Carbon dating machine
The contraption he built looks a little like something you might see from..
But Marvin Rowe is no nut. That machine he built, and what it’s used for, helped Rowe win the prestigious Fryxell Award for Interdisciplinary Research from the Society of American Archeology two years ago.
“We call the process Low Energy Plasma Radiocarbon Sampling,” said New Mexico’s state archeologist Eric Blinman, who credits Rowe with inventing the process. “But a lot of people just refer to this as ‘Marvin’s Machine.’”
The process is important because, unlike other methods of radiocarbon dating that destroy the sample being tested, LEPRS preserves it. It also works on tiny samples – even a flake of ink or paint – and is considered a more accurate means of dating.
“With standard radiocarbon dating, there’s a risk of contamination of carbonates. They have to use acids and, within that process, you lose a large part of your sample and you destroy it,” Blinman explained. “But we now have the ability to date incredibly small amounts of carbon – 40-100 millionths of a gram – and that is the real revolutionary aspect of this. And the ancillary part of that is it’s non-destructive.”
That’s important to Nancy Akins, a research associate with the Office of Archaeological Studies, who in February was having a bison tooth and sheep bone tested by “Marvin’s Machine.” The items were excavated from the site of a rock shelter in Coyote Canyon north of Mora.
“It could be 500 years old or it could be 5,000 years old,” she said of the bison tooth, the result allowing her to complete her report of the site that she’s determined to have been used by humans as a hunting outpost starting 1,700 years ago.
“I’m just waiting on the dates, because it’ll change everything if we get dates where I can actually say, ‘OK, that’s what the sheep bones date to and that’s what the bison dates to.’ It tells us an awful lot about how they were using the land on the east side of the Sangre de Cristos.”
Because a lot of that part of New Mexico is private property or under land grants, such finds as the one in Coyote Canyon are rare, she said.
“Unless there’s a road or something, we don’t have any information at all. This is one of the very, very few sites in Mora County that have been excavated,” she said of the site reported by the state Department of Transportation.
And when she gets her answers and completes her report, she’ll still have the bison tooth and sheep bone.
One of a kind
Rowe won his Fryxell Award “based in his prominent role in developing methods for rock art dating and minimally-destructive dating of fragile organic artifacts,” as well as his scientific analysis, scholarship and student training, according to the SAA website.
The achievement has been decades in the making. Rowe and two colleagues at Texas A&M’s Department of Chemistry built the first plasma dating machine in 1990 while exploring ways to extract organic carbon from pictograph samples.
“Other people have been successful dating charcoal paintings,” Rowe explained. “But, in the United States at least, most of the paintings are not charcoal. Most of them that I’ve encountered are inorganic pigments and that’s where the importance of the small sample comes in.”
Blinman adds that, under the best of circumstances, standard radiocarbon dating requires 30 milligrams of carbon. Rock art pigments don’t have that much carbon in them. But “Marvin’s Machine” can date material 100 millionths of a gram or less.
Blinman said the process’s capability to date very small samples would allow, for instance, determination of the age of the ink on a Chinese text written on bamboo. “The people who will fake texts can get their hands on old bamboo,” he said. Normal carbon dating can’t date the ink because it requires too large a sample. “We can flake off a piece” and date it, Blinman said. “If the ink is old, then it’s real.”
Rowe is probably the world’s foremost authority on radiocarbon rock art dating. He says much of what he learned was by trial and error. In fact, the first machine he and his Texas A&M colleagues built caught fire and was destroyed.
Currently, there are only three LEPRS machines in existence – one in Michigan and one in Arkansas, both procured by former students of Rowe – but the one at the lab located at the New Mexico Office of Archeological Studies off N.M. 599 in south Santa Fe is the most sophisticated.
“Marvin has learned so much from the previous two (machines) about their construction and their use that when we offered him space and the opportunity to build one here, it was sort of like he was able to do all the things he sort of wanted to do, but couldn’t under the circumstances of the research at Texas A&M,” said Blinman.
Using plasma to scrub artifacts
Traditional carbon dating estimates age based on content of carbon-14 (C-14), a naturally occurring, radioactive form of carbon, and requires destruction of an object. A piece of an organic object – a bone fragment or weaving, for example – is washed with acid at high temperature to remove impurities and then burned in a chamber.
