You analyzed a rock on the surface and found 250 atoms of Uranium and 750 atoms
ID: 501633 • Letter: Y
Question
You analyzed a rock on the surface and found 250 atoms of Uranium and 750 atoms of Thorium. Fortunately, you have a great memory, and recalled that from your geology 101 class that this isotope of U decays into Th with a half-life of 700 million years (.7 billion years). How old is this rock specimen?
10. You are a space tourist and just landed on the asteroid Psyche. You analyzed a rock on the surface and found 250 atoms of Uranium and 750 atoms of Thorium. Fortunately, you have a great memory, and recalled that from your geology 101 class that this isotope of U decays into Th with a half-life of 700 million years (.7 billion years). How old is this rock specimen? a) 700 million years b) 1.4 billion years c) 1.7 billion years d) 2.1 billion years e) 2.8 billion yearsExplanation / Answer
We have 250 atoms of Uranium and 750 atoms of Thorium.
Half life of uranium is 700 million years.
A = A0 * 2^(-t/ t1/2)
We have A = 250 and A0 = 250+750 = 1000
T1/2 = 700 million years.
We will be calculating t
250 = 1000 * 2 ^(-t /700 million)
T = 1400
Rock specimen is 1400 million years (1.4 billion years) old.
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