‘Perhaps the most important isotope’: how carbon-14 revolutionised science (2023)

Martin Kamen had worked for three days and three nights without sleep. The US chemist was finishing off a project in which he and a colleague, Sam Ruben, had bombarded a piece of graphite with subatomic particles. The aim of their work was to create new forms of carbon, ones that might have practical uses.

Exhausted, Kamen staggered out of his laboratory at Berkeley in California, having finished off the project in the early hours of 27 February 1940. He desperately needed a break. Rumpled, red eyed and with a three-day growth of beard, he looked a mess.

And that was unfortunate. Berkeley police were then searching for an escaped convict who had just committed several murders. So when they saw the unkempt Kamen they promptly picked him up, bundled him into the back of their patrol car and interrogated him as a suspected killer.

Thus one of most revolutionary pieces of research undertaken in the past century was nearly terminated at birth when one of its lead scientists was accused of murder. It was only when witnesses made it clear that Kamen was not the man the police were after that he was released and allowed to go back to the University of California Radiation Laboratory to look at the lump of graphite that he and Ruben had been irradiating.

It did not take the pair long to realise they had produced a substance with remarkable properties, one that has since transformed a host of different scientific fields and continues to help scientists make major discoveries. By irradiating graphite, they had created carbon-14.

‘Perhaps the most important isotope’: how carbon-14 revolutionised science (1)
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“That gloomy night and morning of 27 February 1940 began a revolution in physiology, biochemistry, archaeology, geology, biomedicine, oceanography, palaeoclimatology and anthropology as well as nuclear chemistry,” says environment researcher John Marra, author of the newly published Hot Carbon: Carbon-14 and a Revolution in Science. “Carbon-14, perhaps the most important isotope to life on Earth, was ‘born’.”

Carbon-14 has six protons and eight neutrons in its nucleus. By contrast, most of the carbon in our bodies and in the outside world, known as carbon-12, has six protons and six neutrons. Crucially, those two extra neutrons make the nucleus of a carbon-14 atom unstable so that it decays radioactively into an atom of nitrogen. More importantly, these decays are relatively infrequent so that it is possible to measure changes in a carbon sample over tens of thousands of years. (See box below.)


What are carbon dating, isotopes and half-lives?


The nucleus of an element is made up of subatomic particles: protons and neutrons. The number of protons in the nucleus of an element defines its chemical behaviour. But atoms of the same element can possess different numbers of neutrons in their nuclei. These different forms are known as isotopes.

Carbon has three main isotopes: carbon-12, carbon-13 and carbon-14. The first two are stable but the last decays radioactively.

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In any sample, carbon-14 atoms will take around 5,730 years to lose half their number. Thus carbon-14 is said to have a half-life of 5,730 years.

Robin McKie

“Carbon is what we are made of,” says Marra, who is professor of earth and environmental sciences at Brooklyn College, New York. “Carbon is life. It is fundamental also to how we live, how the Earth is habitable – pretty much everything. And since the discovery of a long-lived radioisotope of carbon, we have an amazing tool to delve into almost every aspect of existence on Earth – and perhaps the universe.”

As Marra reveals in this remarkable history of carbon-14, scientists quickly realised the isotope must affect living beings today. Cosmic rays batter the upper atmosphere and send cascades of neutrons through the air, they calculated. These neutrons strike atoms of nitrogen, the main component of Earth’s atmosphere, and transform some into atoms of carbon-14. In turn, these atoms combine with oxygen to create radioactive carbon dioxide that is absorbed by plants, which are then eaten by animals. “Every living thing on Earth thus becomes radioactive, albeit slightly,” says Marra.

And it dawned on Willard Libby of Chicago University that the radioactivity generated by carbon-14 could be exploited to tremendous advantage. A chemist who had worked on the Manhattan Project to build the first atom bomb, Libby realised that when an organism dies, it will stop absorbing carbon, including carbon-14, and its existing store of the latter will slowly decay. So, by measuring the radioactivity of a sample taken from the organism, its carbon-14 content could be estimated and the date of its time of death could be measured. The sciences of archaeology and palaeontology were about to be revolutionised.

