A couple of days ago, I re-visited the Bamburgh Research Project site at the so-called Bradford Kaims. This prehistoric site is fascinating and I simply had to do it justice with its own site visit.
These findings show that while socio-economic factors were traditionally considered to shape ancient human societies in this region, the influence of abrupt climate change should not be underestimated.
A team of international scientists led by researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science found that during the first half of the last interglacial period known as the Holocene epoch, which began about 12,000 years ago and continues today, the Middle East most likely experienced wetter conditions in comparison with the last 6,000 years, when the conditions were drier and dustier.
“Evidence for wet early Holocene was previously found in the Eastern Mediterranean Sea region, North and East African lakes and cave deposits from Southwest Asia, and attributed to higher solar insolation during this period,” said Ali Pourmand, assistant professor of marine geosciences at the UM Rosenstiel School, who supervised the project. “Our study, however, is the first of its kind from the interior of West Asia and unique in its resolution and multi-proxy approach.”
The Fertile Crescent, a region in west Asia that extends from Iran and the Arabian Peninsula to the eastern Mediterranean Sea and northern Egypt is one of the most climatically dynamic regions in the world and is widely considered the birthplace of early human civilizations.
“The high-resolution nature of this record afforded us the rare opportunity to examine the influence of abrupt climate change on early human societies. We see that transitions in several major civilizations across this region, as evidenced by the available historical and archeological records, coincided with episodes of high atmospheric dust; higher fluxes of dust are attributed to drier conditions across the region over the last 5,000 years,” said Arash Sharifi, Ph.D. candidate at the department of marine geosciences and the lead author of the study.
The researchers investigated climate variability and changes in paleoenvironmental conditions during the last 13,000 years based on a high-resolution (sub-decadal to centennial) peat record from Neor Lake in Northwest Iran. Abrupt climate changes occur in the span of years to decades.
The study helps to inform the debate about what killed off megafaunal species (or animals over 100 pounds) during the last glacial period – a subject that is highly debated, with some scientists pointing to human hunting and land alteration, and others to climate change. Progress on the debate has been hindered by reliance on fossil evidence in lieu of studies of ancient DNA, which could shed more light on the timing of major animal population changes, like migration or extinction events. Here, to parse out the roles for human activity or changing climate in the Late Pleistocene megafaunal extinction, Alan Cooper and colleagues used a combination of ancient DNA and detailed paleoclimate data.
They evaluated DNA from megafaunal species, looking back over more than 50,000 years of DNA records for extinction events. The researchers compared information on megafauna extinctions to records of severe climate events in the Late Pleistocene obtained through Greenland ice cores and other sources.
They report a close relationship between Pleistocene megafaunal extinction events and the rapid warming events at the start of so-called interstadial periods (or regularly recurring warm phases). They note that the unique megafauna population structures that resulted from climate change events could have been more susceptible to human impact. Their analysis ultimately strengthens the case for climate change as the key driver of megafaunal extinctions, with human impacts playing a subsidiary role.
The reports by Alan Cooper et al. and Maanasa Raghavan et al. are related to a special package from Science‘s News department on ancient DNA, the study of which has already lead to breathtaking finds — including the entire genomes of Neandertals and other kinds of ancient humans. Until recently, extracting and studying ancient DNA was so difficult that it was limited to just a few sophisticated labs. Now, writes Science Deputy News Editor Elizabeth Culotta, techniques for studying ancient DNA are more accessible, being applied widely and broadly to explore an array of questions, and catapulting paleogenetics into a golden era.
In one article in this package, contributing correspondent Ann Gibbons explores how studies of ancient genetic material are prompting scientists to rethink long-held views of human prehistory; for example, ancient DNA has led to the discovery of new types of ancient humans and revealed interbreeding between our ancestors and our archaic cousins. Writing from Mexico City, news writer Lizzie Wade highlights the push to acquire ancient DNA from hot and humid locales, where much of the world’s biodiversity evolved. Samples from such regions (instead of from frigid ones, a more typical source of ancient DNA) could solve myriad controversies, like the origins of the large animals that once dominated South America and Australia.
Looking to the future of the field, news writer Robert Service explores how researchers are using ancient protein, which has some advantages over ancient DNA, to uncover the diets and lifestyles of past cultures and diagnose infection in ancient specimens. The full package includes six articles written by various members of Science‘s News department and edited by Culotta.
Using advances in analysing ancient DNA, radiocarbon dating and other geologic records an international team led by researchers from the University of Adelaide and the University of New South Wales (Australia) have revealed that short, rapid warming events, known as interstadials, recorded during the last ice age or Pleistocene (60,000-12,000 years ago) coincided with major extinction events even before the appearance of man.
Published today in Science, the researchers say by contrast, extreme cold periods, such as the last glacial maximum, do not appear to correspond with these extinctions.
“This abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns,” said University of Adelaide lead author and Director of the Australian Centre for Ancient DNA, Professor Alan Cooper.
“Even without the presence of humans we saw mass extinctions. When you add the modern addition of human pressures and fragmenting of the environment to the rapid changes brought by global warming, it raises serious concerns about the future of our environment.”
The researchers came to their conclusions after detecting a pattern, 10 years ago, in ancient DNA studies suggesting the rapid disappearance of large species. At first the researchers thought these were related to intense cold snaps.
However, as more fossil-DNA became available from museum specimen collections and through improvements in carbon dating and temperature records that showed better resolution through time, they were surprised to find the opposite. It became increasingly clear that rapid warming, not sudden cold snaps, was the cause of the extinctions during the last glacial maximum.
The research helps explain further the sudden disappearance of mammoths and giant sloths that became extinct around 11,000 years ago at the end of the last ice age.
“It is important to recognize that man still played an important role in the disappearance of the major mega fauna species,” said fellow author Professor Chris Turney from the University of New South Wales.
“The abrupt warming of the climate caused massive changes to the environment that set the extinction events in motion, but the rise of humans applied the coup de grace to a population that was already under stress.”
In addition to the finding, the new statistical methods used to interrogate the datasets (led by Adelaide co-author Professor Corey Bradshaw) and the new data itself has created an extraordinarily precise record of climate change and species movement over the Pleistocene.
This new dataset will allow future researchers a better understanding of this important period than has ever been possible before.
"The outsiders, misfits, invisible": Marc Steene on Pallant House Gallery's work with artists from the margins
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