More than 10,000 pre-Columbian earthworks remain hidden throughout Amazonian forests

 

Peer-Reviewed Publication

AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE (AAAS)

More than 10,000 Pre-Columbian archaeological sites likely rest undiscovered throughout the Amazon basin, estimates a new study. The findings, derived from remote sensing data and predictive spatial modeling, address questions about the influence of pre-Columbian societies on the Amazon region. “The massive extent of archaeological sites and widespread human-modified forests across Amazonia is critically important for establishing an accurate understanding of interactions between human societies, Amazonian forests, and Earth’s climate,” write the authors. Indigenous societies have called the Amazon basin home for more than 12,000 years, creating ancient earthwork structures and domesticated landscapes that have had long-lasting effects on modern forest composition. However, the size and scale of Amazon settlement and landscape transformation are poorly understood – sites are remote and often obscured by dense vegetation. As such, there has never been a comprehensive survey of pre-Columbian sites across the Amazon basin. 

Airborne LIDAR (light detection and ranging), a remote sensing technique that can map small changes in topography on the ground surface beneath the forest canopy, has been used to discover many previously unknown pre-Columbian structures and earthworks in heavily forested sites throughout Central and South America. Here, Vinicius Peripato and colleagues searched 5,315 square kilometers of LIDAR survey data and discovered 24 unreported human-made earthworks, including fortified villages, defensive and ceremonial structures, mountaintop settlements, and other geoglyphs, in regions across the Amazon basin. However, the LIDAR survey data covered only 0.08% of the total area of Amazonia. 

To better understand where and how many undocumented pre-Columbian sites might occur, Peripato et al. combined the data from their small basin-wide survey, as well as data on other previously identified sites with a predictive spatial distribution model. According to the model, between 10,272 and 23,648 large-scale pre-Columbian structures remain to be discovered, particularly in southwestern Amazonia. What’s more, the authors identified relationships between the predicted probability of earthworks and the occurrence and abundance of domesticated tree species and found significant association between the two, suggesting that active pre-Columbian Indigenous forest management practices have long shaped the ecology of modern forests across Amazonia. “Amazonian forests clearly merit protection not only for their ecological and environmental value but also for their high archaeological, social, and biocultural value, which can teach modern society how to sustainably manage its natural resources,” write Peripato et al.

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Study confirms age of oldest fossil human footprints in North America

Two new lines of evidence support the 21,000 to 23,000-year age estimate of the footprints first described and dated in 2021

The 2021 results began a global conversation that sparked public imagination and incited dissenting commentary throughout the scientific community as to the accuracy of the ages. 

  

“The immediate reaction in some circles of the archeological community was that the accuracy of our dating was insufficient to make the extraordinary claim that humans were present in North America during the Last Glacial Maximum. But our targeted methodology in this current research really paid off,” said Jeff Pigati, USGS research geologist and co-lead author of a newly published study that confirms the age of the White Sands footprints. 

  

The controversy centered on the accuracy of the original ages, which were obtained by radiocarbon dating. The age of the White Sands footprints was initially determined by dating seeds of the common aquatic plant  Ruppia cirrhosa that were found in the fossilized impressions. But aquatic plants can acquire carbon from dissolved carbon atoms in the water rather than ambient air, which can potentially cause the measured ages to be too old. 

  

“Even as the original work was being published, we were forging ahead to test our results with multiple lines of evidence,” said Kathleen Springer, USGS research geologist and co-lead author on the current Science paper. “We were confident in our original ages, as well as the strong geologic, hydrologic, and stratigraphic evidence, but we knew that independent chronologic control was critical.” 

  

For their follow-up study, the researchers focused on radiocarbon dating of conifer pollen, because it comes from terrestrial plants and therefore avoids potential issues that arise when dating aquatic plants like Ruppia. The researchers used painstaking procedures to isolate approximately 75,000 pollen grains for each sample they dated. Importantly, the pollen samples were collected from the exact same layers as the original seeds, so a direct comparison could be made. In each case, the pollen age was statistically identical to the corresponding seed age. 

