Evolution of the atmosphere

The Acute Effects of Oxygen and Carbon Dioxide on Renal Vascular Resistance in Patients With an Acute Exacerbation of COPD

Early models for the origin of banded iron formations (BIFs) assumed that under a reducing atmosphere the supergene anoxic hydrolysis of mafic silicate minerals would provide an abundance of ferrous iron in solution to be transported to the oceans, there to be oxidised and precipitated by locally produced oxygen in shallow seas. The sparse distribution of BIFs in the Archaean era, its greater abundance during the Palaeoproterozoic era and perceived absence thereafter was considered to be essentially linked to the concentration of O2 in the atmosphere and this was a key factor in hypotheses of atmospheric evolution from anoxic to oxidising. Several assumptions regarding the deposition of BIFs were used to infer atmospheric evolution; however, chemical considerations indicate that the deposition of BIF is independent of atmospheric oxygen levels. Ferrous iron is only soluble in acid solution and in anoxic conditions in natural waters is precipitated as ferrous hydroxide or by carbon dioxide as ferrous carbonate. Silica in solution typically exists in equilibrium between ionic solution and colloidal suspension. Flocculation of colloidal silica is catalysed by the presence of cations and polymerises to a hydrophobic gel, thus removing silica from solution. It is highly unlikely that the oceans could ever have been the reservoir of iron and silica for the deposition of BIFs.Modern interpretations consider BIFs as deep sea sediments with the source of the iron and silica derived from reactions between circulating sea water and hot mafic to ultramafic rocks producing hydrothermal systems venting onto the sea floor. The solubility of ferrous and ferric iron and silica is greatly increased at elevated temperatures and hydrothermal solutions would immediately precipitate iron hydroxide and iron silicates on quenching by cold seawater, even in the absence of ambient oxygen, to form hydrothermal plumes and mound deposits, subsequently resedimented by turbidity and density currents across the ocean floor. No transportation of ferrous iron in solution at ambient temperatures and no external source of O2 or Fe2+ is necessary and the deposition of BIFs was independent of atmospheric oxygen, biogenic processes and continental sources of dissolved ferrous iron and silica, although any or all of these may have been present during deposition.A similar process occurs today with black smoker hydrothermal vents depositing large quantities of iron hydroxide and iron silicates on the ocean floor that will eventually be subducted beneath the continents by plate tectonic processes. During the Archaean era, shallow oceans and immature continents, preserved sea floor deposits as greenstone belts and in marginal sedimentary basins until the formation of large buoyant continents caused the subduction of deep sea ocean crust including BIF deposits. The temporal distribution of BIFs is thus related to the preservation of deep ocean sedimentary rocks that since the onset of modern style plate tectonics in the late Archaean to Proterozoic eras have largely been destroyed by subduction of the ocean floor beneath the continents.

The main objective of this research is to detect the forest fire by sensing temperature and atmospheric carbon dioxide (CO2) levels to prevent the forest fire and to provide exact information using IOT at faster speed. The efficiency of detection using Node Microcontroller Unit (NodeMCU) is compared with Arduino microcontroller. A total of 40 samples are taken from the Serial monitor of the Arduino IDE. Group 1 has temperature values (n = 10) and atmospheric carbon dioxide (CO2) levels (n = 10) with the Node Microcontroller Unit (Node MCU). Group 2 has temperature values (n = 10) and atmospheric carbon dioxide (CO2) levels (n = 10) using Arduino Microcontroller. In this novel forest fire detection, the G-power analysis was done to the samples and the minimum power is acquired to be 0.8 for the system with an error correction of 0.5. The significance values for the temperature sensor are 0.129 and 0.132 for NodeMCU and Arduino Microcontroller respectively. The significance values for atmospheric carbon dioxide (CO2) levels are 0.212 and 0.224 for NodeMCU and Arduino Microcontroller respectively. Results: Through the implementation of this novel forest fire detection, it is observed that the efficiency of NodeMCU is 92.9 % and efficiency of Arduino microcontroller is 89.95 %. This innovative approach with NodeMCU appears to be more efficient (92.9 %) in detecting the occurrence of forest fire using Arduino Microcontroller with the significance value of temperature and atmospheric carbon dioxide level of 0.129 and 0.212 respectively.

