|
Surface Exposure Dating
Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats, erosion history, lava flows, meteorite impacts, rock slides, fault scarps, cave development, and other geological events. It is most useful for rocks which have been exposed for between 103 and 106 years. Cosmogenic radionuclide dating The most common of these dating techniques is ''Cosmogenic radionuclide dating''. Earth is constantly bombarded with primary cosmic rays, high energy charged particles – mostly protons and alpha particles. These particles interact with atoms in atmospheric gases, producing a cascade of secondary particles that may in turn interact and reduce their energies in many reactions as they pass through the atmosphere. This cascade includes a small fraction of hadrons, including neutrons. When one of these particles strikes an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geochronology
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 (and biostratigraphic) indicators the precision of the recovered age can be improved. Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloging and comparing fossil floral and faunal assemblages. Biostratigraphy does not ''directly'' provide an absolute age determination of a rock, but merely places it within an ''interval'' of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand, however, to the point where they share the same system of naming strata (rock layers) and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spallation
Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary physics, spallation describes meteoritic impacts on a planetary surface and the effects of stellar winds and cosmic rays on planetary atmospheres and surfaces. In the context of mining or geology, spallation can refer to pieces of rock breaking off a rock face due to the internal stresses in the rock; it commonly occurs on mine shaft walls. In the context of anthropology, spallation is a process used to make stone tools such as arrowheads by knapping. In nuclear physics, spallation is the process in which a heavy nucleus emits numerous nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic weight. In industrial processes and bioprocessing the loss of tubing material due to the repeated flexing of the tu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proxy (climate)
In the study of past climates ("paleoclimatology"), climate proxies are preserved physical characteristics of the past that stand in for direct meteorological measurements and enable scientists to reconstruct the climatic conditions over a longer fraction of the Earth's history. Reliable global records of climate only began in the 1880s, and proxies provide the only means for scientists to determine climatic patterns before record-keeping began. A large number of climate proxies have been studied from a variety of geologic contexts. Examples of proxies include stable isotope measurements from ice cores, growth rates in tree rings, species composition of sub-fossil pollen in lake sediment or foraminifera in ocean sediments, temperature profiles of boreholes, and stable isotopes and mineralogy of corals and carbonate speleothems. In each case, the proxy indicator has been influenced by a particular seasonal climate parameter (e.g., summer temperature or monsoon intensity) at the t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, that is easily removed to create an ion with a positive charge – a cation, that combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac- colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight), and occurs in many minerals such as orthoclase, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust, and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin ''calx'' "lime", which was obtained from heating limestone. Some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are widely used in many industries: in foods and pharma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chlorine-36
Chlorine-36 (36Cl) is an isotope of chlorine. Chlorine has two stable isotopes and one naturally occurring radioactive isotope, the cosmogenic isotope 36Cl. Its half-life is 301,300 ± 1,500 years. 36Cl decays primarily (98%) by beta-minus decay to 36 Ar, and the balance to 36 S. Trace amounts of radioactive 36Cl exist in the environment, in a ratio of about (7–10) × 10−13 to 1 with stable chlorine isotopes. This corresponds to a concentration of approximately 1 Bq/(kg Cl). 