Radiometric dating is possible if a rock contains
The fourth one is that we know what the concentration of atmospheric C14 was when the organism lived and died.
The story of radiocarbon dating shows science at its finest.
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.
Because it's a statistical measurement, there's always a margin of error in the age figure, but if the procedure is done properly, the margin is very small. We must know the original quantity of the parent isotope in order to date our sample radiometrically. In order to do so, we need an isotope that's part of a mineral compound. Because there's a basic law of chemistry that says "Chemical processes like those that form minerals can't distinguish between different isotopes of the same element." This is because an element's chemical behavior depends only on the number of electrons it has, which is the same as its number of protons.
Obviously, the major question here is "how much of the isotope was originally present in our sample? So to a chemical process, U235 and U238 are identical.
When I first became interested in the creation-evolution debate, in late 1994, I looked around for sources that clearly and simply explained what radiometric dating is and why young-Earth creationists are driven to discredit it.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.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.