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Euxinia
Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen sulfide (H2S). Euxinic bodies of water are frequently strongly stratified; have an oxic, highly productive, thin surface layer; and have anoxic, sulfidic bottom water. The word "euxinia" is derived from the Greek name for the Black Sea (Εὔξεινος Πόντος (''Euxeinos Pontos'')) which translates to "hospitable sea". Euxinic deep water is a key component of the Canfield ocean, a model of oceans during part of the Proterozoic eon (a part specifically known as the Boring Billion) proposed by Donald Canfield, an American geologist, in 1998. There is still debate within the scientific community on both the duration and frequency of euxinic conditions in the ancient oceans. Euxinia is relatively rare in modern bodies of water, but does still happen in places like the Black Sea and certain fjords. Background Euxinia most fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anoxic Event
An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic ( anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geologic record shows that they happened many times in the past. Anoxic events coincided with several mass extinctions and may have contributed to them. These mass extinctions include some that geobiologists use as time markers in biostratigraphic dating. On the other hand, there are widespread, various black-shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions. Many geologists believe oceanic anoxic events are strongly linked to the slowing of ocean circulation, climatic warming, and elevated levels of greenhouse gases. Researchers have proposed enhanced volcanism (the release of CO2) as the "central external trigger for euxinia." Human activities in the Holocene epoch, such as t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Great Oxygenation Event
The Great Oxidation Event (GOE) or Great Oxygenation Event, also called the Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisis or Oxygen Holocaust, was a time interval during the Earth's Paleoproterozoic era when the Earth's atmosphere and shallow seas first experienced a rise in the concentration of free oxygen. This began approximately 2.460–2.426 billion years ago (Ga) during the Siderian period and ended approximately 2.060 Ga ago during the Rhyacian. Geological, isotopic and chemical evidence suggests that biologically produced molecular oxygen (dioxygen or O2) started to accumulate in the Archean prebiotic atmosphere due to microbial photosynthesis, and eventually changed it from a weakly reducing atmosphere practically devoid of oxygen into an oxidizing one containing abundant free oxygen, with oxygen levels being as high as 10% of modern atmospheric level by the end of the GOE. The appearance of highly reactive free oxygen, which can oxidize or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Sea
The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia (country), Georgia, Romania, Russia, Turkey, and Ukraine. The Black Sea is Inflow (hydrology), supplied by major rivers, principally the Danube, Dnieper and Dniester. Consequently, while six countries have a coastline on the sea, its drainage basin includes parts of 24 countries in Europe. The Black Sea, not including the Sea of Azov, covers , has a maximum depth of , and a volume of . Most of its coasts ascend rapidly. These rises are the Pontic Mountains to the south, bar the southwest-facing peninsulas, the Caucasus Mountains to the east, and the Crimean Mountains to the mid-north. In the west, the coast is generally small floodplains below foothills such as the Strandzha; Cape Emine, a dwindling of the east end ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canfield Ocean
The Canfield Ocean model was proposed by Geochemistry, geochemist Donald Canfield to explain the composition of the ocean in the middle to late Proterozoic. History In a paper published in 1998 in ''Nature (journal), Nature'', Canfield argued that the deep ocean was Ocean anoxia, anoxic and Hydrogen sulfide, sulfidic (also known as Euxinia, euxinic) during the time of the Boring Billion (1.80.8 billion years ago (Gya)), and that those conditions ceased the mineral deposition of iron-rich Banded iron formation, banded iron formations (BIF) in ocean sediments. Prior to the Canfield Ocean theory, it was believed that the ocean becoming fully Oxygenation (environmental), oxygenated during the Great Oxidation Event (GOE; ~2.46 Gya) was the mechanism that ceased BIF deposition. Formation By the end of the GOE, oxygen levels in the atmosphere were as high as 10% of present-day levels. Under these conditions, the deep ocean would have likely remained anoxic. However, the atmosphere had ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Banded Iron Formation
Banded iron formations (BIFs; also called banded ironstone formations) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness and extend laterally for several hundred kilometers. Almost all of these formations are of Precambrian age and are thought to record the Great Oxygenation Event, oxygenation of the Earth's oceans. Some of the Earth's oldest rock formations, which formed about (Year#SI prefix multipliers, Ma), are associated with banded iron formations. Banded iron formations are thought to have formed in sea water as the result of oxygen production by photosynthesis, photosynthetic cyanobacteria. The oxygen combined with dissolved iron in Earth's oceans to form insoluble iron oxides, which precipitated out, forming a thin layer on the ocean floor. Each band is similar to a varve, resulting from cyclic variations in oxygen production. Banded iron formations we ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boring Billion
