Unprecedented evidence that humans occupied ‘lava tubes’ could fill gaps in the archaeological record, scientists say

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People living on the Arabian Peninsula thousands of years ago went underground when they wanted to beat the heat. They may have stopped there as they traveled between oases and meadows, then plunged into vast underground tunnels where molten lava had once flowed millions of years earlier, a recent study shows.

Archaeologists have discovered that from the Stone Age onwards, Neolithic herders occupied and occupied these enormous tunnels known as lava tubes. Cooler air underground would have been a welcome respite from sun and wind, and for thousands of years people and their livestock sheltered in the tunnels. The herders left behind objects and even carved images into the rock walls, researchers reported April 17 in the journal PLOS One.

In the Harrat Khaybar lava field, about 125 kilometers north of Medina in Saudi Arabia, there is a tunnel system called Umm Jirsan, the longest in the region. Scientists have not yet confirmed the age of the lava that formed this system, but a 2007 study suggested it was about 3 million years old. Umm Jirsan covers almost 1.5 kilometers, with passages up to 12 meters high and a whopping 45 meters wide.

Archaeologists from Umm Jirsan recently found animal bones dating from 400 years to more than 4,000 years ago, and human remains from 150 years to about 6,000 years ago. The research team also found fragments of fabric, pieces of carvings and dozens of stone tools – the first evidence that humans used the tunnels at least 7,000 years ago.

“We knew from previous reports that fossils had been preserved at the site,” said lead study author Dr. Mathew Stewart, researcher at the Australian Research Center for Human Evolution at Griffith University in Australia.

“However, we did not expect to find evidence of human habitation in the form of petroglyphs, lithic artifacts, stone structures and pottery,” Stewart told CNN in an email. “People have used and occupied these lava tubes for millennia. While most research in Arabia focuses on surface sites, underground sites such as Umm Jirsan offer enormous potential to fill some of the gaps in the data.”

This discovery highlights the importance of Umm Jirsan and other tunnels for understanding human dispersal in the region, said Guillaume Charloux, an archaeologist at the French National Center for Scientific Research. Overall, knowledge about ancient climate and humans in northwest Arabia is limited, “especially during the transitional phase between the Neolithic and the early second millennium,” says Charloux, who studies ancient sites in Saudi Arabia but is not involved was involved in the new developments. research. .

The research team is seen during an excavation at Umm Jirsan.  The archaeologists uncovered human remains, animal bones, carvings and stone tools at the site.  - Green Arabia Project

The research team is seen during an excavation at Umm Jirsan. The archaeologists uncovered human remains, animal bones, carvings and stone tools at the site. – Green Arabia Project

Around this time, locals settled around recently formed oases; The appearance of these desert refuges would shape human migration patterns in the region for millennia, he said by email. “The most important contribution of this innovative and major research project seems to me to be that it reveals the long-term use – probably short-term occupation – of these types of caves, which had not yet been studied, and their enormous potential, especially for understanding paleoenvironmental contexts .”

‘Green Arabia’

For nearly 15 years, Stewart and his colleagues have collected evidence of ancient human life in Arabia, mainly from sites around lake deposits, Stewart said. About 400,000 years ago, recurring periods of humidity began flooding the Arabian deserts with rainfall. During these “Green Arabia” phases, lakes and ponds were plentiful and the landscape flourished with lush vegetation, leading to waves of migrating people spreading into Southwest Asia, Stewart and other researchers previously reported in the journal Nature.

But the last phase of Green Arabia was about 55,000 years ago, and harsh desert environments are not exactly friendly to archaeological evidence. While stone tools are well preserved in arid deserts, bones and other organic materials are easily broken down and destroyed by erosion and extreme heat and cold, leaving researchers little to interpret, Stewart noted.

“To this end, in 2019 we decided to investigate underground environments where organic matter and sediments can be better preserved,” he said.

So the scientists turned their attention to Umm Jirsan. The site had previously been mapped by the Saudi Geological Survey and a 2009 report described it as a haven for wildlife such as foxes, wolves, birds and snakes. The bone deposits in the tunnels included fragments of human skulls estimated at the time to be about 4,000 years old. But until 2019, the tunnel system had not been closely examined by archaeologists, Stewart said.

The researchers enter Umm Jirsan, the longest lava tube system in the region.  - Green Arabia ProjectThe researchers enter Umm Jirsan, the longest lava tube system in the region.  - Green Arabia Project

The researchers enter Umm Jirsan, the longest lava tube system in the region. – Green Arabia Project

“We were able to date the animal bones and sediments, which informed us that humans began occupying the cave 7,000 years ago, and perhaps as early as 10,000 years ago,” Stewart said.

Compared to other sites where people once lived, the amount of archaeological material at Umm Jirsan was “quite sparse,” suggesting that people visited the tunnels as temporary refuges rather than living there permanently, the study authors reported.

Animal carvings

In another tunnel near Umm Jirsan, researchers found 16 panels of engraved rock art. The carvings appeared to be herd scenes, with tool-bearing stick figure people standing next to domesticated animals such as dogs, cattle, goats and sheep. Other carvings showed animals with dramatically curved horns that resembled those of an ibex; However, according to the research, these horned animals may represent a different breed of domesticated goats. The subjects of the carvings and their varnish coating indicate that they date from a regional period known as the Chalcolithic (around 4500 to 3500 BC), which preceded the rise of the Bronze Age.

“Collectively, the archaeological findings at the site and in the surrounding landscape paint a picture of repeated use of the Umm Jirsan Lava Tube over millennia,” Stewart said. The site – which lies along a well-known migration route for Bronze Age shepherds – ‘may have served as a stopover, a refuge protected from the elements.’

This unprecedented evidence of human habitation in ancient Arabian lava tubes sheds light on how humans adapted to life in arid landscapes, and further research of Umm Jirsan and other lava tubes promises to add even more details, Stewart added.

“These sites have enormous potential to fill some of the gaps in the natural and cultural records that remain in the Arab archaeological record.”

Mindy Weisberger is a science writer and media producer whose work has appeared in the magazines LiveScience, Scientific American, and How It Works.

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