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Thorium is a chemical element. It has the symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive gray when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.
The Younger Dryas, which occurred circa 12,900 to 11,700 years BP, was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum, which lasted from circa 27,000 to 20,000 years BP. The Younger Dryas was the last stage of the Pleistocene epoch that spanned from 2,580,000 to 11,700 years BP and it preceded the current, warmer Holocene epoch. The Younger Dryas was the most severe and longest lasting of several interruptions to the warming of the Earth's climate, and it was preceded by the Late Glacial Interstadial, an interval of relative warmth that lasted from 14,670 to 12,900 BP.
Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as paleomagnetism and stable isotope ratios. By combining multiple geochronological indicators the precision of the recovered age can be improved.
Typhoon Lee is an astrophysicist and geochemist at Academia Sinica, Taiwan, where he specializes in isotope geochemistry and nuclear astrophysics.
The Eemian was the interglacial period which began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period. It corresponds to Marine Isotope Stage 5e. Although sometimes referred to as the "last interglacial", it was the second-to-latest interglacial period of the current Ice Age, the most recent being the Holocene which extends to the present day. The prevailing Eemian climate was, on average, around 1 to 2 degrees Celsius warmer than that of the Holocene. During the Eemian, the proportion of CO2 in the atmosphere was about 280 parts per million.
The Bimini Road, sometimes called the Bimini Wall, is an underwater rock formation near North Bimini island in the Bahamas. The Road consists of a 0.8 km (0.50 mi)-long northeast-southwest linear feature composed of roughly rectangular limestone blocks. Various claims have been made for this feature being either a wall, road, pier, breakwater, or other man-made structure. However, credible evidence or arguments are lacking for such an origin.
Uranium–thorium dating, also called thorium-230 dating, uranium-series disequilibrium dating or uranium-series dating, is a radiometric dating technique established in the 1960s which has been used since the 1970s to determine the age of calcium carbonate materials such as speleothem or coral. Unlike other commonly used radiometric dating techniques such as rubidium–strontium or uranium–lead dating, the uranium-thorium technique does not measure accumulation of a stable end-member decay product. Instead, it calculates an age from the degree to which secular equilibrium has been restored between the radioactive isotope thorium-230 and its radioactive parent uranium-234 within a sample.
Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routine precisions in the 0.1–1 percent range.
Thorium (90Th) has seven naturally occurring isotopes but none are stable. One isotope, 232Th, is relatively stable, with a half-life of 1.405×1010 years, considerably longer than the age of the Earth, and even slightly longer than the generally accepted age of the universe. This isotope makes up nearly all natural thorium, so thorium was considered to be mononuclidic. However, in 2013, IUPAC reclassified thorium as binuclidic, due to large amounts of 230Th in deep seawater. Thorium has a characteristic terrestrial isotopic composition and thus a standard atomic weight can be given.
Gideon Mark Henderson FRS is a British geochemist whose research focuses on low-temperature geochemistry, the carbon cycle, the oceans, and on understanding the mechanisms driving climate change.
George Tilton was an American geochemist who specialized in uranium-lead geochronology. He was the first to measure a U-Pb date on zircon and was instrumental in developing analytical techniques for the measurement of U, Th, and Pb in minerals and rocks, using isotope dilution and mass spectrometry.
Minze Stuiver was a Dutch geochemist who was at the forefront of geoscience research from the 1960s until his retirement in 1998. He helped transform radiocarbon dating from a simple tool for archaeology and geology to a precise technique with applications in solar physics, oceanography, geochemistry, and carbon dynamics. Minze Stuiver's research encompassed the use of radiocarbon (14C) to understand solar cycles and radiocarbon production, ocean circulation, lake carbon dynamics and archaeology as well as the use of stable isotopes to document past climate changes.
Electron spin resonance dating, or ESR dating, is a technique used to date materials which radiocarbon dating cannot, including minerals, biological materials, archaeological materials and food. Electron spin resonance dating was first introduced to the science community in 1975, when Japanese nuclear physicist Motoji Ikeya dated a speleothem in Akiyoshi Cave, Japan. ESR dating measures the amount of unpaired electrons in crystalline structures that were previously exposed to natural radiation. The age of a substance can be determined by measuring the dosage of radiation since the time of its formation.
Ouki was an ancient lake in the Bolivian Altiplano. Its existence was postulated in 2006 by a group of scientists who had subdivided the Lake Minchin lake cycle into several lake phases. The Lake Minchin cycle had been previously identified in 1904 as a now disappeared lake in the central Altiplano. Sediments attributed to Lake Minchin may rather be part of Ouki. The dating is uncertain, with radiocarbon and uranium-thorium dating yielding different dates spanning the time between 28,200 and 125,990 ± 9,580 years ago.
Kirsty Elizabeth Helena Penkman is a analytical chemist and geochemist known for her research in biomolecular archaeology, the use of ancient DNA, amino acid dating, and other biomolecules in order to date fossils and learn about the world as it was in prehistoric times. She a professor in chemistry at the University of York.
Edouard Bard, born on September 1, 1962, is a French climatologist, Professor of Climate and Ocean Evolution at the Collège de France and a member of the French Academy of Sciences.
Eric Steig is a Canadian-American scientist specializing in polar climate, glaciology, isotope geochemistry, and ice core science.
Porites lutea is a species of stony coral in the family Poritidae. It is found growing in very shallow water on reefs in the Indo-Pacific region. It sometimes forms "microatolls" in the intertidal zone and these massive structures have been used to study trends in sea levels and sea water temperature.
Elizabeth Niespolo is an American geologist. Her work utilizes geochemical methods to understand archaeological sites and human activity on multiple continents. Niespolo integrates laboratory and field work studying natural materials such as ostrich egg shells, corals, and minerals in rocks to quantify potential human environmental signatures preserved in these materials and their relevance in piecing together understanding of Homo sapiens through time. In the absence of archaeological sites, Niespolo uses high precision isotopic dating of minerals from volcanoes to determine their petrologic and eruptive history.
Sherilyn Fritz is known for her research on paleoclimate and paleoecology, with a particular focus on the use of diatoms to reconstruct past environmental conditions.
References
- ↑ "R. Lawrence Edwards". College of Science and Engineering. Retrieved 2023-09-01.
- 1 2 "These two geochemists have one of the largest publishing networks in science". Nature Index. 2020-06-26. Retrieved 2023-09-01.
- 1 2 Edwards, Richard Lawrence (1988). High Precision Thorium-230 Ages of Corals and the Timing of Sea Level Fluctuations in the Late Quaternary (phd thesis). California Institute of Technology.
- ↑ "R. Lawrence 'Larry' Edwards". University of Minnesota. 2015-09-08. Retrieved 2024-02-02.
- ↑ "These two geochemists have one of the largest publishing networks in science". Nature Index. 2020-06-26. Retrieved 2024-02-02.
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