Depositional model for banded iron formation host to gold in the Archean Rio das Velhas greenstone belt, Brazil, based on geochemistry and LA-ICP-MS magnetite analyses

The Hugushan banded iron formation (BIF) is one of the most representative iron ore deposits in the central part of the North China Craton, and its ore formation mechanism remains highly controversial. This study presents whole-rock and Fe–Si–O isotope geochemical evidence, offering a new perspective on the ore formation mechanism of the Hugushan BIFs. The samples from the upper and lower parts of the Hugushan BIFs are characterized by slight enrichment of heavy and light Fe isotopes, respectively. Additionally, the samples from the upper part of the Hugushan BIFs show characteristics of slightly positive Ce anomalies and negative La anomalies, suggesting that the shallow ancient seawater was in a partially oxidized state, whereas the deep seawater remained in a reductive environment during the depositional period. The low Al2O3 and TiO2 concentrations, as well as the depletion of Zr and Hf in the Hugushan BIFs, suggest that the contribution of terrestrial detrital materials to deposition is extremely limited. The BIFs all exhibit positive Eu anomalies, and the quartz in the BIFs is depleted in 30Si, a characteristic similar to that observed in siliceous rocks formed in hydrothermal vent environments and during hydrothermal plume activity. Additionally, the δ18O values of quartz in Hugushan BIFs are similar to the O isotope compositions of hydrothermal sedimentary siliceous rocks, further suggesting that the silicon in BIFs originates primarily from seafloor hydrothermal activity. The combination of Eu/Sm, Sm/Yb, and Y/Ho ratios indicates that the major components (iron and silica) of the Hugushan Iron Ore Deposit originated from the mixing of high-temperature hydrothermal fluids with seawater, with the hydrothermal fluid contributing slightly less than 0.1%. The magnetite and quartz bands in the BIFs exhibit inhomogeneous and covariant δ56Fe and δ30Si isotope characteristics, suggesting that the alternating siliceous and ferruginous layers are products of original chemical deposition in the ocean. Periodic hydrothermal activity and ocean transgression caused the recurring deposition of siliceous and ferruginous layers, resulting in the characteristic banded structure of the Hugushan Iron Ore Deposit.

Geochemistry and Si–O–Fe isotope constraints on the origin of banded iron formations of the Yuanjiacun Formation, Lvliang Group, Shanxi, China

Atmosphere behavior in gas-closed mouse-algal systems: An experimental and modelling study

