The technique known as potassium-argon dating is used to date old lava flows and

Question

The technique known as potassium-argon dating is used to date old lava flows and thus any skeletons found in them, like this 1.9-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 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 to be 0.10. What is the age of the rock

Explanation / Answer

half life = 

Know/K = 2-t/

so, Ar/k = 1-2-t/

.1 = 1 - 2-t/

-t/ = log2.9 =-.152

t = .19456 billion y

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