The Most Incredible Things Discovered In Sinkholes

According to the United States Geological Survey, sinkholes are primarily caused by groundwater eroding the rock below the land surface, and they are particularly prevalent in areas where said rock is carbonate, salt bed, or limestone. They can develop over tens of thousands of years, then reveal themselves in dramatic fashion in mere seconds as the ground finally gives way.

But sinkholes are so much more than just a big hole in the ground. There are many forms sinkholes can take, they can be vastly different in size, and there's plenty of diversity in where they can be found on the planet — or under it and, in many cases, underwater. Not to mention the array of amazing things that can be found in sinkholes. Exploring a sinkhole can mean stepping back thousands or even millions of years to where ancient layers of the earth and age-old artifacts are exposed. Many sinkholes have also divulged more recent secrets, such as those found harboring manmade objects. Others have revealed previously unknown wonders of nature.

So while sinkholes can be deadly and damaging, they also often reveal wonders.

In 2016, The Guardian reported that scientists exploring a flooded sinkhole in Florida made a series of discoveries that moved the beginning of human settlement back about 1,500 years. For decades, there was general consensus among archeologists, anthropologists, and paleontologists that humans had reached the Americas sometime late during the last Ice Age by way of a so-called "land bridge" exposed beneath what is now the Bering Sea. The generally accepted timeframe of the first human arrival in the Americas from Eurasia was some 13,000 years back.

But the bones, those of a mastodon clearly butchered by human hands as well as those of early dogs who evidently lived with or followed humans, as well as a number of handmade tools, have been dated to approximately 14,550 years of age. The scientists who discovered the ancient artifacts are confident that the bones, tools, and even some fossilized excrement constitute irrefutable evidence that humans had made their way not only to the Americas but all the way across the continent long before initially thought.

And in fact, findings like these throw into doubt more than just the timing of early human migration from one continent to another, but even merit some rethinking of the way our forebears reached North and South America. The theory of early migration via the water has gained much wider acceptance in recent years, per Smithsonian Magazine, and finds like the one in the sinkhole near Tallahassee, Florida only strengthen the case for earlier and perhaps alternative arrival.

You can thank discoveries made in yet another sinkhole for not only further establishing how long ago early humans reached the Americas, but also for adding a new and fascinating element to the ancient tale: apparently, more than one subspecies of ancient human arrived on the continents. According to findings reported in a scientific journal published by PLOS, skeletal remains found in an underwater sinkhole called the Chan Hol cave, located on the Yucatán Peninsula in the south of Mexico, prove that humans had reached latitudes that far down in the Americas by 13,000 years ago, meaning they either arrived in the north and began moving southward earlier than originally thought, or else they reached the Yucatán via a different route than the Bering Strait Land Bridge.

Either way, perhaps the most monumental evidence found in the sinkhole was that of what scientists call "mesocephalic cranial morphology," which is a very science-speak way to describe skull shape, one which was distinctly different than the "dolichocephalic morphology" for the known Paleoindians living in Central Mexico at the same time. To put that in layman's terms, there were groups of early humans with distinctly different characteristics living near each other at or nearly at the same time. As evolution takes a long time, it points to these groups having arrived via different routes and at different times, which creates more questions than it answers, but that's all just the fun of it for scientists and armchair enthusiasts alike.

So another find of mastodon bones in another sinkhole in the southern states of America, what's the big deal, right? After all, we know scientists have found mastodon bones in American sinkholes plenty of times before, so what's special about the specimen recovered from a sinkhole in Tennessee in 2016? According to reporting from Ars Technica, the mastodon remains found in the Gray Fossil Site, so named for being near Gray, TN, are not only remarkable for the completeness of the skeleton, but also because they seem to belong to a species not previously known to have lived in North America at the time. 

