We have to determine the age of a quartz crystal which contains 25% U-235 and 75% Pb-207.
Uranium is a radioactive metal which decays by a series of reactions to form Pb-207.
The half-life of a radioactive element is the time that it takes for 50% of the element to decay.
Analysis of a quartz crystal shows it to contain 25% Uranium 235 and 75% Lead 207. If the half life of Uranium 235 is 704 million years how old is the quartz crystal?