From University of Arizona and UNSW: “Researchers Unlock Secrets of the Past with New International Carbon Dating Standard”

From University of Arizona

8.12.20

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Researcher contacts:
Charlotte Pearson
Laboratory of Tree-Ring Research
520-991-3585
clpearson@email.arizona.edu

Anthony “Tim” Jull
Department of Geosciences
520-481-6661
jull@email.arizona.edu

Media contact:
Mikayla Mace
University Communications
520-621-1878
mikaylamace@arizona.edu

The new and improved tool will allow scientists to learn more about ancient civilizations, the past environment and even the history of the sun.

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Data produced by the University of Arizona Accelerator Mass Spectrometry Laboratory are included in the new calibration curves. P. Brewer/University of Arizona Laboratory of Tree-Ring Research.

Locked inside every slice of tree or piece of fossilized bone or ancient article of clothing is a story.

To pin down where those stories fit in the larger history of the world, scientists rely on radiocarbon dating, a technique that is now set to become more accurate than ever, thanks to research done at the University of Arizona, Lawrence Livermore National Laboratory, the University of California, Woods Hole Oceanographic Institution and Cornell University, in collaboration with international partners.

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Bristlecone pine tree rings from the Laboratory of Tree Ring Research. Measurements of radiocarbon in single rings from ancient trees like these now cover the period 1700-1500 B.C. in IntCal20. P. Brewer, Laboratory of Tree-Ring Research, University of Arizona.

In a series of three papers [see UNSW article below], the team of researchers have recalculated and adjusted the international radiocarbon calibration, or IntCal, curves, which are tools used by researchers across many disciplines to accurately date artifacts and make predictions about the future.

Radiocarbon dating works by assessing the ratio of different kinds, or isotopes, of carbon atoms in an object. The method allows archaeologists and environmental scientists to date everything from the oldest modern human bones to historic climate patterns.

“As we improve the calibration curve, we learn more about our history,” said Paula Reimer, head of the IntCal project and a professor at Queen’s University Belfast. “The IntCal calibration curves are key to helping answer big questions about the environment and our place within it.”

The research team used measurements from over 15,000 samples from objects dating back as far as 60,000 years ago, as part of a seven-year project.

“It’s hard to overstate the importance of these new IntCal curves for improving what we know about our past,” said Charlotte Pearson, UArizona assistant professor of dendrochronology, anthropology and geosciences, and a member of the IntCal Working Group.

Archaeologists can use the curves to date ancient monuments or study the demise of the Neanderthals, while geoscientists on the Intergovernmental Panel on Climate Change rely upon the curves to find out about what the climate was like in the past to better understand and prepare for future changes.

The team of researchers has developed three curves, based upon where the object to be dated is found – IntCal20 for the northern hemisphere, SHCal20 for the southern hemisphere and Marine20 for the world’s oceans.

The new curves are published in the journal Radiocarbon, which is published by the University of Arizona in partnership with Cambridge University Press. The journal began in 1959 and has been published by UArizona since 1989.

“The presence of the journal here reflects the great importance of radiocarbon dating at the University of Arizona, which goes back to the mid-1950s when the first lab was established by professor Emil Haury,” said UArizona geosciences professor Timothy Jull. “Great changes in technology have occurred since then. IntCal has become an essential tool for accurate calibration of radiocarbon dates and gradually improved over the last 35 years.”

The previous radiocarbon calibration curves, developed over the past 50 years, were heavily reliant upon measurements taken from chunks of wood covering 10 to 20 years of consecutive tree ring growth, so they contained enough material to be tested for radiocarbon.

The updated curves instead use tiny samples, such as tree rings covering just single years, that provide previously impossible precision and detail. Thanks to improvements in understanding of the carbon cycle, the curves have now been extended all the way to the approximate limit of the radiocarbon technique, which is 55,000 years ago. Any radioactive carbon older than about 55,000 years will have already decayed.

“This is a really exciting time for radiocarbon research,” Pearson said. “Radiocarbon from individual calendar-dated tree rings is not only giving us a more accurate record for calibration but providing new ways to synchronize past timelines and uncover past solar activity. The newly calculated IntCal curves include high-quality data from a range of sources and extend further back in time than ever before.”

Pearson and her team recently used annual radiocarbon data from tree rings to constrain the date of the ancient Thera volcano eruption – one of the largest eruptions humanity has ever witnessed.

Radiocarbon dating is the most frequently used approach for dating the last 55,000 years and underpins archaeological and environmental science. It was first developed in 1949. It depends upon two flavors, or isotopes, of carbon called stable carbon – containing six protons – and radioactive carbon – containing eight protons.

While a plant or animal is alive it takes in new carbon, so it has the same ratio of these isotopes as the atmosphere at the time. But once an organism dies, it stops taking in new carbon; the stable carbon remains, but the radioactive carbon decays at a known rate. By measuring the ratio of radioactive carbon to stable carbon left in an object, the date of its death can be estimated.

