Radiometric dating (often called radioactive dating) is a technique used to date materials, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides ^[1] It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials. Modern geologists and Geophysicists consider the age of Earth to be around 4 Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating. Radiocarbon dating is a Radiometric dating method that uses the naturally occurring Radioisotope Carbon-14 (14C to determine the age of Potassium-argon dating or K-Ar dating is a Radiometric dating method used in Geochronology and Archeology. Uranium-lead is one of the oldest and most refined Radiometric dating schemes with a routine age range of about 1 million years to over 4 By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. eVolution is the third Album by eLDee, it was due to be released in 2008 Radiometric dating is also used to date archaeological materials, including ancient artifacts. Archaeology, archeology, or archæology (from Greek grc ἀρχαιολογία archaiologia – grc ἀρχαῖος archaīos

Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

Contents 1 Fundamentals of radiometric dating 1.1 Blocking temperature 1.2 The age equation 1.3 Limitation of techniques 2 Modern dating techniques 3 Short-range dating techniques 4 Dating with shortlived extinct radionuclides 5 Types of radiometric dating 6 See also 7 References 8 External links

Fundamentals of radiometric dating

All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus. Matter is commonly defined as being anything that has mass and that takes up space. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom Additionally, elements may exist in different isotopes, with each isotope of an element differing in the number of neutrons in the nucleus. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. A particular isotope of a particular element is called a nuclide. A nuclide (from lat nucleus is a species of Atom characterized by the constitution of its nucleus and hence by the number of Protons, the number of Some nuclides are inherently unstable. That is, at some point in time, an atom of such a nuclide will spontaneously transform into a different nuclide. This transformation may be accomplished in a number of different ways, including radioactive decay, either by emission of particles (usually electrons (beta decay), positrons or alpha particles) or by spontaneous fission, and electron capture. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Spontaneous fission (SF is a form of Radioactive decay characteristic of very heavy Isotopes and is theoretically possible for any atomic nucleus whose mass is greater Electron capture (sometimes called inverse beta decay) is a Decay mode for Isotopes that will occur when there are too many Protons in the

While the moment in time at which a particular nucleus decays is unpredictable, a collection of atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life, usually given in units of years when discussing dating techniques. A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value Half-Life (computer-game page here It's already listed in the disambiguation page After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a "daughter" nuclide or decay product. In Nuclear physics, a decay product, also known as a daughter product, daughter isotope or daughter nuclide, is a Nuclide In many cases, the daughter nuclide itself is radioactive, resulting in a decay chain, eventually ending with the formation of a stable (nonradioactive) daughter nuclide; each step in such a chain is characterized by a distinct half-life. In Nuclear science, the decay chain refers to the Radioactive decay of different discrete radioactive decay products as a chained series of transformations In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in the ultimate transformation of the radioactive nuclide into its stable daughter. Isotopic systems that have been exploited for radiometric dating have half-lives ranging only about 10 years (e. g. , tritium) to over 100 billion years (e. Tritium (ˈtɹɪtiəm symbol or, also known as Hydrogen-3) is a radioactive Isotope of Hydrogen. g. , Samarium-147). Naturally occurring Samarium ( Sm) is composed of 4 stable Isotopes 144Sm 150Sm 152Sm and 154Sm and 3 extremely

In general, the half-life of a nuclide depends solely on its nuclear properties; it is not affected^[2] by external factors such as temperature, pressure, chemical environment, or presence of a magnetic or electric field. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can (For some nuclides which decay by the process of electron capture, such as Beryllium-7, Strontium-85, and Zirconium-89, the decay rate may be slightly affected by local electron density, therefore these isotopes may not be as suitable for radiometric dating. Electron capture (sometimes called inverse beta decay) is a Decay mode for Isotopes that will occur when there are too many Protons in the ) But in general, the half-life of any nuclide is essentially a constant. Therefore, in any material containing a radioactive nuclide, the proportion of the original nuclide to its decay product(s) changes in a predictable way as the original nuclide decays over time. This predictability allows the relative abundances of related nuclides to be used as a clock that measures the time from the incorporation of the original nuclide(s) into a material to the present. Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating Circadian rhythm.