A major problem had to be overcome, however. Carbon-14 exists in only very low levels in the tissue of recently deceased animals and plants: about one in a trillion of their carbon atoms are carbon-14. By contrast, natural background radiation – from thorium and uranium in rocks and other sources – is much, much higher. How could researchers separate carbon-14’s weak signal from this overwhelming background noise?

Libby solved the problem by carefully shielding his detectors and developing ways to tune out any radiation that made it through to the walls of his device. Then he turned to the gas methane, which contains carbon, to provide final validation of his technique, comparing samples from two very different sources. One sample was extracted from natural gas, a fossil fuel whose carbon-14 should have decayed long ago. The second came from the city of Baltimore sewerage system and was extracted from human excrement. It should be rich in carbon-14, having just been produced by humans, Libby reasoned.

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And that is exactly what he found. Ancient methane had no carbon-14. By contrast, methane newly excreted by humans was relatively rich in the isotope. As Marra says: “Human waste from sewer lines sent science onward.”

Libby then provided final proof of his dating technology by measuring the radioactivity – and, by inference, the age – of a series of organic samples of known antiquity: wood from the Egyptian funeral ship of Sesostris III, linen that had wrapped a Dead Sea scroll and a bread roll that had been “cooked” in the volcanic eruption that buried Pompeii. His results perfectly matched the known dates of the items he had scanned.

It was a brilliant undertaking for which Libby was awarded the Nobel prize for chemistry in 1960, though he was lucky in one sense. Libby assumed that the rate of carbon-14 production in the atmosphere had been constant for the past few tens of thousands of years. In fact, it has varied fairly widely, thanks to changes in sunspot activity, atmospheric nuclear bomb tests and rising emissions of carbon dioxide from fossil fuels. These have to be taken carefully into account when estimating ages, scientists now realise, though the underlying basis of radiocarbon dating remains sound.

‘Perhaps the most important isotope’: how carbon-14 revolutionised science (2)

More recently, radiocarbon dating has changed from simply measuring the radioactivity emitted by carbon-14 nuclei to directly counting numbers of atoms of the isotope in a sample. This is done using a technique called accelerator mass spectrometry (AMS), which has allowed scientists to date bones, artefacts and other carbon-based items from the tiniest sample. “This was a huge advance,” says Marra. “Instead of grams of material to analyse, AMS requires only milligrams.”

In this way, the developers of AMS triggered a dating revolution that began in the 60s and has since “ushered in a ‘new archaeology’ revolution”, says Marra. One example involving the use of carbon-14 resulted in the overturning of the idea that past western European cultures had depended on practices and ideas that began in the Middle East and slowly disseminated westwards with the spread of farming. Radiocarbon dating revealed a very different picture and showed that the neolithic cultures of Britain, France and central Europe must have evolved independently.

Later, the technique was used by laboratories in Britain, Switzerland and the United States to date the flax used to weave the Turin shroud. This cloth, marked with the negative image of a bearded man, was believed by some to be the burial shroud in which Jesus was wrapped after crucifixion. Using only a few fragments of cloth, scientists dated it to 1260-1390AD.

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graphic showing how carbon dating works

Over the years, uses of carbon-14 have spread well beyond dating ancient artefacts. Drugs can be labelled with carbon-14 and followed as they pass through the body in order to test their safety and efficacy. Other researchers have used the isotope to trace the way in which plants convert carbon dioxide into sugar, revealing the intricate processes underpinning photosynthesis.

In addition, carbon-14 has been exploited to study plankton and other forms of sea life, revealing how the waters of the oceans circulate in a great interconnected web of currents that sweep round the planet. “The carbon content of a fish will register what it has been eating, which in turn will reflect the chemistry of the surrounding water, which will be influenced by how the ocean has mixed,” says Marra. For good measure, carbon-14 is now playing a major role in uncovering how climates have changed on Earth over tens of thousands of years, work of immense importance as scientists struggle to understand how rising carbon emissions are now triggering dangerous global heating.