 

“Pollen samples also helped us understand the broader environmental context at the time the footprints were made,” said David Wahl, USGS research geographer and a co-author on the current Science article. “The pollen in the samples came from plants typically found in cold and wet glacial conditions, in stark contrast with pollen from the modern playa which reflects the desert vegetation found there today.” 

  

In addition to the pollen samples, the team used a different type of dating called optically stimulated luminescence, which dates the last time quartz grains were exposed to sunlight. Using this method, they found that quartz samples collected within the footprint-bearing layers had a minimum age of ~21,500 years, providing further support to the radiocarbon results. 

 

With three separate lines of evidence pointing to the same approximate age, it is highly unlikely that they are all incorrect or biased and, taken together, provide strong support for the 21,000 to 23,000-year age range for the footprints. 

New radiocarbon (14C) and optically simulated luminescence ages have confirmed the controversial antiquity of the ancient human footprints discovered in White Sands National Park, and reported in a study in 2021. Addressing the widespread criticism of their previous study, researchers report that the independent ages from multiple resolved sources conclusively show that the footprints were left behind between roughly 23,000 and 20,000 years ago, demonstrating that humans were present in southern North America during the Last Glacial Maximum (LGM).

When and how humans first migrated into North America has long been debated and remains poorly understood. Current estimates for the timing of these first occupants range from ~13,000 years ago to more than 20,000 years ago. However, the earliest archaeological evidence for the region’s settlement is sparse and often controversial. In a Science study published in September 2021 (Bennett et al.), researchers reported the discovery of in situ human footprints preserved in an ancient lakebed dating to between ~23,000 and 21,000 years ago in what is now White Sands National Park – findings which suggest nearly 2,000 years of human occupation in North America during the height of the LGM. However, since the study’s publication, the accuracy of the radiocarbon dates has been debated. It’s argued that the ancient seeds from the aquatic plant (Ruppia cirrhosa) that were used to date the surfaces the footprints were embedded in have the potential to be affected by old carbon reservoir effects that could influence the reported radiocarbon ages and make them appear older than they truly are.

Here, Jeffery Pigati, Kathleen Springer, and colleagues report new evidence in the form of multiple independent age estimates of the White Sands footprints, which support their previous study’s claims. “We always knew that we would have to independently evaluate the accuracy of our ages to convince the archaeological community that the peopling of the Americas occurred far earlier than traditionally thought,” said Pigati.

In their new work, Pigati and Springer et al. present calibrated 14C ages of terrestrial pollen collected from the same stratigraphic contexts as the Ruppia seeds. Unlike the seeds, conifer pollen fixes atmospheric carbon and, therefore is not subject to potential old carbon reservoir effects. According to the findings, the resulting calibrated 14C ages range from 23.4 ± 2.5 – 22.6 ± 2.3 thousand years ago. In addition, the authors obtained optically simulated luminescence ages of the sediments from within the footprint-bearing strata, which produced a minimum age of 21.5 ± 1.9 thousand years ago. In both cases, Pigati and Springer et al. show that the resolved dates were statistically indistinguishable from the original calibrated 14C ages of the oldest Ruppia seeds reported previously. In a related Perspective, Bente Phillipson discusses the study and its findings in greater detail.  

“Even as the original work was being published, we were forging ahead to test our results with multiple lines of evidence and independent chronologic techniques,” said Kathleen Springer, co-lead author of the study. “Although we were confident in the original seed ages, we wanted to develop community confidence in them as well. Our new ages, combined with the strong geologic, hydrologic, and stratigraphic evidence, unequivocally support the conclusion that humans were present in North America during the last Glacial Maximum.”

Ancient DNA

Reports and Proceedings

AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE (AAAS)

In this Special Issue of Science, three Reviews highlight how recent advances in the field of ancient DNA have greatly advanced our understanding of the evolutionary history of many plants and animals, including our own species. “This special issue examines the changing landscape of how ancient DNA (aDNA) is studied today, including previously untapped sources, improvements in technology, and ethical challenges, and what we’ve learned about ourselves though ancient DNA,” write Corinne Simonti and Madeleine Seale, associate editors at Science.

