If there occurs a gain or loss of parent isotope the point moves horizontally.If there is a gain then the point moves right and finally if it is a loss the point moves left.If there is a gain or loss of daughter isotope the point moves vertically.A gain moves the point up and a loss moves the point down. A shift from contamination can take place in all of the data points, but such contamination does not affect all data points equally, so it can cause the data points to shift off the true isochron completely. Reconstruction of an isochron from original data obtained from the Peat Deposits From the Site Fili Park. This isochron of the Fili Park Peat deposits indicates an age of 89,000 years. In addition the data points were the five out of ten samples that, "were interpreted to be in the more or less closed-system." However it was concluded that this isochron was the result of contamination as an open system based on the fact that the date was about 50% of the age suggested by the spore and pollen fossils in the deposit.The appeal of isochron dating is that it does not presuppose the initial amount of the daughter nuclide in the decay sequence.
Even when the samples that were originally considered part of an open system are added the result is still a fairly good isochron with only two points showing significant deviation.
 Isochron dating began when scientists recognized difficulties with the assumptions of radiometric dating, especially how much of the daughter products might have been present when the mineral first formed.
Isochron dating has been developed in an attempt to solve such problems.
The result is that contamination can form good looking isochron data and uniformitarian geologists know it.
The real way a "true" isochron is distinguished from a false isochron is by how well it agrees with how old the fossils are considered to be.
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Even uniformitarian geologists recognize the existence of false isochrons, so how do they distinguish good data from bad?