Phanerozoic Research Articles

Functional diversity and resilience of bivalves after the Permian-Triassic mass extinction

The Permian-Triassic mass extinction was the largest extinction event in the Phanerozoic eon, with profound taxonomic and ecological effects on the ecosystem function. Functional diversity, a facet of biodiversity, could reflect the ecosystem function and stability. Although previous studies have shown that the functional richness of global marine organisms was decoupled from their taxonomic diversity during the mass extinctions, the evolution of functional diversity during the Permian-Triassic mass extinction and its aftermath is still under debate. The ecologically diverse clade bivalves may be more representative for understanding the evolution of functional diversity. To investigate the evolutionary dynamics of the functional diversity of bivalves, a global bivalve dataset of 8929 occurrences from the latest Permian to the Late Triassic was constructed. Functional richness, functional evenness, and functional redundancy were calculated to reflect the functional diversity in this study. Our results showed that the functional richness of bivalves was slightly affected by the Permian-Triassic mass extinction, decoupled from the significant decrease in taxonomic diversity. Meanwhile, a decrease in functional redundancy and an increase in functional evenness were observed after the mass extinction. In addition, bivalves showed high resilience to the mass extinction by maintaining the ecospace and reducing the functional redundancy. The high taxonomic diversity, high functional richness, high functional redundancy and relatively higher proportion of infaunal bivalves during the Late Triassic indicate that the Mesozoic marine revolution was already underway.

A 650-Myr history of Earth's axial precession frequency and the evolution of the Earth-Moon system derived from cyclostratigraphy.

The preservation of Milankovitch cycles in the stratigraphic record provides independent geological information to study our ancient solar system and can be leveraged to constrain existing theoretical models. Here, we identify 34 high-quality cyclostratigraphic records spanning the past 650 million years and use them to infer the evolution of the Earth-Moon system through a Bayesian inversion method. We reconstruct the time evolution of Earth's axial precession frequency, lunar distance, length of day, and the periods of obliquity and climatic precession cycles. The results indicate an interval of high tidal energy dissipation in the Earth-Moon system at ~300 to 200 million years ago, and are broadly consistent with an independently calculated tidal evolution model. Our results provide an improved determination of the past periods of obliquity and climatic precession for astrochronology applications and yield important constraints on the history of tidal energy dissipation during the Phanerozoic Eon.

Seawater sulfate dynamics and a new tipping point in the Earth system

Seawater sulfate (SO42−) concentrations have changed by orders of magnitude in response to atmospheric and ocean redox dynamics throughout Earth’s history. A fundamental model that constrains seawater SO42− dynamics based on the principles of mass balance, however, is still lacking. Here, we used a dynamical systems approach to determine the effects of global source and sink strengths on seawater SO42− concentrations. Our stochastic analysis of the SO42− mass balance revealed two most probable seawater SO42− concentration ranges: one under widespread oceanic anoxic conditions with SO42− concentrations <1000 µM, and the other with SO42− concentrations around or above 10,000 µM under widely oxygenated ocean conditions. Swings between these two seawater SO42− concentration ranges are notably evident during the Phanerozoic Eon and developed in response to reoccurring oceanic anoxic events. We also identified a threshold for the extent of oceanic anoxia above which seawater SO42− concentrations collapse to <1000 µM, with corresponding impacts on global biogeochemical cycles, biology, and climate.

Using deep learning to integrate paleoclimate and global biogeochemistry over the Phanerozoic Eon

