5) Uranium dating is used to calibrate 14C age estimates in corals based on the

Question

5)

Uranium dating is used to calibrate 14C age estimates in corals based on the decay of 234U to 230Th (think of this as a first order reaction where U is the reactant and Th is the product). Corals have no 230Th in them when they are formed, but do incorporate 234U. The half life of 234U is 2.52E5 years.

Given that a coral sample has a 234U concentration of 2.34E-9 moles/gram and a 230Th concentration of 4.33E-10 moles/gram, how old is the coral? Assume no 230Th has decayed since the coral was formed.

Explanation / Answer

[U]t = [U]o * e^-k*t

[U]t = 2.34*10^-9

[U]0 = 2.34*10^-9 + 4.33*10^-10

k = ln2 / (2.52*10^5)

t = - ln ([U]t/[U]o) / k = 61724.65 years

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