“We have gained substantial understanding about the natural world over the past 60 to 70 years, in no small part because of carbon-14,” says Marra. Certainly, it is hard to exaggerate the impact it has had on science. Yet its discoverers, Kamen and Ruben, both fared badly in the wake of their breakthrough.

Kamen, who came from a family of Lithuanian and Belarusian émigrés, aroused the suspicion of US security forces after the US entered the second world war and he was observed dining with Soviet consular officials. He was summarily sacked from his laboratory and his passport was impounded. Kamen was later brought before the House Un-American Activities Committee in 1948, accused of passing secrets to the Soviets. It was not until the end of the century that his reputation was rehabilitated.

Ruben had even worse luck. After Pearl Harbor, he began research on the physiological effects of phosgene gas, a chemical weapon. During one test, an ampoule of the gas broke and he was sprayed with phosgene. He died a few hours later.

If the story of carbon-14 is one of the remarkable examples of scientific progress in the 20th century, the sad fates of two of its main players is a sign of the turbulent times in which they lived.

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Why is carbon-14 considered one of the most important isotopes in science? ›

carbon-14, the longest-lived radioactive isotope of carbon, whose decay allows the accurate dating of archaeological artifacts.

How is carbon-14 used in science? ›

Carbon-14 dating is a way of determining the age of certain archeological artifacts of a biological origin up to about 50,000 years old. It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities.

Why is carbon-14 so important? ›

Over time, carbon-14 decays in predictable ways. And with the help of radiocarbon dating, researchers can use that decay as a kind of clock that allows them to peer into the past and determine absolute dates for everything from wood to food, pollen, poop, and even dead animals and humans.

What is special about the c14 carbon-14 isotope? ›

Carbon-14 has a half-life of 5,730 ± 40 years—i.e., half the amount of the radioisotope present at any given time will undergo spontaneous disintegration during the succeeding 5,730 years.

Why is carbon One of the most important elements of life? ›

Life on earth would not be possible without carbon. This is in part due to carbon's ability to readily form bonds with other atoms, giving flexibility to the form and function that biomolecules can take, such as DNA and RNA, which are essential for the defining characteristics of life: growth and replication.

Which is the most important isotopes of carbon and why? ›

3.2 Carbon

Its most important radioactive isotope is carbon-14, a weak beta-emitter having a half-life of 5730 years. Carbon-14 is formed naturally in the upper atmosphere by the action of cosmic rays on nitrogen.

How can carbon-14 be used to determine the age of fossils? ›

Once the organism dies, it stops replenishing its carbon supply, and the total carbon-14 content in the organism slowly disappears. Scientists can determine how long ago an organism died by measuring how much carbon-14 is left relative to the carbon-12.

What is carbon-14 and how is it formed? ›

Carbon-14 is continuously generated in the atmosphere by cosmic radiation. Neutrons are ejected from nuclei of the upper atmosphere in collisions with cosmic rays (A). Captured by nitrogen nuclei (N-14), neutrons transform these nuclei into carbon-14 (B).

How do scientists use the half-life of carbon-14? ›

Once a plant or animal dies the Carbon is no longer being regenerated and so the Carbon-14 starts to decay. In this way, by measuring the amount of Carbon-14 in the body of a prehistoric animal or plant, a scientist can deduce when the plant or animal died. All radioactive materials have a half-life.

What is the importance of isotopes? ›

Isotopes have unique properties, and these properties make them useful in diagnostics and treatment applications. They are important in nuclear medicine, oil and gas exploration, basic research, and national security.

What's the meaning of carbon-14? ›

C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples.

What is unique about carbon-14 and how many protons does it have? ›

Because carbon-14 has six protons, it is still carbon, but the two extra neutrons make the nucleus unstable. In order to reach a more stable state, carbon-14 releases a negatively charged particle from its nucleus that turns one of the neutrons into a proton.

Why is c14 used in carbon dating? ›

The basis of radiocarbon dating is simple: all living things absorb carbon from the atmosphere and food sources around them, including a certain amount of natural, radioactive carbon-14. When the plant or animal dies, they stop absorbing, but the radioactive carbon that they've accumulated continues to decay.