The carbon dioxide gas produced is run through an accelerator mass spectrometer, which measures the decay of radioactive carbon 14 – the more the carbon 14 has decayed, the older the object is. Comparisons are also made with the amounts of C-14 expected to have existed in the atmosphere in the past.
Blinman explained that Rowe’s alternative process is based on plasmas – ionized gas made up of groups of positively and negatively charged particles, and one of the four fundamental states of matter, alongside solid, liquid and gas. Plasmas are used in television displays and in florescent lights, which use electricity to excite gas and create glowing plasma.
In Rowe’s non-destructive method, an entire artifact goes into in a vacuum chamber with plasma. The gas gently scrubs or oxidizes the surface of the object to produce carbon dioxide – CO2 – for the C-14 analysis, without damaging the artifact.
“We can energize the plasmas so that they are really hot, but we can also tune them down so they are extremely gentle,” Blinman said as Rowe and his crew fired up their machine to test the bison tooth and sheep bone.
He showed a picture of a turkey feather that had been tested and hardly looks ruffled. “The experience of the artifact is no different than your body temperature or, worst case, Phoenix on a summer day,” he said.
The plasmas in Rowe’s machine are generated with radio frequencies, rather than electricity, and work like a cleaning agent to scrub off the CO2.
“We have to use the ultra pure gases because any contamination from modern, atmospheric CO2 is going to screw up the data. So he has bled off high-purity oxygen into a reservoir that we will then tap as we generate plasmas,” Blinman said.
And what’s unique about “Marvin’s Machine” is that it has five chambers, so multiple samples can be tested at once. “That helps our efficiency somewhat,” Rowe said. “To my knowledge, nobody has gotten more than one plasma running at one time.”
The Archaeology Institute of America’s Archaeology magazine named Rowe’s non-destructive dating method one of the Top 10 discoveries of 2010. It noted that he has refined the method to work on objects coated in sticky hydrocarbons, such as the resins that cover Egyptian mummy gauze.
“Archaeologists, meanwhile, are hailing the discovery as one of the most important in decades, particularly for issues surrounding the repatriation of human remains from Native American burials, which modern tribes don’t want to see harmed,” said the magazine.
Answers raise other questions
Fast forward a few months from Rowe’s demonstration for the Journal and the results are in. Blinman explains that, after the samples went through “Marvin’s Machine,” the results were sent to a lab in Zurich, Switzerland, for analysis.
“There are very few radiocarbon labs that will direct date carbon dioxide gas,” he said. “Other labs would turn it into graphite and that could add potential error to the system.”
The bottom line is that the bison tooth is most likely from between 530 and 685 AD, with 650 AD considered the mean average.
“It’s one of the earlier dates we have from that site,” said Akins, who now has most of the answers she needs to complete her report on the Coyote Canyon rock shelter. But it doesn’t answer all the questions.
What’s curious, she said, was that there’s bison tooth found there at all. The location is not a spot where buffalo would roam, so it was most likely brought there.
But why? If it were carried in as food supply, why weren’t there more buffalo bones found there? And why bring the head, from which little meat can be extracted?
“Ceremonialism is a pretty strong thing,” she said, purely speculating it could have been used for ceremonial purposes. She noted that deer heads have been found in kivas that date to later times.
And who brought it there in the first place?
“That’s a good question,” Akins said. “Back that early, we just don’t know.”
It could have been early Tewa people or nomadic groups coming in from the plains to escape the heat, she said, “but there’s no way of knowing. That early, we don’t put a label on it.”
The date returned on the sheep bone was a disappointment. It most likely is from the 1930s.
“What we were looking for there was something from the late 1800s or early 1900s,” she said.
The results suggest that people were still herding sheep in the area in the 1930s, “but sheepherders probably didn’t eat their own sheep,” she said.
“Marvin’s Machine” and the Low Energy Plasma Radiocarbon Sampling process don’t answer every question and sometimes raises more questions. But it can bring us closer to understanding our past.
“If you don’t really care about ordering history, you don’t care about dating,” Blinman said. “But if you want to order history, or you want to establish big-picture views about climate change and the extinction of Ice Age mammals and fauna, then this is one of the best tools we have available to us.”