Going Back in Time: Lake Huron Sinkholes Discovery Explains Past Life Conditions on Earth

Researchers from University of Michigan illustrated life conditions on Earth from billions of years by investigating sinkholes in Lake Huron, one of the five Great Lakes of North America.

In 2001, researchers around the world had gotten a fascinating attraction when sinkholes were discovered in the northern Lake Huron, not far from the Michigan coast. According to experts, sinkholes provided a surprising clue to Earth's history.

In a 2003 expedition, further observation revealed that groundwater was actively seeping into three of the sinkholes, including the Middle Island, Misery Bay, and Isolated sinkholes. As it vents at the bottom and seeps into the lake, researchers were able to identify the biogeochemical conditions it contains which shed light on some very interesting theories published this year.

Sinkholes and development of life on Earth

In August 2021, an article published in University of Michigan website linked rise of oxygen levels on early Earth to planetary rotation rate. The team proposed that the "increasing day length on the early Earth-the spinning of the young planet gradually slowed over time, making the days longer-may have boosted the amount of oxygen released by photosynthetic cyanobacteria, thereby shaping the timing of Earth's oxygenation."

Using present-day microbial communities growing under extreme conditions at the bottom of a submerged Lake Huron sinkhole, the researchers were able to arrive with the conclusion that the said area played a huge and significant role in understanding the development of life on Earth.

"Our research suggests that the rate at which the Earth is spinning-in other words, its day length-may have had an important effect on the pattern and timing of Earth's oxygenation," said co-author and geomicrobiologist Gregory Dick, also a professor in the U-M Department of Earth and Environmental Sciences.

First Organisms to capture energy from sunlight

Cyanobacteria are the main culprits behind the toxic algal blooms that plague lakes and other bodies of water worldwide. However, these microbes in particular, formerly known as blue-green algae, have been around for billions of years. Masses of them are credited for releasing oxygen as a byproduct that later allowed for the emergence of multicellular animals.

Meanwhile, at the Middle Island Sinkhole in Lake Huron, purple oxygen-producing cyanobacteria compete with white sulfur-oxidizing bacteria that use sulfur as their main energy source.

"It's possible that a similar type of competition between microbes contributed to the delay in oxygen production on the early Earth," said lead author Judy Klatt.

"The idea is that with a shorter day length and shorter window for high-light conditions in the afternoon, those white sulfur-eating bacteria would be on top of the photosynthetic bacteria for larger portions of the day, limiting oxygen production," Dick explained.

The authors also modeled microbial mat processes to Earth-scale patterns over geological timescales to test their hypothesis that day length and oxygen release are linked.

"Simply speaking, there is just less time for the oxygen to leave the mat in shorter days," Klatt said.