These whole-rock ages were approximately correct, but a much more precise mathod is now in use.
The strategy now used is to plot an isochron, but to correct for the existence of primordial Sr 87, we plot the ratios (Sr-87)/(Sr-86) versus (Rb-87/Sr-86).
Dating techniques are procedures used by scientists to determine the age of an object or a series of events.
The two main types of dating methods are relative and absolute.
Absolute dating methods are used to determine an actual date in years for the age of an object.
Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.
Thus, if a sample had 100 Sr-86 atoms total, it could be assumed that 70 of the Sr-87 atoms were primordial.
If the sample had 100 atoms of each isotope, we could assume that 70 of the Sr-87 atoms were primordial and 30 were produced by the decay of Rb-87.