Radiometric dating - Wikipedia
Radiometric dating is mostly used to determine the age of rocks, of a certain type of particle goes down or decays as they are converted. There are different methods of radiometric dating that will vary due to the type of material that is being dated. For example, uranium-lead dating. A limitation with all forms of radiometric dating is that they depend on the radiometric dating is to cite examples radiometric dating techniques.
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.
Radiometric dating - RationalWiki
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.Creation v. Evolution: How Carbon Dating Works
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.
Radioactive dating - The Australian Museum
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.
Carbon dating has an interesting limitation in that the ratio of regular carbon to carbon in the air is not constant and therefore any date must be calibrated using dendrochronology.
Another limitation is that carbon can only tell you when something was last alive, not when it was used.
A limitation with all forms of radiometric dating is that they depend on the presence of certain elements in the substance to be dated. Carbon dating works on organic matter, all of which contains carbon. However it is less useful for dating metal or other inorganic objects. Most rocks contain uranium, allowing uranium-lead and similar methods to date them.
Other elements used for dating, such as rubidium, occur in some minerals but not others, restricting usefulness. Carbon decays almost completely withinyears of the organism dying, and many fossils and rock strata are hundreds of times older than that.
To date older fossils, other methods are used, such as potassium-argon or argon-argon dating. However, the temperature required to do this is in in the millions of degrees, so this cannot be achieved by any natural process that we know about. The second way that a nucleus could be disrupted is by particles striking it. However, the nucleus has a strong positive charge and the electron shells have a strong negative charge.
Any incoming negative charge would be deflected by the electron shell and any positive charge that penetrated the electron shells would be deflected by the positive charge of the nucleus itself. The decay process is as follows. Particles consist of various subtypes. Those that can decay are mesons and baryonswhich include protons and neutrons ; although decays can involve other particles such as photonselectronspositronsand neutrinos.
This can happen due to one of three forces or "interactions": Historically, these are also known as alpha, gamma, and beta decays, respectively. For example, a neutron-deficient nucleus may decay weakly by converting a proton in a neutron to conserve its positive electric charge, it ejects a positron, as well as a neutrino to conserve the quantum lepton number ; thus the hypothetical atom loses a proton and increments down the table by one element.
A complex set of rules describes the details of particle decays: Decays are very random, but for different elements are observed to conform to statistically averaged different lifetimes. If you had an ensemble of identical particles, the probability of finding a given one of them still as they were - with no decay - after some time is given by the mathematical expression where is the mean lifetime of the particle when at restproportional to its half-life, and is the relativistic Lorentz factor of the particle.
This governs what is known as the "decay rate. This makes different elements useful for different time scales of dating; an element with too short an average lifetime will have too few particles left to reveal much one way or another of potentially longer time scales.
Hence, elements such as potassium, which has an average lifetime of nearly 2 billion years before decaying into argon, are useful for very long time scales, with geological applications such as dating ancient lava flows or Martian rocks. Carbon, on the other hand, with a shorter mean lifetime of over years, is more useful for dating human artifacts. Atoms themselves consist of a heavy central core called the nucleus surrounded by arrangements of electron shellswherein there are different probabilities of precisely locating a certain number of electrons depending on the element.
One way that a nucleus could be disrupted is by particles striking it.