Treasures from the Ice Age have been discovered at the bottom of a "blue hole" on the island. What does this mean? (See photos)

On the Bahamas, on the island of Great Abaco, there is a blue hole known as the Soumille Sinkhole. This sinkhole, located in the middle of the island, is filled with a treasure trove of well-preserved fossils that provide evidence of how the island has changed since the last ice age, according to Science Alert.

According to co-author of the study, David Steadman, an honorary curator at the Florida Museum of Natural History, excavations began in 2005 and were only completed about five years ago. A devastating hurricane struck the island, damaging the site, the fossil collection, and the researchers' plans to protect the untouched blue holes.

Over the course of more than 10 years, prior to the hurricane, scientists managed to collect thousands of fossils from the bottom of the blue hole, but the team notes that many secrets still lie hidden within the depths of the blue hole, likely now buried under water forever.

The blue hole is known to have formed thousands of years ago, after which the sinkhole was flooded due to rising sea levels. According to Steadman, thousands of years ago, the island of Abaco was ten times larger than it is today; however, when sea levels rose after the last ice age, the water flooded the island, reducing its shorelines.

The island is primarily composed of limestone, so during flooding, groundwater flows through the porous rock, causing caves to collapse, which then fill with water, creating blue holes like the Soumille Sinkhole. The sinkhole descends to a depth of about 46 meters below sea level and features an extensive network of underground passages extending for kilometers.

Nearly 20 years ago, diver Brian Kakuk first descended into some of these passages and discovered numerous bones, which opened a door to the "ancient past of the island." Among the diver's finds were turtle shells and crocodile skulls—unfortunately, these animals no longer inhabit Abaco, but scientists gained a chance to study the island's history and how it has changed since the last ice age.

According to Steadman, the Soumille Sinkhole is dark and contains many crevices and passages within the limestone. Dives revealed numerous stalactites and stalagmites in the depths of the sinkhole, remnants from when the cave was above sea level, with ribbon-like helictites and hollow tubes known as "soda straws" protruding from the walls.

The first approximately 9 meters of water consist of a layer of fresh water; however, below that is about 6 meters of "toxic brew" made up of hydrogen sulfide and fresh water—this layer smells like rotten eggs and burns the skin. Beneath this opaque and caustic layer lies saltwater, devoid of oxygen and ultraviolet light, which is ideal for preserving fossils.

During their dives, Kakuk and other divers managed to extract fossils from the bottom of the sinkhole that were surprisingly well-preserved—allowing experts to date them. Next, geologist Nancy Albury was brought in, who first examined a fossilized turtle shell.

Research showed that the remains belonged to a turtle of the well-known species Chelonoidis alburyorum, which has long been extinct. Experts dated the fossils of the crocodile and turtle to be between 1,000 and 5,000 years old after the sinkhole was flooded.

Underneath these fossils, researchers also discovered many other bones, which testify to the rich biodiversity of the island of Abaco. Thousands of years ago, when the Soumille Sinkhole was above sea level, it was home to numerous animals from barn owls to crocodiles. Many of these animals thrived here as far back as 15,000 years ago.

The team studied the discovered fossils, attempting to determine how various animals adapted to climate changes during the Ice Age. Unfortunately, many species did not survive, and humans were the reason for their extinction.

Researchers continued to examine the fossils and found about 17 species of birds that did not survive the rise in sea level around 10,000 years ago. However, other species of birds, as well as reptiles and mammals, survived until about 1,000 years ago, when humans arrived on the island and exterminated them.

The Lucayan people, part of the Taíno culture, likely arrived on Great Abaco from Hispaniola and Jamaica as early as 720 A.D. For this group, large turtles and hutias (a rodent similar to a capybara) became another common food source. Unfortunately, both have since disappeared from the island. One bird species, the Bahama caracara, likely went extinct because its diet was similar to that of humans—the species simply could not compete.

At the same time, according to Albury, humans may not have been at the top of the island's food chain. Scientists believe that local crocodiles hunted not only large turtles but also humans. It is known that Cuban crocodiles inhabited the island, which today are endangered—only a small population remains in Cuba.

The fossils discovered in the sinkhole were displayed in a museum that opened in January 2018. Unfortunately, by September 2019, the museum was completely destroyed—the hurricane Dorian ravaged Abaco. After the hurricane, the museum's collection was submerged underwater.

Fortunately, after the hurricane, scientists were able to locate a catalog of the collection, which had been kept in plastic bags and boxes. Programmers also managed to recover electronic backups. Upon reviewing them, the team discovered that a large portion of the collection had survived—between 80% and 90%.