The Radiocarbon Dating Game
A Geochronologist’s 40-year Love Affair
“Do you know radiocarbon dating?”
Dr. Alex Cherkinsky, a senior research scientist at CAIS, sees the answer in my guilty facial expression. He searches his desk for pen and scrap paper. “I will show you. If you’re going to work here, you should know.”
He doesn’t seem like one to enthuse. He is stoic in the colloquial sense of the term: a gruff-seeming man with a gravelly Russian accent. But the lengths he goes to — sketching graphs, comparing data from his own AMS tests, writing out figures and calculations, patiently watching my face for signs of confusion as he speaks — in order to explain the core of his life’s work, demonstrates a kind of passion that words can’t do justice.
Here’s what I learned:
Radiocarbon dating is a method scientists use to estimate how old a given organic object is by measuring subtle variations in the kinds of Carbon retained in that object.
For example, a woolly mammoth that lived thousands of years ago will have collected Carbon from its environment throughout its lifetime. Carbon ( C ), an abundant element found in the atmosphere and all living things, comes in 3 varieties called isotopes: 12C, 13C, and 14C (pronounced “Carbon 12”, “Carbon 13, “Carbon 14”). The bone of the mammoth will contain concentrations of each isotope.
However, unlike its isotopic cousins, 14C is unstable and so diminishes or decays exponentially over time. Every 5,600 years, 14C decays by half; therefore the half-life of 14C is 5,600 years. The decay allows scientists to compare the bone’s concentration of 14C to its stable concentration of 12C and 13C.
The difference should indicate how many years have passed since the bone’s host died. If we find that the amount of 14C present is 25% of the other carbon concentrations, then we can surmise that 14C has undergone 2 half-lives, which is 2(5,600 years) = 11,200 years. Therefore, the mammoth died 11,200 years ago.
That’s the process in a nutshell.
Because radiocarbon dating relies on 14C, the method is limited to mostly organic objects that are under 50,000 years old. Still, it is a useful tool in satisfying human curiosity about the past. How has the climate changed over the millennia? Why did certain species go extinct? How did ancient humans survive? Do these elements relate in a given place during a given time period?
Alex entered the field of geochronology over forty years ago. By applying radiocarbon dating, he’s analyzed just about everything under the sun. At CAIS, he re-determined the age of a mummified steppe bison called Blue Babe, an apt allusion to Paul Bunyan’s giant ox. Originally dated at 36,000 years old, Alex that its age actually exceeds the limit of 50,000 years.
Keeping with the theme of mega fauna, he has also researched the extinction of giant sloths in Brazil. From Peru, he’s dated Incan quipus, which are impressive pre-literate modes of recordkeeping. And in a rare forensics case, he dated human scalps found in the basement of a drug dealer post-bust.
He has even showed up on two documentary series — one about mummies and one about the controversy over digging up and testing Native American bones. I searched the Internet far and wide for clips of these documentaries to no avail.
When he came to CAIS in 2006, Alex was a seasoned veteran in his field. He started working with radiocarbon dating during his university years and continued that research on into his time at the Russian Academy of Sciences (RAS). RAS is an exclusive society of Russian scientists who are elected based on merit. The collapse of the USSR brought him to the U.S. and eventually he made his way into the CAIS laboratories where he immediately began applying his experience.
For instance, it was Alex who suggested CAIS participate in a program that the University of Glasgow runs wherein labs across the world submit samples of their work in radiocarbon dating. The lab compiles all the samples and plots the data on a graph so that other labs can see where their precision ranks among competitors.
Participation allowed CAIS to check the precision of their methods and make improvements where needed. It was also Alex who helped convince the team at CAIS to invest into Accelerated Mass Spectrometry (AMS), an improved radiocarbon dating technique. With AMS, scientists can date sensitive material such as paintings and sculptures while minimizing damage dealt to test subjects.
The application comes in handy. Alex has dated a few wooden sculptures, one from the Chinese Warring States Period and another from American colonial times. The latter, which he confirmed to be 400 years old, allegedly sold at Christie’s Auction in New York for an obscene amount of money. For those who haven’t heard of it, as I hadn’t, Christie’s is a posh organization that auctions off expensive and rare art.
“The thing was very primitive,” Alex said of the sculpture, laughing, “I wouldn’t buy it for even thirty dollars.”
He is candidly funny like that throughout our two-hour conversation. When I asked why dating old objects is important, he shrugged.
“Why are people interested in life 10,000 years ago? I don’t care about life even 100 years ago. How does it affect me?” Alex said.
Given his line of work, I’m not entirely convinced. He concedes, of course, that value lies in understanding climate change and its effect on environments, flora, fauna, and us (See Carla Hadden’s application of radiocarbon dating to modern fisheries.) And while I’m sure he appreciates the practical applications of geochronology, I suspect the reason he’s worked in this field for four decades has more to do with this simple fact: he loves it.
