As with any experimental procedure in any field of science, these measurements are subject to certain "glitches" and "anomalies," as noted in the literature.
Our understanding of the shape and pattern of the history of life depends on the accuracy of fossils and dating methods.
Age estimates can be cross-tested by using different isotope pairs.
Results from different techniques, often measured in rival labs, continually confirm each other.
In the past 150 years they have not found any fossils that Darwin would not have expected.
For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms.
The fossil record is fundamental to an understanding of evolution.
Fossils document the order of appearance of groups and they tell us about some of the amazing plants and animals that died out long ago.
Paleontologists now apply sophisticated mathematical techniques to assess the relative quality of particular fossil successions, as well as the entire fossil record.
These demonstrate that, of course, we do not know everything (and clearly never will), but we know enough.
The discovery of means for absolute dating in the early 1900s was a huge advance.