Assume that a radioactive isotope decay has a half life of 100 million years. Al

Question

Assume that a radioactive isotope decay has a half life of 100 million years. Also assume that the parent isotope is incorporated into the minerals found in igneous rocks and that the only daughter atoms in the rock formed from the decay of the parent isotope. Measurements show that one mineral in the igneous rock contains 5 million atoms of the parent isotope and 35 million atoms of the daughter.

What is the age of this mineral in years?

What is the age of this rock? Explain how you got the answer.

Explanation / Answer

a) given,

ND= 35 *106

Np= 5*106

No= ND+Np= 40 *106

t1/2= 100*106

N=N0e-.693/t1/2*tf

tf= 130*106years

age of the mineral is 130 million years

b) age of the rock is also 130 million years as the it only becomes a closed system when rock is formed . this is the basic assumption that we take.

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