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The ratio of radioactive and non radioactive form of an element in sample of rock is 1:7.Estimate the age of rock if the half life of radioactive element is 3.1 billion years. 1-3.1billion years, 2-9.3billion years 

Asked by Priyanka 12th November 2017, 1:16 PM
Answered by Expert

It is possible to determine the age of rocks by the method of radioactive dating.


The half life (t ½) of the radioactive element = 3.1 billion years.

This means that if we begin with a pure sample of the element, we know that in 3.1 billion years, half of the element will have decayed to another isotope.

Now, the ratio of radioactive and non-radioactive element = 1:7

This means that subsequent decays have reduced the radioactive element to non-radioactive element and now, the ratio is 1:7

After 1 half life (3.1 billion years) =1/2 remains

After 2 half lives (6.2 billion years) = 1/4 remains

After 3 half lives (9.3 billion years) = 1/8 remains

The given ratio is 1: 7.

So, approximately after 3 half lives, the age of the rock would be 9.3 billion years.

Answered by Expert 13th November 2017, 11:46 AM
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