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Akimasa Masuda - One of the best experts on this subject based on the ideXlab platform.
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Ce and Nd isotope geochemistry on island arc volcanic rocks with negative Ce anomaly: existence of sources with concave REE patterns in the mantle beneath the Solomon and Bonin island arcs
Contributions to Mineralogy and Petrology, 1992Co-Authors: Hiroshi Shimizu, Hideyuki Sawatari, Yousuke Kawata, Peter N. Dunkley, Akimasa MasudaAbstract:^138Ce/^142Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both ε_Ce and ε_Nd. It is shown that these ε_Ce and ε_Ce values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive ε_Nd and negative ε_Ce and the latter have negative ε_Ce and positive or negative ε_Nd. Existence of sources having positive ε_Ce and ε_Nd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian Era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)_N and smaller (Nd/Sm)_N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree.
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Ce and Nd isotope geochemistry on island arc volcanic rocks with negative Ce anomaly: existence of sources with concave REE patterns in the mantle beneath the Solomon and Bonin island arcs
Contributions to Mineralogy and Petrology, 1992Co-Authors: Hiroshi Shimizu, Hideyuki Sawatari, Yousuke Kawata, Peter N. Dunkley, Akimasa MasudaAbstract:138Ce/142Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both eCe and eNd. It is shown that these eCe and eCe values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive eNd and negative eCe and the latter have negative eCe and positive or negative eNd. Existence of sources having positive eCe and eNd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian Era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)N and smaller (Nd/Sm)N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree.
Marc Chaussidon - One of the best experts on this subject based on the ideXlab platform.
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A palaeotempErature curve for the Precambrian oceans based on silicon isotopes in cherts
Nature, 2006Co-Authors: François Robert, Marc ChaussidonAbstract:The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian Era (before 550 million years ago), ranging from surface tempEratures similar to or higher than today's to global glaciation events. The most continuous record of sea surface tempEratures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian Era shows that the observed silicon isotope variations imply seawater tempErature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago.
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A palaeotempErature curve for the Precambrian oceans based on silicon isotopes in cherts
Nature, 2006Co-Authors: François Robert, Marc ChaussidonAbstract:Cherts, dense silicaceous rocks containing microcrystalline quartz, are among the best preserved ocean sediments on Earth and their formation dates cover a period from the early Archaean, 3.5 billion years ago, to the present. New data show that the silicon isotopic composition of cherts varies systematically with geological age and is correlated with the oxygen isotope composition. This means that the isotopic composition of cherts is likely to record their formation tempErature. Using numerical models of the silicon cycle, the isotopic curve derived from this data provides a unique record of Precambrian seawater tempErature variations, with changes from about 70 to 20 °C between 3.5 and 0.8 billion years ago. The terrestrial sediment record indicates that the Earth’s climate varied drastically in the Precambrian Era (before 550 million years ago), ranging from surface tempEratures similar to or higher than today’s to global glaciation events^ 1 . The most continuous record of sea surface tempEratures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments)^ 2 , but the long-term cooling of the oceans inferred from those data^ 3 , 4 , 5 has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments^ 6 . Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence^ 1 , 7 , a model of the silicon cycle in the Precambrian Era shows that the observed silicon isotope variations imply seawater tempErature changes from about 70 °C 3,500 million years ago to about 20 °C 800 million years ago.
Hiroshi Shimizu - One of the best experts on this subject based on the ideXlab platform.
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Ce and Nd isotope geochemistry on island arc volcanic rocks with negative Ce anomaly: existence of sources with concave REE patterns in the mantle beneath the Solomon and Bonin island arcs
Contributions to Mineralogy and Petrology, 1992Co-Authors: Hiroshi Shimizu, Hideyuki Sawatari, Yousuke Kawata, Peter N. Dunkley, Akimasa MasudaAbstract:^138Ce/^142Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both ε_Ce and ε_Nd. It is shown that these ε_Ce and ε_Ce values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive ε_Nd and negative ε_Ce and the latter have negative ε_Ce and positive or negative ε_Nd. Existence of sources having positive ε_Ce and ε_Nd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian Era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)_N and smaller (Nd/Sm)_N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree.
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Ce and Nd isotope geochemistry on island arc volcanic rocks with negative Ce anomaly: existence of sources with concave REE patterns in the mantle beneath the Solomon and Bonin island arcs
Contributions to Mineralogy and Petrology, 1992Co-Authors: Hiroshi Shimizu, Hideyuki Sawatari, Yousuke Kawata, Peter N. Dunkley, Akimasa MasudaAbstract:138Ce/142Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both eCe and eNd. It is shown that these eCe and eCe values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive eNd and negative eCe and the latter have negative eCe and positive or negative eNd. Existence of sources having positive eCe and eNd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian Era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)N and smaller (Nd/Sm)N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree.
