Rb sr dating equation
Such scatter would constitute a geologic component, indicating that one or more of the underlying assumptions has been violated and that the age indicated is probably not valid.
For an isochron to be valid, each sample tested must (1) have had the same initial ratio, (2) have been a closed system over geologic time, and (3) have the same age.
When the rock again cools, the minerals close and again accumulate daughter products to record the time since the second event.
If one assumes for a moment that only the mineral with the lowest blocking temperature loses its daughter isotope, it is easy to imagine that other low-temperature minerals formed at this time may acquire extremely high Sr ratios.
Epidote, a low-temperature alteration mineral with a very high concentration of radiogenic strontium, has been found in rocks wherein biotite has lost strontium by diffusion.
With heat, daughter isotopes diffuse out of their host minerals but are incorporated into other minerals in the rock.
Eventually the Sr ratio in the minerals becomes identical.
Sr) was the first widely used dating system that utilized the isochron method.