Biology Paper: Carbon Dating
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 of the original Carbon-14.
It goes from to 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
of 2000 degrees Celsius or at a temperature of 186 degrees Celsius and are
the same in a vacuum or under pressure of several thousand atmospheres.
Measurements of decay rates under differing gravitational and magnetic
fields also have provided negative