Isochron radiometric dating wikipedia
While isochron dates have been used by both old-Earth and young-Earth proponents to promote their respective viewpoints, attacks on isochron dating have also been made by young-Earth creationists, such as William Overn.
Instead of using the initial quantity of daughter isotope, the ratio of daughter isotope compared to another isotope of the same element (which is not the product of any decay process) is used as the comparison for isochron dating.The process of evaluating the daughter product as a ratio against another isotope of the same element is a valid method because, when a mineral or rock forms from a homogenous state, the elements that are assimilated into crystalline formation are very restricted.The key to the formation of crystals in the rock is that the process is selective between elements, but is indifferent to isotopes of the same element.According to Brent Dalrymple (20-69), "the trick to the isochron diagram is the normalization of both parent and daughter isotope to a third isotope." This third isotope is the non-decay product isotope of the same element as the daughter element.In the initial state, the graph of daughter isotope to the third isotope versus parent isotope to the third isotope should result in a straight, horizontal line.The plot of the ratios of the number of atoms of the parent isotope to the number of atoms in the non-daughter isotope compared to the number of atoms of the daughter isotope to the non-daughter isotope should result in a straight line that intersects the vertical y-axis (which is the ratio of daughter to non-daughter isotopes).
This point of intersection gives the initial ratio of daughter to non-daughter isotopes, which would also be the ratio in a mineral that crystallized without any parent isotope present.
Thus, the daughter product and any other isotopes of the same element will be incorporated into the minerals of a rock with the same ratio.
This initial ratio allows the non-daughter product isotope to be representative of the initial amount of the daughter product (Stassen 1998).
As time progresses, the line connecting the measurements within the sample moves counter-clockwise around a point intersecting the y-axis, a point that represents the initial ratios (Dalrymple 20).
Once the ratios are plotted, the age of the rock being dated can be determined based on the slope of the line.
Points that do not fall on a straight line suggest contamination, and this invalidates the results.