Carbon Dating - WolfWikis
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Carbon Dating
From WolfWikis
Contents
1 Introduction
1.1 What is the technology?
1.2 Why is it important?
1.3 How was it discovered?
2 Analysis
2.1 Physics of Carbon Dating and the C-14 Cycle
3 Conclusion
3.1 What is the future of this technology?
3.2 How is this technology viewed by the public?
3.3 How does this differ from the way it is viewed by the scientific community?
4 Work Cited
Introduction
What is the technology?
Carbon dating is one of archeology's mainstream methods for dating organic objects up to 50,000 years old.
This method is based on the idea of radiative decay of Carbon-14 isotopes over thousands of years. Through
physics scientists have discovered that radioactive molecules decay at a specific rate dependent on the atomic
number and mass of the decaying atoms. This constant can be used to determine the approximate age of the
decaying material through the ratio of radioactive isotopes to the estimated initial concentration of these
isotopes at the time of the organisms death. Scientists have concluded that very little change has occurred in
the ratio of Carbon-12 to Carbon-14 isotopes in the atmosphere meaning that the relationship between these
two should be very similar to how they remain today.
Why is it important?
Without radiocarbon dating, “we would still be foundering in a sea of impressions sometime bred of inspired
guesswork, but more often of imaginative speculation,” (qtd in Higham).
Carbon-14 dating is a revolutionary advancement in the study of the history of our planet. It is in fact leading
to the, “reconstruction of the history of the world,” (Poole 10). This method of dating allows researchers to
learn about past civilizations, changes in the earth, and in the climate. Different civilizations and religions have
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different methods of dating. However, carbon-14 dating offers something particularly valuable, called absolute
dating, which is the age of the substance before the current time. This means that it may be used and compared
to dates anywhere in the world. In fact it is considered the, “most important development in absolute dating in
archaeology and remains the main tool for dating the past 50,000 years,” (Kelly). With this tool scientist hope
to unravel the mysteries of how man developed, when the first man lived, where he went, and create a type of
timetable of human life. “Its development meant an almost complete re-writing of the evolution and cultural
emergence of the human species,” (Higham).
How was it discovered?
Willard F. Libby discovered the
phenomenon of radio carbon dating in 1952.
Libby was led by “Scientific curiosity” as
he called it to look into the possibility of
carbon dating because of study he was
looking into that detailed the effects of
cosmic rays from the discovery of cosmic
radiation by V.F. Hess in 1911, on the
earth’s atmosphere. Libby believed that that
the amounts of cosmic radiation that were
hitting the earth had to be detectable in
some way. Through a series of deductions
based on information from the available
nuclear and cosmic ray literature at the
time, Libby was able to make a quantitative
prediction about the amount of Carbon-14
present in the living biosphere. The steps
that Libby used to justify his quantitative
predictions of the amount of Carbon-14 in
the atmosphere include first, Serge Koriff’s
discovery that cosmic rays generate
Low level anticoincidence apparatus devised by Libby for his
approximately 2 secondary neutrons per
original
C-14 Measurements.(The Remarkable Metrological History
second, second the inference that most
of Radiocarbon Dating)
neutrons undergo the process of
thermalization in the form of nuclear
reaction with atomospheric Nitrogen to
form C-14 via the reaction 14N(n,p)14C, and thirdly that C-14 quickly oxidizes in the earth’s atmosphere to
form radioactive carbon dioxide or 14C¬O2, and that this mixes with the total exchangeable reservoir of
carbon in a period that is short compared to the ca. 8000 year mean lifetime of C-14. Based on the production
rate of cosmic rays, their almost quantitative transformation to C-14 and estimate of the exchangeable
reservoir of approximately 8.5 g/cm2, Libby was then able to make the prediction that the radioactive
concentrations of C-14 was about 14 disintegrations per minute per gram of carbon present. Once living matter
is cut off from this radioactive presence nuclear decay will be clearly manifested and then absolute dating
would be able to take place using the observed half-life of C-14 of 5568 years. Two assumptions must be
made in order to achieve absolute dating, they are that cosmic ray intensity and the exchangeable reservoir
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average for Carbon must be constant for many thousands of years. Libby hypothesized the existence of natural
C-14 in 1946, and in order to validate his hypothesize he needed to prove that C-14 could be found on living
matter. Initially background radiation from cosmic rays and other natural sources of natural radiation within
the earth’s atmosphere made it nearly impossible to get any accurate measurements of C-14 present in living
matter. To get around this problem Libby and Colleagues developed a special detector that was comprised of
the standard Geiger Mueller radiation detector that was modified by placing cosmic ray counters around the
Geiger counter to counteract the effects of cosmic rays on the background radiation being detected by the
Geiger counter. The cosmic ray counters did not eliminate the background radiation problem completely and it
was deemed necessary that in addition to the cosmic ray counters being placed around the Geiger counter, it
should also be enshrined in a steel casing, with steel cantilevered doors. This final modification allowed for a
reduction of the background radiation measurement by 95%. Libby was now able to start using his modified
Geiger counter to successfully measure radiation that was being produced by C-14. Thus began the
revolutionary dating technique we know as Carbon dating. Carbon dating not only revolutionized how scientist
dated materials, but significantly reduced the cost over previous methods used such as the thermal diffusion
enrichment technique. This method of dating could cost in upwards of a thousand US dollars to date a single
mummy. Not only did it cost a lot to perform but the thermal diffusion enrichment technique also required a
lot of sample from the dating subject, and this sometimes caused the subject to become damaged. Libby’s new
dating technique has also given rise to many practical applications such as using Carbon dating to help solve a
crime by dating evidence found at the scene. In addition to the use of DNA evidence, Carbon dating has also
been used to free the wrongly accused. The discovery of Carbon dating by Willard F. Libby, has been
revolutionary particularly to the scientific community. It has given mankind the ability to get a rather clear
look at the past that was not previously thought possible.
