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.
The methods are all based on radioactive decay: The first radiometric dates, generated about 1920, showed that the Earth was hundreds of millions, or billions, of years old.
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.
Fossils can also show us how major crises, such as mass extinctions, happened, and how life recovered after them.
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.
Our understanding of the shape and pattern of the history of life depends on the accuracy of fossils and dating methods.