Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific advancements and more.
Thousands of years ago, people living in the Arabian Peninsula went underground when they wanted to escape the heat. They likely stopped there as they traveled between oases and pastures, diving into vast underground tunnels where molten lava once flowed millions of years ago, according to a recent study.
Archaeologists have discovered that, starting in the Stone Age, Neolithic shepherds descended and occupied these extensive tunnels, known as lava tubes. The cooler air underground provided welcome respite from sun and wind, and humans sheltered in tunnels with their animals for thousands of years. The shepherds left objects behind and even carved pictures into the rocky walls, researchers reported April 17 in the journal PLOS One.
In the Harrat Khyber lava field, about 78 miles (125 kilometers) north of Medina in Saudi Arabia, there is a tunnel system called Umm Jirsan, which is the longest tunnel system in the region. Scientists have not yet confirmed the age of the lava that forms this system, but a 2007 study suggested that the lava was approximately 3 million years old. Umm Jirsan stretches about 1 mile (1.5 kilometers), with passes up to 39 feet (12 meters) high and 148 feet (45 meters) wide.
Archaeologists at Umm Jirsan recently found animal bones from 400 to 4,000 years ago and human remains from 150 to 6,000 years ago. The research team also found pieces of fabric, carved wood pieces, and dozens of stone tools; This was the first evidence that humans used tunnels starting at least 7,000 years ago.
Lead author of the study, Dr. “We knew from previous reports that fossils were preserved in the area,” said Mathew Stewart.
“However, we did not expect to find evidence of human habitation in the form of rock art, stone artifacts, stone structures and pottery,” Stewart told CNN in an email. “Humans have used and occupied these lava tubes for thousands of years. While most research in Arabia has focused on surface areas, subsurface environments like Umm Jirsan offer tremendous potential to fill some of the gaps in the data.”
Archaeologist Guillaume Charloux from the French National Center for Scientific Research said that this discovery highlights the importance of Umm Jirsan and other tunnels for understanding human distribution in the region. Overall, knowledge about the ancient climate and people in northwestern Arabia is limited, “especially in the transitional phase between the Neolithic and the beginning of the 2nd millennium,” said Charloux, who studies ancient sites in Saudi Arabia but was not involved in the new research. research. .
At this time, local people were settling around the newly formed oases; The emergence of these desert refuges would shape human migration patterns in the region for thousands of years, he said via email. “The main contribution of this innovative and major research project seems to me to be that it brings to light the long-term use – possibly temporary occupation – of such caves that have not been studied, and their enormous potential, especially for understanding paleoenvironmental contexts.”
‘Green Arabia’
For about 15 years, Stewart and his colleagues have been piecing together evidence of ancient human life in Arabia, mostly from areas around lake deposits, Stewart said. Recurrent periods of moisture beginning about 400,000 years ago saturated the Arabian deserts with rainfall. As Stewart and other researchers previously reported in the journal Nature, during these “Green Arabia” phases lakes and ponds proliferated and the landscape bloomed with lush vegetation; this led to waves of migrating people dispersed across southwest Asia.
However, the last Green Arabian phase was around 55,000 years ago, and harsh desert environments do not lend themselves well to archaeological evidence. Stewart noted that although stone tools were well preserved in dry deserts, bones and other organic materials were easily decomposed and destroyed by erosion and extreme heat and cold, leaving little for researchers to interpret.
“For this purpose, in 2019, we decided to investigate underground environments where organic matter and sediments can be better preserved,” he said.
So scholars turned their attention to Umm Jisan. The area had previously been mapped by the Saudi Geological Survey, and a 2009 report stated that it was a refuge for wild animals such as foxes, wolves, birds and snakes. Bone deposits in the tunnels contained fragments of human skulls, estimated at the time to be around 4,000 years old. But until 2019, the tunnel system had not yet been closely investigated by archaeologists, Stewart said.
“We were able to date the animal bones and sediments, which told us that humans began occupying the cave as early as 7,000 years ago, perhaps as early as 10,000 years ago,” Stewart said. said.
Compared to other areas where people once lived, the amount of archaeological material at Umm Jirsan was “considerably small,” the study authors reported; This suggested that people visited the tunnels as temporary shelters rather than living there permanently.
animal carvings
In another tunnel near Umm Jirsan, researchers found 16 panels of carved rock art. The carvings appeared to be herding scenes where tool-wearing, stick-figure people stood next to domesticated animals such as dogs, cattle, goats and sheep. Other carvings showed animals with strikingly curved horns resembling those of a mountain goat; However, according to the research, these horned animals may represent a different species of domesticated goat. The subject matter and lacquer finish of the carvings imply that they date from a regional period known as the Chalcolithic (c. 4500 to 3500 BC), before the rise of the Bronze Age.
“Collectively, the archaeological findings at the site and surrounding terrain paint a picture of the Umm Jirsan Lava Tube being used repeatedly over millennia,” Stewart said. Located on a known migration route for Bronze Age shepherds, the site “may have served as a stopover point, a shelter protected from the elements.”
Stewart added that this unprecedented evidence of human habitation in ancient Arabian lava tubes sheds light on how humans adapted to living in arid landscapes, and further exploration of Umm Jirsan and other lava tubes promises to add even more detail.
“These sites have tremendous potential to fill some of the gaps in the natural and cultural archives that persist in the Arab archaeological record.”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works magazines.
For more CNN news and newsletters, create an account at CNN.com