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Cool examples of radiometric dating?

  1. Feb 21, 2013 #1
    So, I know that C-14 dating is being used now to solve crimes/identify bodies. Any other examples of it being used for things besides dating really old rocks/fossils? I'm teaching an Earth Science class and I want to show them a few cool articles.
  2. jcsd
  3. Feb 22, 2013 #2
    I'm a bit surprised about that because of the rather high error rate. Also, neither rocks nor petrified fossils can be dated by 14C dating.

    But it's used widespread for any organic remains, especially in sediment cores to establish a chronology and for archeological artifacs.

    some more here
  4. Feb 24, 2013 #3
    There are relative and absolute dating methods used, and they are used in conjunction with one another to give the age range of a site.

    Relative dating methods say "this is older/younger than x." Examples of relative dating are:

    Stratigraphy- The mapping of layers of sedimentation or artifact deposition. In most cases, the deeper the layer, the older it is, IF there is no disturbance (tunneling animals, digging of post holes for a building, etc.).

    Zooarchaeological analysis- The study of faunal remains in archaeological context. By studying the remains of animals at a site and comparing them to known periods when they were alive, a site can be dated. For instance, finding remains from Pleistocene megafauna (mammoths are the obvious choice) will give you a relative date.

    Palynology- Performing a pollen analysis on the material excavated at the site. Certain plants existed at certain times, in certain places in the past. It also gives climate and environmental information, because those plants live in very specific climatic circumstances.

    Seriation- Analyzing the artifacts used at a site and placing them into categories according to times in the past they were traditionally used. Spearpoints, arrowheads, and pottery are the most likely candidates, as their technology, frequency, and style changes over time. When a new style is being developed, very few of the newer type will be found, but as the style gains widespread use, many will be found before they slowly disappear to make room for the ever-newer style.

    Absolute dating methods- this gives you an exact date ± a set of years.

    Radiocarbon dating- (C14 dating) The most widely-known and used. All living things take in C14 as they live, and stop taking it in when they die. C14 decays at a known rate over time. By analyzing the amount of C14 left in dead material, you know that it died x number of years ago, within a possible date range. It's effective to about 50,000 years before present (YBP). As a rule of thumb, a minimum of three separate samples must be taken from different remains at the site for a meaningful date. This is often used in conjunction with...
    Dendrochronology- Simply put, counting tree rings and analyzing that sample via radiocarbon dating. This gives a much closer approximation of the date of the material, called a "Calibrated Date." For instance, the Clovis, NM site's uncalibrated date is 11,200 YBP, but the calibrated date pushed it back to 13,500 YBP.

    Potassium/Argon dating (K/Ar dating)- This measures the decay of an isotope of Potassium (40K) into Argon over time. This is usually used on volcanic deposits and can measure to ~1.3 Billion years before present to 100,000 YBP. Yes, billion.
    Fission Track Dating- This is relatively new. It measures the damage (or tracks) left by decaying uranium atoms in natural glasses (such as obsidian) and some minerals. It can date materials from 3 million YBP to 100,000 YBP.
    Obsidian Hydration Dating- Measures the amount of water absorbed by a piece of broken obsidian. Water works its way into a flintknapped or otherwise broken piece of obsidian at an observable rate. This can be measured simply using a microscope, where a small sample is taken from the artifact, or by using the much more technical and non-destructive (and therefore better, but much more expensive) Secondary Ion Mass Spectrometry method. This is used to date material as old as eight million YBP.

    Thermoluminescence (TL)- This method can only be used on burned materials like fire-cracked rock, pottery, and sediments exposed to sunlight. It measures the amount of accumulated radiation in an artifact or other sample. When the material is heated, it emits a small amount of light based on the amount of radiation stored within. This amount is measured. It is used to date material up to 50,000 YBP.

    Archaeomagnetic Dating- This depends upon the inclusion of magnetite within an artifact. It analyzes the magnetic properties of the material as it relates to the Earth’s magnetic field at a given time in the past. This is effective on material up to 10,000 YBP.

    Electron Paramagnetic Resonance- These are incredibly technical dating methods. They are based on the electron spin in an artifact by measuring the electromagnetic field of unpaired electrons in bone or calcite formation, and are effective from 1,000 to 2 million YBP. Nuclear Magnetic Resonance is also used- in MRI’s.

    Uranium Series Dating (Uranium/Thorium Dating, Thorium-230 dating, Uranium-Series Disequilibrium Dating)- This measures the amount of Uranium-234 compared to the amount of Thorium-230 in a given sample. Uranium-234 has a measured radioactive decay into Thorium-230. The isotope Uranium-234 must also be measured against its parent isotope, Uranium-238, for an accurate measurement of radioactive decay. This is effective on any materials containing calcium carbonate- bones, mollusk shells, limestone, stalactites and stalagmites. It is used to date materials up to 500,000 YBP.

    Cosmogenic Nuclide Dating- This is an incredibly new process of dating. In one study, it measures the isotopes of Beryllium and the effects of cosmic rays, high-energy particles that come to Earth from space, causing the Beryllium to have differing numbers of neutrons. There are a total of 21 isotopes created by cosmic rays spread over a number of different elements. This dating method is most often used in Geology, focusing on Aluminum, Chlorine, Calcium, and Iodine, which each have half-lifes of 720,000, 308,000, 103,000, and 15,700,000 years, respectively.
    Last edited: Feb 24, 2013
  5. Feb 24, 2013 #4
  6. Feb 25, 2013 #5
    Apparently, thanks to nuclear bomb testing in the 40s, C-14 dating can be used on recent teeth to date someone's year of birth within 3-6 years, which is helpful when trying to identify bodies. There is a new method testing the eye that is even more accurate, but only useful within 3 days of death.

    And I meant radiometric dating as a whole is used for fossils and old rocks, not C-14. The C-14 being used forensically was just an example of radiometric dating being used for something different.
  7. Feb 25, 2013 #6
    That would be interesting to learn more about it. For the mere mortals who would have to use the INTCAL09 calibration table life is not so easy.

    Scroll all the way down to the bottom, notice that 0 cal yrs BP is CE 1950, notice the error margin and the reversing of the scale, so if something was to be dated say 150 radiocarbon years ago then the table would both return ~20 cal BP (CE 1930) and ~145 Cal BP or CE 1805.
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