I saw a baby yesterday who I estimated to be about 3 months old, based on her size and behavior. Was my reasoning valid? You have kids, John, so I’m pretty sure that you, too, can look at a child and make at least a fairly accurate estimate of his or her age.
A coroner can estimate how long someone has been dead by measuring the temperature of the body, along with other parameters such as the ambient temperature and humidity.
Geophysicists can do the same thing with certain kinds of rocks. Their evidence about the rocks’ ages are not size, behavior, temperature, or humidity, though. Instead, their evidence is the isotopic composition of certain elements in the rock. They apply rigorous isochronic techniques that are solidly founded on the laws of physics to derive their estimates.
Grace and peace,