1. The Black Hole

The year was 2007. Alberto Nava, a cartographer, was mapping underwater passageways when he stumbled onto something amazing: a dark and mysterious sinkhole near the city of Tulum, Mexico. The dark hole dropped over 100 feet into a cavernous water pit. While it wasn’t an unusual occurrence for the area, this pit was unknown and had yet to be explored. No one knew what secrets would lie at the watery bottom.

Cenotes, or water-filled caves, are the result of limestone bedrock collapsing, leaving the groundwater underneath exposed. There are an estimated 6,000 cenotes scattered across the Mexican Yucatan Peninsula. Yet this one proved to be much much more unique than all the rest.

2. Impossible Entrance

This particular cenote was named El Hoyo Negro, or as it’s known in English, the “Black Hole of Death.” It was named as such because as the divers would soon find out, it wasn’t just an ordinary pit. This one connected to a series of dark ominous tunnels and off-shooting caves.

One member of the diving team described the Black Hole of Death as an “inescapable trap.” No amount of open-water diving will prepare anyone for cave diving. It’s a dangerous and terrifying task. But that wasn’t about to stop this team from exploring.

3. Exploration Team

Nava, along with director Alejandro Alvarez, Franco Antonelli and other professional cave surveyors and science divers set out to map the previously unexplored underwater pit. Exploring cenotes is scientifically and historically important as they remain largely undisturbed by the outside world and can contain ancient treasures thousands of years old.

The water within the flooded pits is mostly made up of rainwater that seeps into the ground. The rainwater floats on top of the higher-density saline water from the coastal waters. This creates an ideal environment to preserve things for thousands of years.

4. Dive Danger

Alvarez’s team of certified cave divers geared up with special equipment to go down into the Black Hole of Death. The team was tasked with mapping and photo-documenting the cave systems. They took precautionary measures to prevent damage to the site with equipment such as rebreathers to ensure that the air bubbles don’t disturb rock formations.

People say that cave diving is like ice skating on a freshly frozen pond. You will know there is danger when the ice starts to crack, but by that point, it is far too late. At least 400 cave divers are known to have died while attempting to explore the underground networks. That still didn’t scare off this crew.

5. The Cave

The skilled divers were forced to climb down a 30-foot ladder into a nearby sinkhole to reach the networks of caves and pits. Down below the surface, the chilly waters were pitch-black and eerily still. Each diver went in geared to the teeth with two air tanks, safety lines, lights, computers and cameras.

Cave divers must be incredibly careful of their movements. One incorrect move or flick of a flipper can destroy rock formations that will never reform and kick up dirt particles, making visibility impossible. Unlike open-water scuba divers, if something goes wrong underwater they can’t just resurface.

6. Complete Darkness

As the team progressed further and further into the cavernous Black Hole of Death they descended into complete darkness. By the light of their flashlights, they followed one of the tunnels for more than half a mile until the floor suddenly dropped out.

“We had to follow along the wall. I happened to be in the front,” Alvarez recalled. The tunnel led the diver team to a massive underground cavern. It was the size of a professional basketball court. That’s when Alvarez saw something shocking.

7. Risky Business

Right in front of their faces, they found a bone floating in the black water. The cavern was bell-shaped and at least 100 feet deep. Exhausted and running out of air, they collected their finding and turned around to find the exit.

Ever fearful that they themselves would fall victim to the Black Hole of Death, they weren’t about to take any unnecessary risks. The team was thrilled beyond belief at their find. They were determined to stock up on more air tanks and equipment and return the very next day.

8. Subterranean Passageways

Toward the end of the last ice age, researchers believe that the vast network of caves and pits in the Yucatan Peninsula were used as subterranean passageways by animals and humans. Trying to pass through them would have been dangerous though.

Many of the caves lead to cavernous pits that suddenly dropped out over a hundred feet into the ground. But since there were no lakes or rivers in the region, the subterranean system would have been one of the rare locations to find clean freshwater.

9. Megafauna

The first bone that the team found was from a megafauna species called a gomphothere. The gomphothere is a distant relative of modern-day elephants and inhabited North America roughly between 1.2 million and 1.6 million years ago. Unlike the elephant, these creatures had four tusks.