In one Review, María Ávila-Arcos and colleagues discuss the significance of aDNA in addressing non-European regional questions. According to the authors, much of the early human aDNA research was focused on large-scale events, such as continental-scale population migrations or genetic admixture events, with an overrepresentation of European-focused studies. However, many regional questions, particularly those relevant to the Global South, remain underexplored. By reviewing several recent paleogenomics studies that have been successful in highlighting local histories and health in the Americas, Africa, Asia, and Oceana, particularly that of the Indigenous and Descendant communities that live there, Ávila-Arcos et al. underscore the importance of bringing a regional perspective to aDNA research. They further explore the ethical considerations as the field shifts towards answering finer-scale questions. When done correctly, finer-scale aDNA investigations can be a powerful tool with the potential to integrate neglected or oppressed communities and to uncover past histories that have been lost or erased from history.

Another Review, by Hernán Burbano and Rafal Gutaker, discusses the use of aDNA from herbarium specimens – historically collected and preserved plant samples – to provide glimpses into past plant communities. Such insight can provide a better understanding of the evolutionary and ecological processes that shape plants over time and could help inform new conservation efforts. In a third Review, Beth Shapiro and colleagues explore the state-of-the-art in paleogenomics techniques and discuss the key challenges that remain, including technical limitations that impede the ability to evaluate “deep-time” ancient DNA.

Analysis of grinding tools reveals plant, pigment and bone processing in Neolithic Northern Saudi Arabia

Peer-Reviewed Publication

MAX PLANCK INSTITUTE OF GEOANTHROPOLOGY

 

IMAGE: 

RE-FIT OF A GRINDING STONE FROM JEBEL ORAF

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CREDIT: CERI SHIPTON

In recent years, studies have revealed that the now-arid region of northern Arabia was once much wetter and greener, providing Neolithic human populations with access to both water and game. The present aridity of the region, however, preserves little organic matter, making a reconstruction of the Neolithic lifestyle difficult.

Now, in a new study published in the journal PLOS ONE, researchers from the Max Planck Institute of Geoanthropology, the National Research Council of Italy, Institute of Heritage Science (CNR ISPC), and University College London present use-wear analysis of grinding tools recovered from Jebel Oraf in the Nefud desert of Saudi Arabia, revealing new insights into this little-understood chapter of the human story. Use-wear analysis shows that grinding tools were used for the processing of bone, pigment and plants, and were sometimes re-used for different purposes during their life span, before finally being broken up and placed on hearths.

In the new study, researchers use high-powered microscopes to compare use-wear patterns on the archaeological tools with those on experimental tools. In experiments, the grinding of grains, other plants, bone or pigment produces distinctive macro- and micro-traces on the tools’ used surface, including fractures, edge rounding of individual grains, levelled areas, striations, and different types of polish. These distinctive traces were also identified on the Neolithic grinding tools, allowing the scientists to determine which materials were being processed. 

Although faunal remains have previously revealed that meat was cooked and consumed at Jebel Oraf, wear patterns indicate that meat and bones were first processed on grindstones, revealing the possibility that bones were broken to access bone marrow.

Grinding tools were also used to process plants. While there is no evidence for domesticated grains in northern Arabia in this period, the authors argue that wild plants were ground and perhaps baked into simple breads.

“The hearths where we found the grinding tools were extremely short-lived, and people may have been very mobile – breads would have made a good and easily transportable food for them,” says Maria Guagnin, researcher at the Max Planck Institute of Geoanthropology and one of the study’s lead authors.

The researchers also found evidence of pigment processing, which they argue may be linked to Neolithic paintings. Their findings reveal that pigment was ground and processed on a much larger scale than previously assumed, suggesting there may have been more painted Neolithic rock art than the few surviving panels suggest.

“It is clear grinding tools were important for the Neolithic occupants of Jebel Oraf. Many were heavily used, and some even had holes in them that suggest they were transported. That means people carried heavy grinding tools with them and their functionality must have been an important element in daily life,” says Giulio Lucarini of the National Research Council of Italy, the study’s other lead author.

