How Accurate Are Carbon-14 And Other Radioactive Dating Methods?

Atmospheric dispersion tends to create uniform levels of carbon-14 around the globe, and researchers believe that these would be reflected in human tissues regardless of location. Barring any future nuclear detonations, this method should continue to be useful for year-of-birth determinations for people born during the next 10 or 20 years. Everyone born after that would be expected to have the same level of carbon-14 that prevailed before the nuclear testing era. The ratio of radiocarbon to carbon-12 that is in the atmosphere is equal to the ratio that is in plants and plant products — and in human, insect, microbe, and animal bodies.

Marine records, such as corals, have been used to push farther back in time, but these are less robust because levels of carbon-14 in the atmosphere and the ocean are not identical and tend shift with changes in ocean circulation. Both of these complications are dealt with by calibration of the radiocarbon dates against material of known age. The radiocarbon formed in the upper atmosphere is mostly in the form of carbon dioxide.

You don’t need to know how these equations are derived, but you should be prepared to use them so solve problems involving radioactive isotopes. Some things in nature disappear at a more or less constant rate, regardless of how much there is to start with and how much remains. For example, certain drugs, including ethyl alcohol, are metabolized by the body at a fixed number of grams per hour (or whatever units are most convenient). If someone has the equivalent of five drinks in his system, the body takes five times as long to clear the alcohol as it would if he had one drink in his system. In contrast, the blasts from nuclear bombs radiate abundant nitrogen in the atmosphere, producing significant amounts of carbon-14. Thus, nuclear bomb testing increased the 14C/12C ratio—at one point to twice its preindustrial value.

Carbon-14 in Living Things

Many hundreds of ice samples have been taken in Antarctica and this is fundamental to understanding how we are changing the climate today, and how it may change in future when accounting for fluctuations in atmospheric carbon (18). There are complications however and researchers check the known ice records against any new samples, taking into consideration known ice dates in factoring in their margin of error. Atmospheric composition, the amount of ice coverage at a given time… all of these factors are important in examining past climates (19).

Because radioactive decay occurs in the nucleus of the atom, half-life doesn’t change with environmental conditions, from the hellish heat and crushing pressures deep inside Earth to the frigid realm of the far solar system. Carbon dating is a technique used to determine the age of organic materials or, to be more precise, the time elapsed since the death of the plant or animal the material came from. It relies on measuring the amount of radioactive carbon isotope 14C left in the sample and then correlating it with the half-life of carbon 14. The measurement corresponds to a reading of the activity of the isotope.

Radiocarbon Dating May Help Uncover Art Forgeries

The main limitation of these techniques is sample size, as hundreds of grams of carbon are needed to count enough decaying beta particles. This means that it can be difficult to effectively clean the samples and remove enough contaminating carbon to obtain an accurate date. In the late 1970s and early 1980s the dating of small samples became possible using Accelerator Mass Spectrometry (AMS; Muller, 1977; Nelson et al., 1977). This method needs less than 1 mg of carbon and directly measures the abundance of the individual ions of carbon  (14C, 12C and 13C). The slow, steady process of Carbon-14 creation in the upper atmosphere has been dwarfed in the past centuries by humans spewing carbon from fossil fuels into the air. Since fossil fuels are millions of years old, they no longer contain any measurable amount of Carbon-14.

Creationists understand the limitations of dating methods better than evolutionists who claim that they can use processes observed in the present to “prove” that the Earth is billions of years old. In reality, all dating methods, including those that point to a young Earth, rely on unprovable assumptions. The amount of cosmic rays penetrating the Earth’s atmosphere affects the amount of 14C produced and therefore dating the system. The amount of cosmic rays reaching the Earth varies with the sun’s activity, and with the Earth’s passage through magnetic clouds as the solar system travels around the Milky Way galaxy.

Radiocarbon dating methods produce data based on the ratios of different carbon isotopes in a sample that must then be further manipulated in order to calculate a resulting « radiocarbon age ». Radiocarbon dating is also referred to as carbon dating or carbon-14 dating. Calculations of radiocarbon dates are typically made based on measurements from beta counting devices or from accelerator mass spectrometers (AMS).

From the point of view of the archaeologist or paleoanthropologist, this is an unfortunate situation, since bone material is present in many sites where other organics are not. Radiocarbon Dating is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts. Describes radioactive half-life and how to do some simple calculations using half-life.

These data can then be converted into dates within a particular calendrical system to provide an estimate of the material’s age. The technique of radiocarbon dating was developed by Willard Libby and his colleagues at the University of Chicago in 1949. Emilio Segrè asserted in his autobiography that Enrico Fermi suggested the concept to Libby at a seminar in Chicago that year. Libby estimated that the steady-state radioactivity concentration of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, Libby was awarded the Nobel Prize in chemistry for this work. He demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from a series of samples for which the age was known, including an ancient Egyptian royal barge dating from 1850 BCE.

It also includes far more single-year tree-ring measurements than previous versions, accounting for shorter-lived spikes from phenomena such as bursts of solar radiation. Other absolute measurements from natural archives, including ice cores, seasonal lake sediments and cave stalagmites, extend the new curve back to 55,000 years, close to the earliest age radiocarbon dating can track. Other advances, which have made radiometric dating techniques cheaper and more precise, send researchers back to the lab to reanalyze artifacts, says Suzanne Pilaar Birch, an archaeologist at the University of Georgia in Athens.

Thus, radiocarbon dates for tree remains require no reservoir corrections and provide the standard for radiocarbon dating. This approach works well for carbon-14, possibly one of the most familiar isotopes used in radiometric dating. While a plant or animal is alive, it takes in carbon from the environment. Because carbon-14 is created high in Earth’s atmosphere at a fairly constant rate, scientists can readily estimate the amount of that isotope that should be present in a living organism. Today, radiometric dating spans the ages, from recent times to the birth of our solar system.

For the world’s oldest objects, uranium-thorium-lead dating is the most useful method. While radiocarbon dating is  useful only for materials that were once alive, scientists can use uranium-thorium-lead dating to measure the age of objects such as rocks. In this method, scientists measure the quantity of a variety of different radioactive isotopes, all of which decay into stable forms of lead. These separate chains of decay begin with the breakdown of uranium-238, uranium-235 and thorium-232.