1. The problem statement, all variables and given/known data The technique known as potassium-argon dating is used to date old lava flows. The potassium isotope 40K has a 1.28 billion year half-life and is naturally present at very low levels. 40K decays by beta emission into 40Ar. Argon is a gas, and there is no argon in flowing lava because the gas escapes. Once the lava solidifies, any argon produced in the decay of 40K is trapped inside and cannot escape. A geologist brings you a piece of solidified lava in which you find the 40Ar/40K ratio to be 0.12. What is the age of the rock? 2. Relevant equations N=N0(1/2)t/t[1/2] where N is the number of nuclei, N0 is the initial number of nuclei, t is time allowed to decay and t[1/2] is the half life. 3. The attempt at a solution I actually do not know where to start with this one. I'm not sure how to apply the ratio given, and what variable I am even looking for, or if i'm even supposed to look at the relevant equation. Could someone please point me in the right direction? Thanks in advanced!