Radioactive dating assumptions
A very important tool in radiometric dating is the so called isochron diagram and it holds the key to refuting the central creationist claims about radiometric dating.
One of the most beneficial things about it is that it can check itself for accuracy; the method tells you how well the rocks have been closed systems.
So far from rejecting samples because they do not fit a preconceived notion of what the age be, scientists reject samples because there is ample evidence that it has been disturbed: the data points do not lie on the isochron lines.
Scientists do not assume that rocks have been closed systems; it is a well-supported conclusion from experiments.
Those that did the decaying are called parent nuclei.
If you have a rock that contains radioactive isotopes, these will decay over time.
Furthermore, by studying supernovas far away, scientist have determined that decay rates have been constant in the ancient past as well.
If a rock is heated during its lifetime, the system gets disturbed and some of the parent and/or daughter isotopes may move in or out of the rock.An isochron diagram is obtained by looking at many minerals from the same rock or from rocks forming from the same parent mineral.Data is plotted on a simple two dimensional graph; the parent isotope on the x-axis and the daughter isotope on the y-axis.If the samples have been undisturbed closed systems since formation, the data will fall on the same line (the isochron from which the diagram is named).The slope of this line is a function of the age of the rock. The reason scientists normalize with another stable isotope of the same element as the daughter is because most chemical or physical processes that occurs normally in nature does not differentiate between different isotopes of the same element when the difference in mass is as small as it is between isotopes of the same element that is used in radiometric dating.