A synthesis of the Cretaceous wildfire record related to atmospheric oxygen levels?

The Cretaceous was a significant greenhouse period in Earth's history with higher atmospheric CO_(2) levels and temperatures than today. Although evidence of combustion has been widely described from the Cretaceous deposits, our understanding of the spatiotemporal diversification pattern and process of the Cretaceous wildfires is still limited. In this study, we comprehensively synthesize a total of 271 published Cretaceous wildfire occurrences based on the by-products of burning, including fossil charcoal, pyrogenic inertinite(fossil charcoal in coal), and pyrogenic polycyclic aromatic hydrocarbons(PAHs). Spatially, the dataset shows a distinctive distribution of reported wildfire evidence characterized by high concentration in the middle latitudinal areas of the Northern Hemisphere(30°N-60°N) over the Cretaceous. Temporally, an overall increasing trend of the reported wildfire data from the Early Cretaceous to the Late Cretaceous is coincident with higher atmospheric O_(2) levels. However, the spatial and temporal patterns may result from many types of factors, such as taphonomy, preservation, and researcher biases, instead of a real picture of the Cretaceous wildfire evolution. To better understand the spatiotemporal diversification of the Cretaceous wildfire, more investigations on the record of wildfire occurrences during this period would be necessary in the future.

Reaction behavior of trace oxygen during combustion of falling FeSi75 powder in a nitrogen flow

To explore the reaction behavior of trace oxygen during the flash combustion process of falling FeSi75 powder in a nitrogen flow, a flash-combustion-synthesized Fe-Si;N;sample was heat-treated to remove SiO;. The samples before and after the treatment were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, and the formation mechanism of SiO;was investigated. The results show that SiO;in the Fe-Si;N;is mainly located on the surface or around the Si;N;particles in dense areas, existing in both crystalline and amorphous states; when the FeSi75 particles, which are less than 0.074 mm in size, fell in up-flowing hot N;stream, trace oxygen in the N;stream did not significantly hinder the nitridation of FeSi75 particles as it was consumed by the surface oxidation of the generated Si;N;particles to form SiO;. At the reaction zone, the oxidation of Si;N;particles decreased the oxygen partial pressure in the N;stream and greatly reduced the opportunity for FeSi75 particles to be oxidized into SiO;; by virtue of the SiO;film developed on the surface, the Si;N;particles adhered to each other and formed dense areas in the material.

Impact of oxygen in electrical properties and hot-carrier stress-induced degradation of GaN high electron mobility transistors

The role of the oxygen in AlGaN/GaN high electron mobility transistors(HEMTs)before and after semi-on state stress was discussed.Comparing with the electrical characteristics of the devices in vacuum,air,and oxygen atmosphere,it is revealed that the oxygen has significant influence on the electric characteristics and the hot-carrier-stress-induced degradation of the device.Comparing with the situation in vacuum,the gate leakage increased an order of magnitude in oxygen and air atmosphere.Double gate structure was used to separate the barrier leakage and surface leakage of AlGaN/GaN HEMT it is found that surface leakage is the major influencing factor in gate leakage of SiN-passivated devices before and after semi-on state stress.During semi-on state stress in the oxygen atmosphere,the electric-field-driven oxidation process promoted the oxidation of the nitride layer,and the oxidation layer in the SiN/AlGaN interface leads to the decreasing of the surface leakage.

Morphology and Structure of SiO_2 Film Using Thermal Oxidation Process on(111)Silicon Crystals in Dry Oxygen Atmosphere

By means of scanning electron microscope(SEM)and high voltage electron microscope(HVEM)we have observed and analysed morphology and micro-structure of silicon oxide film with different thickness formed on(111)silicon monocrystal under dry oxygen atmosphere at 1100℃.Compared with their oxidation kinetic curves consisted of three stages,we suggested a mechanism on forming silicon oxide film.According to electron and X-ray diffraction analyses the silicon oxide films consisted of silica with different crystal structure.We also have discussed a stacking fault and a dislocation formed in the Si-Sio_2 interface region simulaneously forming silicon oxide film.