Since the industrial revolution, 200 years ago, atmospheric carbon dioxide levels have risen by 90 ppmV, an amount equalling the natural variation between the last glacial maximum and pre-industrial values. To predict the fate and influence of anthropogenic carbon dioxide, it is vital to understand the natural controls on the glacial-interglacial variations in atmospheric composition. The biological pump is known to be an important draw-down of carbon dioxide today due to the complete removal of nutrients from the euphotic zone of most surface waters and regeneration at depth. An exception exists in the Southern Ocean today, where the surface waters have high phosphate concentrations indicating incomplete removal of the nutrients either due to very rapid upwelling rates or iron limitation. There is huge potential for glacial carbon dioxide draw-down if the efficiency of the biological pump had been enhanced in the glacial Southern Ocean. Particle proxies suggest that export productivity increased in the glacial subantarctic Southern Ocean (1) but there has been no clear evidence of a lowering of the glacial surface-water nutrients (2). fil3c in planktonic foraminifera has been found to be unreliable as a nutrient tracer in surface waters due to a number of factors such as susceptibility to isotopic fractionation during air-sea exchange (3). Cd/Ca in foraminifera, a reliable deep-water nutrient tracer, has been uncalibrated for surface waters and is often present at levels too low for determination by existing methods. We have developed a new isotope dilution, mass-spectrometric method for low-level determination of Cd/Ca in foraminifera which has allowed reliable and accurate planktonic analyses to be made. We have investigated the application of Cd/ Ca in planktonic foraminifera for the reconstruction of past surface water phosphate levels. Down-core records of Cd/Ca in G.Bulloides covering the last complete glacial cycle have been obtained from a latitudinal transect of cores spanning the present day Subtropical Convergence Zone (SCZ), at approximately 40~ and the Antarctic Polar Front (APF), at approximately 50~ in the Indian Ocean sector of the Southern Ocean. In each core there is a striking correlation between the Cd/Ca and the 5180 of G.Bulloides over the last glacial cycle indicating low surface water nutrient levels during the glacials and high nutrient levels during the interglacials. The greatest reduction in nutrient levels occurs in the subantarctic zone of the Southern Ocean, with little change south of the APF, consistent with the export productivity conclusions. There are two possible explanations for this glacial lowering of surface water nutrients. Firstly the rate of upwelling remains constant but the efficiency of nutrient removal is increased, possibly by iron fertilization due to an increased atmospheric dust fallout in glacial times. Secondly, the glacial Southern Ocean water column became stratified with a stable thermocline altowing the surface water productivity to deplete the nutrients without constant replenishment from upwelling. It is important to distinguish between these two mechanisms as each has a differing potential for glacial draw-down of atmospheric carbon dioxide. A simple box-model following some of the concepts in (4) has been run to resolve which of these two mechanisms is more consistent with the new surface water nutrient data and the existing export productivity conclusions.

Trace element and isotopic characterization of Neoarchean and Paleoproterozoic iron formations in the Black Hills (South Dakota, USA): Assessment of chemical change during 2.9–1.9 Ga deposition bracketing the 2.4–2.2 Ga first rise of atmospheric oxygen

Palaeo‐Mesoarchean Banded Iron formations (BIFs) of central Bundelkhand greenstone belts occur from Babina (in the west) to Mahoba (in the east) via Mauranipur along with the E–W trending of the Bundelkhand Tectonic Zone (BTZ). In the present study, we report petrological, geochemical, and mineralogical data of BIFs from the Babina, Mauranipur, and Mahoba greenstone belts of central Bundelkhand Greenstone Complex to address their source characteristics and deposition environment. The lithological association of BIFs in the Babina and Mauranipur greenstone belts consists of pillowed basic–ultrabasic volcanics and metasediments, whereas in the Mahoba greenstone belt, BIFs and quartzite occur within basic volcanics. These lithological associations collectively suggest that the entire succession was deposited in a marine environment. Based on geological setting, they are classified as Algoma‐type. The main mineral assemblages of the Babina and Mauranipur BIFs are composed of magnetite, quartz, ±garnet, hornblende, chlorite, and apatite, whereas the Mahoba BIFs along with magnetite and quartz, poised of two distinct mineral assemblages; the first one is Opx–Cpx–Grt and the other one is Grt–Hbl. The preliminary P–T study of these BIFs implies that they had gone through amphibolite‐ to granulite‐facies metamorphism. The geochemical characteristics show that BIFs from the Babina and Mauranipur greenstone belts are dominated by higher quartz and magnetite (total content = 90.63–99.95 wt.%), whereas the Mahoba greenstone belt is characterized by lesser quartz and magnetite components (total content = 86.68–94.58 wt.%). The PAAS (Post Archean Average of Australian Sediments)‐normalized REE patterns display significant positive Eu anomaly (Eu/Eu* up to 2.50) with well‐represented negative Ce anomalies (Ce/Ce* = 0.27–1.20). The REE and trace element ratios of BIFs from the Babina and Mauranipur greenstone belts suggest that they were formed by high‐T hydrothermal fluid activity without or very less continental input. Moreover, the Mahoba greenstone belt BIFs are formed by low‐T hydrothermal fluid activity with substantial continental input. Their chemical variation suggests the shallowing of the proto‐basin from the Babina in the west to Mahoba in the east. Tectonic discrimination plots imply the BIFs of the Babina, Mauranipur, and Mahoba greenstone belts of the central Bundelkhand Greenstone Complex are formed in a back‐arc tectonic setting.

