HOW DOES CARBON-14 DATING (C-14) WORK?
IS IT ACCURATE AND RELIABLE?

THE SCIENTIFIC VIEW

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Note:

The North American meaning of the term "billion" is used in this essay. One billion is equal to 1,000 million.

Overview (according to most scientists):

Carbon-14 dating (a.k.a. C-14 dating) is one of many radioisotope measuring techniques for estimating the age of objects. C-14 dating is limited to the study of carbon-bearing objects. If proper precautions are taken in the preparation of the samples, it is an accurate method for dating items up to about 50,000 years of age.  Other isotope dating techniques which are based on elements other than carbon can date the age of rocks which are many billions of years old.

The C-14 technique was developed by a team of researchers, headed by Willard F. Libby, in 1947. He won the Nobel Prize in Chemistry in 1960 for this discovery.

How the technique works:

All living things -- animal or vegetable -- contain large amounts of carbon. This includes wood, bone, leather, hair, pottery, coral, paper, resin, etc. Of great importance to the analysis of the Shroud of Turin, flax and linen -- which is a product made from flax -- also contain carbon and can be dated with this measuring technique.

Carbon appears in three forms in nature:

This means that a living plant or animal has only one Carbon 14 atom for every trillion Carbon 12 atoms. C-14 is formed when cosmic rays knock neutrons out of atoms in the Earth's upper atmosphere. Some of these neutrons hit Nitrogen-14 nuclei, converting them to C-14.

In a process called photosynthesis, plants use the energy in sunlight to convert carbon dioxide from the atmosphere into carbon-bearing compounds that the plant can utilize. This process continues as long as the plants are alive. Some animals eat plants and use the carbon in the food to help them grow. Some animals eat other animals, and similarly use the carbon that they ingest. Because of the flow of carbon along the food chain, the ratio of C-14 to C-12 in living matter remains approximately the same as the ratio in the atmosphere while the plant or animal lives. In the case of flax, it progresses from seed, to adult plant, to cultivation in a matter of months. There is no opportunity for a significant percentage of C-14 to decay while the flax is alive. C-14 decay only becomes significant in the ongoing centuries after the plant dies.

As an initial working hypothesis, one might assume that the ratio of Carbon 14 to Carbon 12 has been constant through the past 50,000 years. After the plant or animal dies, no more carbon is ingested from the environment. Individual C-14 atoms decay by changing back into N-14, a stable form of Nitrogen. After 5,730 years, only half of the original C-14 is left. After another 5,730 years, only a quarter of the original amount it is left; after another 5,730 years, only one eighth is left. The term "half-life" (t 1/2) refers to the time taken for half of the atoms to decay. C-14's half life is 5,730 years ± 40 years. Thus by measuring the ratio of Carbon 14 to Carbon 12 in the sample, one can estimate the number of years before the present time (BP) when the plant or animal died.

Libby and his team computed the theoretical ratio of C-14 to C-12 that they expected for various ages of objects, subject to the assumption that the ratio in the atmosphere has always been constant. They then tested the C-14 dating technique on a number of carbon-bearing samples from ancient Egypt whose age was known by archaeological methods. For example, they obtained a sample of wood from Pharaoh Zoser's tomb which was part of a living tree circa 2600 BCE. The agreement between the theoretical curve and the actual results was very close. "Each result was within the statistical range of the true historic date of each sample:" ₁ They also counted annual growth rings in some 1000 to 1500 year old tree samples to precisely determine their age. Their initial calibration curve is shown below. Additional points have been determined to confirm that the theoretical curve is accurate beyond 10,000 years before the present. See below.

₂

Limitations and problems with C-14 measurement:

There are five main problems with this instrumental technique:

Extending the calibration curve:

A tree creates a new tree ring each year. It is narrow or broad, depending upon whether the weather during that year was dry or wet, and whether the tree was exposed to some stressors. Bristlecone pines grow so slowly that its rings are paper thin; their width has to be studied under a microscope. Methuselah's tree ring sequence near its core has been matched to the sequence found in pieces of nearby trees which have died. Dr. Henry Michael of the University of Pennsylvania's Museum Applied Science Center for Archaeology (MASCA) scanned the area almost every summer for over three decades. His goal was to find sections of dead trees that could be pieced together to extend the tree ring samples as far back in time as possible. He found  an irregular slab from a bristlecone pine that spanned the years 3050 BCE to 2700 BCE. The tree ring sequence adjacent to the slab's bark matched the sequence near Methuselah's core.

