Radiometric dating - Wikipedia
One isotope, carbon, is particularly useful in determining the age of Using such methods, scientists determined that the age of the Shroud of Turin (Figure One example of a diagnostic application is using radioactive iodine to test. Click here for an excellent site on radiometric techniques, along with some While Iodine (and its unstable isotope I) readily forms. Carbon dating radioactive isotopes - Rich woman looking for older man & younger woman. Read more stable isotope practice test this method what is a useful for. Using naturally - radioactive iodine see iodine see the radioactive isotopes.
This is well-established for most isotopic systems. Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition. Modern dating methods[ edit ] Radiometric dating has been carried out since when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth. In the century since then the techniques have been greatly improved and expanded.
The mass spectrometer was invented in the s and began to be used in radiometric dating in the s. It operates by generating a beam of ionized atoms from the sample under test. 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. 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.
Uranium—lead dating method[ edit ] Main article: Uranium—lead dating A concordia diagram as used in uranium—lead datingwith data from the Pfunze BeltZimbabwe. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years.
Isotopes of iodine - Wikipedia
Zircon has a very high closure 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.
This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample.
Samarium—neodymium dating method[ edit ] Main article: Samarium—neodymium dating This involves the alpha decay of Sm to Nd with a half-life of 1. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable.
Potassium—argon dating This involves electron capture or positron decay of potassium to argon Potassium has a half-life of 1. Rubidium—strontium dating method[ edit ] Main article: Rubidium—strontium dating This is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years. This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples.
Closure 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.
Uranium—thorium dating method[ edit ] Main article: Uranium—thorium dating A relatively short-range dating technique is based on the decay of uranium into thorium, a substance with a half-life of about 80, years. It is accompanied by a sister process, in which uranium decays into protactinium, which has a half-life of 32, years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sedimentsfrom which their ratios are measured.
The scheme has a range of several hundred thousand years. A related method is ionium—thorium datingwhich measures the ratio of ionium thorium to thorium in ocean sediment. Radiocarbon dating method[ edit ] Main article: Carbon is a radioactive isotope of carbon, with a half-life of 5, years,   which is very short compared with the above isotopes and decays into nitrogen.
Carbon, though, is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere and thus remains at a near-constant level on Earth.
The carbon ends up as a trace component in atmospheric carbon dioxide CO2. A carbon-based life form acquires carbon during its lifetime. Plants acquire it through photosynthesisand animals acquire it from consumption of plants and other animals. When an organism dies, it ceases to take in new carbon, and the existing isotope decays with a characteristic half-life years. The proportion of carbon left when the remains of the organism are examined provides an indication of the time elapsed since its death.
This makes carbon an ideal dating method to date the age of bones or the remains of an organism. The carbon dating limit lies around 58, to 62, years. However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon and give inaccurate dates. The releases of carbon dioxide into the biosphere as a consequence of industrialization have also depressed the proportion of carbon by a few percent; conversely, the amount of carbon was increased by above-ground nuclear bomb tests that were conducted into the early s.
Also, an increase in the solar wind or the Earth's magnetic field above the current value would depress the amount of carbon created in the atmosphere. Fission track dating method[ edit ] Main article: This 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 impurities.
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.
This causes induced fission of U, as opposed to the spontaneous fission of U. 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. This scheme has application over a wide range of geologic dates. For dates up to a few million years micastektites glass fragments from volcanic eruptionsand meteorites are best used.
Older materials can be dated using zirconapatitetitaniteepidote and garnet which have a variable amount of uranium content. The technique has potential applications for detailing the thermal history of a deposit.
The residence time of 36Cl in the atmosphere is about 1 week. The timeline of the early molten solar system can be reconstructed by studying short-lived isotopes. Although these isotopes may no longer exist in our solar system, their presence in early rocks and molten matter can be deduced from the presence of their decay products. The ages of the oldest lunar rocks and meteorites indicate that the formation of the major bodies in the solar system was complete by about 4. Most of the meteorites formed within 20 million years of each other, while the Earth and probably the other planets formed within the next million years.
At the beginning of the solar system there were several relatively short-lived radionuclides like 26Al, 60Fe, 53Mn, and I 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.
It has been found, for instance, that meteorites contain the magnesium isotope 26Mg in minerals that normally are made from aluminum. The 26Mg isotope was formed by the decay of the radioactive aluminum isotope 26Al. This is remarkable because the half-life of 26Al is onlyyears and there is no known way in which 26Al could have been made within the solar system.
This means that 26Al must have come from somewhere else. The most likely origin for the 26Al is a supernova explosion of a massive star within the molecular cloud from which both the star and the Sun were formed. The supernova explosion could not have occurred more than a few million years before the formation of the meteorites; otherwise, all of the 26Al would have decayed to 26Mg before it could have been incorporated into meteorites. This tells us that only a few million years elapsed between the start of the collapse of the cloud core and the time that the parent bodies of the meteorites formed.
Another radioactive isotope present in the solar nebula was I Iwhich decays with a half-life of Excesses of Xe Xe in meteorites have been shown to result from decay of I While Iodine and its unstable isotope I readily forms bonds with other elements, Xenon is an inert gas that normally does not. Consequently, the presence of Xenon in a rock mineral implies that it was produced from its parent, I, after the rock solidified.
Otherwise, it would have escaped. A body that solidified early must have originally contained a relatively large quantity of I and should now contain a relatively large quantity of the daughter, Xe. On the other hand, a body that formed millions of years later, after much of the original I had already decayed, should now contain very little Xe.
The fact that Earth rocks contain much less Xenon than do meteorites implies that the Earth was still molten millions of years after the solid meteorites formed. How does Carbon dating work? Carbon has unique properties that are essential for life on Earth.
One rare form, carbon 14Chas 6 protons and 8 neutrons rather than 6.
Isotopes of iodine
Carbon 14C is made when cosmic rays knock neutrons out of atomic nuclei in the upper atmosphere. These displaced neutrons, now moving fast, hit ordinary nitrogen 14N at lower altitudes, converting it into 14C. Unlike common carbon 12C14C is unstable and slowly decays, changing back into nitrogen and releasing energy. This instability makes it radioactive.
Living things are in equilibrium with the atmosphere, and the radioactive carbon dioxide is absorbed and used by plants.