Question

Several different radioisotopes can be used much like carbon-14 for determining the age of rocks and other matter. In the geosciences, the age of rocks may be determined using potassium-40, which decays to argon-40 with a half-life of 1.20 billion years.

1.) Some rocks brought back from the moon were dated as being 3.60 billion years old. What percentage of the potassium-40 has decayed after that time?

Express your answer with the appropriate units.

2.) Give a reason why uranium-238 (half-life of 4.6 billion years) is more useful for confirming this age than is carbon-14.

Answer 1

. halt lite time = 1.20 billion yes. No. of half lives = 3.60 = 3. 1.20 ) 2 Amt remaining atter a half lives = 1 ) = 1 Alemnat decayed = f(1-1) = 7A Roz Snitial art % decay - Pay too . 87.5 "" чи чи ч , че decay = Thox 100 = 87.5 8 Ho 50% decay 75% dechy 87.57. decey half lite os caly is 5700 years and is 4.5 billion yrs. So u-238 can be . used ancient objects while C-14 is used to of recent age. Therefore . U-238 is more contirming this age than 6-14. that of U-238 to determine date fossils useful for