Problems with getting accurate dates from radiometric dating speed dating f fhjdcr
These long time periods are computed by measuring the ratio of daughter to parent substance in a rock and inferring an age based on this ratio.
This age is computed under the assumption that the parent substance (say, uranium) gradually decays to the daughter substance (say, lead), so the higher the ratio of lead to uranium, the older the rock must be.
The age they came back with was only a few thousand years old. And kept their theory that dinosaurs lived "millions of years ago" instead. They then use potassium argon, or other methods, and date the fossils again.
This date did not fit the preconceived notion that dinosaurs lived millions of years ago. They do this many times, using a different dating method each time.
Of course, there are many problems with such dating methods, such as parent or daughter substances entering or leaving the rock, as well as daughter product being present at the beginning.