# half lives

Hi Can someone give me an easy explanation of how to understand working out half lives for this question: Zircon crystals found to have a 207 Pb/235U and ratio of 0.55. calculate the age of the crystals? please note i am not asking for the answer just to be shown how to calculate it in an easy way please as i am abit confused by my papers, i have started to calculate it but then think i work it out wrong, thank you.

timmy
05 April 2011
which equation are you using? A quick look at the literature tells me that the right uranium led dating equation is:
shaunattutorhub
05 April 2011
207Pb/235U = (e^lambda(235)xtime) - 1
shaunattutorhub
05 April 2011
where t is what you are after and lambda is the decay constant. You have 207pb/235u = 0.55, so you can start reversing things to get t, the age.
shaunattutorhub
05 April 2011
the decay constant is the inverse of the half life of U235 (which is 700 million years) times the natural log of 2, so hey presto, you have all you need to calculate t.
shaunattutorhub
05 April 2011
If you want, post your calculations and we'll have a look for you...
shaunattutorhub
05 April 2011 