How reliable are all the different dating methods?
Owen Davis at U of Arizona has a nice set of web pages discussing various dating and paleo-environmental methods associated with his palynology (pollen analysis) class at http://www.geo.arizona.edu/palynology/geos462/. A brief summary follows: Radiocarbon is still the standard between 1950 and about 50,000 years ago. See http://www.geo.arizona.edu/palynology/geos462/10radiometric.html. Although decay counts (conventional radiocarbon dating) are still used, the most precise measurements are generated by Atomic Mass Spectroscopy (AMS ages). AMS ages are precise within better than 1%. However, because they are based on the absorption of atmospheric 14C by organisms, because atmospheric 14C is formed from 14N by energetic radiation, and because the radiation flux varies with the strength of the Earth’s magnetic field, the accuracy of radiocarbon ages varies with time. The radiocarbon technique has been calibrated by dating individual tree rings, themselves accurate to within
Here you will get differing opinions. The fact is that it is impossible to verify very old dates. Some researchers have almost unlimited, unquestioned confidence in radiometric dating methods. Others have doubts. There are several unprovable (but reasonable) assumptions necessary to use radiometric dating. We can not prove the assumptions are valid in particular or general cases. Some swear by their dating methods while others swear at them (as it were…). I have read in one source of a forest encased in an ancient lava flow. We know a tree encased in stone stopped exchanging carbon with the atmosphere on the same day the rock around it was formed, but the rock and tree show dramatically different ages using generally accepted radiometric dating methods. In another case, an ancient animal was found frozen in a glacier and radiometric dating of different parts of the animal gave significantly different ages. These particular examples may have been explained since, but examples like the