The processes that form specific materials are often conveniently selective as to what elements they incorporate during their formation. In the simplest case, the material will incorporate a parent nuclide and reject the daughter nuclide. In this case, the only atoms of the daughter nuclide present in a sample must have been deposited by radioactive decay since the sample formed. When a material incorporates both the parent and daughter nuclides at the time of formation, a correction must be made for the initial proportion of the radioactive substance and its daughter; generally this is done by construction of an isochron, e. Isochron dating is a common technique of Radiometric dating and is applied to date certain events such as Crystallization Metamorphism, shock events and g. in Rubidium-strontium dating. The rubidium-strontium dating method is a Radiometric dating technique that geologists use to determine the age of rocks.

Accurate radiometric dating generally requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation, that the parent has a long enough half-life that it will still be present in significant amounts at the time of measurement (except as described below under "Dating with shortlived extinct radionuclides"), the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material. The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate.

Blocking temperature

If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusion, setting the isotopic "clock" to zero. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement The temperature at which this happens is known as the blocking temperature or closure temperature and is specific to a particular material and isotopic system. "The temperature below which Isotopes in a Mineral are no longer free to move at which point the Radiometric clock starts These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace.

The age equation

Considering that radioactive parent elements decay to stable daughter elements ^[3], the mathematical expression that relates radioactive decay to geologic time, called the age equation, is ^[4]:

where

t = age of the sample

D = number of atoms of the daughter isotope in the sample

P = number of atoms of the parent isotope in the sample

λ = decay constant of the parent isotope

ln = natural logarithm

The decay constant (or rate of decay^[5]) is the fraction of a number of atoms of a radioactive nuclide that disintegrates in a unit of time. A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value The natural logarithm, formerly known as the Hyperbolic logarithm is the Logarithm to the base e, where e is an irrational The decay constant is inversely proportional to the radioactive half-life of the parent isotope, which can be obtained from tables such as the one on this page. Half-Life (computer-game page here It's already listed in the disambiguation page

Limitation of techniques

Although radiometric dating is accurate in principle, the precision is very dependent on the care with which the procedure is performed. The possible confounding effects of initial contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created.

Precision is enhanced if measurements are taken on different samples from the same rock body but at different locations. Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron. Isochron dating is a common technique of Radiometric dating and is applied to date certain events such as Crystallization Metamorphism, shock events and Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample.

The precision of a dating method depends in part on the half-life of the radioactive isotope involved. For instance, carbon-14 has a half-life of about 6000 years. After an organism has been dead for 60,000 years, so little carbon-14 is left in it that accurate dating becomes impossible. On the other hand, the concentration of carbon-14 falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades. The isotope used in uranium-thorium dating has a longer half-life, but other factors make it more accurate than radiocarbon dating. Uranium-thorium dating, also called thorium-230 dating, uranium-series disequilibrium dating or uranium-series dating, is a Radiometric dating Radiocarbon dating is a Radiometric dating method that uses the naturally occurring Radioisotope Carbon-14 (14C to determine the age of

Modern dating techniques

Radiometric dating can be performed on samples as small as a billionth of a gram using a mass spectrometer. Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles The mass spectrometer was invented in the 1940s and began to be used in radiometric dating in the 1950s. The 1940s decade ran from 1940 to 1949 Events and trends The 1940s was a period between the radical 1930s and the conservative 1950s which also leads the period to be The 1950s Decade refers to the years of 1950 to 1959 inclusive The mass spectrometer operates by generating a beam of ionized atoms from the sample under test. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as "Faraday cups", depending on their mass and level of ionization. A Faraday cup is a Metal (conductive cup designed to catch charged particles in vacuum On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams.

The uranium-lead radiometric dating scheme is one of the oldest available, as well as one of the most highly respected. Uranium-lead is one of the oldest and most refined Radiometric dating schemes with a routine age range of about 1 million years to over 4 It has been refined to the point that the error in dates of rocks about three billion years old is no more than two million years.

Uranium-lead dating is often performed on the mineral "zircon" (ZrSiO₄), though it can be used on other materials. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Zircon is a Mineral belonging to the group of nesosilicates. Its chemical name is Zirconium silicate and its corresponding chemical formula is Zircon incorporates uranium atoms into its crystalline structure as substitutes for zirconium, but strongly rejects lead. Zirconium (zɚˈkoʊniəm /ˌzɝˈkoʊniəm/ is a Chemical element with the symbol Zr and Atomic number 40 It has a very high blocking temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event. In situ micro-beam analysis can be achieved via laser ICP-MS or SIMS techniques ^[6] . ICP-MS ( Inductively coupled plasma mass spectrometry) is a type of Mass spectrometry that is highly sensitive and capable of the determination of a range of Metals Secondary ion mass spectrometry (SIMS is a technique used to analyze the composition of solid surfaces and Thin films by Sputtering the surface of the specimen with

One of its great advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238's decay to lead-206 with a half-life of about 4. 5 billion years, providing a built-in crosscheck that allows accurate determination of the age of the sample even if some of the lead has been lost.

