Evolution of the structure and impact of Earth’s biosphere

Life on Earth has existed for over 3.5 billion years and has caused fundamental changes in Earth’s biogeochemistry. However, the timing and impact of major events in the evolution of the biosphere are hotly contested, owing partially to the inherent difficulty in studying events that occurred in deep time. In this Review, we discuss the evolving structure of Earth’s biosphere and major changes in its capacity to alter geochemical cycles. We describe evidence that oxygenic photosynthesis evolved relatively early, but contend that marine primary productivity was low, surface oxygen was scarce and marine anoxia was prevalent for the majority of Earth’s history. Anoxygenic phototrophs were likely a key part of the marine biosphere in these low-oxygen oceans, and nutrient uptake by these organisms was one factor limiting the extent of marine oxygenic photosynthesis. Moreover, there are potential issues with the commonly held idea that the diversification of eukaryotes fundamentally altered ocean nutrient cycling and transformed the marine biological pump. Furthermore, we argue that terrestrial primary productivity was a substantial mode of biological carbon fixation following the widespread emergence of continental land masses, even before the rise of land plants, impacting carbon cycling on a global scale

Evaluating a primary carbonate pathway for manganese enrichments in reducing environments

Most manganese (Mn) enrichments in the sedimentary rock record are hosted in carbonate minerals, which are assumed to have formed by diagenetic reduction of precursor Mn-oxides, and are considered diagnostic of strongly oxidizing conditions. Here we explore an alternative model where Mn-carbonates form in redox-stratified water columns linked to calcium carbonate dissolution. In ferruginous Brownie Lake in Minnesota, USA, we document Mn-carbonates as an HCl-extractable phase present in sediment traps and in reducing portions of the water column. Mn-carbonate becomes supersaturated in the Brownie Lake chemocline where dissolved oxygen concentrations fall below 5 μM, and Mn-oxide reduction increases the dissolved Mn concentration. Supersaturation is enhanced when calcite originating from surface waters dissolves in more acidic waters at the chemocline. In the same zone, sulfate reduction and microaerobic methane oxidation add dissolved inorganic carbon (DIC) with negative . These observations demonstrate that sedimentary Mn enrichments may 1) develop from primary carbonate phases, and 2) can occur in environments with dissolved oxygen concentrations 200 μM), and where Mn and Fe are partitioned by S cycling, photoferrotrophy, or microaerophilic Fe-oxidation. A shallow lysocline enhances Mn-carbonate production by providing additional DIC and nucleation sites for crystal growth. This carbonate model for Mn-enrichments is expected to be viable in both euxinic and ferruginous environments, and provides a more nuanced view of the relationships between Mn and carbon cycling, with applications throughout the rock record

Stepwise oxygenation of the Paleozoic atmosphere

Oxygen is essential for animal life, and while geochemical proxies have been instrumental in determining the broad evolutionary history of oxygen on Earth, much of our insight into Phanerozoic oxygen comes from biogeochemical modelling. The GEOCARBSULF model utilizes carbon and sulphur isotope records to produce the most detailed history of Phanerozoic atmospheric O2 currently available. However, its predictions for the Paleozoic disagree with geochemical proxies, and with non-isotope modelling. Here we show that GEOCARBSULF oversimplifies the geochemistry of sulphur isotope fractionation, returning unrealistic values for the O2 sourced from pyrite burial when oxygen is low. We rebuild the model from first principles, utilizing an improved numerical scheme, the latest carbon isotope data, and we replace the sulphur cycle equations in line with forwards modelling approaches. Our new model, GEOCARBSULFOR, produces a revised, highly-detailed prediction for Phanerozoic O2 that is consistent with available proxy data, and independently supports a Paleozoic Oxygenation Event, which likely contributed to the observed radiation of complex, diverse fauna at this time

Decontamination of hexavalent chromium and tri-ethyl phosphate stimulants through photacatalytic oxidation

In this paper, the photocatalytic decontamination of hexavalent chromium and tri-ethyl phosphate, two important wastewater contaminants, are studied by the ultraviolet / nano-titanium dioxide process. The pH value and synergic effect between the oxidation of tri-ethyl phosphate and the reduction of hexavalent chromium were investigated in different concentrations of tri-ethyl phosphate and hexavalent chromium. Furthermore, the effects of ultraviolet and nano-titanium dioxide were investigated in a solution which contained tri-ethyl phosphate and hexavalent chromium. Results of adsorptions showed that hexavalent chromium was adsorbed better in acidic pH while the better adsorption for tri-ethyl phosphate was occurred in alkalinity pH. The reduction rate of hexavalent chromium was higher in acidic solutions while it was obtained at natural pH for tri-ethyl phosphate. In co-adsorption of hexavalent chromium and triethyl phosphate pollutants, tri-ethyl phosphate slightly increased adsorption of hexavalent chromium, but hexavalent chromium had no influence on the adsorption of tri-ethyl phosphate on nano-titanium dioxide particles. In contrast, triethyl phosphate has an improving effect on the reduction reaction rate of hexavalent chromium which increases with the interaction of the concentration of tri-ethyl phosphate in mixture. The same is true for the oxidation rate of tri-ethyl phosphate

