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Equation 6 · Part 2 · Radioactive Clocks: How Nuclear Physics Gave Evolution Its Time

Symbol N_238

N206N238=eλ238t−1,N207N235=eλ235t−1,\frac{N_{206}}{N_{238}} = e^{\lambda_{238} t} - 1, \qquad \frac{N_{207}}{N_{235}} = e^{\lambda_{235} t} - 1,
N238N_{238}

What this part means

N2N_238 occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

Its job in the formula

N2N_238 occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

The passage around this formula

…event, a single zircon crystal reports two ages that must agree if nothing has disturbed the system since: N206N238=eλ238t−1,N207N235=eλ235t−1\frac{N_{206}}{N_{238}} = e^{\lambda_{238} t} - 1, \qquad \frac{N_{207}}{N_{235}} = e^{\lambda_{235} t} - 1. where N206N_{206} and N207N_{207} are the radiogenic lead atoms accumulated from each chain and N238N_{238} , N235N_{235} are the surviving parent uranium atoms. Plotting these two ratios against each other traces a curve, the concordia, on which a grain that has behaved as a closed system since crystallization must fall; a grain that has lost lead at some later date instead falls off the curve along…

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the surrounding passage

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