Two other radiometric techniques are used for long-term dating. Potassium-argon dating involves electron capture or positron decay of potassium-40 to argon-40. Potassium-argon dating or K-Ar dating is a Radiometric dating method used in Geochronology and Archeology. Electron capture (sometimes called inverse beta decay) is a Decay mode for Isotopes that will occur when there are too many Protons in the The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. Potassium-40 has a half-life of 1. 3 billion years, and so this method is applicable to the oldest rocks. Radioactive potassium-40 is common in micas, feldspars, and hornblendes, though the blocking temperature is fairly low in these materials, about 125°C (mica) to 450°C (hornblende). The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially Feldspar is the name of a group of rock-forming Minerals which make up as much as 60% of the Earth 's crust. Hornblende is a complex inosilicate series of Minerals Hornblende is not a recognized mineral in its own right but the name is used as a general or field term to

Rubidium-strontium dating is based on the beta decay of rubidium-87 to strontium-87, with a half-life of 50 billion years. The rubidium-strontium dating method is a Radiometric dating technique that geologists use to determine the age of rocks. Rubidium (ruːˈbɪdiəm /rəˈbɪdiəm/ is a Chemical element with the symbol Rb and Atomic number 37 Strontium (ˈstrɒntiəm /ˈstrɒnʃiəm/) is a Chemical element with the symbol Sr and the Atomic number 38 This scheme is used to date old igneous and metamorphic rocks, and has also been used to date lunar samples. Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change Blocking temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample.

Short-range dating techniques

There are a number of dating techniques that have short ranges and are so used for historical or archaeological studies. One of the best-known is the carbon-14 (C14) radiometric technique. Radiocarbon dating is a Radiometric dating method that uses the naturally occurring Radioisotope Carbon-14 (14C to determine the age of

Carbon-14 is a radioactive isotope of carbon, with a half-life of 5,730 years (very short compared with the above). In other radiometric dating methods, the heavy parent isotopes were synthesized in the explosions of massive stars that scattered materials through the Galaxy, to be formed into planets and other stars. The parent isotopes have been decaying since that time, and so any parent isotope with a short half-life should be extinct by now.

Carbon-14 is an exception. It is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on The carbon-14 ends up as a trace component in atmospheric carbon dioxide (CO₂). Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single

An organism acquires carbon from carbon dioxide during its lifetime. Plants acquire it through photosynthesis, and animals acquire it from consumption of plants and other animals. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. When an organism dies, it ceases to intake new carbon-14 and the existing isotope decays with a characteristic half-life (5730 years). The proportion of carbon-14 left when the remains of the organism are examined provides an indication of the time lapsed since its death. The carbon-14 dating limit lies around 58,000 to 62,000 years [1].

The rate of creation of carbon-14 appears to be roughly constant, as cross-checks of carbon-14 dating with other dating methods show it gives consistent results. However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon-14 and give inaccurate dates. Plate tectonics and hotspots Divergent plate boundaries At the The releases of carbon dioxide into the biosphere as a consequence of industrialization have also depressed the proportion of carbon-14 by a few percent; conversely, the amount of carbon-14 was increased by above-ground nuclear bomb tests that were conducted into the early 1960s. The biosphere is the broadest level of ecological study the global sum of all Ecosystems. A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 Also, an increase in the solar wind or the earth's magnetic field above the current value would depress the amount of carbon-14 created in the atmosphere. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges These effects are corrected for by the calibration of the radiocarbon dating scale. See the article on radiocarbon dating. Radiocarbon dating is a Radiometric dating method that uses the naturally occurring Radioisotope Carbon-14 (14C to determine the age of

Another relatively short-range dating technique is based on the decay of uranium-238 into thorium-230, a substance with a half-life of about 80,000 years. It is accompanied by a sister process, in which uranium-235 decays into protactinium-231, which has a half-life of 34,300 years.

While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sediments, from which their ratios are measured. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Thorium (ˈθɔːriəm is a Chemical element with the symbol Th and Atomic number 90 Protactinium (ˌproʊtækˈtɪniəm is a Chemical element with the symbol Pa and Atomic number 91 Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of The scheme has a range of several hundred thousand years.