36Cl is produced in the atmosphere by spallation of 36 Ar by interactions with cosmic ray protons. In the top meter of the lithosphere, 36Cl is generated primarily by thermal neutron activation of 35Cl and spallation of 39 K and 40 Ca. In the subsurface environment, muon capture by 40 Ca becomes more important. The production rates are about 4200 atoms 36Cl/yr/mole 39K and 3000 atoms 36Cl/yr/mole 40Ca, due to spallation in rocks at sea level. The half-life of this isotope makes it suitable f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', ''number concentration'', and ''volume concentration''. The concentration can refer to any kind of chemical mixture, but most frequently refers to solutes and solvents in solutions. The molar (amount) concentration has variants, such as normal concentration and osmotic concentration. Etymology The term concentration comes from the word concentrate, from the French , from con– + center, meaning “to put at the center”. Qualitative description Often in informal, non-technical language, concentration is described in a qualitative way, through the use of adjectives such as "dilute" for solutions of relatively low concentration and "concentrated" for solutions of relatively high concentration. To concentrate a solution, one must add more solute (for example, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation from α-quartz to β-quartz takes place abruptly at . Since the transformation is accompanied by a significant change in volume, it can easily induce microfracturing of ceramics or rocks passing through this temperature threshold. There are many different varieties of quartz, several of which are classified as gemstones. Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. Quartz is the mineral defining the val ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Surface Processes And Landforms
''Earth Surface Processes and Landforms'' is a peer-reviewed scientific journal published by John Wiley & Sons on behalf of the British Society for Geomorphology. It covers geomorphology and more in general all aspects of Earth sciences dealing with the Earth surface. The journal was established in 1976 as ''Earth Surface Processes'', obtaining its current name in 1981. The journal primarily publishes original research papers. It also publishes ''Earth Surface Exchanges'' which include commentaries on issues of particular geomorphological interest, discussions of published papers, shorter journal articles suitable for rapid publication, and commissioned reviews on key aspects of geomorphological science. Foci include the physical geography of rivers, valleys, glaciers, mountains, hills, slopes, coasts, deserts, and estuary environments, along with research into Holocene, Pleistocene, or Quaternary science. The editor-in-chief is Stuart Lane (University of Lausanne). Abstracting and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Abundance
In physics, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an isotope varies from planet to planet, and even from place to place on the Earth, but remains relatively constant in time (on a short-term scale). As an example, uranium has three naturally occurring isotopes: 238U, 235U and 234U. Their respective natural mole-fraction abundances are 99.2739–99.2752%, 0.7198–0.7202%, and 0.0050–0.0059%. For example, if 100,000 uranium atoms were analyzed, one would expect to find approximately 99,274 238U atoms, approximately 720 235U atoms, and very few (most likely 5 or 6) 234U atoms. This is because 238U is much more stable than 235U or 234U, as the half-life of each isotope reveals: 4.468 × 109 years for 238U com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silicon-28
Silicon (14Si) has 23 known isotopes, with mass numbers ranging from 22 to 44. 28Si (the most abundant isotope, at 92.23%), 29Si (4.67%), and 30Si (3.1%) are stable. The longest-lived radioisotope is 32Si, which is produced by cosmic ray spallation of argon. Its half-life has been determined to be approximately 150 years (with decay energy 0.21 MeV), and it decays by beta emission to 32 P (which has a 14.28-day half-life) and then to 32 S. After 32Si, 31Si has the second longest half-life at 157.3 minutes. All others have half-lives under 7 seconds. List of isotopes , - , rowspan=2, 22Si , rowspan=2 style="text-align:right" , 14 , rowspan=2 style="text-align:right" , 8 , rowspan=2, 22.03579(54)# , rowspan=2, 29(2) ms , β+ (67.6%) , 22Al , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β+, p (32.4%) , 21Mg , - , rowspan=2, 23Si , rowspan=2 style="text-align:right" , 14 , rowspan=2 style="text-align:right" , 9 , rowspan=2, 23.025 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxygen-16
Oxygen-16 (16O) is a stable isotope of oxygen, having 8 neutrons and 8 protons in its nucleus. It has a mass of . Oxygen-16 is the most abundant isotope of oxygen and accounts for 99.762% of oxygen's natural abundance. The relative and absolute abundance of 16O are high because it is a principal product of stellar evolution and because it is a primordial isotope, meaning it can be made by stars that were initially made exclusively of hydrogen. Most 16O is synthesized at the end of the helium fusion process in stars; the triple-alpha process creates 12C, which captures an additional 4He to make 16O. The neon-burning process creates additional 16O. Oxygen-16 is doubly magic. Solid samples (organic and inorganic) for 16O studies are usually stored in silver cups and measured with pyrolysis and mass spectrometry. Researchers need to avoid improper or prolonged storage of the samples for accurate measurements. Oxygen-16 was originally the standard from which the atomic masses of al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
