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The Archean Eon, in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history, preceded by the Hadean Eon and followed by the Proterozoic. The Archean represents the time period from 4,031 to 2,500 Ma. The Late Heavy Bombardment is hypothesized to overlap with the beginning of the Archean. The Huronian glaciation occurred at the end of the eon.
Oceanic anoxic events or anoxic events (anoxia conditions) describe periods 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."
The iron cycle (Fe) is the biogeochemical cycle of iron through the atmosphere, hydrosphere, biosphere and lithosphere. While Fe is highly abundant in the Earth's crust, it is less common in oxygenated surface waters. Iron is a key micronutrient in primary productivity, and a limiting nutrient in the Southern ocean, eastern equatorial Pacific, and the subarctic Pacific referred to as High-Nutrient, Low-Chlorophyll (HNLC) regions of the ocean.
The sulfur cycle is a biogeochemical cycle in which the sulfur moves between rocks, waterways and living systems. It is important in geology as it affects many minerals and in life because sulfur is an essential element (CHNOPS), being a constituent of many proteins and cofactors, and sulfur compounds can be used as oxidants or reductants in microbial respiration. The global sulfur cycle involves the transformations of sulfur species through different oxidation states, which play an important role in both geological and biological processes. Steps of the sulfur cycle are:
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 Early Earth's Paleoproterozoic Era when the Earth's atmosphere and the shallow ocean first experienced a rise in the concentration of oxygen. This began approximately 2.460–2.426 Ga (billion years) ago, during the Siderian period, and ended approximately 2.060 Ga, during the Rhyacian. Geological, isotopic, and chemical evidence suggests that biologically-produced molecular oxygen (dioxygen or O2) started to accumulate in Earth's atmosphere and 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 their present atmospheric level by the end of the GOE.
Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. Anoxic waters can be contrasted with hypoxic waters, which are low in dissolved oxygen. This condition is generally found in areas that have restricted water exchange.
Cholestane is a saturated tetracyclic triterpene. This 27-carbon biomarker is produced by diagenesis of cholesterol and is one of the most abundant biomarkers in the rock record. Presence of cholestane, its derivatives and related chemical compounds in environmental samples is commonly interpreted as an indicator of animal life and/or traces of O2, as animals are known for exclusively producing cholesterol, and thus has been used to draw evolutionary relationships between ancient organisms of unknown phylogenetic origin and modern metazoan taxa. Cholesterol is made in low abundance by other organisms (e.g., rhodophytes, land plants), but because these other organisms produce a variety of sterols it cannot be used as a conclusive indicator of any one taxon. It is often found in analysis of organic compounds in petroleum.
The Boring Billion, otherwise known as the Mid Proterozoic and Earth's Middle Ages, is the time period between 1.8 and 0.8 billion years ago (Ga) spanning the middle Proterozoic eon, characterized by more or less tectonic stability, climatic stasis, and slow biological evolution. It is bordered by two different oxygenation and glacial events, but the Boring Billion itself had very low oxygen levels and no evidence of glaciation.
The Canfield Ocean model was proposed by geochemist Donald Canfield to explain the composition of the ocean in the middle to late Proterozoic.
The oceanic carbon cycle is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many interacting forces across multiple time and space scales that circulates carbon around the planet, ensuring that carbon is available globally. The Oceanic carbon cycle is a central process to the global carbon cycle and contains both inorganic carbon and organic carbon. Part of the marine carbon cycle transforms carbon between non-living and living matter.
Robert Arbuckle Berner was an American scientist known for his contributions to the modeling of the carbon cycle. He taught Geology and Geophysics from 1965 to 2007 at Yale University, where he latterly served as Professor Emeritus until his death. His work on sedimentary rocks led to the co-founding of the BLAG model of atmospheric carbon dioxide, which takes into account both geochemical and biological contributions to the carbon cycle.
The δ34S value is a standardized method for reporting measurements of the ratio of two stable isotopes of sulfur, 34S:32S, in a sample against the equivalent ratio in a known reference standard. Presently, the most commonly used standard is Vienna-Canyon Diablo Troilite (VCDT). Results are reported as variations from the standard ratio in parts per thousand, per mil or per mille, using the ‰ symbol. Heavy and light sulfur isotopes fractionate at different rates and the resulting δ34S values, recorded in marine sulfate or sedimentary sulfides, have been studied and interpreted as records of the changing sulfur cycle throughout the earth's history.
