Reflections on the history of radiocarbon dating

Alice Spaccasassi explores what the history of radiocarbon dating can teach us about how we celebrate and remember scientific discoveries.

A cyclotron, a type of particle accelerator, was used by Kamen and Ruben to synthesise carbon-14 for the first time. Image credit: National Archives and Records Administration, NAID 558594. Available at Wikimedia Commons.

Few recent discoveries in chemistry have affected as many scientific fields as radiocarbon dating. Archaeologists, geologists, oceanographers and many others use it to determine the age of objects up to 60,000 years old. For reference, that encompasses all human history after the Late Palaeolithic, from artefacts left by early expansions out of Africa to more recent 19th and early 20th century objects.

On a societal level, the ability to assign a relatively exact age to artefacts allows us to understand humanity’s shared history. Before radiocarbon dating, artefacts had to be identified using relative dating techniques such as stratigraphy, a branch of geology that studies rock layers. The deeper the sample, the older it must be. These methods could determine the relative order of historical events, but couldn’t provide a specific date of origin for artefacts. While this could work for individual sites, it prevented experts from comparing distant sites. Radiocarbon dating changed this by analysing the sample itself rather than its surroundings, providing more accurate approximations and therefore a more ordered understanding of historical events.

Radiocarbon dating techniques often use accelerator mass spectrometry (AMS), a technique that accelerates particles to detect specific atoms based on their weight. While the technique is destructive, it only requires very small samples, which has proven indispensable for dating religious or valuable artefacts where preservation is crucial.

A standard and universal dating method made it possible to place human history on a single timeline, making it easier to imagine history as shared between all humanity rather than separated by geographical locations. Similarly to how standard time zones changed the public’s relationship with time in the 19th century, standardised dating techniques have changed how we think of our past since the 1940s. However, the story of radiocarbon dating and the man who developed it holds lessons that we too often ignore.

Radiocarbon dating

Radiocarbon dating, developed by American chemist Willard Libby, measures the concentration of radiocarbon (14C) in organic samples to determine their age. 14C is an isotope of carbon, meaning it has the same number of protons as the original element but with an additional two neutrons in its nucleus. This isotope is generated in the atmosphere, released into the environment as carbon dioxide, and enters the food chain when plants use it for photosynthesis. Since 14C is a radioactive isotope, it is unstable and its atoms decay over time at a known rate. Half of the 14C atoms in an organism will decay after 5,730 years. This causes 14C concentration to logarithmically taper off for approximately 50,000 years.

Libby had previously proven himself in the Manhattan Project, where he worked on gaseous diffusion processes used to enrich uranium-238 into the uranium-235 that was eventually used in the Little Boy bomb. After the war, he realised that organisms would cease to obtain 14C from plant matter following death. The isotope could therefore be an almost ideal unit of measure for the age of any dead organic sample.

To prove this, Libby collaborated with the Patapsco Sewage Plant in the city of Baltimore, Maryland to test the 14C concentration of sewage methane. These values were then contrasted with samples from Egyptian tombs in a 1949 paper to determine their age with a 75 year error margin. Libby was later awarded a Nobel prize in 1960 for his discovery and is now hailed as the father of radiocarbon dating.

Radiocarbon dating is not perfect, as the atmospheric density of 14C can occasionally vary and samples could be contaminated by contact. Concerns have also been raised by climate scientists in the past decade on 14C density decreasing due to the combustion of fossil fuels, potentially skewing predictions made by existing models by up to 1,000 years by 2050. However, it is impossible to deny the impact radiocarbon dating has had on science, remaining, after almost 80 years, the go-to dating method for most fields of study.

Beyond the Nobel

Like most discoveries, Libby’s did not happen in a vacuum. Numerous people collaborated, directly and indirectly, to make that Nobel prize-winning scientific advancement possible. However, direct contributors such as E.C. Anderson and J.R. Arnold, who co-authored the most known papers on radiocarbon with Libby from 1946 to 1949 are often not mentioned in the history of 14C.

After a decade of lost research opportunities, Kamen was welcomed back in the scientific community, but we will never know what discoveries were lost in that decade.