Researchers believe that the animals were herbivores. The gomphotheres died off sometime near the end of the last ice age, eventually becoming extinct. Multiple skeletal remains from these creatures have been found in Mexico and Central America.

10. Back Into The Depths

The next day the team geared up for another, longer trip down into the Black Hole. This time the team brought propulsion equipment and nine additional air tanks with them to speed up their journey and spend a longer period of time underwater.

On their second trip down into the depths, the team discovered a heap of different types of skeletal remains. They took their time not to damage any of their findings or disturb the cave so that future divers and researchers could continue their work should further examination be necessary.

11. Giant Ground Sloths

Among the skeletal remains the divers found were three species of giant ground sloths, also known as megatherium, Greek for “great beast.” One of the species had never been discovered before. In their appearance, the animals greatly resembled the modern day sloth but in size, they were as large as elephants.

Very few of land mammals were larger, such as the mammoth, and they weighed up to four tons. They were native to South America and like the gomphothere, were herbivores. Researchers believe that the giant ground sloth was hunted into extinction by humans.

12. Short-Faced Bear

Embedded deep into the walls of the pit were also short-faced bear fossils. The short-faced bear was once the most terrifying mammal in the Americas. Although they are similar to present-day bears in appearance, they would have stood taller than most humans even while on all-fours.

The short-faced bear had an unusually short snout, as its name suggests. They were possibly the largest carnivorous land-mammal to ever have existed in North America. On its hind-legs, the short-faced bear stood around 8-10 feet tall.

13. More Remains

Among the skeletal remains found at the bottom of the Black Hole of Death were saber-tooth cat remains, also sometimes referred to as saber-tooth tigers. These animals are one of the most famous prehistoric mammals, but unlike their name suggests they are neither closely related to cats nor tigers.

Saber-tooth mammals are actually more closely related to kangaroos and opossums than they are to feline cats. These carnivorous animals are known for their prominent long upper canine teeth. But that’s not everything they found at the bottom of the Black Hole of Death.

14. Amazing Discovery

During their second trip down into the Black Hole, the team made their most celebrated discovery yet, human remains. The team first spotted a human skull resting on a ledge. It was propped up by an arm and bared a full set of teeth.

“We knew this was a very important find, but for two years we could not figure out just what to do with it,” diver Alvarez later told reporters. It wasn’t until 2009 that US and Canadian investigators, in cooperation with Mexico, began to fully investigate and test the remains lying at the bottom of the underground cavern.

15. Scientific Significance

According to scientific analysis, the human remains were that of a 15-year-old girl who is believed to have lived some 12,000 to 13,000 years ago. The findings at the bottom of the Black Hole of Death have been deemed a “discovery of a lifetime.”

Scientists named the girl Naia after an ancient Greek name related to water nymphs. Naia is the most complete and oldest human remains found in the Americas to date. Her skeletal remains held ancient secrets on the first humans to inhabit the Americas, putting old myths to rest.

16. The First Americans

For centuries researchers have debated the question of who were the first people to colonize the Americas. Traditional theories have suggested that the Native Americans were the first to arrive in North America via the Bering land bridge connecting modern-day Russia and Alaska.

Researchers believe that humans, as well as animals, crossed the land bridge around 20,000 years ago. The land bridge eventually disappeared due to rising water levels after the end of the last ice age. But this doesn’t answer the question as to why the oldest human remains found in the Americas do not carry the same physical traits as Native Americans.

17. Great American Interchange

The wide diversity of animal remains found in Hoyo Negro is due in part to the formation of the Great American Interchange, connecting North and South America via the Panamanian land bridge. The two continents were formerly disconnected, isolating animal populations. After the volcanic Isthmus of Panama rose out of the sea floor the two continents were connected, allowing for fauna to cross.

Animals such as the armadillo, porcupine and opossum traveled north across the new land bridge and animals such as dogs, horses, bears and raccoons traveled the opposite direction, south. The discovery of Hoyo Negro’s short-faced bear gave evidence, for the very first time, that they traveled from South America to North America.

18. More Questions

Naia’s skeleton however raised some shocking questions. Her remains showed distinct physical differences from those of Native Americans. Raising the question of whether Native Americans the first humans to inhabit North America. Initially, researchers hypothesized that the differences were merely the result of evolutionary changes.

