Symbol R_t
each mineral’s measured present-day strontium-87 to strontium-86 ratio.
Read this term in its guide →Published equation contexts
Why this formula appears here
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…
Read the representative guide
Symbol N_87
7 occurs above the fraction bar. The numerator is divided by the entire denominator below it.
Read this term in its guide →Symbol N_86
each mineral’s measured rubidium-87 to strontium-86 ratio [ 18 ].
Read this term in its guide →Symbol e^λ t
e^λ t is one of the signed contributions combined to compute the quantity on the left.
Read this term in its guide →How to interpret it
With a fixed numerator, increasing a nonzero denominator reduces the fraction. Read it with the definitions, units, and assumptions supplied by the article.
Research cited beside this formula
Published contexts (1)
A symbol can carry a different meaning in another article. Each occurrence keeps its own guide and term definitions.
Equation 11 · Evolutionary Nuclear Physics
Radioactive Clocks: How Nuclear Physics Gave Evolution Its Time
This equation states an equality: the expressions on both sides have the same value under the article’s assumptions.
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…
Meanings in this article
- : each mineral’s measured present-day strontium-87 to strontium-86 ratio.
- : the shared initial ratio recovered as the line’s intercept.
- : each mineral’s measured rubidium-87 to strontium-86 ratio [ 18 ].