Rb sr dating equation
Isochron methods avoid the problems which can potentially result from both of the above assumptions.
Isochron dating requires a fourth measurement to be taken, which is the amount of a different isotope of the same element as the daughter product of radioactive decay.
The simplest form of isotopic age computation involves substituting three measurements into an equation of four variables, and solving for the fourth.
The equation is the one which describes radioactive decay: If one of these assumptions has been violated, the simple computation above yields an incorrect age.
Note that the mere existence of these assumptions do not render the simpler dating methods entirely useless.
In many cases, there are independent cues (such as geologic setting or the chemistry of the specimen) which can suggest that such assumptions are entirely reasonable.
It is not easily explained, in the general case, in any other way.
(The range of uncertainty varies, and may be as much as an order of magnitude different from the approximate value above.
It depends on the accuracy of the measurements and the fit of the data to the line in each individual case.) For example, with Rb/Sr isochron dating, any age less than a few tens of millions of years is usually indistinguishable from zero.
That encompasses the entire young-Earth timescale thousands of times over." in the decay equation.
(Rocks which include several different minerals are excellent for this.) Each group of measurements is plotted as a data point on a graph.
The X-axis of the graph is the ratio of in a closed system over time.