The solid line drawn through the samples will thus progressively rotate from the horizontal to steeper and steeper slopes.
Atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life, usually given in units of years when discussing dating techniques.
After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a “daughter” nuclide or decay product.
This change is shown by the dashed arrows, the lengths of which are proportional to the rubidium/strontium ratio.
The dashed arrows are slanted because the rubidium/strontium ratio is decreasing in proportion to the increase in strontium-87/strontium-86.
The table below gives the ages, in billions of years, from twelve different studies using five different techniques on one particular rock formation in Western Greenland, the Amitsoq gneisses.
Note that scientists give their results with a stated uncertainty.For example some of the oldest rocks on earth are found in Western Greenland.Because of their great age, they have been especially well studied.There are now well over forty different radiometric dating techniques, each based on a different radioactive isotope.Most dating techniques involve multiple tests using different methods and on different minerals within a rock (isochrons).Should you want to examine the geologic record in more detail I suggest this book.