Question

In uranium mineral, the atomic ratio $N_{U-238}/N_{Pb-206}$ is nearly equal to one. The age (in years) of the mineral is nearly: (half-life period of U-238 is $4.5\times {10}^9$ years)

• A. $3.0\times {10}^8$
• B. $4.5\times {10}^9$
• C. $3.0\times {10}^9$
• D. $4.5\times {10}^8$

Answer 1

The correct option is B $4.5\times {10}^9$

To determine age by rock-dating
$1+\frac{\left[Pb\right]}{\left[U\right]}=2^y$
$(1+1)=(2{)}^y$
$y=1$
$\frac{t}{T_{50}}=y=1$
$t=T_{50}=4.5\times {10}^9$ year