The Boring Billion, otherwise known as the Mid Proterozoic and Earth's Middle Ages, is an informal geological time period between 1.8 and 0.8 billion years ago ( Ga) during the middle Proterozoic eon spanning from the Statherian to the Tonian periods, characterized by more or less tectonic stability, climatic stasis and slow biological evolution. Although it is bordered by two different oxygenation events (the Great Oxygenation Event and Neoproterozoic Oxygenation Event) and two global glacial events (the Huronian and Cryogenian glaciations), the Boring Billion period itself actually had very low oxygen levels and no geological evidence of glaciations. The oceans during the Boring Billion may have been oxygen-poor, nutrient-poor and sulfidic ( euxinia), populated by mainly anoxygenic purple bacteria, a type of bacteriochlorophyll-based photosynthetic bacteria which uses hydrogen sulfide (H2S) for carbon fixation instead of water and produces sulfur as a byproduct in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anoxic
Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved oxygen * Anoxic event, when the Earth's oceans become completely depleted of oxygen below the surface levels * Euxinic, anoxic conditions in the presence of hydrogen sulfide * Hypoxia (environmental), low oxygen conditions * Hypoxia (medicine), when the body or a region of the body is deprived of adequate oxygen supply ** Cerebral anoxia, when the brain is completely deprived of oxygen, an extreme form of cerebral hypoxia See also * ''Anoxia'' (beetle), a genus of scarab beetles * Oxygen saturation Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is Dissolution (chemistry), dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
How Oceans Become Euxinic
How may refer to: * How (greeting), a word used in some misrepresentations of Native American/First Nations speech * How, an interrogative word in English grammar Art and entertainment Literature * ''How'' (book), a 2007 book by Dov Seidman * ''HOW'' (magazine), a magazine for graphic designers * H.O.W. Journal, an American art and literary journal Music * ''How?'' (EP), by BoyNextDoor, 2024 * "How?" (song), by John Lennon, 1971 * "How", a song by Clairo from ''Diary 001'', 2018 * "How", a song by the Cranberries from ''Everybody Else Is Doing It, So Why Can't We?'', 1993 * "How", a song by Daughter from ''Not to Disappear'', 2016 * "How", a song by Lil Baby from '' My Turn'', 2020 * "How", a song by Maroon 5 from '' Hands All Over'', 2010 * "How", a song by Regina Spektor from ''What We Saw from the Cheap Seats'', 2012 * "How", a song by Robyn from ''Robyn Is Here'', 1995 Other media * HOW (graffiti artist), Raoul Perre, New York graffiti muralist * ''How'' (TV series ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many are prepared from that acid. Spelling "Sulfate" is the spelling recommended by IUPAC, but "sulphate" was traditionally used in British English. Structure The sulfate anion consists of a central sulfur atom surrounded by four equivalent oxygen atoms in a tetrahedral arrangement. The symmetry of the isolated anion is the same as that of methane. The sulfur atom is in the +6 oxidation state while the four oxygen atoms are each in the −2 state. The sulfate ion carries an overall charge of −2 and it is the conjugate base of the bisulfate (or hydrogensulfate) ion, , which is in turn the conjugate base of , sulfuric acid. Organic sulfate esters, such as dimethyl sulfate, are covalent compounds and esters of sulfuric acid. The tetrahedral ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfate-reducing Bacteria
Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as terminal electron acceptor, reducing it to hydrogen sulfide (H2S). Therefore, these sulfidogenic microorganisms "breathe" sulfate rather than Allotropes of oxygen, molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in Anaerobic respiration, aerobic respiration. Most sulfate-reducing microorganisms can also reduce some other oxidized inorganic sulfur Chemical compound, compounds, such as sulfite (), dithionite (), thiosulfate (), trithionate (), tetrathionate (), Allotropes of sulfur, elemental sulfur (S8), and polysulfides (). Other than sulfate reduction, some sulfate-reducing microorganisms are also capable of other reactions like disproportionation of sulfur compounds. Depending on the context, "sulfate-reduc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anaerobic Respiration
Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing respiration, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen. Molecular oxygen is an excellent electron acceptor. Anaerobes instead use less-oxidizing substances such as nitrate (), fumarate (), sulfate (), or elemental sulfur (S). These terminal electron acceptors have smaller reduction potentials than O2. Less energy per oxidized molecule is released. Therefore, anaerobic respiration is less efficient than aerobic. As compared with fermentation Anaerobic cellular respiration and fermentation generate ATP in very different ways, and the terms should not be treated as synonyms. Cellular respiration (both aerobic and anaerobic) uses highly reduced chemical compounds such as NADH and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redox
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. The oxidation and reduction processes occur simultaneously in the chemical reaction. There are two classes of redox reactions: * Electron transfer, Electron-transfer – Only one (usually) electron flows from the atom, ion, or molecule being oxidized to the atom, ion, or molecule that is reduced. This type of redox reaction is often discussed in terms of redox couples and electrode potentials. * Atom transfer – An atom transfers from one Substrate (chemistry), substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as the iron converts to an oxide, and simultaneously, the oxidation state of oxygen decreases as it accepts electrons r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