The skeleton recovered at the Gray Fossil Site has a skull distinctly different than that of the aptly named American mastodon (or Mammut americanum), the most common ancient pachyderm of the area. It's entirely possible that the fossil found in the sinkhole represents a previously unknown species of ancient creature, but the confirmation may still be long in the offing as scientists work to re-assemble the full skeleton and piece together just what happened to the animal. Regardless of what they eventually learn about this specific animal, we know the sinkhole in which it perished is some five million years old, meaning mastodons had already been plodding about the planet for some 20 million years before it was created, based on data about mastodon life on earth sourced from the National Library of Medicine.

According to World Atlas, Lake Huron is the second largest of North America's famed Great Lakes, with an area of 23,000-plus square miles and with some 850 cubic miles of water in total. It is more than 200 miles across at its widest point and 750 feet deep at its deepest. In other words, this is a very large lake. Ironic, then, that some of the most fascinating things ever found in Lake Huron are so small you can't see them with the naked eye.

Regional interest publication US-23 Heritage Route relates how a sinkhole beneath Lake Huron has been found to be the home of some surprising creatures. In the Middle Island Sinkhole, scientists have found groundwater vents that emit high concentrations of sulfates and around which dissolved oxygen is scarce. But rather than this creating barren, lifeless underwater areas as one might expect, instead, life thrives around the vents, just not life as you might expect. Sinkholes including and similar to the Middle Island Sinkhole are heavily colonized by single-celled microorganisms like bacteria and archaea, a type of prokaryote, according to Britannica.

And in shallower areas of the Great Lakes, where sunlight easily penetrates to the lakebed, other organisms hold sway, such as photosynthetic cyanobacteria that create vibrant purple layers covering much of the surface down beneath the waters.

The Well of Barhout, also known as the Well of Hell, has long been a no-go spot for locals living in Yemen's al-Mahra province, an eastern region near the border with Oman. But according to Live Science, when a group of intrepid explorers finally did descend down into the depths of this very deep sinkhole, they did not find themselves in hell after all. There were lots of snakes, though.

Long rumored to be a gateway to the underworld, this desert sinkhole, which measures just under 100 feet across, was also said to be the lair of malevolent genies and other spirits. Scarce few facts were known about the geological structure until just last year when several cavers with the Omani Caves Exploration Team (OCET) descended all the way to the floor of the Well, which turned out to be an impressive 367 feet below the surface of the desert.

Down in the Well of Hell, the cavers many dead animals who had apparently made their way into the Well never to escape it, many living snakes, via Penn Live – though don't start picturing a slithering snake pit, Indiana Jones-style — and some frogs, along with beautiful natural formations like stalactites and cave pearls, which are "small, almost spherical concretion of calcite that is formed in a pool of water in a cave," according to Britannica. The sinkhole is likely millions of years old, and as far as we know, had never before been explored by humans. The exact nature of its creation is not yet known but may be revealed with more exploration.

In 2021, a crew working to install a railroad that would bring tourists to an ancient Mayan site on the Yucatán Peninsula ironically found an ancient Mayan artifact that was every bit as interesting as the ruins they were making more accessible. According to reporting in Cosmos Magazine, the railroad workers came across a Mayan canoe resting at the bottom of a water-filled sinkhole — also called a "cenote" locally — where it had evidently been hiding out for centuries. The canoe, which is a little more than five feet long and about two and a half feet wide, according to The Guardian, is likely from sometime between the years 830 and 950 CE, which puts it near the height of the Mayan culture's existence.

The ancient artifact was discovered purely by good luck, one of the workers on the Maya Train spotted it while taking a dip in the sinkhole while on a break. The region has also uncovered artifacts such as pottery shards, paintings on cave walls, and what are knives apparently used in rituals, all of which has led experts to assume the area held special spiritual significance for the ancient Maya. The canoe itself may have been used to transport holy objects or in the execution of rituals, or it may have served a more banal purpose, perhaps having been used to transport water from the freshwater sinkholes to ancient Mayans living nearby.