Many people assume that the dates scientists quote of millions of years are as reliable as our knowledge of the structure of the atom or nuclear power.
And radioactive dating is so shrouded with mystery that many don’t even try to understand how the method works; they just believe it must be right.
When I have asked an audience this question they have looked at me incredulously and said, “Starting time?
” They realize that you cannot know how long the swimmer took unless you knew the time on the wristwatch when the race started.
Once we understand what we actually need to do we can apply the same principles to radioactive dating, and see if the methods do what they are claimed to do.
Picture a swimmer competing in a 1,500 metre race and an observer with an accurate wristwatch.
But the basic concept of radioactive dating, sometimes called radiometric dating, is not difficult, especially since all of us regularly calculate how much time has passed: for example, since our birth, or since we started on a walk.
A swimming race is a familiar situation that illustrates the simple principles involved in measuring time.
By evaluating the concentrations of all of these isotopes in a rock sample, scientists can determine what its original make-up of strontium and rubidium were.
Example: wood found in a grave of known age by historically reliable documents is the standard for that time for the C14 content.
This standard content of C14 can then be used for wood not associated with a historically documented date.
Then, by assessing the isotope concentrations of rubidium and strontium, scientists can back-calculate to determine when the rock was formed.
The three isotopes mentioned can be used for dating rock formations and meteorites; the method typically works best on igneous rocks. The data from radioisotope analysis tends to be somewhat scattered.