Review Lecture - Ore-deposition through geological time

1978 ◽  
Vol 362 (1710) ◽  
pp. 305-328 ◽  
Keyword(s):  
Mineral Deposits ◽  
Banded Iron Formations ◽  
Geological Time ◽  
The Earth ◽  
Recent Developments ◽  
Changing Role ◽  
Iron Formations ◽  
Ore Deposition

Economic mineral deposits represent abnormal concentrations of metals which must be regarded as records of unusual geological events. The recognition of any long-term changes in styles of mineralization must depend on the identification of anomalies within the geological régimes characteristic of successive stages of the Earth’s history. This question will be discussed in relation to recent developments in the Earth sciences. The recognition of structural and chemical inhomogeneities in the lithospheric mantle suggests that mapping of mantle age-provinces may become possible; such studies bear on the significance of certain metallogenic provinces. Coordinated geochemical, structural and palaeomagnetic studies which are throwing light on the evolution of early tectonic systems should help to illuminate the significance of changes in style of mineralization at the Archaean/Proterozoic boundary, as well as the distribution of some types of Proterozoic deposits. Geochemical evidence concerning the changing rôle of organic processes in sedimentation and diagenesis has a bearing on the origin of sedimentary ores, especially over the controversial period characterized by accumulation of banded iron-formations.

scholarly journals Microbial processes during deposition and diagenesis of Banded Iron Formations

PalZ ◽  
2021 ◽  
Author(s):  
Carolin L. Dreher ◽  
Manuel Schad ◽  
Leslie J. Robbins ◽  
Kurt O. Konhauser ◽  
Andreas Kappler ◽  
...  
Keyword(s):  
Microbial Reduction ◽  
Iron Cycling ◽  
Banded Iron Formations ◽  
Geochemical Composition ◽  
High Pressure And Temperature ◽  
Microbial Life ◽  
Reducing Bacteria ◽  
Iron Formations ◽  
Chemical Sediments

AbstractBanded Iron Formations (BIFs) are marine chemical sediments consisting of alternating iron (Fe)-rich and silica (Si)-rich bands which were deposited throughout much of the Precambrian era. BIFs represent important proxies for the geochemical composition of Precambrian seawater and provide evidence for early microbial life. Iron present in BIFs was likely precipitated in the form of Fe3+ (Fe(III)) minerals, such as ferrihydrite (Fe(OH)3), either through the metabolic activity of anoxygenic photoautotrophic Fe2+ (Fe(II))-oxidizing bacteria (photoferrotrophs), by microaerophilic bacteria, or by the oxidation of dissolved Fe(II) by O2 produced by early cyanobacteria. However, in addition to oxidized Fe-bearing minerals such as hematite (FeIII2O3), (partially) reduced minerals such as magnetite (FeIIFeIII2O4) and siderite (FeIICO3) are found in BIFs as well. The presence of reduced Fe in BIFs has been suggested to reflect the reduction of primary Fe(III) minerals by dissimilatory Fe(III)-reducing bacteria, or by metamorphic (high pressure and temperature) reactions occurring in presence of buried organic matter. Here, we present the current understanding of the role of Fe-metabolizing bacteria in the deposition of BIFs, as well as competing hypotheses that favor an abiotic model for BIF deposition. We also discuss the potential abiotic and microbial reduction of Fe(III) in BIFs after deposition. Further, we review the availability of essential nutrients (e.g. P and Ni) and their implications on early Earth biogeochemistry. Overall, the combined results of various ancient seawater analogue experiments aimed at assessing microbial iron cycling pathways, coupled with the analysis of the BIF rock record, point towards a strong biotic influence during BIF genesis.

The role of the Microbial Conveyor Belt on Earth´s system resilience

2021 ◽  
Author(s):  
Mireia Mestre ◽  
Juan Höfer
Keyword(s):  
Human Impacts ◽  
Conveyor Belt ◽  
Earth System ◽  
Planetary Scale ◽  
Microbial Biogeography ◽  
The Earth ◽  
System Resilience ◽  
Global Biogeochemical Cycles

