Biology Paper: Carbon Dating


Period: 8



During the first part of class we talked about Isotopes and carbon dating. This subject caught my attention unlike other lessons, so I decided to do my report on this topic. It is not very controversial, the only controversy being if it is accurate or not. Carbon dating is controversial in that is shares some of the fundamental assumptions inherent to all Radiometric Dating techniques. In order for Carbon Dating to have any value, Carbon-14, produced in our outer atmosphere as Nitrogen-14 and changed into radioactive Carbon-14 by cosmic-ray bombardment, and must be at equilibrium in our atmosphere. In other words, the production rate must be equal to the decay rate. Therefore, the question I pose is this; is carbon dating an effective way of telling the date of artifacts?



The first thing I will discuss is how carbon dating works. Carbon-14 is the radioactive version of Carbon. Radiation from the sun strikes the atmosphere of the earth all day long. This energy produces radioactive Carbon-14. This radioactive Carbon-14 slowly decays into normal, stable Carbon-12. Laboratory testing has shown that about half of the Carbon-14 molecules will decay in 5730 years. After another 5730 years half of the remaining Carbon-14 will decay, leaving only ¼ of the original Carbon-14. It goes from ½ to ¼ to 1/8, ect. In theory it would never totally disappear, but after about 5 half lives the difference is not measurable with any degree of accuracy. This is why most people say that carbon dating is only good for objects less than 30,000 years old.


Since sunlight causes the formation of Carbon-14 in the atmosphere, and normal radioactive decay takes it out, there must be a point where the formation rate and the decay rate equalize. This is called the point of equilibrium. Let me illustrate; if you were trying to fill a barrel with water but there were holes drilled up the side of the barrel, as you filled the barrel it would began leaking out the holes. At some point you would be putting water in and water would be leaking out at the same rate. You will not be able to fill the barrel pas this point. In the same way Carbon-14 is being formed and is decaying out simultaneously. A freshly created earth would require about 30,000 years for the amount of Carbon-14 in the atmosphere to reach this point of equilibrium because it would leak out as it is being filled. Tests indicate that the earth has yet to reach equilibrium. This would mean that the earth is not yet 30,000 years old. This also means that plants and animals that lived in the past had less Carbon-14 in them than they do today. This one fact totally upsets data obtained by Carbon-14 dating.


Yet another example is a candle you find burning in a room. You could measure the present height of the candle (say, seven inches) and the rate of burn (say, an inch per hour). In order to find the length of time since the candle was lit we would be forced to make some assumptions. We would obviously have to assume that the candle has always burned at the same rate, and the initial height of the candle. The answer changes based on the assumptions. Similarly, scientists do not know that the Carbon-14 decay rate has been constant. They do not know that the amount of Carbon-14 in the atmosphere is constant. Present testing shows the amount of Carbon-14 in the atmosphere has been increasing ever since it was first measured in the 1950’s. This may be tied in to the declining strength of the magnetic field, but this has not yet been proven.


This dating technique assumes that Carbon-14 has reached equilibrium. There is more Carbon-14 in our atmosphere today then there was at any time in the past. Thus, Carbon Dating is controversial. If there’s more Carbon-14 in the atmosphere today than there was 50 years ago, then an animal that died 100 years ago would test at an artificially higher age.


Many experiments have been done in attempts to change radioactive decay rates, but these experiments have failed to produce any significant changes. We have found that decay constants are the same at a temperature