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Research led by the University of Arizona Tree Ring Research has anchored a long succession of tree rings and created a context for the civilizations that existed during the Bronze and Iron Ages.
Charlotte Pearson’s eyes searched a palm-sized piece of an old tree. They chose a ring that looked “unusually light” and made a note without thinking about it. Three years later, with new methods and technologies, she discovered that the light ring could mark the year in which the Thera volcano erupted on the Greek island of Santorini over the ancient Minoan civilization. The date of the outbreak, one of the greatest people ever seen, has been debated for decades.
Pearson, assistant professor of dendrochronology and anthropology at the University of Arizona, is the lead author of an article published in the Proceedings of the National Academy of Sciences, in which she and her colleagues used a new hybrid approach to assign calendar dates to tree rings that are stratified span the period Thera broke out, except for one year after a calendar date. This enables them to present new evidence that an eruption date around 1560 BC Chr. Could support.
Fill in the gaps
“You have this time capsule in every tree ring that you can unpack,” said Pearson.
Trees grow in accordance with the conditions of their local environment. Every year, trees produce a new layer of concentric growth, called a tree ring, that can record information about rainfall, temperature, forest fires, soil conditions, and more. Trees can even record solar activity as it grows and fades.
When a series of rings of trees of different ages overlap and add, they can span hundreds or thousands of years and provide insight into past climatic conditions and the context for simultaneous civilizations.
“The longest chronology in the world goes back 12,000 years. In the Mediterranean, however, the problem is that we don’t have a full, continuous record that goes back to Thera’s time, ”said Pearson. “We have recorded very well over the past 2000 years, but then there is a gap. We have tree rings from earlier periods, but we don’t know exactly what dates the rings correspond to. This is known as a “pending chronology”. “
Filling this gap could help determine the date of the Thera outbreak and provide a climatic background for the various civilizations that stood out and fell during the Bronze and Iron Ages, which spanned 5,000 to 2,500 years ago.
“Until you can set an exact year for events of a magnitude that makes sense to people – a year – it’s not quite as powerful,” said Pearson. “This study is really about dating the chronology of Peter Kuniholm (my co-author and professor of tree ring laboratory research) that he has put together over 45 years of work in a way that was not possible before. Most importantly, it is timed as if we filled our tree ring gap. “
A hybrid approach
Since the founding of the UArizona Laboratory of Tree-Ring Research in 1937, a selection of tree ring samples from around the world have accumulated under the Arizona Stadium under less than ideal conditions. Since the completion of the university’s modernized Bryant Bannister Tree Ring building in 2013, the curation team, led by Peter Brewer, has relocated, organized and stored samples for future research.
“This is the collection that created the tree ring research field and by far the largest in the world,” said Brewer. “Researchers come from everywhere to use our collection.”
“It’s just crammed with the remains of old forests and archaeological sites that no longer exist, and it contains wood samples that were fundamental to the growth of the discipline of dendrochronology,” said Pearson.
The collection includes woods from the Midas Mound Tumulus in Gordion, Turkey – a huge grave of a man who was probably Midas’ father or grandfather. Kuniholm has been building a tree ring chronology from the Mediterranean for almost half a century from such woods. Together Kununholms record from the B.C. The period spans more than 2,000 years, including trees that grow before the wind of the Thera eruption. This makes him the key to the team’s research.
Despite the length of this chronology, it remained undated. To capture it, the team decided to try something new.
When cosmic rays from space enter the earth’s atmosphere, neutrons collide with nitrogen atoms to create a radioactive version of carbon called carbon-14 that spreads across the planet. All other life on Earth, including tree rings, absorb carbon-14, and since tree rings lock out a measurement of carbon-14 for each year they grow, they contain patterns that show how it goes over time Time has changed. These patterns of carbon-14 in tree rings around the world should match.
Pearson and her team used the carbon-14 patterns captured in the Gordion tree rings to anchor the pending chronology with similar patterns from other calendar-dated tree ring sequences.
“It’s a new way to anchor floating tree ring chronologies that take advantage of tree ring annual precision,” said Pearson.
To confirm their results, the team turned to the calendar-dated rings of high-lying bristle pines from western North America that lived at the same time as the Gordion.
“If there are large volcanic eruptions, bristles are often scarred by freezing during the growing season, creating a frost ring,” said second author Matthew Salzer, a researcher at the tree ring laboratory. “Then we compared the frost ring data with that of the Mediterranean trees, which respond to volcanoes by growing wider rings. And it worked. It was shown that the wide rings in the Mediterranean chronology occurred in the same years as the frost rings in the bristle cone. We took that as confirmation that the dating was probably correct. “
The team then considered using a new technology called X-ray fluorescence machine in the laboratory to scan the wood for chemical changes.
“We scanned the entire period that Thera is known to have happened,” said Pearson, “and we found a very low calcium deficiency right where I saw this lighter ring years ago.”
Although it is a slight fluctuation, it is significant and occurs only at one point in the years around 1560 BC. BC.
“We have included this in the newspaper and are tentatively suggesting that it is a possible date for Thera,” said Pearson.
Something changed the chemistry of the environment in which the tree grew; Acid capture from a volcano is one way wildfire another, but since the date coincides with other tree ring marks for a major eruption, Pearson says it is worth further investigation.
“I think to do good science you have to study everything and be open until enough data comes together,” said Pearson. “This is another little piece of the puzzle.”
Header Image – Public Domain
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