Leaching can also cause uranium to be leached into rocks that have little or no uranium in them.
Therefore, in virtually every case, scientists do not know what the original condition of the rock was; and, even if they did know, they don't any more due to heat contamination, mixing, and leaching. Snelling in an article on this topic Note: As for the few cases where scientists do know what the "original" condition (or date of eruption) was, they still have not been able to come up with the correct "date" for the age of the rock without all sorts of fancy footwork and massaging of data.
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.
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 ...
In fact, about 98% of common lead is "radiogenic" (containing lead 206, 207, 208) and only 2% non-radiogenic.
The third assumption is that the sample has remained in a closed system.
This is necessary due to outside influences such as heat and groundwater that can seriously alter the original material.
And since the earth is not a closed system, these last two assumptions make radiometric dating highly subjective and questionable.
If an igneous or other rock is metamorphosed, its radiometric clock is reset, and potassium-argon measurements can be used to tell the number of years that has passed since metamorphism.
For example, if a rock sample was below the water table at any time, leaching would take place.
For Uranium/Lead dating this means that some of the uranium that was initially present would be "leached" out of the rock.
One of the most popular of these is known as radiometric dating. can be In other words, something in the past caused a significant amount of helium to build up inside these zircons (such as from a rapid decay episode of uranium), yet, in spite of the fact that helium has been observed to leak out readily from these zircons, it has not done so: simply because it hasn't had enough time to do so -- suggesting that the zircons themselves are only a few thousand years old."There is evidence to show ...
However, not as well known is the fact that such methods have serious flaws which are often glossed over, or ignored when writing on, or discussing this subject in public. that (the) half-lives (of uranium-thorium-lead) are not constant but vary with time. comes from the study of pleochroic haloes which form in a rock in the following way.
And even though various radioactive elements have been used to "date" these rocks, for the most part, the methods are basically the same. This means that if you had some pure uranium-238 with no lead in it, 4.5 billion years later one half of it would have decayed into its stable daughter product (lead-206). Where these alpha particles finally stop, crystal deformation occurs (and) shows up as a discolouration or a darkening of the crystals.