Question

A sample of rock from moon contains equal number of atoms of uranium and lead (t1/2 for U = 4.5 × 109 years). The age of the rock would be :

• A. 9.0 × 109 years
• B. 4.5 × 109 years
• C. 13.5 ×109 years
• D. 2.25 × 109 years

Answer 1

Answer: (B)

4.5 × 109 years

Answer 2

$T = \frac{2.303}{\lambda}\log_{10}\left\lbrack \frac{n + n}{n} \right\rbrack$

$\text{t = }\frac{\text{2.303}}{\text{0.693}}\text{ }\text{×}\text{ 4.5 }\text{×}\text{ 1}\text{0}^{9}\text{ lo}\text{g}_{\text{10}}\lbrack 2\rbrack\text{ = 4.5 }\text{×}\text{ 1}\text{0}^{9}\text{ years}$