Should they follow the evidence of carbon-dated fossils going back millions of years...
Forgive the pedantry, but this
is a science discussion, right?
Anyway, due to the relatively short half-life of carbon-14, radiocarbon dating is only good to about 60,000 years ago. There are, however, several other methods for dating fossils, even ones from billions of years ago.
There are two basic methods used to date fossils: direct and indirect. Direct dating is a test applied to the material of a fossil and indirect dating aims either to date the rocks directly above and below the fossil strata or by using DNA analysis to estimate the date of divergence between related fossils.
- Dendrochronology, i.e., counting tree rings, can directly date fossil trees, and can indirectly date other fossils found in the same strata.
- Radiometric dating - carbon dating is the best known radiometric dating method and it is a direct dating method. But other radioisotopes with longer half-lives than C14 can be used to determine the age of rocks above and below fossil strata thereby putting an upper and lower limit on the age of the strata. Radiometric dating uses the ratio of radioactive isotopes to their decay products in a sample. Two of the most useful are uranium-thorium dating (good to about a half-million years ago) and uranium-lead dating (accurate from 1 million to 4.5 billion years ago).
- Optically stimulated luminescence dating - uses the decay of optical defects caused by exposure to sunlight. In paleontology it is used primarily to date sandy sediments and is accurate to about 100,000 years ago.
- Paleomagnetic dating - uses the historical pattern of earth's magnetic pole reversals imprinted on rock formed at the Midatlantic Ridge or in layers of sediment. Paleomagnetic dating is used for rocks a few hundred thousand years to a few million years old.
- Molecular divergence dating (molecular coalescence) - determines approximate age by examining the DNA of two or more related descendants and using the molecular clock method of dating to calculate the probable upper and lower dates that a common ancestor existed.
Creationists often cite problems and limitations of carbon=14 and other radiometric dating methods in their attempts to poke holes in evolutionary theory. There are, however, many parallel lines of evidence for evolution*, and much in the same fashion there are many lines of evidence for the dating of fossils. Each of the dating methods I described has strengths and weaknesses, but the most important thing about them for evolutionary theory is that the methods do not contradict each other and in several cases one method can be directly applied to confirm the efficacy of another.
* Fossils, branching evolution (common descent), morphological similarities, embryology, vestigial body parts, biogeography, and molecular evidence are all different facts of biology that are explained by the theory of evolution. Sometimes creationists sneer that evolution is "only a theory" - and the correct response to that challenge is to say, "Yes, evolution is a theory, but it is the only theory that explains all the facts of biology, such as fossils, embryology, biogeography, etc., etc.