature and can thus be used as a geothermometer for H2 formation or re-equilibration temperatures. Multiple studies have produced theoretical calculations for hydrogen isotopic equilibrium between H2 and water vapor. However, only three published experimental calibrations used in geochemistry exist for the H2O-H2 system: two between 51 and 742 °C for H2O(g)-H2(g) (Suess, 1949; Cerrai et al., 1954), and one in the H2O(l)-H2(g) system for temperatures <100 °C (Rolston et al., 1976). Despite these calibrations existing, there is uncertainty on their accuracy at low temperatures (<100 °C; e.g., Horibe and Craig, 1995). Here we present a new experimental calibration of the equilibrium hydrogen isotopic fractionation factor for liquid water and molecular hydrogen from 3 to 90 °C. Equilibration was achieved using platinum catalysts and verified via experimental bracketing by approaching final values of DαH2O(l)-H2(g) at a given temperature from both higher (top-bracket) and lower (bottom-bracket) initial Dα values. Our calibration yields the following equation: [Formula presented] Where T is in Kelvin. We find that our calibrations differ from prior experimental calibrations by, on average, up to 20 ‰ and prior theoretical results by up to, on average, 25 ‰. Good agreement with theoretical results (<11 ‰ differences) is found for calculations that consider both anharmonic effects and the Diagonal Born-Oppenheimer correction.

Türkiyes geographic position between Europe, Asia, and Africa gives it pivotal importance for understanding the local, interregional, and intercontinental dynamics of Neogene vertebrate evolution. Although rich in vertebrate fossil deposits spanning the Middle and Late Miocene, associated geochronology has been limited by the lack of available volcanic materials that allow radioisotopic dating and geochemical correlation. As a result, calibrating mammalian evolution has been largely restricted to the semicircular application of paleomagnetic inferences combined with temporally ill-constrained and geographically remote biochronological deductions. For example, fossils from three Greek localities and one Anatolian locality assigned to the primate genus Ouranopithecus lack datable samples, leaving its ages poorly constrained. Chronological calibration based on the 40Ar/39Ar results reported here demonstrates how a fauna-focused, precision geochronology can enhance a better understanding of evolving species lineages and the ecosystems they comprise.

Object-based identification algorithms for atmospheric features are commonly utilized to attribute global precipitation. This study employs a systematic approach to examine feature co-occurrences and their relationships to mean and extreme precipitation. Four features are identified using existing data sets for atmospheric rivers (ARs), mesoscale convective systems (MCSs), low-pressure systems (LPSs), and fronts (FTs). Often, a single atmospheric phenomenon satisfies the criteria set by multiple feature identification algorithms, yielding an association between precipitation and multiple features. Over the extra-tropics, the number of features attributed to a single event typically increases with precipitation intensity. Over two-thirds of the precipitation is from co-occurring features, with a considerable fraction related to AR-FT co-occurrences. Over the tropics, about one-quarter of precipitation is associated with co-occurring features, with LPS-MCS co-occurrences contributing substantially in monsoon regions. MCSs are the leading single-feature contributors over tropical land and oceans. In the extra-tropics, FTs, ARs, and their co-occurrences account for over half of the total precipitation over oceans. AR-FT-MCS and FT-MCS co-occurrences contribute to extremes (precipitation exceeding the 95th percentile) over both oceans (over 30%) and land (over 20%). Any combination of features involving MCSs shows a larger contribution to high percentiles of precipitation intensity. A case analysis indicates that AR-FT-MCS co-occurrences exhibit convective instability and deep vertical motion, suggesting that the feature trackers and reanalysis are capturing physics relevant to both convective and frontal systems. The results here emphasize the need for simultaneous identifications of multiple features when attributing precipitation to atmospheric phenomena.

The northern lowlands of early Mars could have contained a significant quantity of liquid water. However, the ocean hypothesis remains controversial due to the lack of conclusive evidence from the Martian subsurface. We use data from the Zhurong Rover Penetrating Radar on the southern Utopia Planitia to identify subsurface dipping reflectors indicative of an ancient prograding shoreline. The reflectors dip unidirectionally with inclinations in the range 6° to 20° and are imaged to a thickness of 10 to 35 m along an uninterrupted 1.3 km northward shoreline-perpendicular traverse. The consistent dip inclinations, absence of dissection by fluvial channels along the extended traverse, and low permittivity of the sediments are consistent with terrestrial coastal deposits-and discount fluvial, aeolian, or magmatic origins favored elsewhere on Mars. The structure, thickness, and length of the section support voluminous supply of onshore sediments into a large body of water, rather than a merely localized and short-lived melt event. Our findings not only provide support for the existence of an ancient Martian ocean in the northern plains but also offer crucial insights into the evolution of the ancient Martian environment.

The triple oxygen isotope composition of sulphate minerals has been used to constrain the evolution of Earths surface environment (e.g., pO2, pCO2 and gross primary productivity) throughout the Proterozoic Eon. This approach presumes the incorporation of atmospheric O2 atoms into riverine sulphate via the oxidative weathering of pyrite. However, this is not borne out in recent geological or modern sulphate records, where an atmospheric signal is imperceptible and where terrestrial pyrite weathering occurs predominantly in bedrock fractures that are physically more removed from atmospheric O2. To better define the transition from a Proterozoic to a modern-like weathering regime, here we present new measurements from twelve marine evaporite basins spanning the Phanerozoic. These data display a step-like transition in the triple oxygen isotope composition of evaporite sulphate during the mid-Paleozoic (420 to 387.7 million years ago). We propose that the evolution of early root systems deepened the locus of pyrite oxidation and reduced the incorporation of O2 into sulphate. Further, the early Devonian proliferation of land plants increased terrestrial organic carbon burial, releasing free oxygen that fueled increased redox recycling of soil-bound iron and resulted in the final rise in pO2 to modern-like levels.

Geophysical models for pressure solution are typically developed for diffusion-controlled or reaction-controlled scenarios. We present a unified analytical model that considers fully coupled diffusion and reaction during pressure solution. The model recovers the diffusion-controlled and reaction-controlled models in the literature as specific limiting cases. When diffusion and reaction exhibit comparable influences, we validate the proposed model against independent numerical simulations. The proposed model is then employed in interpreting experimental measurements, demonstrating a better agreement compared to previous interpretations.

Correction to: Naturehttps://doi.org/10.1038/s41586-024-08455-0 Published online 22 January 2025 In the version of the article initially published, the affiliations of Hana A. Chang (Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, CA, USA) and Ron Milo (Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot, Israel) were incorrect and have now been amended in the HTML and PDF versions of the article.