Fossil record
The fossil record is one of the primary sources of data relevant to the study of evolution. Scientists examine fossils in order to understand the process of evolution and the way specific species have evolved, yet some observers are perplexed by the rarity of transitional species. The conventional explanation for this rarity was given by Darwin, who stated that "the extreme imperfection of the geological record", combined with the short duration and narrow geographical range of transitional species, made it unlikely that many such fossils would be found.
Dating methods, such as radiometric dating (but not carbon-14 dating, which works only for 0-50,000 years before present), show that some of these fossils are tens of millions of years old. Various dating methods have been used and are used today, and while there is some variance in the results from these dating methods, nearly all of them provide evidence for a very old Earth and for evolution.