was entering the system some 12-20% faster than it was leaving.Imagine the same tank, this time it is not yet full and the top tap is flowing more quickly than the bottom one is leaking out—this gives you a way of measuring how long ago the whole system was ‘switched on’ and it also tells you that that can’t have been too long ago (see diagram above).
In other words, we have a ‘clock’ which starts ticking at the moment something dies.Obviously this only works for things which once contained carbon—it can’t be used to date rocks and minerals, for example. We obviously need to know this to be able to work out at what point the ‘clock’ began to tick., we find that this ration is the same if we sample a leaf from a tree, or a part of your body.Think of it like a teaspoon of cocoa mixed into a cake dough—after a while, the ‘ratio’ of cocoa to flour particles would be roughly the same no matter which part of the cake you sampled.How do we know what the ratio was before then, though, say thousands of years ago?
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).
Because Libby believed that the Earth was millions of years old, he assumed that there had been plenty of time for the system to be in equilibrium.
In fact, the whole method is a giant ‘clock’ which seems to put a very young upper limit on the age of the atmosphere.
The article is in straightforward language and the non-technical reader could profitably work through it.
The fact that the C doesn’t matter in a living thing—because it is constantly exchanging carbon with its surroundings, the ‘mixture’ will be the same as in the atmosphere and in all living things.