Why Do We Trust Carbon14 Dates?

Illustration by Jayne Doucette, Woods Hole Oceanographic Institution

When it comes to history and especially archaeology one of the biggest questions is "When did it happen?" In 1940 Martin Kamen introduced the world to Carbon14. Carbon14 (C14) is an isotope of Carbon. If you are not sure why it is Carbon14 as opposed to just Carbon or a different isotope, such as Carbon12 (C12), it has to do with the number of protons and neutrons that each contain. All carbon atoms have 6 protons, but the isotopes C14 and C12 have different numbers of neutrons and thus have differing levels of radioactivity, a C12 isotope has 6 neutrons therefore C14 has 8 neutrons, this difference in numbers of neutrons also changes the mass(weight) of the atoms as well.

Willard F. Libby via ACS

Seven years later Willard F. Libby presented the world with a method using C14 for radiocarbon dating. The theory of radiocarbon dating is based on the belief that the atmosphere contains a constant amount of C14 and therefore, each living thing dies containing a constant amount of C14. This 'constant' presence combined with the constant rate of decay is the foundation of radiocarbon dating. Using a comparison between the base level of C14 of living or carbon based items against the current level of C14 in a sample the methods states that the sample can be accurately dated. This is determined by the constant decay rate of the isotopes over time. Thus by taking the original number of isotopes at the time of death, a number thought to be an universal constant always (something that I think very arrogant) and comparing it to the number of isotopes left in the specimen when tested an 'accurate' date is determined.

Atomic Explosion via Wikipedia

The method is more complex than explained above, for one, since, the atom bomb had been invented prior to the method of radiocarbon dating, Libby used the amount of C14 isotopes based on numbers from pre-industrial age samples. In order to help with the proper determination of dates scientists have applied information from tree-rings to calibrate dates suggested by radiocarbon analysis. This practice quietly admits problems with radiocarbon dating. The problem is twofold actually, first any radioactive release into the atmosphere, say by a nuclear explosion can greatly increase the amount of C14 in the atmosphere, on the other hand, the increase in carbon monoxide and other byproducts referred to collectively as greenhouse gasses, such as from burning fossil fuels, actually reduces the amount of C14 in the atmosphere. It is known that these radiations and greenhouse gases can be introduced into the atmosphere by other than man-made means. We also have no conclusive information about contaminants having been introduced by any means in ancient or pre-historic times. These issues show that we cannot be sure of the amount of C14 in the atmosphere at any time in history. Therefore, any date that is based solely on C14 is suspect at best.

via disclose.tv

This addition of information to determine dates, does not eliminate several issues with the process as a whole. It is not totally the method that is flawed, however, the results will be flawed with the addition of carbon into a sample, thus resulting in newer or younger dates than should be. And the older the original piece is will determine just how flawed the results can be. And the amount of 'extra' carbon does not need to be significant to cause flaws that could place samples in totally different and more recent epochs than they should be. And the amount of C14 as the base-line number is such that in the absolute best circumstances you can only get an accurate date of up to 50,000 years ago give or take on the statistical variance. That is a geologic and thus historic blink of the eye.

Time of Extinction

One of the questions that skeptics of the radiocarbon model pose is that there is no absolute way to know if things in Earth's past could not have changed the level of C14 isotopes in the atmosphere over a significant period of time, thus implying that the constant has not always been the same. While geologists recognize things such as earthquakes and volcanic eruptions, they seem to discount the fact that catastrophes can have significant and or dramatic impact on the Earth over time. There also seems to be little belief that things such as cosmic ray bombardment or solar storms could have anything to do with climate on Earth and there is little knowledge about how much radiation can be added to the atmosphere and how long it remains when it does happen.

Northern Lights

We allow for the extinction of the dinosaurs by an asteroid impact, yet we do not allow for any cosmic impact in the time of man. This being said there was a Solar Flare Storm in the 19th century that disrupted all manners of communication and industry in the Northern hemisphere. The event is well documented, yet, due to technological limitations and knowledge, no one at the time tested for the increase of radiation to the atmosphere.  In addition, much more of the hemisphere was witness to the amazing spectre of the Aurora borealis, which was a direct visual result of the increased radioactive debris that was flung into the atmosphere. Another, issue is that as previously stated in developing the method it was known that atomic explosions, which released radioactive waves into the atmosphere, can also occur with impacts of asteroids and meteorites, which can be on the magnitude of several atomic bombs and even create nuclear winters, will increase the C14 amounts. This is why a date prior to the industrial age was chosen as the base line date for determining the proper amount of C14 for dating purposes. However, not being at a point where we understood or cared about the impact of the industrial age on our environment we did not realize the effect over time that it would have on the atmosphere. This reduction of C14 brought on by industrial pollution now means that a piece of linen made and tested today would give the same date results as a piece of linen worn by William the Conquer about 1000 years ago.