A geologist discovers a rock containing 12.5% of its original lead-202. He knows the half-life of lead-202 is 52,500 years.How old is the rock?
One formula that you can use is: A(t) = A0·(½)( t / t1/2 )
where t = time = unknown
A(t) = the amount remaining after time t = 0.125
A0 = the initial amount = 1.000
t1/2 = the half-life = 52 500
A(t) = A0·(½)( t / t1/2 ) ---> 0.125 = 1.000 · (½)( t / 52 500 )
---> 0.125 = (½)( t / 52 500 )
---> log(0.125) = log( (½)( t / 52 500 ) )
---> log(0.125) = ( t / 52 500 ) · log( 1/2 )
---> log(0.125) / log(1/2) = t / 52 50
---> [ log(0.125) / log(1/2) ] · 52 500 = t