Abstract. Databases of 3D paleoclimate model simulations are increasingly used within global biogeochemical models for the Phanerozoic Eon. This improves the accuracy of the surface processes within the biogeochemical models, but the approach is limited by the availability of large numbers of paleoclimate simulations at different pCO2 levels and for different continental configurations. In this paper we apply the Frame Interpolation for Large Motion (FILM) deep learning method to a set of Phanerozoic paleoclimate model simulations to upscale their time resolution from one model run every ∼25 million years to one model run every 1 million years (Myr). Testing the method on a 5 Myr time-resolution set of continental configurations and paleoclimates confirms the accuracy of our approach when reconstructing intermediate frames from configurations separated by up to 40 Myr. We then apply the method to upscale the paleoclimate data structure in the SCION climate-biogeochemical model. The interpolated surface temperature and runoff are reasonable and present a logical progression between the original key frames. When updated to use the high-time-resolution climate data structure, the SCION model predicts climate shifts that were not present in the original model outputs due to its previous use of widely spaced datasets and simple linear interpolation. We conclude that a time resolution of ∼10 Myr in Phanerozoic paleoclimate simulations is likely sufficient for investigating the long-term carbon cycle and that deep learning methods may be critical in attaining this time resolution at reasonable computational expense, as well as for developing new fully continuous methods in which 3D continental processes are able to translate over a moving continental surface in deep time. However, the efficacy of deep learning methods in interpolating runoff data, compared to that of paleogeography and temperature, is diminished by the heterogeneous distribution of runoff. Consequently, interpolated climates must be confirmed by running a paleoclimate model if scientific conclusions are to be based directly on them.

PALEOPARASITOLOGICAL CONTRIBUTIONS TO THE STUDY ON ANCIENT INFECTIONS OF HOMINIDS AND OTHER VERTEBRATES IN BRAZIL: A REVIEW

Paleoparasitology is an interdisciplinary science that studies the parasitic infections in the past, using fossils and subfossils recovered from archeological and paleontological lithostratigraphic units. During the 20th and 21st centuries, it has improved the biological knowledge on helminths and protozoans, as well as provided numerous sociocultural insights into the past civilizations. Here, we present an updated review of the paleoparasitological contributions to the analyses of ancient infections in vertebrate remains recovered from different regions of Brazil. Since its emergence, the Paleoparasitology has been important to a multidisciplinary knowledge related to sociocultural aspects of the American Pre-Columbian civilizations and may provide an important ecological, evolutionary, and biogeographical understanding of parasites of vertebrates other than humans throughout the geological time. The present data compilation suggests a prominent role in the scientific community assumed by paleoparasitological approaches, since they have been contributing to a better understanding of helminth and protozoan distribution in South America, during the Phanerozoic eon and consolidating the Paleoparasitology as a global science. Keywords: Coprolite, mummy, helminth, protozoa.

Role of volcanism and impact heating in mass extinction climate shifts

This study investigates the mechanisms underlying the varied climate changes witnessed during mass extinctions in the Phanerozoic Eon. Climate shifts during mass extinctions have manifested as either predominant global cooling or predominant warming, yet the causes behind these occurrences remain unclear. We emphasize the significance of sedimentary rock temperature in comprehending these climate shifts. Our research reveals that low-temperature heating of sulfide leads to global cooling through the release of sulfur dioxide (SO2), while intermediate-temperature heating of hydrocarbons and carbonates releases substantial carbon dioxide (CO2), contributing to global warming. High-temperature heating additionally generates SO2 from sulfate, further contributing to global cooling. Different degrees of contact heating of the host rock can lead to different dominant volatile gas emissions, crucially driving either warming or cooling. Moreover, medium to high-temperature shock-heating resulting from asteroid impacts produces soot from hydrocarbons, also contributing to global cooling. Large-scale volcanic activity and asteroid impacts are both events that heat rocks, emitting the same gases and particles, causing climate changes. The findings elucidate the critical role of heating temperature and heating time in understanding major climate changes during mass extinctions.

Quantitative estimation of global mean precipitation throughout the Phanerozoic era

Quantitative estimation of global mean precipitation throughout the Phanerozoic era

An evolutionary system of mineralogy, Part VIII: The evolution of metamorphic minerals