Analysis
Physics of Carbon Dating and the C-14 Cycle
Carbon has unique properties that are
essential for life on earth. Familiar to us as
the black substance in charred wood, as
diamonds, and the graphite in “lead”
pencils, carbon comes in several forms, or
isotopes. One less abundant form of carbon
has atoms that are 14 times as heavy as
hydrogen atoms: carbon-14, or 14C, or
radiocarbon.
Carbon-14 is a radioactive substance. At
any given moment carbon-14 is decaying in
an object, and if that object is living, it is
also being replaced at a steady rate. Carbon14 is created when a neutron is excited by a
cosmic ray, and then that neutron collides
with a nitrogen atom. The carbon isotope is
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then absorbed by plants through
photosynthesis and consumed by animals.
Due to the way the sunlight reacts with the
atmosphere it is also taken in by respiration.
The carbon-14 dating method assumes that
all living things have the same percent of
carbon-14 inside of them at any given
moment and the ratio of carbon-12 to
carbon-14 in the atmosphere and in living
objects is virtually constant. However, after
a living thing dies, carbon is no longer
being taken in. The amount of carbon-12
does not lessen, but the amount of carbon14 does. This unstable isotope of carbon
decays at an exponential rate back into
nitrogen-14 because it is a radioactive. By
An image of the Carbon-14 life cycle (Brain, How Stuff Works).
comparing the amount of carbon-12 in an
object to the amount of carbon-14 scientist
can figure out a fairly accurate age of the object. Carbon-14 decays by the following equation:
Where N is the current amount, N_o is the original amount, lambda is the proportionality constant for the
growth rate (which is negative for decay), and t is the amount of time that has passed.
Carbon-14 has a half life of approximately 5,730 years, meaning by this time half of the carbon-14 in the
object has decayed. At the time of death organic materials stop absorbing Carbon-14, and the decay process
begins. Carbon-14s half life of a little under 6 thousand years means that after this period of time the original
mass of Carbon-14 is halved and an equal amount of Nitrogen-14 is present through Beta decay. The quantity
of carbon-14 left in a material is determined by burning a small piece so that it converts it into carbon dioxide
gas. Then the electrons that are given off by the decaying carbon-14 are measured by radiation counters. From
this information scientist are able to determine the artifacts age. This age determined is the relationship
between Carbon-14 and its daughter element Nitrogen-14. The Exponential decay equation given above is a
simple why to describe the continual halving of the Carbon mass with each half life term.
Conclusion
What is the future of this technology?
Human influence has both hindered and increased the potential of Carbon Dating. New methods and
advancements have increased the dating range that Carbon-14 can predict, however humans have affected the
carbon levels present on Earth potentially skewing results. A accelerator techniques of Carbon-14 dating
through the use of mass spectrometers have aloud the date range of Carbon-14 dating to be extended to
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100,000 years. Issues with this technique though comes in the form of Nitrogen-14. Since so many half lives
have occurred the mass of Carbon-14 is very low, thus the dating technique is based on the mass of Nitrogen14 the daughter product of Carbon-14. However Nitrogen-14 and CH2 have very comparable masses when
scanned with a mass spectrometer. This blurs the Nitrogen content and changes with potential age of the
organic compound. Nuclear testing throughout the last century has dramatically increased the Carbon-14 levels
in the atmosphere. Experts have presumed that the levels have actually doubled. This fact can greatly effect the
reliability of Carbon Dating in the future and alternative methods may have to be used in order to compensate
for this error.
How is this technology viewed by the public?
The general public gets most of its exposure to carbon dating through various news outlets such as the New
York Times, Washington Post, and other various news outlets throughout the world. Even though the general
public may or may not understand the physics behind carbon dating most can appreciate its value to society.
