Radiometric dating of the most ancient fossils uses the
Older dates may change by a few million years up and down, but younger dates are stable.For example, it has been known since the 1960s that the famous Cretaceous-Tertiary boundary, the line marking the end of the dinosaurs, was 65 million years old.A key point is that it is no longer necessary simply to accept one chemical determination of a rock’s age.Age estimates can be cross-tested by using different isotope pairs.All these labors have not led to a single unexpected finding such as a human fossil from the time of the dinosaurs, or a Jurassic dinosaur in the same rocks as Silurian trilobites.
In the past 150 years they have not found any fossils that Darwin would not have expected.
Repeated recalibrations and retests, using ever more sophisticated techniques and equipment, cannot shift that date. With modern, extremely precise, methods, error bars are often only 1% or so.