Dating geological specimens
Even the use of isochron dating, which is supposed to eliminate some initial condition assumptions, produces dates that are not reliable.
There's a small amount of radioactive carbon-14 in all living organisms.
When they die no new carbon-14 is taken in by the dead organism.
The carbon-14 it contained at the time of death decays over a long period of time.
These low levels also make it conceivable that some of the detected carbon-14 is due to a ubiquitous carbon-14 background.
Cosmic rays are continuously producing radiocarbon from nitrogen-14.
The textbooks speak of the radiometric dating techniques, and the dates themselves, as factual information.