<p>Despite being major players on the global biogeochemical cycles, microorganisms are generally not included in holistic views of Earth’s system. The Microbial Conveyor Belt is a conceptual framework that represents a recurrent and cyclical flux of microorganisms across the globe, connecting distant ecosystems and Earth compartments. This long-range dispersion of microorganisms directly influences the microbial biogeography, the global cycling of inorganic and organic matter, and thus the Earth system’s functioning and long-term resilience. Planetary-scale human impacts disrupting the natural flux of microorganisms pose a major threat to the Microbial Conveyor Belt, thus compromising microbial ecosystem services. Perturbations that modify the natural dispersion of microorganisms are, for example, the modification of the intensity/direction of air fluxes and ocean currents due to climate change, the vanishing of certain dispersion vectors (e.g., species extinction or drying rivers) or the introduction of new ones (e.g., microplastics, wildfires). Transdisciplinary approaches are needed to disentangle the Microbial Conveyor Belt, its major threats and their consequences for Earth´s system resilience.</p>

Introduction

2004 ◽  
Author(s):  
Robert A. Berner
Keyword(s):  
Climate Change ◽  
Carbon Dioxide ◽  
Carbon Cycle ◽  
Global Climate ◽  
Geological Time ◽  
Short Term ◽  
Quaternary Period ◽  
Geological Time Scale ◽  
The Earth

The cycle of carbon is essential to the maintenance of life, to climate, and to the composition of the atmosphere and oceans. What is normally thought of as the “carbon cycle” is the transfer of carbon between the atmosphere, the oceans, and life. This is not the subject of interest of this book. To understand this apparently confusing statement, it is necessary to separate the carbon cycle into two cycles: the short-term cycle and the long-term cycle. The “carbon cycle,” as most people understand it, is represented in figure 1.1. Carbon dioxide is taken up via photosynthesis by green plants on the continents or phytoplankton in the ocean. On land carbon is transferred to soils by the dropping of leaves, root growth, and respiration, the death of plants, and the development of soil biota. Land herbivores eat the plants, and carnivores eat the herbivores. In the oceans the phytoplankton are eaten by zooplankton that are in turn eaten by larger and larger organisms. The plants, plankton, and animals respire CO2. Upon death the plants and animals are decomposed by microorganisms with the ultimate production of CO2. Carbon dioxide is exchanged between the oceans and atmosphere, and dissolved organic matter is carried in solution by rivers from soils to the sea. This all constitutes the shortterm carbon cycle. The word “short-term” is used because the characteristic times for transferring carbon between reservoirs range from days to tens of thousands of years. Because the earth is more than four billion years old, this is short on a geological time scale. As the short-term cycle proceeds, concentrations of the two principal atmospheric gases, CO2 and CH4, can change as a result of perturbations of the cycle. Because these two are both greenhouse gases—in other words, they adsorb outgoing infrared radiation from the earth surface—changes in their concentrations can involve global warming and cooling over centuries and many millennia. Such changes have accompanied global climate change over the Quaternary period (past 2 million years), although other factors, such as variations in the receipt of solar radiation due to changes in characteristics of the earth’s orbit, have also contributed to climate change.

Irregular Migration, Human Smuggling, and the Eastern Enlargement of the European Union

2007 ◽  
Vol 41 (2) ◽  
pp. 291-315 ◽  
Author(s):  
Michael Jandl
Keyword(s):  
Eu Enlargement ◽  
Human Smuggling ◽  
The European Union ◽  
Eastern Enlargement ◽  
Irregular Migration ◽  
Ample Evidence ◽  
Recent Developments ◽  
Long Term Trends

This article examines the consequences of the latest round of EU-Enlargement in May 2004 on irregular migration across Central and Eastern Europe. Drawing on a unique collection of both quantitative and qualitative data related to irregular migration and human smuggling, the article first presents some long-term trends in irregular migration across the region before taking up more recent developments in 2003 and 2004. While border apprehensions have broadly declined since about 2000 there is ample evidence for an increasing role of human smugglers in facilitating irregular migration. In addition, there are noticeable changes in the modus operandi of human smugglers.