Abstract Part VIII of the evolutionary system of mineralogy focuses on 1220 metamorphic mineral species, which correspond to 755 root mineral kinds associated with varied metamorphic rock types, most of which likely formed prior to the Phanerozoic Eon. A catalog of the mineral modes of 2785 metamorphic rocks from around the world reveals that 94 mineral kinds often occur as major phases. Of these common metamorphic minerals, 66 are silicates, 14 are oxides or hydroxides, 8 are carbonates or phosphates, 4 are sulfides, and 2 are polymorphs of carbon. Collectively, these 94 minerals incorporate 23 different essential chemical elements. Patterns of coexistence among these 94 minerals, as revealed by network analysis and Louvain community detection, point to six major communities of metamorphic phases, three of which correspond to different pressure-temperature (P-T) regimes of metamorphosed siliceous igneous and sedimentary rocks, while three represent thermally altered carbonate and calc-silicate lithologies. Metamorphic rocks display characteristics of an evolving chemical system, with significant increases in mineral diversity and chemical complexity through billions of years of Earth history. Earth's first metamorphic minerals 27 formed in thermally altered xenoliths and contact zones (hornfels and sanidinite facies) associated with early Hadean igneous activity (> 4.5 Ga). The appearance of new Hadean lithologies, including clay-rich sediments, arkosic sandstones, and carbonates, provided additional protoliths for thermal metamorphism prior to 4.0 Ga. Orogenesis and erosion exposed extensive regional metamorphic terrains, with lithologies corresponding to the Barrovian sequence of index mineral metamorphic zones appearing by the Mesoarchean Era (> 2.8 Ga). More recently, rapid subduction and rebound of crustal wedges, coupled with a shallowing geothermal gradient, has produced distinctive suites of blueschist, eclogite, and ultrahigh pressure metamorphic suites (< 1.0 Ga). The evolution of metamorphic minerals thus exemplifies changes in physical and chemical processes in Earth's crust and upper mantle.

Geographic range of plants drives long-term climate change

Long computation times in vegetation and climate models hamper our ability to evaluate the potentially powerful role of plants on weathering and carbon sequestration over the Phanerozoic Eon. Simulated vegetation over deep time is often homogenous, and disregards the spatial distribution of plants and the impact of local climatic variables on plant function. Here we couple a fast vegetation model (FLORA) to a spatially-resolved long-term climate-biogeochemical model (SCION), to assess links between plant geographical range, the long-term carbon cycle and climate. Model results show lower rates of carbon fixation and up to double the previously predicted atmospheric CO2 concentration due to a limited plant geographical range over the arid Pangea supercontinent. The Mesozoic dispersion of the continents increases modelled plant geographical range from 65% to > 90%, amplifying global CO2 removal, consistent with geological data. We demonstrate that plant geographical range likely exerted a major, under-explored control on long-term climate change.

Evidence of huge evaporite mine clusters under extreme arid climatic conditions of Cretaceous to Paleogene in South China: Example of the Huichang large salt deposit

Large amounts of evaporites are distributed throughout all epochs of the Phanerozoic eon, which is closely related to important tectonic activities and extremely arid paleoclimates in specific geological periods. During the Cretaceous-Paleogene period, the Earth's climate was always arid, providing unique conditions for evaporite formation. The large number of evaporites in South China Block is an important part of the puzzle in the study of massive global evaporite deposition. The Huichang typical salt deposit is in the Upper Cretaceous Zhoutian Formation in the Huichang Basin, where the rock salt are interbedded with argillaceous rocks, constituting a rhythmical deposit. Halite was dominant among the saline minerals, followed by gypsum. The homogenization temperatures of halite inclusions ranged from 11.1 ℃ to 24.7 ℃, with a concentration of 15.1–22.2 ℃ and an average of 17.9 ℃. The δEu and δCe of the argillaceous rock studied ranged from 0.84 to 1.14 and 0.96–1.06, respectively, which combined with V/(V + Ni), V/Cr, Ni/Co, and U/Th indicators reflect that the environmental of the sedimentary water body has a weak Redox property. The spore-pollen assemblage is dominated by gymnosperms (Classopollis annulatu and Classopollis minimus) and fern spores (Schizaeoisporites kulandyensis), representing an arid environment in the early stage, and the increase in hygrophilous Taxodiaceaepollenites hiatus in the later stage indicates a shift from an arid to a humid climate. The Milankovitch Earth orbital periods of 401, 93–138, 38–45, 24–27, and 14 kyr were identified by the multiple rhythmic deposition of the rock salt and argillaceous rocks, indicating that the deposition was controlled by climate change, which was driven by the long-and-short eccentricity, obliquity, and precession cycle of the Earth orbit. In addition, the differences in the thickness and alternating frequency of the upper, lower, and middle sediments in the 'Huichang Gypsum-salt Section' also indicated that the intensity and duration of regional tectonic activities and the supply of material sources are important factors that control rock salt deposition. The strong subduction of the paleo-Pacific plate into the Eurasian plate caused the paleogeographic pattern of high in the east and low in the west, in the South China Block during the Cretaceous period, forming a large number of 'high mountain and deep basin' tectonic groups. Under the conditions of an extremely arid climate, combined with the coupling effect of regional tectonic activities and material sources, a large evaporite mineral concentration area was formed in South China, with the Huichang salt basin as a typical representative.

