Carbon-14 Dating
1. Introduction
One of the tools available to scientists who study ancient environments is carbon-14 dating. Because so many things are dated by carbon-14 methods covering thousands of years, its results are used on a wide range of recent deposits and landforms. The most accessible materials tested are wood charcoal, shell, and bone. There are also many carbonaceous materials found in the sediment covering the earth, involving many intermediate and gateway processes assumed in theories of the geological column. Most of these materials give widely varying ages, which suggests that they are often contaminated with recent carbon. The method can check to fairly accurately see if the carbon has been disturbed over the supposed thousands of years journey to the present. This new knowledge has enabled scientists to troubleshoot and avoid dating materials on these topics. Carbon-14 dating thus presents a widely available and powerful tool for an array of disciplines.
2. Principles of Carbon-14 Dating
Radiocarbon, present in living organisms at the time of death, decays steadily at a known rate. The best known and most often used techniques are radiocarbon dating and potassium-argon dating. Although K-Ar dating is the most widely used method for many others like thermoluminescence dating and obsidian hydration dating are also used. From the day of the rock’s creation, this radioactivity begins to deplete. The isotope concentrations can be measured very accurately, but isotope concentrations are measured in years. The half-life of this decay is the period of time it takes for half the isotope in a sample to decay. It takes about 5,730 years for half of a sample of radiocarbon to decay back into nitrogen. It takes about 1.3 billion years for half of a sample of potassium-40 to decay into argon. Unlike common carbon (12C), 14C is unstable and slowly decays, changing it back to nitrogen and releasing energy. This decay, or loss of energy, results in an atom (element) becoming a different isotope of the same element.
Radiocarbon, or carbon-14, dating is probably one of the most widely used and best known absolute dating methods. It was developed in 1949 and has become an indispensable part of the archaeologist’s toolkit since. Its development revolutionized archaeology by providing a means of dating deposits independent of artifacts and local stratigraphic sequences. The radiocarbon dating method remains arguably the most dependable and widely applied dating technique for the late Pleistocene and Holocene periods.
3. Applications of Carbon-14 Dating
A long series of studies of C-14 content produced an equally long series of corrected dates. Often this data is used to extrapolate back to a more accurate date for the origin of the earth. Use of the “marine” (or “schooner”) correction to obtain the calibration curve is where the marine reservoir effect and hard water effect are corrected for. Both are completely innocent in the calculations, but it has since been established that both methods have grossly underestimated the age of samples and the C-14 samples themselves. With a more accurate calibration of the amount of C-14 to a stable isotope, it would be possible to work to find out the exact age of a sample.
Carbon-14 has a number of practical applications. In general, we can think of these as “environmental” and “geological”. The former includes the use of the method, for instance, to date the death of individuals on the basis of the decay of 14C in their remains. The latter may be done in a number of different ways, including (for example) the direct dating of geological events and the use of dated materials to locate events in time.
4. Limitations of Carbon-14 Dating
One of the most essential tools for determining an ancient object’s age, carbon-14 dating, might seem like a sure-fire way to establish age. However, there are a number of serious limitations. First of all, radiocarbon dating is only rarely applied to fossils. It is primarily used for dating cloth, wood, and plant fibers that were created within the past 50,000 years. Though it is in principle possible to date such things as the pith in the atlatl (throwing spear) by dating the material around it, carbon-14 dating has been rarely applied to artifacts from the Paleo-Indian time period. This is too short a half-life to date dinosaurs; C-14 dating is useful for dating items up to about 50,000-60,000 years old. Next comes the question of how scientists use this knowledge to date things. If carbon-14 has formed at a constant rate for a very long time and continues to form, then the objects around the site would have the same amount of carbon-14 in them as the rock or tree which they were once part of. With no clues to the passage of time, the first artifact would have to be placed at 50,000 years old and the other artifacts placed in order relative to this. So if an artifact is found to have the same level of C-14 as an object stored in a museum, what conclusions can we draw? Another limitation is that this technique can only be applied to organic material such as bone, flesh, or wood. It can’t be used to date rocks directly. Carbon-14 comes from nitrogen and is independent of the carbon-12 reservoir. If even a small percentage of the carbon in the object has decayed, then given a known rate of decay, the age of the object can be calculated.
5. Conclusion
There is a small amount of very useful isotope 14C, or radiocarbon, in the carbon dioxide present in the biota. Compare the amount of 14C in a sample with the amount of a reference isotope to determine the formation rate. Using the ratio of 14C to 12C, we can calculate the time passed since formation. This method has potential for several areas of scholarship. For instance, it may be possible to date an intrusion of magma by examining the 14C in fossils contained within the magma. It is not possible to put an exact number on the age. The most that can be said is that the intrusion is younger than the rocks around it. This ranges from 1890.6 to 572.0 14C years, using my formula from #3 above. So the error is greater for the near future, due to the smaller 14C losses and changes to the earth’s magnetic field. When calibrated with tree ring dates, it is found that the transition was only from about 491 years too young to 81 years too old. This exercise has been so valuable that it has been used in cross-dating with Potassium-Argon and Uranium-Lead to minimize error in age dating on the more ancient events. This in turn has changed the way scholars interpret the history of man and its environment. But currently the most valuable and precise application of 14C Dating is to the age of carbonaceous samples, more commonly known as organic material.
