Respiratory protein-driven selectivity during the Permian-Triassic mass extinction.

Extinction selectivity determines the direction of macroevolution, especially during mass extinction; however, its driving mechanisms remain poorly understood. By investigating the physiological selectivity of marine animals during the Permian-Triassic mass extinction, we found that marine clades with lower O2-carrying capacity hemerythrin proteins and those relying on O2 diffusion experienced significantly greater extinction intensity and body-size reduction than those with higher O2-carrying capacity hemoglobin or hemocyanin proteins. Our findings suggest that animals with high O2-carrying capacity obtained the necessary O2 even under hypoxia and compensated for the increased energy requirements caused by ocean acidification, which enabled their survival during the Permian-Triassic mass extinction. Thus, high O2-carrying capacity may have been crucial for the transition from the Paleozoic to the Modern Evolutionary Fauna.

Mid-latitudinal habitable environment for marine eukaryotes during the waning stage of the Marinoan snowball glaciation.

During the Marinoan Ice Age (ca. 654-635 Ma), one of the 'Snowball Earth' events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event, as evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedded with glacial diamictites of the late Cryogenian Nantuo Formation in South China. However, the environmental conditions that allowed these organisms to thrive are poorly known. Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia for eukaryotic organisms during the waning stage of the Marinoan Ice Age.

A Mesozoic fossil lagerstätte from 250.8 million years ago shows a modern-type marine ecosystem.

Finely preserved fossil assemblages (lagerstätten) provide crucial insights into evolutionary innovations in deep time. We report an exceptionally preserved Early Triassic fossil assemblage, the Guiyang Biota, from the Daye Formation near Guiyang, South China. High-precision uranium-lead dating shows that the age of the Guiyang Biota is 250.83 +0.07/-0.06 million years ago. This is only 1.08 ± 0.08 million years after the severe Permian-Triassic mass extinction, and this assemblage therefore represents the oldest known Mesozoic lagerstätte found so far. The Guiyang Biota comprises at least 12 classes and 19 orders, including diverse fish fauna and malacostracans, revealing a trophically complex marine ecosystem. Therefore, this assemblage demonstrates the rapid rise of modern-type marine ecosystems after the Permian-Triassic mass extinction.

Thresholds of temperature change for mass extinctions.

Climate change is a critical factor affecting biodiversity. However, the quantitative relationship between temperature change and extinction is unclear. Here, we analyze magnitudes and rates of temperature change and extinction rates of marine fossils through the past 450 million years (Myr). The results show that both the rate and magnitude of temperature change are significantly positively correlated with the extinction rate of marine animals. Major mass extinctions in the Phanerozoic can be linked to thresholds in climate change (warming or cooling) that equate to magnitudes >5.2 °C and rates >10 °C/Myr. The significant relationship between temperature change and extinction still exists when we exclude the five largest mass extinctions of the Phanerozoic. Our findings predict that a temperature increase of 5.2 °C above the pre-industrial level at present rates of increase would likely result in mass extinction comparable to that of the major Phanerozoic events, even without other, non-climatic anthropogenic impacts.

Six-fold increase of atmospheric pCO2 during the Permian-Triassic mass extinction.

The Permian-Triassic mass extinction was marked by a massive release of carbon into the ocean-atmosphere system, evidenced by a sharp negative carbon isotope excursion. Large carbon emissions would have increased atmospheric pCO2 and caused global warming. However, the magnitude of pCO2 changes during the PTME has not yet been estimated. Here, we present a continuous pCO2 record across the PTME reconstructed from high-resolution δ13C of C3 plants from southwestern China. We show that pCO2 increased from 426 +133/-96 ppmv in the latest Permian to 2507 +4764/-1193 ppmv at the PTME within about 75 kyr, and that the reconstructed pCO2 significantly correlates with sea surface temperatures. Mass balance modelling suggests that volcanic CO2 is probably not the only trigger of the carbon cycle perturbation, and that large quantities of 13C-depleted carbon emission from organic matter and methane were likely required during complex interactions with the Siberian Traps volcanism.

Refined protocol for δ13 C analysis of calcite and dolomite in carbonate mixture samples.

