About 12,000 years ago, early inhabitants of Mexico’s Yucatan coast went deep into a dark, dangerous cave system, archaeologists reported a few years ago, based on their find of human remains. No evidence of habitation was found in the Quintana Roo cave system, however, which begged the question of what the ancient people were doing there.
Now we know. The paleo-spelunkers were mining for ocher, according to an international team including scientists, officials from Mexico’s Instituto Nacional de Antropología e Historia, and divers from the nonprofit group El Centro Investigador del Sistema Acuífero de Quintana Roo. They discovered the antiquities while exploring the partially submerged cave system for entirely different reasons, the journal Science Advances reports.
“Most evidence of ancient mining on the surface has been altered through natural and human processes, obscuring the record. These underwater caves are a time capsule,” says co-author Eduard Reinhardt, and expert diver and professor at the School of Geography and Earth Sciences at McMaster University in Ontario.
The divers found charcoal from the fires and torches the prehistoric miners lit to find their way in the pitch black, pits and trenches the miners dug, as well as tools they used to obtain the ocher. The team also found what seem to be navigational markers left by the miners who exploited the ocher from 10,000 to 12,000 years ago.
At that point the cave system gradually flooded as the Ice Age ebbed and global sea levels began to rise, and that was that.
The mines of Quintana Roo are the earliest known subterranean effort for ocher in the Americas, the team says. Elsewhere, ocher can be sourced on the surface, though not in this region, apparently.
The conventional wisdom regarding ocher is that it’s hardened reddish clay. Not exactly.
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“‘Ocher’ is a catchall term for rocks and minerals that are very high in iron oxides and that can produce a stain or streak, and that has to be pigmentaceous,” lead author Brandi MacDonald, professor at the Archaeometry Laboratory at the University of Missouri, told Haaretz.
Iron-rich clay deposits can count as ocher, but there are also extremely hard rocks that do too, such as dense iron ores mined to produce steel today. When ground, they produce blood-red powder. “That is ocher too,” MacDonald says.
Ocher can actually range from yellow to orange and red to purple. It can form in a wide range of different geologic environments, many of which are on the surface, MacDonald explains. There is evidence for surface-ocher collection in many areas of North America during the late Pleistocene and early Holocene.
Just this week the state of Wyoming announced the discovery of an ocher mine that had been in use during almost the same period as the Quintana Roo discoveries: between 11,000 and 13,000 years ago.
Back at Quintana Roo, “This is the first example of very clear evidence of intensive mining activity,” MacDonald says. “We can still see preservation of pits and trenches and digging tools and evidence for prospection. The miners knew how to dig down and break through flowstone deposits – sheets of mineral deposits. Embedded in the flowstone are deposits of ocher. They would have had to smash open long beds of flowstone to access it.”
In fact, the explorers found evidence of prehistoric ocher mining in three caves within the Quintana Roo system, exploited for 2,000 years. The dating is based on carbon-dating charcoal and wood remaining from the torches that the prehistoric miners would have had to bring into the caves so they could see what they were doing.
Navigating in the dark
The Americas were the last great landmass to be occupied by humans, who may have crossed in waves from Eurasia over the Bering land bridge when sea levels were low. When they arrived – and who arrived – is hotly debated. In any case, the oldest human remains discovered at Quintana Roo are over 13,000 years old; the latest are 10,000 years old.
The Quintana Roo caves aren’t exactly on the coast, they’re several hundred meters inland and were even further inland then. The last interglacial period began and the seas started to rise about 16,000 years ago. By about 10,000 years ago, the caves became unusable due to flooding, partly from seawater incursion through underground channels and partly groundwater as the local water table rose.
However, even when the caves were bone dry, the ocher caches were highly inaccessible. “In the cave areas we called La Mina, where we see clear evidence of anthropogenic mining, it’s well into the dark zone of the cave,” MacDonald says.
“I think the shortest distance to natural light is at least 650 meters [711 yards]; most of the activity is at least 900 meters into the cave. The terrain is very difficult to navigate with narrow passages, uneven floors and overhead hazards. They would have had to light fires to safely navigate the passages.”
Which begs the question of how the paleoamericans found the ocher in the first place. There is no sign of prehistoric habitation in the Quintana Roo system; no anthropogenic features, stone slabs or altars, or evidence of animal remains or domestication objects. All we can say 10,000 to 12,000 years after the event is that people did go there; perhaps they recognized geological features that portended the existence of lovely high-quality blood-red ocher, MacDonald suggests.
And then they passed down that knowledge from generation to generation until the caves flooded. If scientists had been wondering why people were in the caves at all, now they have a theory: It was for the ocher.
