Posts Tagged ‘carbon dating’

IMAGE: Professor Elisabetta Boaretto and Dr. Tobias Richter. In the foreground is a Natufian hearth at Shubayqa, Jordan. 
Credit: The Weizmann Institute of Science


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New dates for a 15,000-year-old site in Jordan challenge some prevailing assumptions about the beginnings of permanent settlement
Weizmann Institute of Science

Around 15,000 years ago, the Natufian culture appeared in what is today’s Middle East. This culture, which straddled the border between nomadic and settled lifestyles, had diverse, complex origins – much more than researchers have assumed. This finding arises from new research by a team of scientists and archaeologists from the Weizmann Institute of Science and the University of Copenhagen.
The hunter-gatherers of the Natufian culture were spread over modern-day Israel, Jordan, Lebanon and Syria around 14,500 – 11,500 years ago. They were some of the first people to build permanent houses and tend to edible plants. These innovations were most likely crucial to the subsequent emergence of agriculture during the Neolithic era. Previous research had suggested that the center of this culture was the Mount Carmel and Galilee region, and that it had spread from there to other parts of the region. The new study by the Copenhagen-Weizmann team, published in Scientific Reports, challenges this “core region” theory.
The new paper is based on evidence from a Natufian site located in Jordan, some 150 km northeast of Amman. The site, called Shubayqa 1, was excavated by a University of Copenhagen team led by Dr. Tobias Richter from 2012-2015. The excavations uncovered a well-preserved Natufian site, which included, among other things, a large assemblage of charred plant remains. These kinds of botanical remains, which are rare in many Natufian sites in the region, enabled the Weizmann-Copenhagen team to obtain the largest number of dates for any Natufian site yet in Israel or Jordan. The dating was undertaken by Prof. Elisabetta Boaretto at the Weizmann Institute of Science using Accelerator Mass Spectrometry, or AMS, dating. Boaretto is head of the Dangoor Research Accelerator Mass Spectrometry (D-REAMS) lab in the Weizmann Institute. This is one of the few labs in the world that works with the technology and methods that can analyze even the smallest organic remains from a site and precisely date them. With the lab’s specially designed mass spectrometer, Boaretto is able to reveal the amount of carbon-14 in a sample down to the single atom. Based on the half-life of the radioactive carbon-14 atoms, the dating done in her lab is accurate to around 50 years, plus or minus. To ensure the highest accuracy, the team selected only samples from short-lived plant species or their parts – for example, seeds or twigs – to obtain the dates.
Over twenty samples from different layers of the site were dated, making it one of the best and most accurately dated Natufian sites anywhere. The dates showed, among other things, that the site was first settled not long after the earliest dates obtained for northern Israel. Either Natufians expanded very rapidly into the region (which is the less-likely explanation), or the settlement patterns emerged more or less simultaneously in different parts of the region.
“The early date of Shubayqa 1 shows that Natufian hunter-gatherers were more versatile than previously thought. Past research had linked the emergence of Natufian culture to the rich habitat of the Mediterranean woodland zone. But the early dates from Shubayqa show that these late Pleistocene hunter-gatherers were also able to live quite comfortably in more open parkland steppe zones further east,” says Richter. Some of their subsistence appears to have relied heavily on the exploitation of club rush tubers, as well as other wild plants and the hunting of birds, gazelle and other animals.
These new dates do not always jibe with the idea that climate change was the main driver of abandonment or resettlement, although it clearly played a role.
Boaretto says that the “core area” theory may have come about, in part, because the Mt. Carmel sites have been the best preserved and studied, until now. In addition to calling into question the idea of the Natufian beginning in one settlement and spreading outwards, the study suggests that the hunter-gatherers who lived 15,000 to 12,000 years ago were ingenious and resourceful. They learned to make use of numerous plants and animals where ever they were, and to tend them in a way that led to early settlement. The authors say that this supports a view in which there were many pathways to agriculture and “the ‘Neolithic way of life’ was a highly variable and complex process that cannot be explained on the basis of single-cause models.”
Prof. Elisabetta Boaretto’s research is supprted by the Helen and Martin Kimmel Center for Archaeological Science, which she heads; and the Dangoor Accelerator Mass Spectrometer Laboratory.
The Weizmann Institute of Science in Rehovot, Israel, is one of the world’s top-ranking multidisciplinary research institutions. Noted for its wide-ranging exploration of the natural and exact sciences, the Institute is home to scientists, students, technicians and supporting staff. Institute research efforts include the search for new ways of fighting disease and hunger, examining leading questions in mathematics and computer science, probing the physics of matter and the universe, creating novel materials and developing new strategies for protecting the environment.

