The amount of substance left of a radioactive element of half life, 
after a time, t, is given by:
Given that <span>potassium-40 has a half life of approximately 1.25 billion years.
The number of years it will take for 0.1% of potassium-40 to remain is obtained as follows:
Therefore, </span><span>the maximum age of a fossil that we could date using 40k is 12.5 billion years.</span>
Given that <span>potassium-40 has a half life of approximately 1.25 billion years.
The number of years it will take for 0.1% of potassium-40 to remain is obtained as follows:
Therefore, </span><span>the maximum age of a fossil that we could date using 40k is 12.5 billion years.</span>