RATIONALE: The carbon isotope composition of carbonates is widely used in petrology and paleoenvironments as a proxy for carbon sources and environmental parameters during mineral formation or late diagenesis. However, most carbonate minerals in nature are complicated mixtures (i.e., coexisting calcite and dolomite). Precise separation of individual signals in mixed carbonate minerals is essential to obtain information regarding these indexes because of the diverse isotopic behavior of different minerals. METHODS: The conditions for pretreating calcite-dolomite mixtures to determine each of their δ13 C values were optimized with a series of experiments varying the purging and reaction conditions using an isotope ratio mass spectrometer equipped with an online GasBench II interface. Sequential phosphoric acid reactions of pure calcite and dolomite were performed to measure the characteristics of single minerals under different temperatures and reaction times. Artificial mixtures with varied proportions of calcite and dolomite were used to verify the precision of the proposed method. RESULTS: The optimized pretreatment conditions for δ13 C analysis of calcite in the mixture involved purging the sample bottle using helium and then reacting it with 99% H3 PO4 for 100 min in a cold water bath at 2°C. The optimized pretreatment conditions for δ13 C analysis of dolomite in the mixture involved purging the sample bottle using helium gas after δ13 Ccal measurement and reacting it with H3 PO4 on a heating plate for 10 h at 45°C. CONCLUSIONS: This study introduced a workflow with ultimate precision for the selective δ13 C measurements of calcite-dolomite mixtures combining a GasBench II with a continuous flow isotope ratio mass spectrometer.

The onset of widespread marine red beds and the evolution of ferruginous oceans.

Banded iron formations were a prevalent feature of marine sedimentation ~3.8-1.8 billion years ago and they provide key evidence for ferruginous oceans. The disappearance of banded iron formations at ~1.8 billion years ago was traditionally taken as evidence for the demise of ferruginous oceans, but recent geochemical studies show that ferruginous conditions persisted throughout the later Precambrian, and were even a feature of Phanerozoic ocean anoxic events. Here, to reconcile these observations, we track the evolution of oceanic Fe-concentrations by considering the temporal record of banded iron formations and marine red beds. We find that marine red beds are a prominent feature of the sedimentary record since the middle Ediacaran (~580 million years ago). Geochemical analyses and thermodynamic modelling reveal that marine red beds formed when deep-ocean Fe-concentrations were > 4 nM. By contrast, banded iron formations formed when Fe-concentrations were much higher (> 50 µM). Thus, the first widespread development of marine red beds constrains the timing of deep-ocean oxygenation.The evolution of oceanic redox state in the past is poorly known. Here, the authors present a temporal record of banded iron formations and marine red beds, which indicate deep-ocean oxygenation occurred in the middle Ediacaran, coinciding with the onset of widespread marine red beds.

Early Triassic wrinkle structures on land: stressed environments and oases for life.

Wrinkle structures in rocks younger than the Permian-Triassic (P-Tr) extinction have been reported repeatedly in marine strata, but rarely mentioned in rocks recording land. Here, three newly studied terrestrial P-Tr boundary rock succession in North China have yielded diverse wrinkle structures. All of these wrinkles are preserved in barely bioturbated shore-shallow lacustrine siliciclastic deposits of the Liujiagou Formation. Conversely, both the lacustrine siliciclastic deposits of the underlying Sunjiagou Formation and the overlying Heshanggou Formation show rich bioturbation, but no wrinkle structures or other microbial-related structures. The occurrence of terrestrial wrinkle structures in the studied sections reflects abnormal hydrochemical and physical environments, presumably associated with the extinction of terrestrial organisms. Only very rare trace fossils occurred in the aftermath of the P-Tr extinction, but most of them were preserved together with the microbial mats. This suggests that microbial mats acted as potential oases for the surviving aquatic animals, as a source of food and oxygen. The new finds suggests that extreme environmental stresses were prevalent both in the sea and on land through most of the Early Triassic.

Anoxia/high temperature double whammy during the Permian-Triassic marine crisis and its aftermath.

The Permian-Triassic mass extinction was the most severe biotic crisis in the past 500 million years. Many hypotheses have been proposed to explain the crisis, but few account for the spectrum of extinction selectivity and subsequent recovery. Here we show that selective losses are best accounted for by a combination of lethally warm, shallow waters and anoxic deep waters that acted to severely restrict the habitable area to a narrow mid-water refuge zone. The relative tolerance of groups to this double whammy provides the first clear explanation for the selective extinction losses during this double-pulsed crisis and also the fitful recovery. Thus, high temperature intolerant shallow-water dwellers, such as corals, large foraminifers and radiolarians were eliminated first whilst high temperature tolerant ostracods thrived except in anoxic deeper-waters. In contrast, hypoxia tolerant but temperature intolerant small foraminifers were driven from shallow-waters but thrived on dysoxic slopes margins. Only those mollusc groups, which are tolerant of both hypoxia and high temperatures, were able to thrive in the immediate aftermath of the extinction. Limited Early Triassic benthic recovery was restricted to mid-water depths and coincided with intervals of cooling and deepening of water column anoxia that expanded the habitable mid-water refuge zone.