If k 40 has a half-life of 1.4 x 100 years and only 10% of the original k 40 remains, how old is the earth?

t = 465.16 years

Explanation:

Given that:

Half life = 1.4 x 100 years = 140 years

Where, k is rate constant

So,  

The rate constant, k = 0.00495 year⁻¹

Using integrated rate law for first order kinetics as:

Where,  

is the concentration at time t

is the initial concentration

As 10% of the initial remains, so:

So,  

t = 465.16 years

answer; i believe the correct answer is (solid gold);

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