Her near-pristine skeleton would soon answer all those questions. Naia is the oldest and most complete skeleton ever found. The divers found all of her teeth, most of her vertebra, ribs, all of her limbs as well as her pelvis and pubic bone. Researchers hail the condition of Naia’s remains as “just amazing.”

19. Naia’s Death

Experts believe that Naia fell to her death inside the Black Hole of Death while searching for fresh water. She would have fallen around a half mile down into the inescapable pit. During the time she would have lived, around 12,000 to 13,000 years ago, the networks of caves would have been used by humans and animals as passageways.

The pits would have collected rainwater, attracting anything in search of water. The Yucatan Peninsula is devoid of rivers and lakes, making the pits in the area the only source of fresh drinking water.

20. Skeletal Remains

The pristine condition of the nearly-intact skeleton of Naia was made possible due to the isolated underground pit. The remains were found at around 130 feet below sea level and locked underground where nothing was able to disturb them.

Neither human nor animal had been in the Black Hole of Death in thousands of years. “The girl’s skeleton is exceptionally complete because of the environment in which she died — she ended up in the right water and in a quiet place without any soil. Her pristine preservation enabled our team to extract enough DNA to determine her shared genetic code with modern Native Americans,” one expert from Northwestern University stated.

21. DNA Testing

Experts were able to determine the age of Naia by taking DNA samples from one of her rib bones and a tooth. Seeds and bat droppings found in the underwater pit were also used to help determine that she died around 12,000 to 13,000 years ago.

Compared to modern humans Naia was incredibly small for her age, possibly due to malnutrition. There were also skeletal signs that she had recently given birth to a child. Apart from determining Naia’s age and dating her death researchers began working to examine her genetics to find out if her genetic code match that of Native Americans that would have traversed the land bridge crossing the Bering Strait.

22. Physical Features

Researchers were able to determine that Naia would have been around five feet tall during her life and weighed no more than 110 pounds at most. Her skeletal remains showed signed that she had broken her arm at some point during her lifetime and that it later mended.

Genetic reconstruction technology shows that Naia had a narrow face with wide-set eyes and a low prominent forehead. Her nose would have been low and flat, her teeth had an outward-projecting form. Her physical features would have been “about the opposite of what Native Americans look like today.”

23. Genetic Markers

Despite having opposite physical features, analysis of genetic markers in Naia showed that she indeed had similar lineage with Native American DNA. Recent genetic analysis of modern Native Americans shows that their ancestors originated in Asia.

The Native American genome shows that they were isolated for several thousands of years from other groups of people. This most likely occurred during their long journey across Beringia, the area that once connected Russia to Alaska.

24. Origins

While her genes show similarities to Native Americans, that doesn’t answer the question as to why Naia’s physical features differ. Experts believe that the changes in her physical appearance coincide with evolutionary adaptations over the past 13,000 years. In fact, archaeologists discovered another skeleton known as the Kennewick Man who exhibits similar physical traits.

While this theory is widely accepted, some researchers suggest a radically different origin story. A report published in 2015 suggests that Naia is in no way related to the Native Americans that crossed the land bridge from Asia.

25. Alternative Theories

Research published in the American Journal of Physical Anthropology, focusing on Naia’s skull morphology, offers a wildly different theory on where her ancestor’s originated from. The authors state that her remains are “described as much closer to African and Australo-Melanesians populations than to the modern series of Native Americans.”

They suggest that there were more than one entry into the Americas, apart from across the Russian-Alaskan land bridge. They suggest that it is possible that ancient peoples could have migrated from Australia, possibly by boats, as Naia’s skeletal morphology resembles that of Australian aboriginals.

26. Unauthorized Divers

Naia’s remains were left in the Black Hole of Death after the initial dives into the underground caves. Word of the discovery soon spread throughout the world, peaking the interest of other divers. Numerous unauthorized divers decided to undertake the daunting adventure down into the caves to get a look at Naia’s remains.

Some, however, didn’t just want to look. They wanted souvenirs to keep for themselves, and of course, sell on the black market. The unauthorized divers disturbed the underwater caves and significantly destroyed many remains. In such an environment even air bubbles break rock formations.

