What information is obtained from radioactive dating
I found several good sources, but none that seemed both complete enough to stand alone and simple enough for a nongeologist to understand them.
Thus this essay, which is my attempt at producing such a source.
(Note that this doesn't mean the half-life of an element is a constant.
Different isotopes of the same element can have substantially different half-lives.) It's important to understand that the half-life is a purely statistical measurement. A sample of U238 ten thousand years old will have precisely the same half-life as one ten billion years old.
Some isotopes can break down in more than one way -- in these cases, each different breakdown type has its own half-life.
The decay rate and therefore the half-life are fixed characteristics of an isotope. That's the first axiom of radiometric dating techniques: the half-life of a given isotope is a constant.
So, if we know how much of the isotope was originally present, and how much there is now, we can easily calculate how long it would take for the missing amount to decay, and therefore how long it's been since that particular sample was formed.
Only things that once were alive and now are dead: bones, teeth, flesh, leaves, etc.Contents: The half-life of a radioactive isotope is defined as the time it takes half of a sample of the element to decay.A mathematical formula can be used to calculate the half-life from the number of breakdowns per second in a sample of the isotope.When we know how much has decayed, we know how old the sample is.Many archaeological sites have been dated by applying radiocarbon dating to samples of bone, wood, or cloth found there. One is that the thing being dated is organic in origin.
Radiometric dating methods are the strongest direct evidence that geologists have for the age of the Earth.