If the level of atmospheric radioactive carbon were constant, this would be easy. However, it has fluctuated significantly throughout history. In order to date organisms precisely, scientists need a reliable historical record of its variation to accurately transform radioactive carbon measurements into calendar ages. The new IntCal curves provide this link.

The curves are created based on collecting a huge number of archives that store past radiocarbon but can also be dated using another method. Such archives include tree rings from up to 14,000 years ago, stalagmites found in caves, corals from the sea and cores drilled from lake and ocean sediments.

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U NSW bloc

From University of New South Wales

13 Aug 2020

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While loading the 16th century samples, Dr. Adam Sookdeo ensures the magazine sits securely on the tracks of the sample changer. Photo: Richard Freeman / UNSW.

Radiocarbon dating is set to become more accurate after an international team of scientists improved the technique for assessing the age of historical events and objects. The new curves will help scientists build up a more accurate picture of the past.

Three researchers at UNSW Sydney, in collaboration with international colleagues, measured 15,000 samples from objects dating back as far as 55,000 years ago, as part of a seven-year project.

They used the measurements to create new international radiocarbon calibration (IntCal) curves, which are fundamental across the scientific spectrum for accurately dating artefacts and making projections about the future.

“Radiocarbon dating has revolutionised the field of archaeology and environmental science. As we improve the calibration curve, we learn more about our history,” says Professor Paula Reimer from Queen’s University Belfast, head of the IntCal project.

“The radiocarbon calibration curves are key to helping answer big questions about the environment and our place within it.”

Radiocarbon dating is vital to fields such as archaeology and geoscience to date everything from abrupt and extreme climate change to ancient human bones.

Archaeologists can use that knowledge to correctly restore historic monuments or study the demise of the Neanderthals, while geoscientists on the Intergovernmental Panel on Climate Change (IPCC) rely on the curves to accurately find out about past climate patterns and extremes in order to better understand and prepare for the future.

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Dr. Adam Sookdeo loading a magazine of samples from the 16th century into the MICADAS. Photo: Richard Freeman / UNSW.

‘Scientific workhorse’ for the community

UNSW project lead Professor Chris Turney, who contributed to the new curves along with UNSW colleagues Dr Adam Sookdeo and Dr Jonathan Palmer, says dating the past is essential for improving our understanding of how the Earth evolved and how climatic variations impacted its inhabitants, including humans.

“Radiocarbon dating has been the workhorse of archaeological and environmental science,” he says.

“We know the world faces many terrible environmental crises, but there still remains uncertainty surrounding the scale and timing of future impacts. A major reason for this is because scientific observations only go back a few hundred years at best. While the past obviously isn’t a perfect analogue for the future, the last 55,000 years provides valuable insights into the carbon cycle, abrupt and extreme shifts in climate, extinction events, and human migrations around the planet.”

Prof. Turney says analysing these key past events and processes can help us model our future.

“For example, ice core records show rapid warmings have occurred in the past over the polar regions. So one of the questions that radiocarbon can help answer is how do these changes translate to where people live today? By dating climate records preserved in lakes, peats and the oceans in lower latitudes, we can determine if any one region of the world warms earlier or faster than another, providing insights into the future.

“Radiocarbon dating helps us understand so many different aspects of the environment. This is especially important in Australia as the driest inhabited continent on the planet. For instance, as part of the ARC Centre of Excellence in Australian Biodiversity and Heritage (CABAH), we’re looking at human migration and adaption in Australia during multiyear-long droughts known as megadroughts. Working with colleagues, we’re interrogating fossil records of megafauna to try to understand when and why they went extinct. Radiocarbon dating helps the scientific community bring the timing of these different elements together, which gives us a better sense of where we might be going.”

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Professor Chris Turney and Dr Adam Sookdeo with a 12,000 year old section of ancient wood at the Chronos 14Carbon-Cycle Facility, UNSW Sydney. Photo: Richard Freeman / UNSW.

Three curves, 15,000 measurements

For this update, the team of researchers developed three curves, published today in Radiocarbon: IntCal20 for objects found in the Northern Hemisphere, SHCal20 for the Southern Hemisphere, and Marine20 for the world’s oceans.

The curves are created based on collecting a huge number of archives which store past radiocarbon but can also be dated using other methods. Such archives include tree-rings from preserved logs in bogs, stalagmites found in caves, corals from the sea and cores drilled from lake and ocean sediments. In total, the new curves are based on almost 15,000 measurements of radiocarbon taken from objects as old as 55,000 years.

Previous versions of the radiocarbon calibration curve that were periodically compiled over the past 50 years were heavily reliant on measurements taken from blocks of wood containing 10 to 20 years of growth so they were big enough to be tested for radiocarbon. Advances in radiocarbon measurement mean the updated curves instead use tiny samples, such as tree-rings covering just single years, providing previously impossible precision and detail in the new calibration curves. Additionally, improvements in understanding of the carbon cycle have meant the curves have now been extended all the way to the limit of the radiocarbon technique, to 55,000 years ago.

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See the full U Arizona article here .

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