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Carbon Dating Fossil Fuels

  1. Feb 17, 2016 #1
    I have a fair understanding of radioactivity and a general grasp of molecular dating, but I was curious as to how radiocarbon in fossil fuels has survived millions of years despite its half life being only 5,750ish years. From what I've seen through minimal research is that most of the C14 in a sample is decayed by 50,000 years. Any information on the topic would be appreciated.
  2. jcsd
  3. Feb 17, 2016 #2


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    Why do you think there is C14 in fossil fuels.? Do you have a source or a measurement? This NOAA web site says the following, "Fossil fuels are, well, fossils, and are millions of years old. Because of this, all of the radiocarbon initially present has decayed away, leaving no 14C in this ancient organic matter."

    This Wikipedia site also has some relevant info.
  4. Feb 20, 2016 #3
    Because all C14 has decayed after 50,000 years, you need to use another element with a longer half-life, like the Potassium->Argon decay:


    Unlike carbon dating, the sample can be taken from the rock surrounding the fossil, which is good because you need a big bag of rocks to have sufficient Potassium for an accurate dating. For a C14 dating, you need to destroy part of the object itself
  5. Feb 20, 2016 #4


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    The natural occurrence of C-14 in the environment is only about 1 part per trillion. Even at this rarified level of concentration, it is nevertheless possible to measure the radioactivity coming from the decay of this isotope.


    Fossil fuels are for the most part made up of plain old C-12 and C-13.
  6. Feb 21, 2016 #5


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    Perhaps you have misread something? Ratio of C13/C12 in atmosphere is used to show that most of the atmospheric carbon dioxide comes from the burning of the fossil fuels. The rationale behind is that plants prefer C12 during photosynthesis, so the C12/C13 ratio in fossil fuels is much higher than in abiogenic deposits containing carbon. Now that we burn fossil fuels at a high rate most of the carbon dioxide produced is C12 rich so the C13 gets diluted.
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