A new reconstruction of Phanerozoic Earth evolution: Toward a big-data approach to global paleogeography

Reliable reconstruction of global paleogeography through deep geologic time provides a key surface boundary condition for investigating many first-order Earth system and geodynamic processes such as climate change, geomagnetic field stability, regional geological and tectonic history, and biological evolution. Over the past decade, the development of the GPlates software led to a resurgence of community efforts in creating state-of-the-art plate tectonic models that integrate paleomagnetic, geological, and paleontological datasets, resulting in a plethora of reconstruction models. In this paper, we briefly review the strengths and weaknesses of existing global models, which depict alternative and sometimes contradictory tectonic scenarios. We then provide an overview of the general procedure in our construction of a revised Phanerozoic global paleogeographic model, including (1) evaluation of the paleomagnetic data that quantitatively dictate continental paleolatitudes and orientations, (2) selection of reference frames in which continents were positioned, and (3) calibration of continental longitudes in deep time. We update the apparent polar wander paths (APWPs) of the major continents using a recently developed weighted running mean approach, which rectifies two major issues with the conventional running mean approach regarding missing paleopoles in age windows and the enforced assumption of the Fisherian distribution. We re-evaluate the Phanerozoic continental reconstructions in a paleomagnetic framework using the updated APWPs, and calibrate continental paleolongitudes following the extended orthoversion hypothesis by placing the centroids of supercontinents Rodinia and Pangea 90° apart, with that of Rodinia at ∼90°E. We emphasize that the resulting global model is not intended to provide solutions to all global tectonic issues throughout the entire Phanerozoic Eon. Rather, we present our results as one viable model of Phanerozoic tectonic history which, like many existing interpretations, is built upon our understanding of the paleomagnetic, geological, and paleontological observations. Our goals are for this study to highlight the fundamental differences between reconstruction models and to serve as a starting point for future studies to fill key data gaps and test alternative hypotheses and tectonic scenarios.

Landscape dynamics and the Phanerozoic diversification of the biosphere

The long-term diversification of the biosphere responds to changes in the physical environment. Yet, over the continents, the nearly monotonic expansion of life started later in the early part of the Phanerozoic eon1 than the expansion in the marine realm, where instead the number of genera waxed and waned over time2. A comprehensive evaluation of the changes in the geodynamic and climatic forcing fails to provide a unified theory for the long-term pattern of evolution of life on Earth. Here we couple climate and plate tectonics models to numerically reconstruct the evolution of the Earth’s landscape over the entire Phanerozoic eon, which we then compare to palaeo-diversity datasets from marine animal and land plant genera. Our results indicate that biodiversity is strongly reliant on landscape dynamics, which at all times determine the carrying capacity of both the continental domain and the oceanic domain. In the oceans, diversity closely adjusted to the riverine sedimentary flux that provides nutrients for primary production. On land, plant expansion was hampered by poor edaphic conditions until widespread endorheic basins resurfaced continents with a sedimentary cover that facilitated the development of soil-dependent rooted flora, and the increasing variety of the landscape additionally promoted their development.