This type of analysis has only rarely been applied to archaeological materials from the Arabian peninsula, but can provide important information on the manufacture, use, and re-use of grinding tools, which in turn provides insight into the subsistence, economy, and art of the people who produced them.

Researchers involved in this study work in close partnership with the Saudi Ministry of Culture. Additional partners include King Saud University and key institutions in the United Kingdom, Ireland and Australia.

Early human migrants followed lush corridor-route out of Africa

 

Peer-Reviewed Publication

UNIVERSITY OF SOUTHAMPTON

 

IMAGE: 

ONE OF TWO FLAKES, OR HAND TOOLS, SEEN FROM THREE DIFFERENT ANGLES, DISCOVERED IN THE JORDAN RIFT VALLEY. THE FLAKES HELPED SCIENTISTS DATE HUMAN MIGRATION.

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CREDIT: UNIVERSITY OF SOUTHAMPTON

An international team of scientists has found early human migrants left Africa for Eurasia, across the Sinai peninsula and on through Jordan, over 80-thousand years ago.

Researchers from the University of Southampton (UK) and Shantou University (China), together with colleagues in Jordan, Australia and the Czech Republic(1), have proved there was a “well-watered corridor” which funnelled hunter-gatherers through The Levant towards western Asia and northern Arabia via Jordan.

Their findings, published in the journal Science Advances, support previous research conducted in Arabia suggesting this green, overland route, which is now desert, was favoured by travelling Homo sapiens heading north.

‘Modern’ humans evolved in Africa between 300 and 200 thousand years ago and dispersed out of the continent in several stages. It’s thought that over tens of thousands of years they went on to populate Asia and then Europe.

For this latest research, the team conducted fieldwork in the Jordan Rift Valley where they uncovered hand tools, known as ‘flakes’, on the edge of wadis – now dry river channels which, tens of thousands of years ago, were full of water. The scientists used luminescence dating techniques to help establish the age of the sediment the tools were buried in. This method estimates how long it has been since sediment was last exposed to light.

The results showed the tools were likely to have been used approximately 84 thousand years ago and then abandoned on the banks of the wadis and subsequently buried over time.

Paul Carling, Professor of Geomorphology at the University of Southampton, comments: “It’s long been thought that when the sea level was low, humans used a southern crossing, via the Red Sea from the horn of Africa, to get to southwestern Arabia. However, our study confirms there was a well-trodden passage to the north, across the only land-route from Africa to Eurasia.

“Our newly published evidence is a key piece of the puzzle that shows humans migrated using a northern route – using small wetland areas as bases whilst hunting abundant wildlife in the drier grasslands.   Although previous studies have looked for large lakes as potential watering holes, in fact small wetlands were very important as staging posts during the migration.”

Dr Mahmoud Abbas, the study’s lead author from Shantou University, China, said: “The Levant acted as a well-watered corridor for modern humans to disperse out of Africa during the last interglacial, and we have now demonstrated this is the case in the Jordan Rift Valley zone.

“The paleohydrological evidence from the Jordan desert enhances our understanding of the environmental setting at that time. Rather than dry desert, savannah grasslands would have provided the much-needed resources for humans to survive during their journey out of Africa and into southwest Asia and beyond.”

The researchers say their study demonstrates the intimate relationship between climate change, human survival and migrations.

Prehistoric people occupied upland regions of inland Spain in even the coldest periods of the last Ice Age

 

15,000-21,000 years ago, inland Iberia may have been more populated than traditionally thought

Peer-Reviewed Publication

PLOS

 

IMAGE: VIEW FROM THE TOP OF THE CHARCO VERDE II ARCHEOLOGICAL DEPOSIT DURING THE 2021 EXCAVATION SEASON. view more 

CREDIT: ARAGONCILLO-DEL RÍO ET AL., 2023, PLOS ONE, CC-BY 4.0 (HTTPS://CREATIVECOMMONS.ORG/LICENSES/BY/4.0/)

Paleolithic human populations survived even in the coldest and driest upland parts of Spain, according to a study published October 4, 2023 in the open-access journal PLOS ONE by Manuel Alcaraz-Castaño of the University of Alcalá, Spain, Javier Aragoncillo-del Rió of the Molina-Alto Tajo UNESCO Global Geopark, Spain and colleagues.