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Above: Burning fish stew and pic 2 the residue

Topic: Pottery shards obtain ancient food

Some years ago in northern Germany, archaeologist Sönke Hartz carried out excavations at a prehistoric camp-site belonging to the Ertebølle culture, close by the river Trave.

During these excavations he discovered an ancient pottery sherd which held remnants of burnt food. Hartz, an expert in the Stone Age of northern Europe, sent the pot sherd away for carbon-14 dating and was amazed when the laboratory came back with a date of 5200 BC.

“It was an archaeological sensation! This pottery was many hundreds of years older than all the pottery that was previously found in Northern Germany. It was older than everyone expected. But, then I was in doubt. I had found the pot by the river, so the food crust could possibly consist of fish. I remembered that there were dating problems with freshwater fish, which could give misleading ages,“ explained Hartz.

Reservoir effect

In order to obtain a radiocarbon date, the amount of remaining Carbon-14 atoms in a sample are measured. The less Carbon-14 that is left, the older the sample.

Hard water contains less Carbon-14 than the atmosphere, because dissolved carbonates are Carbon-14 free. A fish caught in hard water has thus a higher Carbon-14 age than contemporaneous terrestrial samples. If such a fish is then cooked in a ceramic pot, the radiocarbon age of the food crust will be higher than if a terrestrial animal was cooked in the pot.

This is known as the “reservoir effect” because the fish’s carbon actually comes from another “reservoir” than the carbon in terrestrial animals from the surrounding area. “Reservoir age” is the difference between the true age and the Carbon-14 date.

The effect, highlighted by the erroneous date from the carbonised residue on Sönkes’ ceramic sherd, persuaded The AMS 14C Dating Centre at Aarhus University in Denmark that they needed to carry out further investigations.

Variety and size of error surprising

On examining freshly caught fish from the River Trave the results revealed not only a large reservoir effect, but also a dramatic variance from between 500 to 2100 years. In effect, this means that some of the fish swimming in the Trave today seem to be over 2000 years old, when radiocarbon dated.

Felix Riede, an archaeologist at Aarhus University who regularly uses Carbon-14 dating in his work, is well aware that fish diets can give anomalous results, but this new research on the variety and size of the error surprised him.

“I had not anticipated an error of up to 2000 years,” he said.

“The implications of this discovery are fairly frightening, because it is crucial for archaeology to have a reliable dating procedure.”

“An error of a few hundred years is acceptable when you date Palaeolithic finds, but an error of 2000 years is of great importance, even for the oldest periods.”

Riede highlighted the need to look at more reliable dates (for example Carbon-14 dates of short-lived terrestrial plants or twigs) and compare them to the now highly unreliable dates from cooking pots.

It is worth noting that even charcoal from a camp fire could be another error source – the “old wood effect”: where the charcoal dated might be from the innermost ring of a 500-year-old tree which was felled 100 years before it finally ended up in the camp fire. Knowing what might cause an error is vital when it comes to dating.

An added surprise

Now armed with the knowledge produced by The Aarhus AMS 14C Dating Centre, a group of researchers actually cooked some fish stew in ceramic pots.

The group, after making their own pots, boiled up the various ingredients – including a freshly caught fish with a Carbon-14 age of 700 years. They then succeeded in burning the meal onto the pot fabric, which was then taken for dating.

Even though the food crust was made only weeks before, Carbon-14 dating returned a 14th century date and thus provided evidence that food crusts on pottery take on the same age as the ingredients.

These results reveal that freshwater reservoir effects have to be seriously considered and understood whenever residues on prehistoric pottery is radiocarbon dated. The same also applies to the bones of humans who had eaten significant amounts of freshwater fish.

This is real food for thought.

Original article:


By: Bente Philippsen and Rasmus Rørbæk
March 25, 2013


Above: Burning fish stew on purpose!

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