Abel Moreno - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Crystalline Silica–Carbonate Biomorphs of Ba(II) under the Presence of RNA and Positively and Negatively Charged ITO Electrodes: Obtainment of Graphite via Bioreduction of CO2 and Its Implications to the Chemical Origin of Life on Primit
ACS omega, 2020Co-Authors: Mayra Cuéllar-cruz, Abel MorenoAbstract:Since Earth was formed, in the Precambrian Era up until our present days, electric current has participated in the morphology and chemical composition of organic and inorganic structures. Attemptin...
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The Role of Calcium and Strontium as the Most Dominant Elements during Combinations of Different Alkaline Earth Metals in the Synthesis of Crystalline Silica-Carbonate Biomorphs
Crystals, 2019Co-Authors: Mayra Cuéllar-cruz, Abel MorenoAbstract:The origin of life from the chemical point of view is an intriguing and fascinating topic, and is of continuous interest. Currently, the chemical elements that are part of the different cellular types from microorganisms to higher organisms have been described. However, although science has advanced in this context, it has not been elucidated yet which were the first chemical elements that gave origin to the first primitive cells, nor how evolution eliminated or incorporated other chemical elements to give origin to other types of cells through evolution. Calcium, barium, and strontium silica-carbonates have been obtained in vitro and named biomorphs, because they mimic living organism structures. Therefore, it is considered that these forms can resemble the first structures that were part of primitive organisms. Hence, the objective of this work was to synthesize biomorphs starting with different mixtures of alkaline earth metals—beryllium (Be2+), magnesium (Mg2+), calcium (Ca2+), barium (Ba2+), and strontium (Sr2+)—in the presence of nucleic acids, RNA and genomic DNA (gDNA). Our results allow us to infer that the stability of calcium followed by strontium had played an important role in the evolution of life since the Precambrian Era until our current age. In this way, the presence of these two chemical elements as well as silica (in the primitive life) and some organic molecules give origin to a great variety of life forms, in which calcium is the most common dominating element in many living organisms as we know nowadays.
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Influence of Nucleic Acids on the Synthesis of Crystalline Ca(II), Ba(II), and Sr(II) Silica–Carbonate Biomorphs: Implications for the Chemical Origin of Life on Primitive Earth
Crystal Growth & Design, 2019Co-Authors: Mayra Cuéllar-cruz, Selene R. Islas, Gonzalo Gonzalez, Abel MorenoAbstract:The Precambrian Era is associated with the origin of life on primitive Earth. It was, in fact, in that Era that ribonucleic acid (RNA) was first acquired. From this evolved the genomic deoxyribonucleic acid (DNA) that later genErated the biomolecules that formed the first cell. In this way, with the ongoing changes in environmental factors, the first cells evolved to give rise to higher multicellular organisms, i.e., plants and animals. Radiolarians and diatoms are organisms that have been conserved since the Precambrian Era. However, although these organisms are alive (they can be considered as living fossils), they do not suffice to explain the origin of life. To understand the origin of life, the intEractions among inorganic compounds that existed in the Precambrian Era must be elucidated. In this context, calcium, barium, or strontium silico-carbonates (usually called silica-biomorphs) have been simply named biomorphs that emulate the morphologies of organisms, such as flowers, leaves, stems, helices,...
François Robert - One of the best experts on this subject based on the ideXlab platform.
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A palaeotempErature curve for the Precambrian oceans based on silicon isotopes in cherts
Nature, 2006Co-Authors: François Robert, Marc ChaussidonAbstract:The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian Era (before 550 million years ago), ranging from surface tempEratures similar to or higher than today's to global glaciation events. The most continuous record of sea surface tempEratures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian Era shows that the observed silicon isotope variations imply seawater tempErature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago.
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A palaeotempErature curve for the Precambrian oceans based on silicon isotopes in cherts
Nature, 2006Co-Authors: François Robert, Marc ChaussidonAbstract:Cherts, dense silicaceous rocks containing microcrystalline quartz, are among the best preserved ocean sediments on Earth and their formation dates cover a period from the early Archaean, 3.5 billion years ago, to the present. New data show that the silicon isotopic composition of cherts varies systematically with geological age and is correlated with the oxygen isotope composition. This means that the isotopic composition of cherts is likely to record their formation tempErature. Using numerical models of the silicon cycle, the isotopic curve derived from this data provides a unique record of Precambrian seawater tempErature variations, with changes from about 70 to 20 °C between 3.5 and 0.8 billion years ago. The terrestrial sediment record indicates that the Earth’s climate varied drastically in the Precambrian Era (before 550 million years ago), ranging from surface tempEratures similar to or higher than today’s to global glaciation events^ 1 . The most continuous record of sea surface tempEratures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments)^ 2 , but the long-term cooling of the oceans inferred from those data^ 3 , 4 , 5 has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments^ 6 . Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence^ 1 , 7 , a model of the silicon cycle in the Precambrian Era shows that the observed silicon isotope variations imply seawater tempErature changes from about 70 °C 3,500 million years ago to about 20 °C 800 million years ago.