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Equation 3 · Radioactive Clocks: How Nuclear Physics Gave Evolution Its Time

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λ\lambda

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the decay constant characteristic of the isotope. Read the equation part by part below; each part has a contextual explanation and a link to its mathematical background.

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λ\lambda

Symbol λ

the decay constant characteristic of the isotope.

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where N0N_0 is the initial population, λ\lambda is the decay constant characteristic of the isotope, and t1/2t_{1/2} is the half-life derived from it. This is the one place in the article where the evolutionary-population analogy is exact rather than suggestive: a sample of N0N_0 identical atoms behaves, statistically, exactly as a population geneticist’s model of a large population with a fixed per-individual probability of an event per unit time behaves. Individual atoms are unpredictable; the population’s decline is not.

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