Crustal and tectonic structure of Northern Mozambique inferred by 2D gravity modeling

The northern region of Mozambique has a complex geological history, with an evolution that spans from the Precambrian Era to the Phanerozoic Era. In this work, we have integrated gravity and geothermal data to delineate the geotectonic evolution of the region, by estimating the thickness of the crust and the lithosphere through which was essential to generate a representative crustal model. It was necessary to complement the knowledge of structural geometry and tectonic evolution of the region. The data used in this study are the Bouguer and geoid anomalies, topography data, and radiogenic heat. These data were pre-processed, topography and geoid anomaly data were filtered by low-pass filter in the frequency and harmonic domains to remove undesirable effects associated with the sources. The data were used to estimate the thickness of the crust and lithosphere, as well as to determine the mean density distribution within the mantle. This was achieved by using a one-dimensional approach, considering the principle of local isostatic compensation, associated with equations governing the distribution of temperature in the crust. The Bouguer anomaly was used to generate a representative crustal 2D model of this region. The results showed that the crust is thinner in Nampula and Cabo Delgado provinces, with thickness ranging from 27 to 31 km, whereas in Niassa varies between 33 and 39 km. The analysis of lithospheric thickness indicates that the provinces of Nampula and Cabo Delgado present a thinning of the lithosphere, with values ranging from 150 to 165 km. Rather than Niassa province which exhibits a thicker lithosphere, ranging from 165 to 195 km. The obtained results underwent a comparative analysis with prior investigations, unveiling a noteworthy concurrence among these findings.

Oxygen bounty for Earth-like exoplanets: spectra of Earth through the Phanerozoic

ABSTRACT In the search for life in the Universe, Earth provides a template of evolution for the one habitable planet we know. Earth’s atmospheric composition has changed significantly throughout its history. The last 500 Myr – the Phanerozoic Eon, which includes the origins of animals, dinosaurs, and land plants – saw oxygen rise from ≤10 per cent to 35 per cent. But the resulting transmission spectra are a crucial missing piece in our search for signs of life in exoplanet atmospheres. Here, we simulate the atmosphere and transmission spectra of the Phanerozoic, using estimates from established climate models, and present the first high-resolution transmission spectra for Phanerozoic Earth. We demonstrate that the spectral biosignature pairs O2 + CH4 and O3 + CH4 in the atmosphere of a transiting Earth-like planet would indicate a biosphere, with O2 and O3 features potentially stronger than for modern Earth. The full model and high-resolution transmission spectra, covering 0.4–20 µm, are available online and provides a tool to plan and optimize observations, train retrieval methods, and interpret upcoming observations with ground- and space-based telescopes.

Stratospheric dynamics modulates ozone layer response to molecular oxygen variations

Photolysis of molecular oxygen (O2) sustains the stratospheric ozone layer and is thereby protecting living organisms on Earth by absorbing harmful ultraviolet radiation. In the past, atmospheric O2 levels were not constant, and their variations are thought to be responsible for the extinction of some species due to the thinning of the ozone layer. Over the Phanerozoic Eon (last ∼500 Mio years), the O2 volume mixing ratio ranged between 10% and 35% depending on the level of photosynthetic activity of plants and oceans. Previous estimates, mostly performed by simplified 1-D models, showed different ozone (O3) responses to atmospheric O2 changes within this range, such as monotonically positive or negative correlations, or displaying a maximum in the O3 column around a certain O2 level. Here, we assess the ozone layer sensitivity to atmospheric O2 varying between 5% and 40% with a state-of-the-art 3-D chemistry-climate model (CCM). Our findings show that the O3 layer thickness maximizes around the current mixing ratio of O2, 21% ± 5%, while lower or higher levels of O2 result globally in a reduction of total column O3. At low latitudes, the total column O3 is less sensitive to O2 variations, because of the “self-healing” effect, namely, a vertical dipole in the tropical ozone response. Mid- and high-latitude O3 columns that are largely affected by transport of O3 from the tropics, however, are much more sensitive to O2 with changes up to 20 DU even for small (±5%) O2 perturbations. We show that these variations are largely driven by the radiative impact of O3 on stratospheric temperatures and on the strength of the Brewer-Dobson circulation (BDC), indicating chemistry-radiation-transport feedback. High O2 cases result in an acceleration of the BDC and vice versa, which always works in favor of the negative part of the O3 anomaly dipole in the tropics being more effectively transported to the mid- and high-latitudes than the positive one. Although there are other factors strongly influencing O3/O2 relationship on the Phanerozoic Eon timescales that have not been considered here, our results and the presented mechanism bring useful insights for other studies focusing on the long-term O3/O2 relationship.

