by Tas Walker A geologist works out the relative age of a rock by carefully studying where the rock is found in the field.
The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them.
The two cascades are different—235U becomes 207Pb and 238U becomes 206Pb.
What makes this fact useful is that they occur at different rates, as expressed in their half-lives (the time it takes for half the atoms to decay).
By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field.The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium.On the other hand, the abundance of argon in the is relatively small because of its escape to the atmosphere during processes associated with volcanism.This has to do with figuring out the age of ancient things.If you could watch a single atom of a radioactive isotope, U-238, for example, you wouldn’t be able to predict when that particular atom might decay.