Diffusion measurements and the potassium argon method of dating dating services olympia wa
Sr) was the first widely used dating system that utilized the isochron method.Rubidium is a relatively abundant trace element in Earth’s crust and can be found in many common rock-forming minerals in which it substitutes for the major element potassium.As a liquid rock cools, first one mineral and then another achieves saturation and precipitates, each extracting specific elements in the process.Strontium is extracted in many minerals that are formed early, whereas rubidium is gradually concentrated in the final liquid phase.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.Well-preserved, unweathered rocks that crystallized rapidly and have not been subjected to major reheating events are most likely to give valid isochrons.
Volcanic rocks are most susceptible to such changes because their minerals are fine-grained and unstable glass may be present.
Thus, if well-dated, unaltered fossil shells containing strontium from ancient seawater are analyzed, changes in this ratio with time can be observed and applied in reverse to estimate the time when fossils of unknown age were deposited.
The rubidium–strontium pair is ideally suited for the isochron dating of igneous rocks.
In most cases, the changes in the Sr ratio are so large that an initial value can be assumed without jeopardizing the accuracy of the results.
When minerals with a low-rubidium or a high-strontium content are analyzed, the isochron-diagram approach can be used to provide an evaluation of the data.
Using estimates of measurement precision, the crucial question of whether or not scatter outside of measurement error exists is addressed.