What are carbon isotopes used for? ›

Carbon isotopes are used in many different ways by scientists to reconstruct Earth's past. For example, we can use carbon isotopes to determine when life first evolved on Earth, and to learn more about what types of foods ancient animals ate.

Why is carbon so important in chemistry? ›

Why is carbon so basic to life? The reason is carbon's ability to form stable bonds with many elements, including itself. This property allows carbon to form a huge variety of very large and complex molecules.

What are 3 reasons carbon is so important? ›

Most living things on Earth are made of carbon . Living things need carbon the most in order to live, grow, and reproduce. Also, carbon is a finite resource that cycles through the Earth in many forms.

How is carbon important to life? ›

Carbon is an essential element for all life forms on Earth. Whether these life forms take in carbon to help manufacture food or release carbon as part of respiration, the intake and output of carbon is a component of all plant and animal life. Carbon is in a constant state of movement from place to place.

What are the most important isotopes of carbon? ›

By far the most common isotope of carbon is carbon-12 (12C), which contains six neutrons in addition to its six protons. The next heaviest carbon isotope, carbon-13 (13C), has seven neutrons. Both 12C and 13C are called stable isotopes since they do not decay into other forms or elements over time.

What is an isotope and what are its uses and importance? ›

A radioactive isotope, also known as a radioisotope, radionuclide, or radioactive nuclide, is any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.

Why are carbon isotopes important to climate scientists? ›

Powell: “Geological materials like coal, oil, and natural gas are so old that they no longer have any carbon-14.” So by studying isotopes, scientists can measure exactly how much of the carbon in the atmosphere today came from fossil fuels.

What is carbon-14 best used to find the age of? ›

Archaeologists have long used carbon-14 dating (also known as radiocarbon dating) to estimate the age of certain objects. Traditional radiocarbon dating is applied to organic remains between 500 and 50,000 years old and exploits the fact that trace amounts of radioactive carbon are found in the natural environment.

What is the carbon-14 method of finding the age of rocks? ›

Half of the remaining carbon-14 decays every 5,700 years. If you measure how much carbon-14 is left in a fossil, you can determine how many half-lives (and how many years) have passed since the organism died.

Can carbon-14 be used to determine the age of the Earth explain? ›

Carbon-14 dating has been instrumental in mapping human history over the last several tens of thousands of years. When an object is more than about 50,000 years old, however, the amount of carbon-14 left in it is so small that this dating method cannot be used.

How do scientists determine how much carbon-14 is in a sample? ›

Accelerator mass spectrometry (AMS) is a modern radiocarbon dating method that is considered to be the more efficient way to measure radiocarbon content of a sample. In this method, the carbon 14 content is directly measured relative to the carbon 12 and carbon 13 present.

What does knowing the half-life of carbon-14 help scientists determine the absolute or relative age of a rock? ›

Exponential decay of a radioactive isotope such as carbon-14 occurs with a unique, predictable half-life (t½) of 5,370 years. The amount of carbon-14 remaining in a fossil organism thus indicates the time elapsed since death, giving a measure of absolute age.

Why does carbon-14 have a long half-life? ›

The half-life of radiocarbon (14C) is 5700 ± 30 yr, which makes it particularly useful for dating in archaeology. However, only an exceptional hindrance of the beta decay from 14C to 14N—a so-called Gamow-Teller ß-decay—makes this half-life so long.

What isotopes are most useful? ›

Carbon-14, perhaps the most important isotope to life on Earth, was 'born'.” Carbon-14 has six protons and eight neutrons in its nucleus. By contrast, most of the carbon in our bodies and in the outside world, known as carbon-12, has six protons and six neutrons.

What is an isotope and how are they used in biology? ›

Isotopes are variations of chemical elements containing different numbers of neutrons. Because isotopes are recognizable, they provide an efficient way to track biological processes during experimentation. There are many potential uses for isotopes in experimentation, but several applications are more prevalent.

What does c14 decay into? ›

Beta Decay

During this process, an atom of 14C decays into an atom of 14N, during which one of the neutrons in the carbon atom becomes a proton. This increases the number of protons in the atom by one, creating a nitrogen atom rather than a carbon atom.