An investigation on the level of dental senior students knowledge about endocarditis prophylaxis incases with cardiac disease receiving dental treatment

Dental practices such as oral, periodontal and endodontic surgeries cause damages to"nthe intraoral tissues, so having knowledge of the dental procedures that necessiciate endocarditis prophylaxis"nis of high importance."nPurpose: The aim of the present study was to determine the knowledge level of dental senior students in"nTehran dental faculties about endocarditis,"nMaterials and Methods: In this cross- sectional descriptive- analytic study, 253 senior students of four"ndentistry faculties in Tehran took part as follows: Tehran University: 71 students (M:42, F:29), Shahid"nBeheshti University: 74 students (M:40, F:34), Shahed University: 35 students (M:35, F:38), Azad University:"n73 students (M:35, F:38). The questionnaire used in this research consisted of three parts as follows: part one:"ninformation on cardiac diseases, part two: dental procedures requiring endocarditis prophylaxis, part three:"nantibiotic diet in endocarditis prophylaxis. Sex and place of education of the students were also studied in"ndetail. For statistical analysis, Chi-square test was used."nResults: On the basis of the sex, the correct answers of the female respondents of different universities were"nranked as: Azad University: 72.5%, Tehran University: 71.1%, Shahid Beheshti: 57%, ShahedUniversity:"n55.7%. In the same way, the male respondents were reported as: Tehran Universitys: 71.6%, Azad University:"n66.2%, Shahed University: 57.3%, Shahid Behesti University: 52.1%, On the basis of the place of education,"nthe following results were reported: Tehran University students managed to answer 71.3% , Azad University,"nShahed University and Shahid Beheshti University students could answer 69.5%, 56.5% and 54.6%,"nrespectively. All these differences were statistically significant, indicating that first ranked students have more"ninformation than the students of other schools."nConclusion: It is recommended to develop more practical training programme in dental schools on cardiac"ndiseases, dental procedures requiring endocarditis prophylaxis and antibiotic diets

Hexavalent chromium removal from aqueous solutions by using low-cost biological wastes: equilibrium and kinetic studies

The batch removal of hexavalent chromium from aqueous solutions using almond shell, activated sawdust, and activated carbon, which are low-cost biological wastes under different experimental conditions, was investigated in this study. The influences of initial concentration, adsorbent dose, adsorbent particle size, agitation speed, temperature, contact time, and pH of solution were investigated. The adsorption was solution pH dependent and the maximum adsorption was observed at a solution pH of 2.0. The capacity of chromium adsorption under equilibrium conditions increased with the decrease in particle sizes. The equilibrium was achieved for chromium ion after 30 min. Experimental results showed that low-cost biosorbents are effective for the removal of pollutants from aqueous solution. The pseudo-second-order kinetic model gave a better fit of the experimental data as compared to the pseudo-first-order kinetic model. Experimental data showed a good fit with the Freundlich isotherm model. Changes in the thermodynamic parameters, including Gibbs free energy (ΔGo), enthalpy (ΔHo), and entropy (ΔSo), indicated that the biosorption of hexavalent chromium onto almond shell, activated sawdust, and activated carbon was feasible, spontaneous, and endothermic in the temperature range 28–50 ° C

Effectiveness of Transcranial Direct Current Stimulation for the Reduction of Symptoms in Patients with Major Depressive Disorder Admitted to Public, Educational, and Private Hospitals in Ilam, Iran

Objectives: The current study aimed at analyzing the effect of transcranial direct current stimulation (TDCS) on reduction of depression symptoms in patients admitted to public, educational, and private hospitals in Ilam, Iran. Methods: In the current clinical trial, pre-tests and post-tests were used to analyze data. The study population consisted of patients diagnosed with depression admitted to public, educational, and private hospitals of Ilam. After explaining the study objectives, 40 patients agreed to cooperate. The convenience sampling method was used in the current study through which patients were selected randomly and allocated into 2 groups of 10 and 20 stimulation sessions, respectively. The Beck depression inventory was used to collect data. The t test and Pearson correlation test were used in hypothesis assessment procedure. Results: The results of the current study revealed that TDCS reduced depression in the studied patients. Conclusions: The duration of electrical current pulses to the brain is associated with the reduction of depression symptoms in patients with depression. No study demonstrated compatibility and incompatibility with this hypothesis. The counselling centers, institutes, university and other institutions can benefit from the results of the current and other similar ones