On Earth’s habitability over the Sun’s main-sequence history: joint influence of space weather and Earth’s magnetic field evolution

ABSTRACT The aim of this study is to analyse the Earth habitability with respect to the direct exposition of the Earth atmosphere to the solar wind (SW) along the Sun’s evolution on the main sequence including the realistic evolution of the space weather conditions and the Earth magnetic field. The MHD code PLUTO in spherical coordinates is applied to perform parametric studies with respect to the SW dynamic pressure and the interplanetary magnetic field intensity for different Earth magnetic field configurations. Quiet space weather conditions may not impact the Earth habitability. On the other hand, the impact of interplanetary coronal mass ejections (ICME) could lead to the erosion of the primary Earth atmosphere during the Hadean eon. A dipolar field of 30 μT is strong enough to shield the Earth from the Eo-Archean age as well as 15 and 5 μT dipolar fields from the Meso-Archean and Meso-Proterozoic, respectively. Multipolar weak field period during the Meso-Proterozoic age may not be a threat for ICME-like space weather conditions if the field intensity is at least 15 μT and the ratio between the quadrupolar (Q) and dipolar (D) coefficients is $\frac{Q}{D} \le 0.5$. By contrast, the Earth habitability in the Phanerozoic eon (including the present time) can be hampered during multipolar low field periods with a strength of 5 μT and $\frac{Q}{D} \ge 0.5$ associated with geomagnetic reversals. Consequently, the effect of the SW should be considered as a possible driver of Earth’s habitability.

Tightly coupled Ca-Zn-Sr isotope co-variations in basalts caused by recycled calcium carbonate in the mantle source

The deep carbon cycle requires tracers to understand carbon sequestration and mobility in the deep Earth. Recently, the use of metal stable isotopes has emerged as a promising and innovative approach to address element cycles, such as the use of magnesium and zinc isotopes to trace the magnesium carbonate cycle. However, despite the prevalence of calcium carbonate as the dominant sedimentary carbonate during the Phanerozoic era, its tracking through the use of metal stable isotopes has proven challenging. Here we show that deep subduction of Phanerozoic calcium carbonates can significantly decrease the δ44/40Ca value, while simultaneously increasing the δ66Zn value and 87Sr/86Sr ratio of the mantle. The Neogene Dalihu basalts in Inner Mongolia have high 87Sr/86Sr ratios, ranging from 0.7058 to 0.7063, which are positively correlated with Sr/Nd ratio, indicating the presence of sedimentary carbonate within their mantle source. The Dalihu basalts exhibit significantly lower δ44/40Ca values (0.51 to 0.70‰) but higher δ66Zn values (0.35 to 0.45 ‰) than the mantle. These low δ44/40Ca values cannot be attributed to partial melting, even when considering the jadeite effect. Our calculations indicate that adding 5–10% recycled calcium carbonate into the mantle source explains the high 87Sr/86Sr ratio and δ66Zn values but low δ44/40Ca values of the Dalihu basalt. Therefore, recycled calcium carbonate directly influences correlated Ca-Zn-Sr isotope variation, thereby providing compelling evidence for its role in the deep carbon cycle. Our findings suggest that combining metal stable isotopes with radiogenic Sr isotope is a powerful tracer of the deep carbon cycle.

