Re: I need some dates and references

["Michael D. Miller" <millerm@thunder.indstate.edu>]

There are many ways to date rocks, but some of the best are 
fission-tracking, in which case zircon or some other mineral is dated by 
the use of "grooves" made in the crystal by escaping electrons as the 
rock ages.  Another is radioactive dating, probably the most widely used, 
which involves parent/daughter ratio counts on such things as Rb:Sr 
(bubidium/strontium), U:Pb (uranium/lead), and K:Ar (potassium/argon) 
where the first is parent material and the latter daughter material (you 
will often hear reference to half-lives when dealing with radioactive 
dating). There are other methods and other elements which can be dated 
(Ar40:Ar39) - in fact, a professor of mine and I along with a few other 
students recently wrote an article highly dependent on radioactive dating.
Anyway, my point is that there are many ways in which things can be dated 
with varying amounts of certainty.  We can date things back to billions 
of years.  Books can be written (and have been) about this.