Equation 11 · Part 4 · Radioactive Clocks: How Nuclear Physics Gave Evolution Its Time
Symbol N_86
What this part means
each mineral’s measured rubidium-87 to strontium-86 ratio [ 18 ].
Its job in the formula
6 occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.
Full expression→Symbol N_86→Article meaning
Where the article explains it
where is each mineral’s measured present-day strontium-87 to strontium-86 ratio, is the shared initial ratio recovered as the line’s intercept, and / is each mineral’s measured rubidium-87 to strontium-86 ratio [ 18 ] .
The passage around this formula
The uranium-lead and argon-argon methods both need to know, or be able to ignore, how much daughter isotope was already present when the mineral formed. The isochron method, used most often with the rubidium-strontium and samarium-neodymium systems, solves this by measuring several minerals from the same rock, each of which crystallized from the same well-mixed magma at the same time and so began with the same strontium or neodymium isotopic composition, but which incorporated different amounts of the radioactive parent isotope depending on their individual chemistry. Plotting each mineral’s present-day ratio of radiogenic daughter to stable reference isotope against its ratio of parent to…
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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