I just wanted to add a bit to what Schraf posted (see
message 9 for original context).
Another way we are confident about radiometric dating is because it is supported and confirmed by the rocks themselves.
In the field, geologists use relative dating methods to date the rocks by simply looking at their positions with respect to other rocks.
If you are looking at an outcrop of limestone, for example, and see that it is cut by an igneous dike, you can say that the dike is younger. Say you keep following the layers and the dike in you have interpreted as the 'up' direction and you come upon an erosional surface that cuts both the limestone and the dike and directly above you have a fluvial conglomerate. You can now say that the conglomerate is the youngest rock unit, the igneous dike the second youngest and the limestone the oldest. Keep going. Now say you find a layer of ash above the coglomerate. At this point, you have a perfectly good age relation of the rocks you've been looking at, however, you would like to know their approximate absolute ages.
After dating the igneous dike and the ash layer, you find that you consistently get an older age for the ash layer and a younger one for the dike. But how can this be??? You saw that the ash lay above the dike.
So you go back out to the field to make sure you interpreted the relative ages correctly. You did. However, more diligent field work reveals the presence of previously unknown faults and folds, and it's now entirely possible that your section may have been overturned. To confirm this you drive to other areas and look for the same section. Low and behold you find that every other section shows the ash below the limestone.
Further research also exposes several other dates on rocks taken above and below your section by others and everything fits.
This happens every day in geology. If radiometric dating did not work, we would not see this, and the method would be thrown out.
The idea that we keep dating rocks until we get the 'right' age is completely unfounded and ridiculous. In order to do this we would have to analyze way too many rocks, which can get really expensive. Either that or lie.
In the real world, geologists don't care if their work supports or hurts evolutionary theory. We want to know what the rocks are telling us because it helps us find valuable minerals, oil, and explains why one of the largest earthquakes in U.S. history happened in the mid-continent rather than California... among a host of thousands of other things.
(edited several times to add link and fix spelling and grammatical errors - grrrr!)
[This message has been edited by roxrkool, 12-01-2003]
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