AUDIE CORNISH, HOST:
A mystery that's billions of years old could be answered by scientists researching one of the Great Lakes. The researchers are diving deep to explore these sinkholes with purple-colored mats of microbes in order to understand the role they play in oxygenating the planet. Ben Thorp with member station WCMU has the story.
BEN THORP, BYLINE: About 2.4 billion years ago, oxygen first appeared on Earth in what's called the Great Oxidation Event. But it wouldn't show up at levels habitable for most organisms, like you or me, for another 2 billion years. And the answer to the question of why it took that long could lie at the bottom of Lake Huron. Today, the research vessel Storm is heading out to sinkholes less than a quarter-mile offshore. On deck, divers are prepping their gear for an 80-minute dive. And then...
(SOUNDBITE OF SPLASHING)
GREGORY DICK: So we are visiting what's a pretty unusual microbial mat community.
THORP: That's Gregory Dick, a research scientist at the University of Michigan. He says microbial mats are like a large, mushy, purple carpet covering the floor of the lake. He says they're responsible for life on Earth.
DICK: These microbial mats, we think, are representative of the types of organisms that would have lived billions of years ago and played a really important role in Earth's oxygenation. That is the addition of oxygen to Earth's atmosphere.
THORP: The mats are made up of cyanobacteria, some of the first organisms able to perform photosynthesis - or turn light into oxygen. But here's the thing about our purple friends, they don't always produce oxygen.
DICK: They can either produce or not produce oxygen, and we're very interested in what are the environmental and biological controls on that oxygen production?
THORP: If scientists can figure out what controls oxygen production in these mats, they might be able to answer the question of why it took so long for oxygen to reach current levels.
Dirk de Beer is a scientist from Bremen, Germany. He says having access to sites like this one is rare.
DIRK DE BEER: Difficult - they're very difficult to find. Yeah, you have to have a unique set of conditions.
THORP: To help them understand these mats, de Beer and his team are using high-tech microsensors.
DE BEER: So I have an instrument that is equipped with microsensors. These are thinner than hair.
THORP: Divers survey the mats with a combination of microsensors and camera snapshots.
Back on the boat, scientists merge that data to build a map showing where the oxygen is being produced. One of the scientists shows me a color-coded layout of where oxygen is being produced in the mats on his laptop.
UNIDENTIFIED MAN: That looks like that. You see?
THORP: What makes this so compelling to scientists is that it gets at the question of how the Earth came to support life.
Trinity Hamilton is a professor of biological science at the University of Cincinnati. She says there's a huge gap in our knowledge of Earth history.
TRINITY HAMILTON: This is a question that folks have been working on for a really, really long time. And so - yeah, it has a really, really broad implications in the field, for sure.
THORP: And Gregory Dick says it's part of a larger question. How rare are the conditions that allow for life?
DICK: What about life on other planets? How common is this process? And what are the processes that lead to a planet with an oxygen-rich atmosphere that can support animal life?
THORP: So the next time you take a deep breath, give a quiet thanks to the microbial mats that more than 2-billion years ago helped to make that possible. For NPR News, I'm Ben Thorp.
CORNISH: And that piece comes from the public radio station collaboration Great Lakes Today. Transcript provided by NPR, Copyright NPR.