Okenane, the diagenetic end product of okenone, is a biomarker for Chromatiaceae, the purple sulfur bacteria. These anoxygenic phototrophs use light for energy and sulfide as their electron donor and sulfur source. Discovery of okenane in marine sediments implies a past euxinic environment, where water columns were anoxic and sulfidic. This is potentially tremendously important for reconstructing past oceanic conditions, but so far okenane has only been identified in one Paleoproterozoic rock sample from Northern Australia.
Marine biogeochemical cycles are biogeochemical cycles that occur within marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. These biogeochemical cycles are the pathways chemical substances and elements move through within the marine environment. In addition, substances and elements can be imported into or exported from the marine environment. These imports and exports can occur as exchanges with the atmosphere above, the ocean floor below, or as runoff from the land.
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 the Proterozoic period (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.
Carbonate-associated sulfates (CAS) are sulfate species found in association with carbonate minerals, either as inclusions, adsorbed phases, or in distorted sites within the carbonate mineral lattice. It is derived primarily from dissolved sulfate in the solution from which the carbonate precipitates. In the ocean, the source of this sulfate is a combination of riverine and atmospheric inputs, as well as the products of marine hydrothermal reactions and biomass remineralisation. CAS is a common component of most carbonate rocks, having concentrations in the parts per thousand within biogenic carbonates and parts per million within abiogenic carbonates. Through its abundance and sulfur isotope composition, it provides a valuable record of the global sulfur cycle across time and space.
An oxygen minimum zone (OMZ) is characterized as an oxygen-deficient layer in the world's oceans. Typically found between 200m to 1500m deep below regions of high productivity, such as the western coasts of continents. OMZs can be seasonal following the spring-summer upwelling season. Upwelling of nutrient-rich water leads to high productivity and labile organic matter, that is respired by heterotrophs as it sinks down the water column. High respiration rates deplete the oxygen in the water column to concentrations of 2 mg/L or less forming the OMZ. OMZs are expanding, with increasing ocean deoxygenation. Under these oxygen-starved conditions, energy is diverted from higher trophic levels to microbial communities that have evolved to use other biogeochemical species instead of oxygen, these species include Nitrate, Nitrite, Sulphate etc. Several Bacteria and Archea have adapted to live in these environments by using these alternate chemical species and thrive. The most abundant phyla in OMZs are Pseudomonadota, Bacteroidota, Actinomycetota, and Planctomycetota.
Ruth E. Blake is an American geochemist and environmental scientist. She is a professor at Yale University in earth & planetary sciences, environmental studies, and chemical & environmental engineering. Blake's work focuses on marine biogeochemical processes, paleoclimate, astrobiology, and stable isotope geochemistry.
Sulfur isotope biogeochemistry is the study of the distribution of sulfur isotopes in biological and geological materials. In addition to its common isotope, 32S, sulfur has three rare stable isotopes: 34S, 36S, and 33S. The distribution of these isotopes in the environment is controlled by many biochemical and physical processes, including biological metabolisms, mineral formation processes, and atmospheric chemistry. Measuring the abundance of sulfur stable isotopes in natural materials, like bacterial cultures, minerals, or seawater, can reveal information about these processes both in the modern environment and over Earth history.
The Neoproterozoic Oxygenation Event (NOE), also called the Second Great Oxidation Event, was a time interval between around 850 and 540 million years ago which saw a very significant increase in oxygen levels in Earth's atmosphere and oceans. Bringing an end to the Boring Billion, a period of extremely low atmospheric oxygen spanning from the Statherian to the Tonian, the NOE was the second major increase in environmental oxygen on Earth, though it was not as major as the Great Oxidation Event (GOE). Unlike the GOE, it is unclear whether the NOE was a synchronous, global event or a series of asynchronous, regional oxygenation intervals with unrelated causes.
References
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- 1 2 "NAS Member Directory: Donald E. Canfield". 2007. Archived from the original on 2015-03-02.
- 1 2 Canfield, Donald (2015). "Robert A. Berner (1935–2015) Geochemist who quantified the carbon cycle". Nature. 518 (7540): 484. doi: 10.1038/518484a . PMID 25719659.
