[DiogenesLamp]

So how does tree rings help them when they get them off of long dead trees with no indications as to when the trees started growing?

Wouldn't a 5000 year old tree with a hundred rings be indistinguishable from a 4000 year old tree with a hundred rings?

Somehow there has to be a fixed standard from which to measure tree rings. There must be some distinguishing characteristic about the tree that allows you to date it's beginning, and from there you can measure changes in it's rings.

I don't understand what they are doing here.

[SunkenCiv]

The point of using individual rings -- something made possible as the equipment became more sensitive, thus able to test much smaller samples -- and the annual variance of the RC accumulation is calculated. The sequence of values is then matched up, "wiggle-matching", so that there's a continuous sequence of data even though no one tree covers the whole thing.