I’m guessing they use radiocarbon dating.
I want to know how all that stuff gets buried so deep in the ground over time.
I heard a prof on Art Bell years ago that had a book out. One of the subjects it covered was "When does dust become dirt".
You could look that up, as well as that documentary series on what happens to the infrastructure when humans are gone. Well, once liberals and progressives chase out everybody that can walk and chew gum at the same time.
By world-wide cataclysmic flood.