Research into ancient hunter-gatherer populations of the Iberian Peninsula has mainly focused on coastal regions, with relatively little investigation into the inland. A classic hypothesis has been that the cold and dry conditions of inland Iberia would have been too harsh for such populations to inhabit during the coldest periods of the Last Glacial, but recent findings have begun to challenge this view. In this study, researchers report new evidence for high-altitude human occupation from the Upper Paleolithic of Spain.

This evidence comes from a site called Charco Verde II, located in the Guadalajara province. This site is situated over 1,000 meters above sea level, in one of the coldest regions of Spain. Despite this, the abundance of tools and ornaments at the site reveals a recurring sequence of human occupation between around 21,000 and 15,000 years ago. This time span is especially notable since it includes two of the coldest periods of the Last Glacial.

This discovery further challenges the idea that Upper Palaeolithic humans avoided inland Iberia due to its harsh climate, and instead shows that the inland hosted complex and relatively dense settlements even during very cold and arid periods. These findings add to the growing evidence for Middle and Upper Paleolithic occupations throughout this region, altogether indicating that the historic lack of evidence for hunter-gatherer sites in inland Iberia is not an accurate reflection of prehistoric human distributions, but instead a result of modern research hitherto prioritizing study of coastal regions and neglecting the inland.

 The freely available article in PLOS ONE: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0291516

A prehistoric cosmic airburst preceded the advent of agriculture in the Levant

 

Agriculture in Syria started with a bang 12,800 years ago as a fragmented comet slammed into the Earth’s atmosphere. The explosion and subsequent environmental changes forced hunter-gatherers in the prehistoric settlement of Abu Hureyra to adopt agricultural practices to boost their chances for survival.

That’s the assertion made by an international group of scientists in one of four related research papers, all appearing in the journal Science Open: Airbursts and Cratering Impacts. The papers are the latest results in the investigation of the Younger Dryas Impact Hypothesis, the idea that an anomalous cooling of the Earth almost 13 millennia ago was the result of a cosmic impact.

“In this general region, there was a change from more humid conditions that were forested and with diverse sources of food for hunter-gatherers, to drier, cooler conditions when they could no longer subsist only as hunter-gatherers,” said Earth scientist James Kennett, a professor emeritus of UC Santa Barbara . The settlement at Abu Hureyra is famous among archaeologists for its evidence of the earliest known transition from foraging to farming. “The villagers started to cultivate barley, wheat and legumes,” he noted. “This is what the evidence clearly shows.”

These days, Abu Hureyra and its rich archaeological record lie under Lake Assad, a reservoir created by construction of the Taqba Dam on the Euphrates River in the 1970s. But before this flood, archaeologists managed to extract loads of material to study. “The village occupants,” the researchers state in the paper, “left an abundant and continuous record of seeds, legumes and other foods.” By studying these layers of remains, the scientists were able to discern the types of plants that were being collected in the warmer, humid days before the climate changed and in the cooler, drier days after the onset of what we know now as the Younger Dryas cool period.

Before the impact, the researchers found, the inhabitants’ prehistoric diet involved wild legumes and wild-type grains, and “small but significant amounts of wild fruits and berries.” In the layers corresponding to the time after cooling, fruits and berries disappeared and their diet shifted toward more domestic-type grains and lentils, as the people experimented with early cultivation methods. By about 1,000 years later, all of the Neolithic “founder crops” — emmer wheat, einkorn wheat, hulled barley, rye, peas, lentils, bitter vetch, chickpeas and flax — were being cultivated in what is now called the Fertile Crescent. Drought-resistant plants, both edible and inedible, become more prominent in the record as well, reflecting a drier climate that followed the sudden impact winter at the onset of the Younger Dryas.

The evidence also indicates a significant drop in the area’s population, and changes in the settlement’s architecture to reflect a more agrarian lifestyle, including the initial penning of livestock and other markers of animal domestication.