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- ↑ Canfield, Donald (2014). Oxygen: a four billion year history. Princeton: Princeton University Press. ISBN 978-0-691-14502-0.
- ↑ Fischer, W. W. (2014). "Breathing Life into Oxygen". Science. 343 (6173): 840. Bibcode:2014Sci...343..840F. doi:10.1126/science.1248669. S2CID 51599638.
- ↑ Falkowski, P.; Scholes, R. J.; Boyle, E.; Canadell, J.; Canfield, D.; Elser, J.; Gruber, N.; Hibbard, K.; Högberg, P.; Linder, S.; MacKenzie, F. T.; Moore III, B.; Pedersen, T.; Rosenthal, Y.; Seitzinger, S.; Smetacek, V.; Steffen, W. (2000). "The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System". Science. 290 (5490): 291–296. Bibcode:2000Sci...290..291F. doi:10.1126/science.290.5490.291. PMID 11030643.
- ↑ Canfield, D. E.; Raiswell, R.; Westrich, J. T.; Reaves, C. M.; Berner, R. A. (1986). "The use of chromium reduction in the analysis of reduced inorganic sulfur in sediments and shales". Chemical Geology. 54 (1–2): 149–155. Bibcode:1986ChGeo..54..149C. doi:10.1016/0009-2541(86)90078-1.
- ↑ Canfield, D. E. (1989). "Reactive iron in marine sediments". Geochimica et Cosmochimica Acta. 53 (3): 619–32. Bibcode:1989GeCoA..53..619C. doi:10.1016/0016-7037(89)90005-7. PMID 11539783.
- ↑ Canfield, D. E. (1998). "A new model for Proterozoic ocean chemistry". Letters to Nature. Nature. 396 (6710): 450–453. Bibcode:1998Natur.396..450C. doi:10.1038/24839. S2CID 4414140.
- ↑ Canfield, Donald Eugene (1988). Sulfate reduction and the diagenesis of iron in anoxic marine sediments (PhD thesis). Yale University. OCLC 40356769.
- ↑ Canfield, D. E. (1999). "The evolution of the sulfur cycle". American Journal of Science. 299 (7–9): 697–723. Bibcode:1999AmJS..299..697C. doi:10.2475/ajs.299.7-9.697.
- ↑ Canfield, D. E.; Teske, A. (1996). "Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies". Nature. 382 (6587): 127–32. Bibcode:1996Natur.382..127C. doi:10.1038/382127a0. PMID 11536736. S2CID 4360682.
- ↑ Stolper, D. A.; Revsbech, N. P.; Canfield, D. E. (2010). "Aerobic growth at nanomolar oxygen concentrations". Proceedings of the National Academy of Sciences. 107 (44): 18755–60. doi: 10.1073/pnas.1013435107 . PMC 2973883 . PMID 20974919.
- ↑ Canfield, D. E. (1989). "Sulfate reduction and oxic respiration in marine sediments: Implications for organic carbon preservation in euxinic environments". Deep-Sea Research Part A: Oceanographic Research Papers. 36 (1): 121–38. Bibcode:1989DSRA...36..121C. doi:10.1016/0198-0149(89)90022-8. PMID 11542177.
- ↑ Canfield, D. E.; Poulton, S. W.; Narbonne, G. M. (2007). "Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life". Science. 315 (5808): 92–5. Bibcode:2007Sci...315...92C. doi: 10.1126/science.1135013 . PMID 17158290. S2CID 24761414.
- ↑ Canfield, D. E. (2004). "The evolution of the Earth surface sulfur reservoir". American Journal of Science. 304 (10): 839–861. Bibcode:2004AmJS..304..839C. doi: 10.2475/ajs.304.10.839 .
- ↑ Canfield, D. E.; Habicht, K. S.; Thamdrup, B. (2000). "The Archean sulfur cycle and the early history of atmospheric oxygen". Science. 288 (5466): 658–61. Bibcode:2000Sci...288..658C. doi:10.1126/science.288.5466.658. PMID 10784446.
- ↑ "Vladimir Ivanovich Vernadsky Medal 2010". Archived from the original on 2011-10-05.
- ↑ University of Southern Denmark (2005-10-06). "The travelling scientist". Archived from the original on 2007-09-11. Retrieved 2007-06-30.
- ↑ "DIAS Chairs appointed Knight of The Order of Dannebrog" . Retrieved 11 July 2022.
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