Carbon dating model
It is assumed that the ratio has been constant for a very long time before the industrial revolution. (For on it hangs the whole validity of the system.) Why did W. Libby, the brilliant discoverer of this system, assume this?
Libby knew that C was entering and leaving the atmosphere (and hence the carbon cycle).
Consider this—if a specimen is older than 50,000 years, it has been calculated, it would have such a small amount of C that for practical purposes it would show an ‘infinite’ radiocarbon age. Readers are referred to this article for other interesting conclusions about these dates.
So it was expected that most deposits such as coal, gas, petrified trees, etc. In fact, of 15,000 dates in the journal to 1968, only three were classed ‘un-dateable’—most were of the sort which should have been in this category. [Editor’s note: The graph below was reproduced from a sketch in the original magazine.
The article is in straightforward language and the non-technical reader could profitably work through it.
, we find that this ration is the same if we sample a leaf from a tree, or a part of your body.
Libby invented carbon dating for which he received the Nobel Prize in chemistry in 1960.
The halflife of carbon 14 is 5730 ± 30 years, and the method of dating lies in trying to determine how much carbon 14 (the radioactive isotope of carbon) is present in the artifact and comparing it to levels currently present in the atmosphere.
We’ve seen that it would have been the same as in the atmosphere at the time the specimen died. Do scientists assume that it was the same as it is now? It is well known that the industrial revolution, with its burning of huge masses of coal, etc.
The model of radiocarbon dating which Libby developed, using his incorrect ‘uniform’ assumption, must therefore be corrected to fit the facts about C to start with, so they have an even greater error.
In other words, the further you go back, the more you have to shrink the radiocarbon dates to make them fit the facts.
As soon as it dies, however, the C ration gets smaller.
In other words, we have a ‘clock’ which starts ticking at the moment something dies.