Q.

The half - life of Uranium - 238 is about 4.5 billion years, and its end product is lead - 206. We notice that the oldest Uranium - bearing rocks on Earth contain about a 50 : 50 mixture of 238U and 206Pb. What is the age of these rocks?

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a

4.5×104.5 yrs

b

4.5×109 yrs

c

2.25×109 yrs

d

9×109 yrs

answer is B.

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Detailed Solution

T1/2=4.5×109 yrs

only 50% remained now. 

Hence, age of rock = 4.5×109 yrs

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