Atmospheric and Oceanic Oxygenation and Evolution of Early Life on Earth: New Contributions from China

The buildup of oxygen in the Earth＇s atmosphere and oceans has fundamentally reshaped the dynamics of nearly all major biogeochemical cycles and ultimately paved the way for the diversification of complex life on Earth. Over the past decades there have been sustained efforts to develop a more comprehensive understanding of ocean-atmosphere redox evolution and its relationship to the evolution of early life （Fig. 1）. It is generally accepted that the development of oxygenic photosynthesis at ~2.7 Ga may have been responsible for the Great Oxidation Event （GOE） at the beginning of the Proterozoic Eon, whereas a second big O2 rise at the end of the Proterozoic Eon （the so-called Neoproterozoic Oxidation Event or NOE） was responsible for the diversification of metazoans （Lyons et al., 2014）.

Inertinite in coal and its geoenvironmental significance:Insights from AI and big data analysis

Inertinite,as an important and abundant maceral group in coal,is critical for the study of palaeowildfires and their roles in the Earth’s ecosystems.Recently,there has been a significant amount of research on the relationship between palaeowildfire,palaeoclimate change and palaeovegetation evolution based on inertinite data.The reflectance of fusinite and semifusinite has been used to estimate the combustion temperature and type of palaeowildfires,and then to evaluate the combustion characteristics of different types of palaeowildfires.The relative abundance of inertinite can be used to estimate the atmospheric oxygen contents.The rapid development of artificial intelligence(AI)and online tools to search scientific databases has presented an opportunity for us to find,collect,arrange,and analyse data from the earliest to latest publications on inertinite.The data extraction tool Deep Shovel is used to collect and analyse global inertinite data from the Silurian to the Neogene.The software programs such as Gplates,ArcGIS pro and Tableau are then applied to model the relative abundance of inertinite over geological time,which can be correlated with other parameters such as atmospheric oxygen contents,plant evolution and palaeoclimate changes.The distribution of inertinite in coals varied over different geological periods,being typified by the“high inertinite content-high atmospheric oxygen level”period in the Permian and the“low inertinite content-low atmospheric oxygen level”period in the Cenozoic.This study has proposed a possible model of the positive and negative feedbacks between inertinite characteristics and palaeoenvironmental factors,and has revealed the exceptional role of inertinite in palaeoenvironmental studies.Future research on inertinite will be focused on the integrated study of organic petrology and organic geochemistry of inertinite,the big data-driven research on the temporal and spatial distribution of the global inertinite,the exploration of the functions of palaeowildfires in the Earth systems in different climatic backgrounds,and the study of modern wildfires to better predict the future frequency and intensity of wildfires due to climate changes.

A shift in redox conditions near the Ediacaran/Cambrian transition and its possible influence on early animal evolution,CorumbáGroup,Brazil

The Ediacaran-Cambrian transition witnessed some of the most important biological,tectonic,climatic and geochemical changes in Earth's history.Of utmost importance for early animal evolution is the likely shift in redox conditions of bottom waters,which might have taken place in distinct pulses during the late Ediacaran and early Paleozoic.To track redox changes during this transition,we present new trace element,total organic carbon and both inorganic and organic carbon isotopes,and the first iron speciation data on the Tamengo and Guaicurus formations of the CorumbáGroup in western Brazil,which record important paleobiological changes between 555 Ma to<541 Ma.The stratigraphically older Tamengo Formation is composed mainly of limestone with interbedded marls and mudrocks,and bears fragments of upper Ediacaran biomineralized fossils such as Cloudina lucianoi and Corumbella werneri.The younger Guaicurus Formation represents a regional transgression of the shallow carbonate platform and is composed of a homogeneous fine-grained siliciclastic succession,bearing meiofaunal bilateral burrows.The new iron speciation data reveal predominantly anoxic and ferruginous(non-sulfidic)bottom water conditions during deposition of the Tamengo Formation,with FeHR/FeT around 0.8 and FePy/FeHR below 0.7.The transition from the Tamengo to the Guaicurus Formation is marked by a stratigraphically rapid drop in FeHR/FeT to below 0.2,recording a shift to likely oxic bottom waters,which persist upsection.Redox-sensitive element(RSE)concentrations are muted in both formations,but consistent with non-sulfidic bottom water conditions throughout.We interpret the collected data to reflect a transition between two distinct paleoenvironmental settings.The Tamengo Formation represents an environment with anoxic bottom waters,with fragments of biomineralized organisms that lived on shallower,proba-bly mildly oxygenated surficial waters,and that were then transported down-slope.Similar to coeval suc-cessions(e.g.,the Nama Group in Namibia),our data support the hypothesis that late Ediacaran biomineralized organisms lived in a thin oxygenated surface layer above a relatively shallow chemocline.The Guaicurus Formation,on the other hand,records the expansion of oxic conditions to deeper waters during a sea level rise.Although the relationship between global biogeochemical changes and the activities of early bioturbators remains complex,these results demonstrate an unequivocal synchronous relationship between oxygenation of the Corumbábasin and the local appearance of meiofaunal bioturbators.

