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KCC's Quizzes AQQ245 on Fossil Dating with Carbon14

   

You probably heard the method of dating fossils by measuring Carbon14 (also note C14 concentration. To refresh, the concentration of C14 in the air and on earth surface is constant (thanks to cosmic radiation) since ever (in fact it is assumed so). C14 is not stable and is changed into Nitrogen and an electron: C14 concentration versus the standard carbon (C12) decades with time. That speed is characterized by Its half-life period which is 5568 years for C14 (quantity of C14 still present in an isolated place decays by half after each 5568 years).  

Today, in free air and on the earth surface, the ratio N0 = C14/C12 is 0.8 10-12

A mammoth bone has been just extracted and the concentration of C14/C12 is 0.2 10-12.

 Questions:

1. How old is that bone?

2. Since humanity is constantly putting more carbon in the atmosphere. How it affects the Carbon14 dating? For example, if C12 concentration is doubled. How will be the dating of our previous bone?

Good Luck!

P.S. If you think there are colleagues who should try those quizzes, please forward them the link!



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[edited by: StephenV at 3:24 PM (GMT -4) on 18 Oct 2023]
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Parents
  • 1. Since the 14C concentration is reduced by a factor of 4, the bone has 2x5568= 11136 years (exponential decay law)

    2. If, to calculate the age of a "carbon isolated" bone, we compare the 14C/12C concentration we find in this bone with current atmosphere concentration, then, if the 12C concentration in the atmoshere is doubled, No=14C/12C is halved and the bone age results 5568 years.  

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  • 1. Since the 14C concentration is reduced by a factor of 4, the bone has 2x5568= 11136 years (exponential decay law)

    2. If, to calculate the age of a "carbon isolated" bone, we compare the 14C/12C concentration we find in this bone with current atmosphere concentration, then, if the 12C concentration in the atmoshere is doubled, No=14C/12C is halved and the bone age results 5568 years.  

Children
  • Right Gaetano for question 1!

    On question 2: I am not sure.... If the concentration of C12 is more than expected, this means the ratio C14/C12 is decreased. And if it decreases, it means we will conclude for a much linger date (and not shorter. Do you agree?

  • I think we are using different assumptions? Under my hypothesis (If, to calculate the age of a "carbon isolated" bone - so N is still 0.2 -, we compare the 14C/12C concentration we find in this bone with current atmosphere concentration, then, if the 12C concentration in the atmosphere NOW is doubled, No=14C/12C is halved) the formula t = Ln(No/N) * (T/Ln2) provides shorter times.