posted by Lena .
How would I calculate the age of a rock only given the amount of each in grams and half-life?
40K decays to 40Ar.
Half life of 40K is 1.25 billion years.
40K = 20 grams
40Ar= 5 grams
I think the formula is
Final Amount of 40K = Initial Amount of 40K * (1/2)^(time/half-life)
If I plug in the values I still don't have a value for time. And where would the grams of 40Ar fit in?
You started with 25 grams, you now have 20 grams
log both sides...
time= 1.25billion* log(.8)/log(.5)