Variations in climate habitability parameters and their effect on Earth's biosphere during the Phanerozoic Eon

Essential insights on the characterization and quality of a detectable biosphere are gained by analyzing the effects of its environmental parameters. We compiled environmental and biological properties of the Phanerozoic Eon from various published data sets and conducted a correlation analysis to assess variations in parameters relevant to the habitability of Earth’s biosphere. We showed that environmental parameters such as oxygen, global average surface temperatures, runoff rates and carbon dioxide are interrelated and play a key role in the changes of biomass and biodiversity. We showed that there were several periods with a highly thriving biosphere, with one even surpassing present day biodiversity and biomass. Those periods were characterized by increased oxygen levels and global runoff rates, as well as moderate global average surface temperatures, as long as no large or rapid positive and/or negative temperature excursions occurred. High oxygen contents are diagnostic of biomass production by continental plant life. We find that exceptionally high oxygen levels can at least in one instance compensate for decreased relative humidities, providing an even more habitable environment compared to today. Beyond Earth, these results will help us to understand how environmental parameters affect biospheres on extrasolar planets and guide us in our search for extraterrestrial life.

Controls on potassium incorporation in foraminifera and other marine calcifying organisms

Seawater chemistry exerts an important control on the incorporation of trace elements into the shells of marine calcifying organisms. Variability in the major ion chemistry of seawater is a tracer of past geological processes, and the influence of seawater chemistry on trace element incorporation in calcium carbonate can be harnessed to determine changes in the composition of seawater through time. Here, we investigate whether key oceanographic parameters (temperature, salinity, and the carbonate system) affect the incorporation of potassium (K) into foraminiferal calcite, and explore the utility of K/Ca ratios in foraminifera as an indicator of past variability in the seawater Ca2+ concentration. We analysed both low-Mg and high-Mg modern foraminifera, including planktonic (Globigerinoides ruber) and shallow-dwelling larger benthic (Operculina ammonoides) species, using laser-ablation sector-field inductively-coupled plasma mass spectrometry (LA-SF-ICPMS). Both species show no resolvable influence of temperature, salinity, pH, or [CO32−] on K incorporation across the range that these vary at our samples sites. In order to determine the effect of the seawater Ca concentration ([Ca2+]sw) on K incorporation, we analysed laboratory-cultured O. ammonoides, the close living relative of the abundant Eocene Nummulites, grown at four different [Ca2+]sw. We find a significant relationship between seawater and shell K/Ca, albeit with a shallower slope compared to most other trace elements which we suggest is driven by a crystal growth rate effect on K incorporation, constrained using culture experiments of O. ammonoides grown at different pH. If the K+ concentration has remained relatively constant throughout the Phanerozoic Eon, our data may pave the way forward for the use of K/Ca as a direct proxy for past [Ca2+]sw variability. Alternatively, coupling K/Ca with the similar Na/Ca proxy would allow more accurate reconstruction of [Ca2+]sw or verification of whether [K+]sw and [Na+]sw have indeed remained within narrow bounds.

Diversity-Dependent Diversification in the History of Marine Animals.

AbstractBy comparing detrended estimates of diversity (taxonomic richness) and rates of origination, extinction, and net diversification, I show that at the global scale over the course of the Phanerozoic eon, rates of diversification and origination are negatively correlated with diversity. By contrast, extinction rates are only weakly correlated with diversity for the most part. These results hold for both genus- and species-level data and for many alternative analytical protocols. The asymmetry between extinction on the one hand and origination and net diversification on the other hand supports a model whereby extinction is largely driven by abiotic perturbations, with subsequent origination filling the void left by depleted diversity. Diversity dependence is somewhat weaker, but still evident, if the initial Ordovician radiation or rebounds from major mass extinctions are omitted from analysis; thus, diversity dependence is influenced, but not dominated, by these special intervals of Earth history. In the transition from Paleozoic to post-Paleozoic time, diversity dependence of origination weakens while that of extinction strengthens; however, diversity dependence of net diversification barely changes in strength. Despite nuances, individual clades largely yield results consistent with those for the aggregate data on all animals. On the whole, diversity-dependent diversification appears to be a pervasive factor in the macroevolution of marine animal life.