can we be sure the U and Th have always decayed at the same rates we measure today? The second assumption is much more speculative since there is no way to verify whether or not some (or most) of the daughter element was already present when the rock solidified. However, in some cases, a few scientists are telling us that they have solved this problem.
For example, with the uranium/lead method scientists have attempted to estimate what the original ratio (of uranium-238 to lead-206) was when the Earth formed.
Using the earth for radiometric dating Live face to face adult chat
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.
Another problem that calls into question the credibility of radiometric dating is heat contamination.
For example, In 1973, in Alberta, Canada (near the town of Grand Prairie) a high voltage line fell which caused nearby tree roots to fossilize almost instantly.
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.
In this regard, pro-evolution scientists are very selective about which dates they accept and which ones they reject: such as any date that is contrary to the Geological Time Chart -- to which all radiometric dates must fall in line with.
In this regard it should also be pointed out that for the theory of life from non-life, and/or from amoeba to jellyfish, to man to have any chance at all of being true, then the earth must be very old. can be summarized as follows: 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 ...
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.