Depositional age and tectonic environment of the Gouap banded iron formations from the Nyong group, SW Cameroon: Insights from isotopic, geochemical and geochronological studies of drillcore samples

Petrography and geochemistry of the Dales Gorge banded iron formation: Paragenetic sequence, source and implications for palaeo-ocean chemistry

The Early Palaeoproterozoic Brockman Supersequence comprises banded iron formation (BIF), bedded chert, limestone, mudrock, sandstone, breccia, tuffaceous mudstone, ashfall tuff and, in sections not reported here, basalt and rhyolite. Density current rhythms are preserved in sandstones, mudrocks, tuffaceous mudstones and limestones. Relics of similar rhythms in BIF imply that its precursor sediments were also deposited by density currents. Hemipelagic deposits are siliciclastic or mixed siliciclastic–volcaniclastic mudstones. Bedded chert, chert nodules and the chert matrix of BIF preserve evidence for formation by diagenetic replacement. For bedded chert (and chert nodules), silica replacement occurred before compaction close to or at the sediment–water interface, indicating that it is siliceous hardground. The chert matrix of BIF formed during compaction but before burial metamorphism. Original sediments were resedimented from two sources: (1) limestone, mudrock, sandstone, breccia and tuffaceous mudstone from a shelf; and (2) BIF from within the basin realm. Shelf sediments were resedimented to basin‐floor fans during third‐order lowstands. The precursor sediments to BIF are interpreted to have been granular hydrothermal muds, composed of iron‐rich smectite and particles of iron oxyhydroxide and siderite that were deposited on the flanks of submarine volcanoes and resedimented by density currents. Resedimentation occurred by either bottom currents or gravity‐driven turbidity currents, and the resulting sediment bodies may have been contourite drifts. The concept that BIF records high‐frequency alternating precipitation from ambient sea water of iron minerals and silica is negated by this study. Instead, it is postulated that the precursor sediments to BIF originated in much the same way as modern Red Sea hydrothermal iron oxide deposits, implying that at least the particles of iron oxyhydroxide originated from the oxidation of vent fluids by sea water. Several orders of cyclicity in basin filling establish a relationship between rising to high sea levels, episodic sea‐floor hydrothermal activity and BIF that is reminiscent of the link between eustacy and spreading‐ridge pulses.

Effects of fuel and forest conservation on future levels of atmospheric carbon dioxide

In adding carbon dioxide to the atmosphere, mankind is unintentionally conducting a great biological and geophysical experiment. This experiment can be expected to increase scientific understanding of ecological systems and of the processes in the ocean and the atmosphere that partially determine world climate. But from the standpoint of governments and peoples, the major problem to be solved is to understand the nature of the impacts on societies of rising levels of atmospheric carbon dioxide (CO/sub 2/), with the objective of avoiding or ameliorating unfavorable impacts and gaining most benefit from favorable impacts. The research program proposed herein is designed to provide the understanding needed to achieve this objective. It is based on a recognition of the distinctive characteristics of the CO/sub 2/ problem. It is concluded that three kinds of research on the consequences of rising levels of atmospheric carbon dioxide and possible climatic changes are called for: assessment of risks; research to enhance beneficial effects and lessen harmful ones, where this is possible, and to slow down rates of carbon dioxide emission; and study of potential social and institutional responses to projected climatic changes.