MadSci Network: Evolution

Re: how is carbon dating done

Date: Fri Mar 26 17:46:38 1999
Posted By: Matthew Champion, Grad student, Biochemistry/Biophysics, TexasA&M University
Area of science: Evolution
ID: 921451611.Ev

     What a neat thing to ask about.  I was much older than you when I even 
 first heard of carbon dating, so I think your curiousity is wonderful.  
You have two questions, one about your discovery of bones, and the other is 
about carbon dating.  Let's talk about the carbon first.
     Carbon dating, as you seem to know, is a way we can get a rough 
estimate of how old something is that was once alive.  Most of the carbon 
around us, (And in us) is regular, ordinary carbon, but a small percentage 
is exactly what you mentioned, carbon 14.
     Carbon 14 is formed in the atmosphere at a very constant rate over 
time, and like regular carbon it gets put into growing things, such as 
trees, animals, and people.  When they die, they stop growing and so, no 
more carbon 14 gets into them.
     Carbon 14 is different than regular carbon because it is radioactive. 
And radioactive things have half-lives, which means that after 1 half life, 
you will only have half of what you started with.  For example, carbon 14 
has a half life of about 5730 years, so after this much time, there is half 
as much carbon 14 as you started with.  In carbon dating, we can count how 
much carbon is left in an old bone, and count the number of half-lives it 
took and we can get an idea of how old it was when it died.  If a mummy is 
found that had one half life of carbon 14 gone, we would know that they 
died about 5730 years ago.  This only works on stuff less than about 50,000 
years old because after that there isn't enough carbon 14 to count anymore. 
So, this does not work very well for dinosaur bones, for example because 
they are millions of years old.

     As for your bones, I think they are probably not too old, because you 
are right, the ocean does make things look old, and this means that water 
also makes things rot and break down quickly too, unless the bones were 
washed from rock by the ocean and then they came to your shore.  I think a 
good place to try and find out what they are would be to look at books that 
have lots of pictures of animal bones in them, you might find something 
that matches.  If you still cannot figure it out, I would go to a school 
and ask a biology teacher, or to a University and ask a zoology or biology 
professor if they can take a look.  What a great find, I think they could 
be anything, a fish, maybe a cow, a dolphin, or monkey... Or who knows, 
maybe even a dinosaur.  Happy hunting.

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