The Carbon Chronicles

SQ WINTER INSIDER 2020

The Carbon Chronicles

Text by MAHIMA ADVANI

Illustration by CRISTINA CORRAL

Carbon is omnipresent. It appears in our writing utensils, our diamonds, and even our blood. Scientists have manipulated carbon’s ubiquity to develop novel technology, especially in relation to forensic science. Residing at the center of modern radiocarbon dating, this element’s isotopic nature enables us to identify the birth and death years of human remains, answering once-unsolvable crime cases.

Carbon-14, one useful form of carbon, has an unequal number of protons and neutrons, forming a radioactive isotope of the usual carbon-12 atom. The Australian Radiation Protection and Nuclear Safety Agency explains the isotopic atom’s instability releases negatively-charged, “high-speed” electrons, or beta particles–these particles can be detected and mark carbon-14 as “radioactive.” Every 5,700 years, half of a given quantity of carbon-14 decays and emits beta particles, according to the National Earth Science Teachers Association. This lengthy half-life, along with the atmosphere’s steady ratio of carbon-14 to carbon-12 is how William Libby, a 20th century physical chemist, discovered radiocarbon dating.

Radiocarbon dating allows scientists to identify the age of once-living, carbon-based beings. According to the National Ocean Service, the carbon cycle, a never-ending rotation of carbon from the atmosphere to the Earth, occurs because of our world’s processes–volcanic eruptions, the food web, and much more. All living beings, as part of this carbon cycle, reflect the atmosphere’s constant carbon-14 to carbon-12 ratio. However, carbon-14 decays after an individual’s passing; each half-life decreases the carbon-14 to carbon-12 ratio, and technology can identify the age of the remains.

To quantify decayed carbon-14, scientists burn a piece of remains and count the number of beta particles released. Comparing the ratio of carbons in the remains to the atmosphere’s ratio reveals the remains’ age. This technology initialized a “radioactive revolution” in paleontology, archaeology, and our Earth’s history. As carbon dating transformed fossils and rocks into natural “time capsules,” scientists no longer relied upon misleading geological layers to establish chronology of events. According to the American Chemical Society, the carbon ratio in certain artifacts even revealed multiple origin sites of human civilization, contradicting previous beliefs of only European origins.

Prior to the 1950s, radiocarbon dating identified artifacts from 500 to 50,000 years old. However, as the National Institute of Justice reveals, nuclear weapons usage fluctuated atmospheric radiocarbon amounts post mid-20th century. This seemingly unrelated political event led to modern developments in radiocarbon dating–the amount of radiocarbon in a once-living being’s tissues now corresponded with this specific time’s atmospheric radiocarbon content. This newfound ability to analyze remains at a finer time scale expanded the boundaries of human remains analysis and crime scene work–a victory for the forensic science community.

Forensic scientists frequently use radiocarbon dating to identify birth and death years of corpses. Body parts that emerge early in a human’s life, like tooth enamel, reflect the atmospheric amount of radiocarbon at their time of formation, correlating with the birth year of a once-living being. However, body parts that regenerate more, like nails or tissues, correlate with current atmospheric radiocarbon levels and can identify one’s death year. Such techniques provide new perspectives to older, unresolved cases.

One cold case involved the discovery of a child’s skull in 1968 near a Canadian river. According to a paper published in the Journal of Forensic Sciences, anthropologists first estimated the child’s age to be seven to nine years, which did not match any missing children at the time. However, in 2005, scientists reopened the case with modern forensic science methods. Dental material analysis indicated that the birth year was around 1960, with death about four to five years later, rather than seven to nine. The discovered cranium was connected with a missing child from over 40 years ago by revealing the correct age and death year– thus, solving the once unsolvable.

However, this technique also has its limitations. Nuclear weapons in World War II and the Nuclear-Test Ban Treaty in 1963 restored atmospheric radiocarbon levels closer to the initial constant ratio. These events may prevent future scientists from telling the age difference between remains using radiocarbon dating—a disappointing conclusion to a revolutionary scientific development.

Understanding how carbon’s chemistry interacts with living beings and the carbon cycle, or how a human’s anatomy can identify birth or death years, reveals forensic science’s close relationship to chemical and biological phenomena. Even political events, which emphasize modern radiocarbon dating’s problematic dependence on nuclear testing, control biological developments in unpredictable ways. Modern radiocarbon dating’s relevance has been established by not only solved unsolvable cases, but also by revealing the ever-growing influence and intersectionality of forensic science.