Natural sources of radiation in the environment knock loose electrons in, say, a piece of pottery, and these electrons accumulate in defects in the material's crystal lattice structure. Heating the object will release the captured electrons, producing a luminescence. When the sample is heated, at a certain temperature it will glow from the emission of electrons released from the defects, and this glow can be used to estimate the age of the sample to a threshold of approximately 15 percent of its true age. The date of a rock is reset when volcanic activity remelts it. The date of a piece of pottery is reset by the heat of the kiln. Typically temperatures greater than 400 degrees Celsius will reset the "clock". This is termed thermoluminescence. Some mineral substances such as Fluorite store energy when exposed to Ultraviolet or other Ionising radiation.

Finally, fission track dating involves inspection of a polished slice of a material to determine the density of "track" markings left in it by the spontaneous fission of uranium-238 impurities. Fission track dating is a Radiometric dating technique based on analyses of the damage trails or tracks left by fission fragments in certain Uranium bearing Spontaneous fission (SF is a form of Radioactive decay characteristic of very heavy Isotopes and is theoretically possible for any atomic nucleus whose mass is greater

The uranium content of the sample has to be known, but that can be determined by placing a plastic film over the polished slice of the material, and bombarding it with slow neutrons. The neutron temperature, also called the neutron energy, indicates a free neutron's Kinetic energy, usually given in Electron volts The term This causes induced fission of ²³⁵U, as opposed to the spontaneous fission of ²³⁸U. The fission tracks produced by this process are recorded in the plastic film. The uranium content of the material can then be calculated from the number of tracks and the neutron flux. In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks

This scheme has application over a wide range of geologic dates. For dates up to a few million years micas, tektites (glass fragments from volcanic eruptions), and meteorites are best used. The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially Tektites (from Greek tektos, molten are natural Glass objects up to a few centimeters in size which most scientists argue were formed by the impact of Older materials can be dated using zircon, apatite, titanite, epidote and garnet which have a variable amount of uranium content. Zircon is a Mineral belonging to the group of nesosilicates. Its chemical name is Zirconium silicate and its corresponding chemical formula is Titanite or sphene is a Calcium Titanium nesosilicate Mineral, Ca[[titanium Ti]] Si[[oxygen O]]5 Epidote is a Calcium Aluminium Iron sorosilicate Mineral, Ca2Al2(Fe3+Al(SiO4(Si2O7O(OH The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives Because the fission tracks are healed by temperatures over about 200°C the technique has limitations as well as benefits. The technique has potential applications for detailing the thermal history of a deposit.

Large amounts of otherwise rare ³⁶Cl were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. The residence time of ³⁶Cl in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, ³⁶Cl is also useful for dating waters less than 50 years before the present. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations ³⁶Cl has seen use in other areas of the geological sciences, including dating ice and sediments.

Dating with shortlived extinct radionuclides

At the beginning of the solar system there were several relatively shortlived radionuclides like ²⁶Al, ⁶⁰Fe, ⁵³Mn, and ¹²⁹I present within the solar nebula. These radionuclides—possibly produced by the explosion of a supernova—are extinct today but their decay products can be detected in very old material such as meteorites. A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface Measuring the decay products of extinct radionuclides with a mass spectrometer and using isochronplots it is possible to determine relative ages between different events in the early history of the solar system. Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles Dating methods based on extinct radionuclides can also be calibrated with the U-Pb method to give absolute ages.

Types of radiometric dating

• argon-argon (Ar-Ar)
• fission track dating
• helium (He-He)
• iodine-xenon (I-Xe)
• lanthanum-barium (La-Ba)
• lead-lead (Pb-Pb)
• lutetium-hafnium (Lu-Hf)
• neon-neon (Ne-Ne)
• optically stimulated luminescence dating
• potassium-argon (K-Ar)
• radiocarbon dating
• rhenium-osmium (Re-Os)
• rubidium-strontium (Rb-Sr)
• samarium-neodymium (Sm-Nd)
• uranium-lead (U-Pb)
• uranium-lead-helium (U-Pb-He)
• uranium-thorium (U-Th)
• uranium-uranium (U-U)

See also

• Age of the Earth
• Exponential decay
• Half-life
• Isochron dating
• Isotope geochemistry
• Isotopic signature
• Radioactive decay
• Radioactivity
• sensitive high resolution ion microprobe (SHRIMP)

References

External links

• USGS page on the radiometric time scale
• Principles of radiometric dating.
• Simple explanation of relationship between radiometric and biostratigraphic dating
• Radioactive Isotope information with relation to the Periodic Table

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