The changing role of eosinophils in long-term hyperreactivity following a single ozone exposure

2005 ◽  
Vol 289 (4) ◽  
pp. L627-L635 ◽  
Author(s):  
Bethany L. Yost ◽  
Gerald J. Gleich ◽  
David B. Jacoby ◽  
Allison D. Fryer
Keyword(s):  
Smooth Muscle ◽  
Vagal Stimulation ◽  
Airway Hyperreactivity ◽  
Ozone Exposure ◽  
Single Exposure ◽  
Eosinophil Major Basic Protein ◽  
Changing Role ◽  
Eosinophil Accumulation

Ozone hyperreactivity over 24 h is mediated by blockade of inhibitory M2 muscarinic autoreceptors by eosinophil major basic protein. Because eosinophil populations in the lungs fluctuate following ozone, the contribution of eosinophils to M2 dysfunction and airway hyperreactivity was measured over several days. After one exposure to ozone, M2 function, vagal reactivity, smooth muscle responsiveness, and inflammation were measured in anesthetized guinea pigs. Ozone-induced hyperreactivity to vagal stimulation persisted over 3 days. Although hyperreactivity one day after ozone is mediated by eosinophils, AbVLA-4 did not inhibit either eosinophil accumulation in the lungs or around the nerves or prevent hyperreactivity at this time point. Two days after ozone, eosinophils in BAL, around airway nerves and in lungs, were decreased, and neuronal M2 receptor function was normal, although animals were still hyperreactive to vagal stimulation. Depleting eosinophils with AbIL-5 prevented hyperreactivity, thus eosinophils contribute to vagal hyperreactivity by mechanisms separate from M2 receptor blockade. Three days after ozone, vagal hyperreactivity persisted, eosinophils were again elevated in BAL in lungs and around nerves, and M2 receptors were again dysfunctional. At this point, airway smooth muscle was also hyperresponsive to methacholine. Eosinophil depletion with AbIL-5, AbVLA-4, or cyclophosphamide protected M2 function 3 days after ozone and prevented smooth muscle hyperreactivity. However, vagal hyperreactivity was significantly potentiated by eosinophil depletion. The site of hyperreactivity, muscle or nerve, changes over 3 days after a single exposure to ozone. Additionally, the role of eosinophils is complex; they mediate hyperreactivity acutely while chronically may be involved in repair.

scholarly journals The role of green space in the urbanization of Hanoi city

2019 ◽  
Vol 97 ◽  
pp. 01013 ◽  
Author(s):  
Minh Tuan Le ◽  
Thi Anh Tuyet Cao ◽  
Nguyen Anh Quan Tran
Keyword(s):  
Green Space ◽  
Ground Surface ◽  
Heat Island ◽  
Cooling Efficiency ◽  
Threshold Values ◽  
Excess Temperature ◽  
Rapid Urbanization ◽  
The Earth

Rapid urbanization causes significant changes on the earth surface directly and internal itself temperature. The transformation of land use purposes crucially affects the surface temperature and exacerbates the effect of the negative heat island. It is necessary to develope a long-term strategy optimize urban cooling. In this study, the determinated object is Hanoi - city - a widen urbanized city in Vietnam. The authors proposed, defined and calculated the concept of cooling efficiency and threshold values. The results show that the surface heat capacity increases in proportion to the reduction of green space. Plots with excess temperature difference of the ground surface of 4.34 ℃ with reduced green space.

scholarly journals Conserving evolutionary history does not result in greater diversity over geological time scales

2019 ◽  
Vol 286 (1904) ◽  
pp. 20182896 ◽  
Author(s):  
J. L. Cantalapiedra ◽  
T. Aze ◽  
M. W. Cadotte ◽  
G. V. Dalla Riva ◽  
D. Huang ◽  
...  
Keyword(s):  
Time Scales ◽  
Phylogenetic Trees ◽  
Evolutionary History ◽  
Phylogenetic Diversity ◽  
Random Sets ◽  
Geological Time ◽  
The Future ◽  
Species Production

Alternative prioritization strategies have been proposed to safeguard biodiversity over macroevolutionary time scales. The first prioritizes the most distantly related species—maximizing phylogenetic diversity (PD)—in the hopes of capturing at least some lineages that will successfully diversify into the future. The second prioritizes lineages that are currently speciating, in the hopes that successful lineages will continue to generate species into the future. These contrasting schemes also map onto contrasting predictions about the role of slow diversifiers in the production of biodiversity over palaeontological time scales. We consider the performance of the two schemes across 10 dated species-level palaeo-phylogenetic trees ranging from Foraminifera to dinosaurs. We find that prioritizing PD for conservation generally led to fewer subsequent lineages, while prioritizing diversifiers led to modestly more subsequent diversity, compared with random sets of lineages. Importantly for conservation, the tree shape when decisions are made cannot predict which scheme will be most successful. These patterns are inconsistent with the notion that long-lived lineages are the source of new species. While there may be sound reasons for prioritizing PD for conservation, long-term species production might not be one of them.

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