Here is a study that attempted to replicate the Cardone findings and found them unreliable: http://arxiv.org/abs/0911.1387
"Lead also diffuses out of zircon, although much more slowly than helium does. In addition to studying helium, Gentry and his team (1982b) at Oak Ridge also studied lead retention in 50-75 Ã‚Âµm zircons from the same rock unit."
If lead also diffuses out then we would be underestimating how much decay has taken place and thus the age of the rock!
Geochronologists come to the conclusion that decay rates are stable based on their being a direct consequence of qunatum first principles and being a consequence of the electroweak fundamental force. If the electroweak force varied we would not observe the remarkable uniformity across the Universe. The following page explains possible factors affecting decay rates:
The only real player is electron density: the magnitude of the effect is very small; for a few alpha emitters, the change has been estimated to be of the order of 1 part in 107. This would be unmeasurable and thus not effect radiometric dating.
When we look out on a cloudless night we look beyond recorded history to the deep past. We observe the fundamental forces to be the same.
The bridge analogy is that both it and radiometric dating draw upon fundamental forces: gravity and the electroweak force. Engineering presupposes a uniform strength of gravity and there is no reason why geochronologists should not be so certain.
Radiometric dating has been shown to be accurate by succefully dating rocks from the Vesuvius erruption whose origin were historically recorded. Why then doubt that a rock dated to have solidified more than 10,000 years ago could be so old?
I am entering this late and haven't read all the posts, (sorry)
To me knowing the rate of decay does nothing.
Here is a candle analogy I hope which will explain this.
Lets say you walk into a room with a burning candle. You can measure the height of the candle, you can measure the rate that the candle burns however from these two how can you determine how long the candle has been burning?
You can't, since you have no initial height of the candle to reference its current height, as such it could have been 4 foot tall and have been burning for weeks, or it could have been a few centimetres higher than when you entered the room.
With no initial Uranium concentration, knowing the rate of decay does nothing. You NEED an initial concentration to compare the current concentration and the rate of decay to. This is one of the assumptions.
Furthermore, it is assumed that the spread of the radioactive isotopes was relatively the same, ie- same concentration for air, soil and living things. This is another assumption.
With the leaching of helium and lead, can the rate of leaching be determined?