To be clear, Kennett said, agriculture eventually arose in several places on Earth in the Neolithic Era, but it arose first in the Levant (present-day Syria, Jordan, Lebanon, Palestine, Israel and parts of Turkey) initiated by the severe climate conditions that followed the impact.

And what an impact it must have been. 

In the 12,800-year-old layers corresponding to the shift between hunting and gathering and agriculture, the record at Abu Hureyra shows evidence of massive burning. The evidence includes a carbon-rich “black mat” layer with high concentrations of platinum, nanodiamonds and tiny metallic spherules that could only have been formed under extremely high temperatures — higher than any that could have been produced by man’s technology at the time. The airburst flattened trees and straw huts, splashing meltglass onto cereals and grains, as well as on the early buildings, tools and animal bones found in the mound — and most likely on people, too. 

This event is not the only such evidence of a cosmic airburst on a human settlement. The authors previously reported a smaller but similar event which destroyed the biblical city at Tall el-Hammam in the Jordan Valley about 1600 BCE.

The black mat layer, nanodiamonds and melted minerals have also been found at about 50 other sites across North and South America and Europe, the collection of which has been called the Younger Dryas strewnfield. According to the researchers, it’s evidence of a widespread simultaneous destructive event, consistent with a fragmented comet that slammed into the Earth’s atmosphere. The explosions, fires and subsequent impact winter,  they say, caused the extinction of most large animals, including the mammoths, saber-toothed cats, American horses, and American camels, as well as the collapse of the North American Clovis culture.

Because the impact appears to have produced an aerial explosion there is no evidence of craters in the ground. “But a crater is not required,” Kennett said. “Many accepted impacts have no visible crater.” The scientists continue to compile evidence of relatively lower-pressure cosmic explosions — the kind that occur when the shockwave originates in the air and travels downward to the Earth’s surface. 

“Shocked quartz is well known and is probably the most robust proxy for a cosmic impact,” he continued. Only forces on par with cosmic-level explosions could have produced the microscopic deformations within quartz sand grains at the time of the impacts, and these deformations have been found in abundance in the minerals gathered from impact craters.

This “crème de la crème” of cosmic impact evidence has also been identified at Abu Hureyra and at other Younger Dryas Boundary (YDB) sites, despite an absence of craters. However, it has been argued that the kind of shock-fractured quartz found in the YDB sites is not equivalent to that found in the large crater-forming sites, so the researchers worked to link these deformations to lower-pressure cosmic events.

To do so, they turned to manmade explosions of the magnitude of cosmic airbursts: nuclear tests conducted at the Alamogordo Bombing Range in New Mexico in 1945 and in Kazakhstan, in 1949 and 1953. Similar to cosmic airbursts, the nuclear explosions occurred above ground, sending shockwaves toward Earth.

“In the papers, we characterize what the morphologies are of these shock fractures in these lower-pressure events,” Kennett said. “And we did this because we wanted to compare it with what we have in the shock-fractured quartz in the Younger Dryas Boundary, to see if there was any comparison or similarities between what we see at the Trinity atomic test site and other atomic bomb explosions.” Between the shocked quartz at the nuclear test sites and the quartz found at Abu Hureyra, the scientists found close associations in their characteristics, namely glass-filled shock fractures, indicative of temperatures greater than 2,000 degrees Celsius, above the melting point of quartz.

“For the first time, we propose that shock metamorphism in quartz grains exposed to an atomic detonation is essentially the same as during a low-altitude, lower-pressure cosmic airburst,” Kennett said. However, the so-called “lower pressure” is still very high — probably greater than 3 GPa or about 400,000 pounds per square inch, equivalent to about five 737 airplanes stacked on a small coin. The novel protocol the researchers developed for identifying shock fractures in quartz grains will be useful in identifying previously unknown airbursts that are estimated to recur every few centuries to millennia.

Taken together, the evidence presented by these papers, according to the scientists, “implies a novel causative link among extraterrestrial impacts, hemispheric environmental and climatic change, and transformative shifts in human societies and culture, including agricultural development.”

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