Padawanbater2
Well-Known Member
Radiocarbon dating (usually referred to as simply carbon dating) is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 (14C) to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e., uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" (BP), with "present" defined as CE 1950. Such raw ages can be calibrated to give calendar dates. One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites. When plants fix atmospheric carbon dioxide (CO2) into organic matter during photosynthesis they incorporate a quantity of 14C that approximately matches the level of this isotope in the atmosphere. After plants die or they are consumed by other organisms (for example, by humans or other animals), the accumulation of 14C fraction stops and the material declines at a fixed exponential rate due to the radioactive decay of 14C. Comparing the remaining 14C fraction of a sample to that expected from atmospheric 14C allows the age of the sample to be estimated.I believe carbon 12 has a half life of approximately 6000 years. I remember learning about carbon dating in chemistry and I believe that this meant that after 12,000 years the carbon atoms have mostly decayed and therefore the accuracy of those results decrease dramatically after that amount of time. The 1-3% you speak of is only accurate within 12,000 years at the most. I've read that scientists conduct the experiments and if they get more than one possible scenario, they simply use the one that most supports their hypothesis which would be incorrect.
Anything dating back further than that time frame is using based on another type of dating, which would be radioactive dating through certain isotopes. The problem with this is that you need an abundant enough source of radioactive materials to find something and when dealing with ancient civilizations, why the hell would they have such materials nearby? For example a certain phosphorus isotope has a half life of 32 days whereas a certain uranium isotope has a half life of up to 4.5 billion years.
If you're curious, they take a sample of material, they measure it's mass and they measure the amount of radioactivity it emits. Uranium decays into other isotopes at a constant rate therefore you can accurately date the sample based on ratio between the mass and the radioactivity (each atom also emits a certain amount of radiation so it's not exactly a "rocket science" calculation). The same thing is done with carbon dating.
In conclusion: carbon-12 dating (building block of life) will not show us anything over 12,000 years old. For that we must rely on other materials, many of which are rare to find in most archeological discoveries since we haven't used them in the past.
The technique of radiocarbon dating was developed by Willard Libby and his colleagues at the University of Chicago in 1949. Emilio Segrè asserted in his autobiography that Enrico Fermi suggested the concept to Libby at a seminar in Chicago that year. Libby estimated that the steady state radioactivity concentration of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, he was awarded the Nobel Prize in chemistry for this work. He demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from a series of samples for which the age was known, including an ancient Egyptian royal barge of 1850 BCE.
http://en.wikipedia.org/wiki/Carbon_dating