Sometimes he was lucky. He found a piece that contained 600 rings; another contained 150 rings. Other times, he had to fit together pieces of tree like a jigsaw puzzle. "Dendrochronologists [scientists who study tree rings] have built sequences for a number of tree species, including German, Irish and Polish oaks, Patagonian cypresses, Lebanese cedars, pine, yew, spruce, and chestnut. They've plotted rings from shipwreck timbers and roof beams, and wood from the Mediterranean, Russia, and China. The bristlecone pine series, the longest built from a single species in a single location, stretches back to 7040...BCE [9045 BP]. It is based on thousands of rings from 81 living trees and 118 dead trees, and Michael found more than three-quarters of the samples. He also recovered one older piece of wood, carbon dated to more than 10,000 years ago, whose rings cannot yet be linked to the the sequence." ₃

Current status:

According to EvoWiki -- a project inspired by Wiukipedia and Talk.Origins: "Correlation by use of annual growth layers in coral, sediment layers, and speleothems extend the calibration back 26,000 years. In addition recent studies of correlation of dated ocean sediment cores with Greenland ice cores, varves (layering in lake sediments) from Japan and a detailed study of speleothems from a submerged cave in the Bahamas will add confidence and perhaps extend the calibration back to about 45,000 years. Research and fine-tuning continues." ₄

Samples as small as 100 mg can be measured with modern instrumental techniques. However, flukes can occur. It is important to measure multiple samples when possible to confirm the accuracy of the data. In the case of the Shroud of Turin, 12 samples were distributed among three labs to assure accuracy.

Acceptance and rejection of the C-14 dating method:

With the exception of a small minority of scientists who are conservative Christians, essentially all researchers have reached the consensus that careful C-14 dating is a reliable method of estimating the age of carbon-bearing objects.

Radiocarbon Web-info suggests that: "The radiocarbon dating method remains arguably the most dependable and widely applied dating technique for the late Pleistocene and Holocene periods." ₁ British prehistorian Desmond Clark has said that without Carbon-14 dating "we would still be foundering in a sea of imprecisions sometime bred of inspired guesswork but more often of imaginative speculation." ₅

A minority of Fundamentalist and other Evangelical Christians are "old-Earth creationists;" they interpret the creation story/stories in the book of Genesis in the Hebrew Scriptures (Old Testament) as compatible with the belief that the age of the earth is over four billion years. They generally accept C-14 and other radiometric dating methods as accurate.

However, most conservative Protestants are "new-Earth creationists" who interpret the book of Genesis literally. They typically believe that the Earth was created at some time between 8000 and 4000 BCE during an interval of six days, each 24 hours long. They are faced with a conflict between the text of the Bible, whose authors they believe were inspired by God to write text without error, and a scientific method of measuring the age of objects. Their only option is to assume that C-14 dating is hopelessly unreliable, at least for objects which the method finds existed more than 10,000 years ago. ₆ Thus, dating of the well known Venus of Willendorf figurine at 24,000 years BP must be in error by a factor of at least 2.4 times. ₇ The use of radiometric methods that are not carbon based and which date rocks circa 4.5 billion years BP must be in error by a factor of almost a half million times. More details.

Religious implications of C-14 dating:

The accuracy and reproducibility of the C-14 technique is accepted by essentially all scientists, and by much of the public. Reactions to such dating by devout believers differ:

C-14 testing directly contradicts a number of stories in the Hebrew Scriptures (Old Testament). Some of the most obvious from the Hebrew Scriptures (Old Testament) are:

Since most of the new-earth creationists believe in inspiration by God of the authors of the Bible and the inerrancy of the biblical text, they must reject the validity of C-14 dating, and thus disallow any results obtained by that technique.

They must also reject similar radiometric measurements using such elements as Potassium and Argon. These measurements use the same basic technique as C-14 dating, but employ different isotopes.  Potassium in the form of ⁴⁰K is unstable and decays to the stable Argon isotope ⁴⁰Ar with a half life of about 1.3 billion years. _9,10 Scientists have reached a consensus that such measurements can accurately date rocks in excess of four billion years of age.

References used:

1. Radiocarbon WEBinfo site, at: http://www.c14dating.com/
2. Arnold and Libby, "Age determinations by radiocarbon content: Checks with samples of known age" Science (1949).
3. Tom Gidwitz, "Telling Time. By reading the rings of pines as old as the earliest pharaohs, Henry Michael has changed the way we look at the past," Archaeology, 2001-MAR/APR. Online at: http://www.tomgidwitz.com/ The quotation is taken from the online version.
4. Living snails were C14 dated at 2,300 and 27,000 years old," EvoWiki.org, at: http://wiki.cotch.net/
5. "Jim", "How does carbon dating work?", Ask Yahoo at: http://ask.yahoo.com/
6. "How accurate are Carbon 14 and other radioactive dating methods?," ChristianAnswers.net at: http://christiananswers.net/
7. Christopher L. C. E. Witcombe, "Women in Prehistory : The Venus of Willendorf,"  Sweet Briar College, at: http://witcombe.sbc.edu/
8. Dates of biblical events are taken from the Schofield Reference Bible which many new-earth creationists believe contains accurate dating.
9. "Geological Time," Evolution for Teaching, at: http://sci.waikato.ac.nz/
10. "Chronological Methods 9 - Potassium-Argon Dating," University of California, at: http://id-archserve.ucsb.edu/

Copyright © 2005 by Ontario Consultants on Religious Tolerance
Originally posted: 2005-FEB-08
Latest update: 2005-APR-27
Author: B.A. Robinson