Using the number of half-lives that have passed since the dike (D) formed and th
ID: 152479 • Letter: U
Question
Using the number of half-lives that have passed since the dike (D) formed and the half-life of the isotope used in dating the dike, what is the age of the dike? (Be careful the table in this question may be different from the worksheet and textbook) 1. Half-Life of | Isotope # Parent Atoms -Daughter | Lives that Age AtomsHave Passed Granite (G) 0.on years250 1750 3875 Dike (D) 50 million years125 5 Million Years 25 Million Years 50 Million Years 100 Million Years 150 Million Years 200 Million Years 250 Million Years 1550 Million Years IFExplanation / Answer
For the granite , daughter atoms are 1750, and parent atoms are 250. Total atoms =250+1750= 2000. All these 2000 atoms were once the parent atoms. Therefore percentage of parent atoms left =250×100/2000 = 12.5 %.
Now , we know that in first half life , atoms left =50percent .
After 2nd = 25 percent and after 3rd half life 12.5 percent .
There fore. 3 half life have passed.
Half life is 0.75 billion. Therefore age = no of half life × 0.75
= 2.25 billon years.
For dike percentage of parent atom left = 125 ×100/125+3875
= 3.125 . After 4th half life , no of parent atom left = 6.25 percent .and after 5th , 3.125 percent parent atom are left. Therefore . 5 half life are there for dike.
Age of dike = 250×5 = no of half life × years in each half life
= 250 Million years .
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