Radiometric Dating Assumptions

There are many types of sciences, the two focused in radiometric dating are operational science and historical science. Operational science is a systematic approach to understanding that uses observable, testable, and repeatable experimentation to understand how nature commonly behaves. Historical science is interpreting evidence from past events based on a presupposed philosophical point of view.

Radiometric dating uses both of these types of science (measuring the amount of daughter element in the rock sample is an example of operational science, the conditions present when the rock formed can only be studied through historical science.)
Since radiometric dating uses both of these types of science, we can't directly measure the age of something. A combination of scientific techniques of the present and assumptions of historical science would be needed to estimate the age. There are three critical assumptions that can affect the results during radiometric dating:

1.     The initial conditions of the rock sample are accurately known.

2.     The amount of parent and daughter elements in a sample have not been changed by processes other than radioactive decay.

3.     The decay rate of the parent isotope has remained constant since the rock formed.

To better understand radiometric dating, an hourglass will be used. We can observe an hourglass with sand at the top and bottom, we could easily calculate how long the hourglass has been running. We could calculate how much time elapsed since the hourglass was turned over, based on our estimations on how fast the sand is falling and measuring the sand on the bottom. Our calculations could be correct, but the result entirely wrong. This is because we failed to include the critical assumptions:

  1.     Was there any sand at the bottom when the hourglass was turned over (initial condition)?

  2.     Has any sand been added or taken out of the hourglass? 

  3.     Has the sand always been falling at a constant rate?

Since the initial conditions were not observed, we must make assumptions. All three of these assumptions can affect our time estimates. If the three critical assumptions are not considered, radiometric dating can give incorrect dates.