The global oxygen budget and its future projection

Atmospheric oxygen （02） is the most crucial element on earth for the aerobic organisms that depend on it to release energy from carbon-based macromolecules. This is the first study to systematically analyze the global O2 budget and its changes over the past 100 years. It is found that anthropogenic fossil fuel combustion is the largest contributor to the current O2 deficit, which consumed 2.0 Gt/a in 1900 and has increased to 38.2 Gt/a by 2015. Under the Representative Concentration Pathways （RCPs） RCP8,5 scenario, approximately 100Gt （gigatonnes） of O2 would be removed from the atmosphere per year until 2100, and the O2 concentration will decrease from its current level of 20.946% to 20.825%. Human activities have caused irreversible decline of atmospheric O2. It is time to take actions to promote O2 production and reduce O2 consumption.

Sintering of transparent Nd:YAG ceramics in oxygen atmosphere

Yttrium aluminum garnet （YAG） transparent ceramics were fabricated by sintering at oxygen atmosphere. Tetraethyl orthosilicate （TEOS） was added as the sintering additive to control the grain growth and densification. Pores were eliminated clearly at temperature lower than 1700oC, while grain size was around 3 μm. The in-line transmittance was 80% at 1064 nm when samples were sintered at 1710oC. The effect of TEOS was studied in oxygen atmosphere sintering for Nd：YAG transparent ceramics. At higher temperature like 1710oC, the grain growth mechanism was solute drag, while at 1630 and 1550 oC the grain growth was controlled by liquid phase sintering mechanism. And 0.5 wt.% TEOS was the best adding content for Nd：YAG sintered in oxygen atmosphere.

Quantitative model evaluation of organic carbon oxidation hypotheses for the Ediacaran Shuram carbon isotopic excursion

The largest global carbon-cycle perturbation in Earth history was recorded in the Ediacaran—a persistent negative shift in the global marine dissolved inorganic carbon(DIC) reservoir that lasted for ~25–50 million years, with a nadir of –12‰(i.e.,the Shuram Excursion, or SE). This event is considered to have been a result of full or partial oxidation of a large dissolved organic carbon(DOC) reservoir, which, if correct, provides evidence for massive DOC storage in the Ediacaran ocean owing to an intensive microbial carbon pump(MCP). However, this scenario was recently challenged by new hypotheses that relate the SE to oxidization of recycled continentally derived organic carbon or hydrocarbons from marine seeps. In order to test these competing hypotheses,this paper numerically simulates changes in global carbon cycle fluxes and isotopic compositions during the SE, revealing that:(1) given oxygen levels in the Ediacaran atmosphere-ocean of ≤40% PAL, the recycled continental organic carbon hypothesis and the full oxidation of oceanic DOC reservoir hypothesis are challenged by the atmospheric oxygen availability which would have been depleted in 4 and 6 million years, respectively;(2) the marine-seep hydrocarbon oxidation hypothesis is challenged by the exceedingly large hydrocarbon fluxes required to sustain the SE for >25 Myr; and(3) the heterogeneous(partial) DOC oxidation hypothesis is quantitatively able to account for the SE because the total amount of oxidants needed for partial oxidation(<50%)of the global DOC reservoir could have been met.