Please Help! The technique known as potassium-argon dating is used to date old l
ID: 1304165 • Letter: P
Question
Please Help!
The technique known as potassium-argon dating is used to date old lava flows and thus any fossilized skeletons found in them, like this 1.8-million-year-old hominid skull. 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 the stable isotope 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.
What is the age of a piece of solidified lava with a 40Ar/40K ratio of 0.34?
In billion years
Explanation / Answer
in the above reaction the half life of 40K is = 1.28 billion years
so the rate constant = ln 2 / 1.2 billion years
now after the decay by the reaction
40 K --> 40 Ar + beta emmission
we get that there will be a mixture of argon and K
so time * K = ln [conc of initial K / 0.34 times the initial conc of K ]
= time * ln 2/1.28 = ln [100/34]
= time = 1.99 billion years