Like all scientists, Libby continued the work of those who came before him. Indirectly, radiocarbon dating is possible today also thanks to the work of Martin Kamen, an American chemist and contemporary of Libby. Kamen and his colleague Sam Ruben were the first to synthesise 14C in a lab, discovering the isotope’s unexpectedly long half-life. Kamen, the son of Russian immigrants, became the victim of red scare policies that led to a ten-year legal battle to prove he was not a communist spy. After a decade of lost research opportunities, Kamen was welcomed back in the scientific community, but we will never know what discoveries were lost in that decade.

This story is not unusual. Left-leaning and LGBTQ+ figures were openly discriminated against due to unfounded and often unsubstantiated accusations of treason in the US between the 1940s and 50s. This practice, known as McCarthyism, deeply affected the scientific community, erasing the contributions of scientists like Kamen. Even larger than life figures like Albert Einstein were regularly monitored under McCarthyism and marked as a communist threat by government agencies.  

Libby found himself on the opposite end of cold war sentiments, being appointed to the US Atomic Energy Commission in 1950 and promoted to commissioner by President Eisenhower in 1954. Libby was well known during his time as a staunch conservative, openly supporting hydrogen bomb testing and increasing US nuclear armaments. At a time when most of his fellow commissioners sided with Oppenheimer’s scepticism towards further nuclear armament, statements such as “let’s build them as big as we can and build all we can”, allowed Libby to benefit from red scare sentiments.

The history of radiocarbon is irreversibly tied to the time in which it was discovered and popularised, a time of war and fear-mongering that marked who could be rewarded for their work and who couldn’t.

Re-thinking history

How we tell stories says a lot about our culture and shared values, and how we remember scientific history is no different. While it is impossible to argue against Libby’s role in the development of radiocarbon dating, others who made it possible are ignored in favour of a simpler story. In focusing our attention into one great man we cast a shadow over an ocean of scientists, some of whom were deprived of the opportunity to contribute to the field by the same social systems that uplifted Libby.

We often say that we stand on the shoulders of giants, but what the history of radiocarbon shows us is that we are uplifted by a pyramid of people. From Kamen, to Anderson and Arnold and even the people who worked at Baltimore’s sewage plants, a society of people contributes varying degrees of labour to make science happen. While a Nobel prize may be enticing, using them to remember our history can blind us to those who were not treated as kindly for their contributions.

The history of science is not only “Eureka!” and awards, but also a collection of minds that persevered despite systematic oppression.

This article has presented figures that are known but often ignored. However, those who are most often left behind by the ‘great men’ view of history are the ones we one day forget altogether. The red scare is only one example of systematic prejudice used to erase the achievements of oppressed groups. Numerous contributions by women and people of colour in science are forgotten due to lack of documentation and altogether indifference to their stories.

The history of science is not only “Eureka!” and awards, but also a collection of minds that persevered despite systematic oppression. Perhaps the greatest injustice of all in Kamen’s story is that he was forced into a deadlock while his field continued to grow. On top of the race being rigged, those who are shot in the leg are unable to prove themselves at all. To understand the history of science we must look further than individuals, to structures of power and whom they chose to privilege and oppress.

By all means, we should keep celebrating great minds and their achievements, but let’s not confine history to idols and sound bites that don’t celebrate the wider communities that built the pyramids they stand on. There are countless more components to scientific discoveries; even those who made use of Baltimore’s sewage system in 1946 have given something to science.

Written by Alice Spaccasassi and edited by Ailie McWhinnie.

Alice’s thoughts… I’ve always found science to be inescapably political. Who science acknowledges and profits are decisions that are made by humans, and as such can’t be expected to occur in an ideologically sterile environment. Mixed with the story discussed in the article, this can depict a somewhat bleak image of scientific institutions. However, being aware of our biases is the first step to improving how our society functions. As we rightfully start questioning the ethical implications of many institutions in our society, we should welcome uncomfortable conversations about science and its history.

Alice Spaccasassi is an MScR student in Science and Technology Studies. After spending one year writing in the B2B manufacturing industry she is now concentrating on telling stories of science’s role in society. Find her on Twitter @AliceStonebreak and LinkedIn @Alice Spaccasassi.

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