You have carried out radiometric dating analysis on four igneous rocks uncovered
ID: 481921 • Letter: Y
Question
You have carried out radiometric dating analysis on four igneous rocks uncovered at several sites that you have been exploring. From the % lead you determine in each case, what is the appropriate age of the rock? (Hint you can use the chart in your book on p. 376 to help you with dating).
Rock A: 75% lead. Age of the rock __________________
Rock B: 50% lead. Age of the rock __________________
Rock C: 30% lead. Age of the rock __________________
Rock D: 10% lead. Age of the rock __________________
Explanation / Answer
Generally rocks contain 210Pb is 22.3 years.(here in this problem it is not given)
= 0.693 / t1/2
= decay constant
t = 2.303 log a/(a-x)
Here = 0.693/22.3 years = 0.310 year-1 ; a= initial concentration ; a-x = concentration after decay
Rock A
75% Pb means 25% decayed
t = age of rock = (2.303/0.310) log 100/75 =
7.43 x 0.123 = 0.91 year
Rock B
50% Pb means 50% decayed
t = age of rock = (2.303/0.310) log 100/50 = 7.43 x 0.3010 = 2.23 years
Rock C
30% Pb means 70% decayed
t = age of rock = (2.303/0.310) log 100/30 = 7.43 x 0.5224 = 3.88 years
Rock D
10% Pb means 90% decayed
t = age of rock = (2.303/0.310) log 100/10 = 7.43 x 1 = 7.43 years
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.