How many atoms are there in carbon-14? ›

There are 14 carbon atoms in the ring, three methyl groups, and an isopropyl group for a total of 20 carbon atoms.

How many C-14 atoms are present in the product? ›

The product contains 2 C14 atoms.

How does an isotope work? ›

An isotope is one of two or more forms of the same chemical element. Different isotopes of an element have the same number of protons in the nucleus, giving them the same atomic number, but a different number of neutrons giving each elemental isotope a different atomic weight.

What is important about the isotopes of carbon? ›

Both 12C and 13C are called stable isotopes since they do not decay into other forms or elements over time. The rare carbon-14 (14C) isotope contains eight neutrons in its nucleus. Unlike 12C and 13C, this isotope is unstable, or radioactive. Over time, a 14C atom will decay into a stable product.

Why is carbon-14 useful to determine the age of organic remains? ›

Once the organism dies, it stops replenishing its carbon supply, and the total carbon-14 content in the organism slowly disappears. Scientists can determine how long ago an organism died by measuring how much carbon-14 is left relative to the carbon-12.

Why are carbon-14 and carbon-12 considered to be isotopes select all that apply? ›

Isotopes are forms of the same element with equal numbers of protons but different numbers of neutrons. For example, both carbon-12 and carbon-14 have 6 protons. But carbon-12 has 6 neutrons while carbon-14 has 8 neutrons. By definition, carbon-12, carbon-13 and carbon-14 are all isotopes of the carbon.

Why are isotopes important to science? ›

Isotopes have unique properties, and these properties make them useful in diagnostics and treatment applications. They are important in nuclear medicine, oil and gas exploration, basic research, and national security.

What is an isotope and why is it important? ›

"An isotope is just a name for a different version of a nucleus. In nature, nuclei of atoms have in them neutrons and protons; the number of protons determines what element it is. For example, calcium is calcium because there are 20 protons in the nucleus. The number of neutrons determines what the isotope is."

Where does carbon-14 in nature come from? ›

Carbon-14 is produced in the stratosphere by nuclear reactions of atmospheric nitrogen with thermal neutrons produced naturally by cosmic rays (with the highest production rate 10 to 13 miles above Earth's poles), as well as by atmospheric nuclear weapons testing in the 1950s and '60s.

Is carbon-14 useful for establishing earth's age Why or why not quizlet? ›

How useful is it in dating ancient fossils? Carbon-14 is not very useful in dating ancient fossils because it has a relatively short half-life.

How do scientists use isotopes of carbon? ›

Scientists can roughly determine human regions of origin or residence by measuring carbon isotope ratios in relation to dietary plants and other foods. Using various combinations of isotope measurements, the researchers tried to identify body mass index, age, and diet of members of the sample group.

How isotopes are used in the study of environmental science? ›

The environmental isotopes are a subset of isotopes, both stable and radioactive, which are the object of isotope geochemistry. They are primarily used as tracers to see how things move around within the ocean-atmosphere system, within terrestrial biomes, within the Earth's surface, and between these broad domains.

Which isotopes are used in climate studies? ›

The stable isotope variations most frequently applied in climatological investigations are those of the heavy isotopes of hydrogen and oxygen, i.e. hydrogen-2 (or deuterium) and oxygen-18, which allow the effective tracing of climate-induced changes in the hydrological cycle.

What is the difference between the isotopes carbon-12 and carbon-14? ›

Carbon-14 has six protons and eight neutrons in its nucleus. By contrast, most of the carbon in our bodies and in the outside world, known as carbon-12, has six protons and six neutrons.

Why is carbon-12 and 14 so important? ›

As Carbon 14 decays, it is used for the determination of archaeological samples. Carbon 12 has its own importance, as it is used as a standard form for measuring the atomic weight of all elements.

Why is the ratio of carbon-14 and carbon-12 atoms important in dating? ›

Half of the carbon-14 degrades every 5,730 years as indicated by its half-life. By measuring the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of the artifact.


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