Many of the world’s news outlets will occasionally print articles pertaining to the uses of carbon dating. For
example the New York Times has ran 6 stories over the last 3 years about artifacts or remains that have been
found somewhere in the world and the article will talk about the fact that carbon dating was used to date
whatever the discovery happened to be. The New York Times ran a story in 2006 about how carbon dating put
humans in Europe much earlier than once thought. While this story does not go into detail about how carbon
dating works the mere fact that it was written by a journalist and put into a publicly circulated newspaper does
shows that the public in general does have a willingness to learn about carbon dating and can appreciate the
improvement it brings to society. To a small group of people mostly the religious right wingers, carbon dating,
they say, presents tremendous opposition to their faith and challenges the very foundations of their religion.
While this is very much debatable this small group of people tends to hold the belief that if it goes against
their religion or faith then carbon dating cannot be accurate. Even with minor opposition carbon dating has
managed to find a place in many different areas of the lives of the masses, like television. Many crime shows
such as CSI, NCIS, Cold Case, Bones etc, sometimes refer to the use of carbon dating in order to solve a
crime that has occurred on the show. Even though carbon dating is a relatively new technology and it is
opposed by a few people, it continues to gain more and more popularity. The more the public gets exposed to
and learns about carbon dating more it will received.
How does this differ from
the way it is viewed by the
scientific community?
“Seldom has a single discovery in
chemistry had such an impact on
the thinking in so many fields of
human endeavor. Seldom has a
single discovery generated such
wide public interest” (qtd in
Westgren).
In 1960 Willard Libby received a
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Nobel Prize for the development of
carbon dating, showcasing this
method as a valuable tool for
scientists. “His method has
obtained widespread use and has
become indispensable in
Source
archaeology, geology, geophysics
(http://www.umanitoba.ca/faculties/afs/soil_science/MSSS/Ecology/Cartoons/Cartoons%20Images/Radio%20Carbon%20Dating.jp
and other sciences,”(Westgren).
Not only is it priceless, but it is
also relatively easy to comprehended for those who are not quite so familiar with the sciences. Soon after its
discovery, the carbon-14 dating method drew attention from the scientific community and research laboratories
began to show up in multiple countries.
The technique has had many triumphs, and yet, some scientists still question its validity for various reasons.
Some discoveries may seem unbelievable. In 1991 a frozen Stone Age man was determined to be 5300 years
old by the carbon dating method. However, since this was the oldest corpse to ever be found, the “discovery
caused a great stir in the scientific community,” (Vaidya). One particular reason scientists disagree with this
method, and one thing they are trying to fix is the fact that the technique assumes the amount of carbon-14 in
the atmosphere is constant. Carbon-14 is measured in comparison to carbon-12, however this ratio may
fluctuate overtime and is somewhat unpredictable. For example, the quantity of carbon-14 in the atmosphere
compared to other carbon isotopes was predominantly affected because of nuclear activity in the 1950s and
1960s. Other environmental conditions may also affect how much carbon-14 is present in an object. Different
plants absorb carbon-14 differently, since animals consume these plants, something as simple as an animal’s
diet can alter the amount of carbon-14 found. “An animal that ingested plants with relatively low C-14
proportions would be dated older than their true age,” (NDT). For these reasons, while the carbon-14 dating
method is viewed as a valuable tool, it is also cross-examined by the scientific community.
Work Cited
Brain, Marshall. "How Carbon-14 Dating Works." 03 October 2000. HowStuffWorks.com.
<http://science.howstuffworks.com/carbon-14.htm> 18 March 2009.
Higham, Thomas. "The Method." 1999. <http://www.c14dating.com/int.html>. 13 April 2009.
Long, Kelly. "Why Is Radiocarbon Dating Important to Archaeology." California State Parks.
<http://www.parks.ca.gov/?page_id=24000> 1 March 2009.
Nave, R. "Accelerator techniques for carbon dating." <http://hyperphysics.phyastr.gsu.edu/hbase/nuclear/cardat.html>15 April 2009.
Nondestructive Testing Resource Center (NDT). “Carbon-14 Dating.” <http://www.ndted.org/EducationResources/CommunityCollege/Radiography/Physics/carbondating.htm>. 8 April 2009.
Poole, Lynn, and Gray Poole. Carbon-14. United States of America: Whittlesey House, 1961.
Vaidya, Akanksha. "How Things Work:Radio Carbon Dating." 23 Feb. 2009. The Tartan Online.
<http://www.thetartan.org/2009/2/23/scitech/howthingswork> 8 April 2009.
Westgren, Professor A. “Nobel Prize in Chemistry 1960.” 1960.
<http://nobelprize.org/nobel_prizes/chemistry/laureates/1960/press.html> 8 April 2009.
Libby, Willard F. Radiocarbon Dating. Chicago, IL: University of Chicago Press, 1955.
Currie, LLoyd A. "The Remarkable Metrological History Of Radiocarbon Dating [II]." Journal of
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Research of the National Institute of Standards and Technology 109.2 (2004): 185-217.
Retrieved from "http://wikis.lib.ncsu.edu/index.php/Carbon_Dating"
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