Question

Radiometric isotope x decays to daughter isotope y with a half-life of 220,000 years. at present you have 1/4 gram of x in the rock. from the amount of daughter isotope y presently in the rock, you determine that the rock contained 16 grams of isotope x when it formed. how many half-lives have gone by? how old is the rock?

Answer 1

The amount left after 1 half life = 16*1/2 = 8 g Then after each half life the amount of x will be 4 , 2 ,1 , 1/2, 1/4 grams

That's a total of 6 half-lives. Answer

Age s rock = 6*220,000 = 1,320,000 years Answer