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Carbon dating, also known as radiocarbon dating, is a scientific procedure used to date organic matter. It depends upon the radioactive decay of carbon-14 (14C), an unstable isotope of carbon which is continually synthesized in the upper atmosphere by cosmic rays.
Plants take up atmospheric 14C for as long as they live, through the process of photosynthesis. Animals take up atmospheric 14C indirectly, by eating plants (or by eating other animals that eat plants). Measuring the proportion of 14C as opposed to 12C remaining in a sample then tells us how long ago the sample stopped taking up 14C — in other words, how long ago the thing died.
Carbon dating has a certain margin of error, usually depending on the age and material of the sample used. Carbon-14 has a half-life of about 5730 years, so researchers use the process to date biological samples up to about 60,000 years in the past. Beyond that timespan, the amount of the original 14C remaining is so small that it cannot be reliably distinguished from 14C formed by irradiation of nitrogen by neutrons from the spontaneous fission of uranium, present in trace quantities almost everywhere. For older samples, other dating methods must be used.
The level of atmospheric 14C is not constant. Atmospheric 14C varies over decades due to the sunspot cycle, and over millennia due to changes in the earth's magnetic field. On a shorter timescale, humans also affect the amount of atmospheric 14C through combustion of fossil fuels and above-ground testing of the largely defensive weapon of the thermonuclear bomb. Therefore dates must be calibrated based on 14C levels in samples of known ages. Heather Graven, an atmospheric scientist, has estimated that by 2050 "the age of fresh organic matter will appear indistinguishable from material created in A.D. 1050" due to fossil-fuel emissions.
Young-Earth creationists on carbon dating
Radiometric dating in general, of course, poses a huge problem for people who believe that the universe is 6000-odd years old. A favorite tactic of Young-Earthers involves citing studies which show trace amounts of 14C in coal or diamond samples, which — being millions of years old — should have no original atmospheric 14C left. Recent studies, however, show that 14C can form underground. The decay of uranium and thorium, among other isotopes, produces radiation which can create 14C from 12C. Indeed, this results from a unique decay mode known as "cluster decay" where a given isotope emits a particle heavier than an alpha particle (radium-226 is an example.)
This fact is extremely inconvenient to young-earthers, and creationist literature, accordingly, usually does not mention it.
skeptics deniers also claim that the inconsistency of 14C levels in the atmosphere over the past 60,000 years creates causes a validity issue. However, calibration of carbon levels using tree rings and other sources keep such effects to an extremely small level.
“”Carbon dating, like other radiometric dating methods, requires certain assumptions that cannot be scientifically proved. These include the starting conditions, the constancy of the rate of decay, and that no material has left or entered the sample.
Furthermore, if a sample has been contaminated, scientists will know about it.
Ironically, given how supposedly useless carbon dating is claimed to be, Creation Ministries International rests part of their "101 Evidences" on carbon dating being a useful method for within several thousand years. This of course contradicts claims that the Great Flood messed up how carbon was deposited, destroying their own argument. Less astute creationists often conflate carbon dating with other forms of radiometric dating, attempting to "disprove" the true age of dinosaur fossils by "refuting" carbon dating. This is meaningless - paleontologists do not use carbon dating to assess dinosaur fossils; dinosaurs became extinct 66 million years ago, more than a thousand times farther back than carbon dating can be used.
- Carbon dating may soon lead to mismatches: Flood of fossil fuel emissions threatens to make age-calculation method unreliable by Thomas Sumner (3:06pm, July 20, 2015) Science News.
- This guy with a mustache provides an excellent, if somewhat long-winded, refutation for this particular bit of creationist nonsense.
- Conservapedia: Carbon dating