Relative dating and absolute dating techniques
Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.
These skeptics do not provide scientific evidence for their views.
Biologists actually have at their disposal several independent ways of looking at the history of life - not only from the order of fossils in the rocks, but also through phylogenetic trees. Relative dating is done by observing fossils, as described above, and recording which fossil is younger, which is older.
The discovery of means for absolute dating in the early 1900s was a huge advance.
This was roughly the dating method used by scientists in the early days of palaeontology and archaeology, before the emergence of absolute radiometric dating methods (radiocarbon, potassium-argon, thermoluminescence, OSL, etc.)The relative dating method is still helpful, since basically it gives reasonably good results.
And not every fossil or archaeological object can be dated, since radiometric dating methods are mostly rather costly, and the financial means of most research teams are limited.
Current understanding of the history of life is probably close to the truth because it is based on repeated and careful testing and consideration of data.
The rejection of the validity of fossils and of dating by religious fundamentalists creates a problem for them: Fossil sequences were recognized and established in their broad outlines long before Charles Darwin had even thought of evolution.
Fossils can also show us how major crises, such as mass extinctions, happened, and how life recovered after them.
And in some cases older objects may be moved out of their original context and get mixed with younger objects, in a stratigraphically younger layer.
This is the reason why most palaeontologists and archaeologists collaborate with geologists, in order to explain the processes which were at the origin of the sedimentation of the layers.
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.