Closed system radiometric dating
For Uranium/Lead dating this means that some of the uranium that was initially present would be "leached" out of the rock.Leaching can also cause uranium to be leached into rocks that have little or no uranium in them.And since the earth is not a closed system, these last two assumptions make radiometric dating highly subjective and questionable.For example, if a rock sample was below the water table at any time, leaching would take place.When scientists at the University of Regina, Saskatchewan were asked what the results would be if these roots were dated by Potassium Argon method.
Few people realize it but all radiometric dating methods require making at least three assumptions. Now the magnitude of the radius of a pleochroic halo in a particular mineral depends on the amount of energy that the alpha particle has ... depends on the half-life of the particular decay responsible for this alpha particle emission.To do this they have selected a certain meteorite, which contained various types of lead (including lead 204, 206, 207 and 208) but no uranium, and they have assumed that this ratio is equivalent to the earth's original lead ratio.They did this because it is almost certain that these lead isotopes were all present in large quantities when the earth was created.In other words, the magnitude of the radius of a pleochroic halo in a particular crystal depends on the half-life of the decay responsible for the alpha particle emission. the radii of pleochroic haloes corresponding to a definite decay in a particular mineral are ...