Which in turn begs the question of how the archaeologists found the now submerged mines. Getting there is no picnic today, either. The answer is that they were twigged to the extraordinary discovery by expert divers who have been exploring the underwater caves in the area for studying the coastal aquifer for over two decades.
Reacting to a compliment about diving into elongated lightless crevices, diver Sam Meacham of El Centro Investigador del Sistema Acuífero de Quintana Roo explains: “It’s what we do. We are a very specialized, highly trained, specially equipped team of divers, and our first and foremost mission is to explore these caves.
“As we explore we come across any number of things of interest to the scientific community – biological, geological, hydrological or paleotonological/archaeological. We are extremely observant and we record everything we do.” And when they find something of interest they contact the scientists.
“It’s a sublime and very beautiful place to go into,” Meacham adds, noting that you need the training and proper equipment to do it. “But I’ve been doing this for 25 years and I’m still alive.”
The divers also collected samples of the charcoal and ocher to bring to the surface for analysis, says MacDonald, who was contacted about the submerged discovery in 2018.
Having been alerted to the caves’ archaeological potential, one wonders if the scientists braved the dangers divers did. Ocher expert MacDonald, for one, did. In any case, the divers used video, virtual-reality goggles and 3D-digital models to share the experience with the terrestrial scientists.
While no signs of habitation were found, at least to date, what the researchers did find is evidence of a massive smashing-up of the cave deposits and extraction of ocher, MacDonald says. “We don’t even see evidence for the bringing of tools from outside the cave,” she says.
“All the tools that were used to extract the ocher were made immediately on site, in an expedient fashion. They broke off stalactites from the ceiling and used them as hammerstones and piledrivers to smash open the rocks.”
Arguably, to risk life and limb venturing into the dark with torches and bash rocks with detached stalactites and lug the resulting ocher away, the ancients of Quintana Roo prized the pigment highly. What might they have done with it?
In North America, ocher has been found in paleoamerican flooring, on tools, grinding stones and animal bones, and in ceremonial contexts – on skeletons and grave goods. We can assume the ocher habit came to the Americans with migrants from Eurasia, where ocher was used for at least tens of thousands of years. Ocher was found at a Neanderthal site in the Netherlands dating to about 250,000 years ago, and lo, the rock was not local. It had to be brought there intentionally.
In Africa, ocher use goes back over 300,000 years, when Homo sapiens is thought to have already existed. That gives rise to the belief that perhaps the common ancestor of Homo sapiens and Neanderthals, which lived well over half a million years ago, used ocher.
Possibly the hominins may have been decorating their faces and/or bodies to look fearsome, and no question about it, painting one’s visage blood red would achieve that effect. Discover Magazine suggests a nuance along that theme, noting that some languages have only two words for color: red and not-red, so painting ourselves red could have been some sort of signal. (Me Tarzan, you dead meat?)
Perhaps ocher even served as a sunscreen: Prof. Michael Petraglia of Germany’s Max Planck Institute has suggested that ocher applied to the skin could have facilitated the spread of humankind during the Middle Stone Age.
But what it was used for in Quintana Roo isn’t known, MacDonald says. “We don’t have very many sites at the surface that are of the same age, and the preservation of archaeological sites that old is fairly poor. We don’t have the end-use context. We know they were collecting really large amounts and transporting it but don’t know why,” she says.
“Elsewhere in prehistoric Mexico where sites were better preserved, ocher was used in mortuary practices, sprinkled on the remains of the deceased, used to paint portable art, objects, and to paint ceremonial stone tools such as obsidian blades which were apparently not used in hunting.”
And possibly ocher had very practical uses, too. The suggestion has been made before that the stuff had or was thought to have medicinal properties. It has been used in Chinese medicine “to pacify the liver, to move qi downward, and to arrest bleeding,” according to Acupuncture Today.
More scientifically, the high-grade beautiful ocher of Quintana Roo, which faded to yellow underwater but regained its blood-red hue once dry, contained high concentrations of arsenic, MacDonald realized through chemical analysis. Asked why that's a good thing, she explained that if daubed on the body, the arsenic-heavy ocher could serve as a terrific pest repellent.
In mosquito-ridden Tel Aviv, one is tempted to emulate the prehistoric peoples of Quintana Roo, but as MacDonald points out, at a concentration of 4,000 parts per million, long-term use of the arsenic-enriched ocher would be absorbed by the skin and could cause chronic poisoning. We don’t know for certain if that was a main functional role of ocher in prehistory, but it is one possibility among a diversity of possible uses.