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The following radioactive decay processes have proven particularly useful in radioactive dating for geologic processes:. Note that uranium and uranium give rise to two of the natural radioactive series , but rubidium and potassium do not give rise to series. They each stop with a single daughter product which is stable. Some of the decays which are useful for dating, with their half-lives and decay constants are:. The half-life is for the parent isotope and so includes both decays. Some decays with shorter half-lives are also useful. Of these, the 14 C is unique and used in carbon dating.
A fossil from Classical Latin fossilis ; literally, "obtained by digging"  is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons , stone imprints of animals or microbes , objects preserved in amber , hair, petrified wood , oil, coal, and DNA remnants. The totality of fossils is known as the fossil record. Paleontology is the study of fossils: their age, method of formation, and evolutionary significance.
When news is announced on the discovery of an archaeological find, we often hear about how the age of the sample was determined using radiocarbon dating, otherwise simply known as carbon dating. Deemed the gold standard of archaeology, the method was developed in the late s and is based on the idea that radiocarbon carbon 14 is being constantly created in the atmosphere by cosmic rays which then combine with atmospheric oxygen to form CO2, which is then incorporated into plants during photosynthesis. When the plant or animal that consumed the foliage dies, it stops exchanging carbon with the environment and from there on in it is simply a case of measuring how much carbon 14 has been emitted, giving its age. But new research conducted by Cornell University could be about to throw the field of archaeology on its head with the claim that there could be a number of inaccuracies in commonly accepted carbon dating standards. If this is true, then many of our established historical timelines are thrown into question, potentially needing a re-write of the history books. In a paper published to the Proceedings of the National Academy of Sciences , the team led by archaeologist Stuart Manning identified variations in the carbon 14 cycle at certain periods of time throwing off timelines by as much as 20 years.