27. Transfer

Due to the entry of unauthorized divers the decision was made that Naia’s remains would have to be moved in order to protect them. The decision was a dangerous one. Having been locked 140 feet below sea level for thousands of years there was a chance that her skull could shatter at the slightest touch.

“We were praying that it would not just shatter in their hands. It turned out, she’s as solid as a rock.” Fortunately, they were able to carry out the task successfully. Now, the next phase of research could begin.

28. 3D Mapping

Researchers believe that the Hoyo Negro site contains more artifacts and remains yet to be discovered. In an effort to locate them without risking multiple dives to examine them, researchers decided to create a 3D map of the network of caves.

This would allow researchers all over the world to explore and examine the findings at the bottom of the cave without having to be near the location. By using photos of the caves technicians were able to create a 3D map for archaeologists to study.

29. Additional Findings

Artifacts and remains found at the bottom of the Black Hole of Death provide highly valuable insight into the lives and ancestry of ancient Native Americans. Naia’s discovery supports the hypothesis that Native Americans migrated from Asia and crossed the Bering Strait land bridge.

In the process they isolated themselves for thousands of years from other population groups, leaving themselves with a distinct and unique genetic code. While the discovery does not prove without a doubt that Naia came from these people, she does provide much support.

30. Anzick Discovery

Prior to the discovery of Naia, a 12,700-year-old infant skull was discovered in Montana in 1968. He was buried near tools that belonged to the pre-historic Clovis culture. DNA researched showed that he was a direct descendant of native peoples from Central and South America.

The Anzick child’s discovery was scientifically significant because it disproved the Solutrean hypothesis that ancient migrants from Western Europe founded the Clovis culture of Montana. The infant’s remains were named after the woman, Sarah Anzick, who found the remains on her land.

31. Common Ancestry

Prior to the Aznick discovery in 1968, very little genetic data from the earliest Americans was available. The discovery helped solidify the hypothesis that the Native Americans originated in Asia. The Anzick remains, however, are far less complete than the skeletal remains of Naia in the Black Hole of Death.

Both Anzick and Naia come from a common ancient ancestor. Researchers believe that the physical differences between the two findings are a result of an evolutionary change. The details of what that change was or what drove that change is still unknown.

32. Eve of Naharon

Another skeleton was found in an underwater cave near the site where Naia was discovered. The remains belonged to a 25 to 30-year-old woman. Carbon dating revealed that she died around 13,600 years ago. Her remains have been named Eve of Naharon.

Excavation teams worked for four years exploring and researching her cave and remains. Eve of Naharon’s skull also provided clues that put the Bering Strait theory into question. Researchers stated that the remains far more resemble that from South Asia as opposed to North Asia.

33. Human Settlement

Current scientific hypotheses indicate that the first humans originated somewhere in Africa over 100,000 years ago. Out of that duration, humans only arrived to the Americas no earlier than 20,000 years ago. Archaeological evidence leads us to believe that the first humans to enter the Americas occurred sometime towards the end of the last glacial period.

The topic of who and where the first Americans came from is still highly debated and as technology advances and archaeologists keep looking for evidence, we get closer and closer to answering the question.

34. Ancient Cenotes

As glaciers melted around 12,000 years ago, the water levels rose and flooded the underground passages. Artifacts and skeletons located in the system remained at the bottom of the pits, undisturbed. In pre-Columbian times, the Maya civilization worshiped at the Sacred Cenote at Chichen Itza.

There, they would perform sacrifices to the Maya rain god Chaac by throwing gold, jade, pottery and incense into the watery pit. Evidence also shows that human sacrifices were performed at the site. Human remains exhumed from this cenote showed signs that they were ritually stabbed then thrown into the cenote to die.

35. Mayan Shamans

Both male and female remains, including children, have been found in some of the cenotes that dot the peninsula. Evidence shows that Mayan shamans only considered certain cenotes holy. Some people witnessed this in more recent times, including Franciscan leader Diego de Landa, who lived from 1524 to 1597, was the Roman Catholic Archdiocese of Yucatan.

He claimed that he personally witnessed human sacrifices being performed at the Sacred Cenote. During his reign as archdiocese, he instigated an inquisition against people practicing indigenous religions. Landa forced conversions, tortured people for confessions, destroyed ancient artifacts and burned sacred Mayan texts.

Sources: National Geographic