Scientists Discover Mysterious Sinkholes On Lake Michigan's Floor: A Window Into Early Earth

The Great Lakes Environmental Research Laboratory (GLERL) of the National Oceanic and Atmospheric Administration (NOAA) has identified nearly 40 circular structures on the floor of Lake Michigan, according to a report by Live Science.

In 2022, NOAA researchers conducting a survey of the Great Lakes used sonar to detect unusual circular depressions on the lakebed. These depressions, which measure between 91 meters (300 feet) and 183 meters (600 feet) in diameter, also attracted the attention of a shipwreck hunter at the time. However, it is only recently that scientists have been able to study them more thoroughly.

During an expedition in August, the team identified approximately 40 of these features, which are thought to be sinkholes formed through natural geological processes. Located about 22.5 kilometers (14 miles) southeast of Sheboygan, the formations are aligned in a line extending toward Port Washington.

"There were dozens of them in our search grid," said Brendon Baillod, the shipwreck hunter who first spotted them in 2022, during an interview with Live Science. "Most ranged between 500 and 1,000 feet [152 to 309 meters] in diameter and were irregular in shape."

According to the US Geological Survey, sinkholes are most commonly found in areas known as "karst terrain." In these regions, specific types of rock beneath the surface, such as salt beds, gypsum, limestone, and other carbonate formations, can dissolve naturally due to groundwater circulation.

Lake Michigan's limestone bedrock offers a clear explanation for the formation of these sinkholes. Although their creation is a known geological process, these formations are anything but ordinary. Similar sinkholes in Lake Huron, for example, host unique microbial ecosystems that thrive in oxygen-poor, sulfur-rich groundwater—conditions reminiscent of Earth around 2.5 billion years ago.

"Much like early Earth, microorganisms dominate the Middle Island Sinkhole in Lake Huron. Scientists recognize three major domains of life: Bacteria, known for their diversity and adaptability; Archaea, noted for their ability to survive in extreme conditions and produce methane; and Eukarya, which includes plants, animals, fungi, and protists," notes a study on Lake Huron sinkholes.

On the lakebed, bacteria form a distinctive purple mat. "DNA analysis revealed that the majority of the purple mat consists of Phormidium autumnale, a photosynthetic cyanobacterium," the researchers noted. "These filamentous organisms use light energy to convert dissolved carbon dioxide (CO2) into organic carbon."

These microorganisms are found in a wide range of environments, from Yellowstone National Park to the ice-covered lakes of Antarctica.

Further investigation in Lake Michigan is required to determine if it harbors similar life forms. However, GLERL scientists told the Milwaukee Journal Sentinel that they believe the sinkholes in Lake Michigan are similar to those in Lake Huron and may offer valuable insights into early Earth conditions.