A fossil was found that contained 20% of the parent element + 80% of the daughter element. It was determined that the fossil was about 28500 years old. What is most likely the parent element? What is the daughter element?

1 Answer
Feb 9, 2018

Carbon 14 is most likely the parent element or isotope, and Carbon 12 the daughter isotope.


There are several problems with this answer or question.

  1. a fossil only 28,500 years old is not significant as a fossil.
  2. It is impossible to determine Carbon 12 that results from radioactive decay from Carbon 12 that is normal carbon. The information on the 80% daughter elements is not valid if the answer is Carbon 14
  3. The percentages do not add up Carbon 14 has a half life of approximately 5,700 years.
    after about 11,400 years only 25 percent of the original Carbon 14 would be left.
    after 17100 years only 12.5 percent of the original Carbon 14 would be left.
    after 22,800 years only 6.25 percent would be left.
    At 28,500 years only 3.125 percent of the Carbon 14 would be left not 20%

There are no other radioactive isotopes used for recent dating besides Carbon 14. But Carbon 14 does not work for this data.
However 28,500 is an exact multiple of the half-life of Carbon 14 by it is 4 half lives or # 1/2^4# This means that there would be only # 1/16# of the original Carbon 14 left not 20%