logarithms

Question

a certain element has a life of 4.5 billion years. a. you find a rock containing a mixture of the element and lead. You determine that 30% of the original element remains the other 70% decade into lead. How old is the rock? b. Analysis of another rock shows that it contains 55% of its original element the other 45% decade into lead. How old is the rock?

Answer 1

I believe you mean half-life of 4.5 billion years.

 

Logarithm formula has the form

A = A₀ * 2^(t/h)

where A is the present amount

A₀ is the initial amount

t is the time elapsed (i.e. - age in your problem)

h is the half life or decay rate

 

A/A₀ would be your percentage of element in decimal form (0.30 in a and 0.55 in b)