Great Lakes May Hold Clues to Beginning of Life on Earth

Diver prepares to head into waters of Lake Huron (photo: Ben Thorp)

By Ben Thorpe

Alpena, Mich. -- The research vessel Storm sits in the Thunder Bay National Marine Sanctuary -- in water is so clear you can just make out the bottom. Divers prep their gear on deck and then sink into the waters of Lake Huron.

In roughly a minute, they’re at the bottom of an 80-foot sinkhole. Down there, with almost no oxygen and a large amount of sulfate seeping up through the ground, it’s a perfect place for microbes to gather in layers along rocks. They form one of earth’s strangest organisms: microbial mats.

“These microbial mats, we think, are representative of the types of organisms that would have lived billions of years ago,” says Gregory Dick, a University of Michigan research scientist on the Storm.

And these mats may help answer an important question: How did Earth develop an atmosphere rich in oxygen?

Dick says the mats may help scientists understand the slow increase of oxygen after Earth’s “Great Oxidation Event.”

“And at this time oxygen levels went from essentially zero to about 1 to 10 percent of current levels,” he says. “What’s really interesting is that they didn’t come all the way up to what we currently have for another two billion years and that’s a big question: Why did oxygen stay so low for so long?”

The microbial mats may be a key to understanding Earth’s oxidation because they are able to change between two types of photosynthesis.

We’re most familiar with plant photosynthesis -- turning light into oxygen. But these mats can also use light to create elemental sulfur.

Dirk de Beer, a scientist from Bremen, Germany, and others are trying to figure out why the mats switch from producing sulfur to oxygen.  

“We hope to learn from these mats, from these communities here, what controls oxygenic photosynthesis."

And to that end de Beer and his team are pulling out the big guns -- or more specifically -- micro sensors.

“I have an instrument that is equipped with micro-sensors that are thinner than a hair. They measure oxygen, sulfide, pH. We have also light sensors and they are moved with small steps within these mats,” he says.

One diver moves the micro-sensor hub to different parts of the mat, while another takes snapshots of the area.

Back on the Storm, another scientist will merge those data sets to build a map showing where the different kinds of photosynthesis are happening. That should give them a better idea for why it’s happening.

Sites like this one are rare, Dick says.

“There are other good sites for this around the world but they are often in remote and extreme environments,” he says. “Places like ice-covered lakes in Antarctica, hot springs in certain regions, but this one is right here in our backyard. This is a really valuable place to study this issue.”

What makes all of this so compelling to scientists is that it gets at the question of how the Earth could come to support life.

And, Dick says, it’s a part of a larger question: How rare are the conditions that allow for life?

He adds, “What about life on other planets? How common is this process? What are the processes that lead to a planet with an oxygen rich atmosphere that can support animal life? We’re understanding our own planet's history and understanding how it could happen on other planets as well.”

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