Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated. They are drawn up mathematically, using lists of morphological external form or molecular gene sequence characters. In the past years they have not found any fossils that Darwin would not have expected. The answer is that you use radioactive carbon dating to get the dates. That emitted light, the signal, can be used to calculate when the sample was last exposed to sunlight.
However, because ostrich eggshell is thought to be a rather closed system, it is claimed that items found in association with it can be dated more accurately by the amino-acid-racemization method.
Dating Fossils – How Are Fossils Dated?
Miller, R. Uranium series dating: Both plants and animals exchange carbon with their environment until they die. The relatively new fossil category created by evolutionists, the "archaic Homo sapiens" category, contains at least 64 fossil individuals. Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating. Silicate rocks, like quartz, are particularly good at trapping electrons. Lubenow, Bones of Contention.