The Geomicrobiologist Searching for the Origins of Life

Penn State professor and geomicrobiologist-slash-astrobiologist Jenn Macalady is answering how we and other organisms could survive on other planets, by looking deep into Earth’s history.
August 23, 2018, 5:38pm

THE MOST UNKNOWN is Motherboard's love letter to the scientific process. For the next nine weeks, we'll be profiling the people trying to answer science's most difficult questions. Our feature-length documentary is now available on Netflix, and bonus episodes are available on YouTube.

There are two distinct moments when a new explorer’s body and mind start to adjust to the strange, alien environment of a cave. The first comes about 15 minutes into the expedition, when their eyes start to adapt to the darkness. Gradually, they can see—in light so dim that moments before felt impenetrably dark.


Then, when nothing bad happens in the first half-hour or so, the second heightened sense arrives: Their observational powers start to focus less on fear—the awkward footing, the slippery rocks, dirt, and darkness—and more on the absolute awe of this strange new world. And, if they’re a scientist, the mind may turn to collecting data to bring back to the surface.

Last spring Jennifer Macalady, a geomicrobiologist, astrobiologist, and professor of geoscience at Penn State University, led a group of radio astronomy students on a caving expedition to learn about how we plan to detect life on other planets. They went into the earth to inform how to look out into the universe.

As an astrobiologist, going down to look up is a paradox Macalady spends a lot of time reflecting on, and it shapes the question she and her colleagues continually ask of their work: If you had to describe life on Earth to someone who’s never been here, what would you say?


Watching her shuffle down the muddy walls of Italy’s Frasassi Caves in Motherboard’s documentary The Most Unknown, it’s easy to see the connection between geomicrobiology and astrobiology. The cave’s surfaces are pockmarked and asteroid-like, hanging in fields of blackness. Shadows cast by her headlamp swing and twist in weird, eerie ways across the rocky surfaces. Specks of dust appear suspended like stars in the lamp’s beams. It looks like another planet—or more accurately, a planet within a planet, where Macalady’s found herself a terranaut exploring where humans don’t typically tread.

Jenn on an expedition. Photo credit: Xavier Aaronson

Macalady has studied geology and soil science, but it wasn’t until she was hired by the Penn State Astrobiology Research Center that she finally began thinking of herself as an astrobiologist.

When she’s caving, she’s seeking what she calls “the slime.” Most of the trillions of species of life forms on Earth are microbial, which means that individually, with the naked eye, they're too small to see. But they like to grow attached to surfaces, in diverse communities of species that all live together—and caves are one of the places they gather. Together, giant communities of microbes can often be seen.

"It was the alien environment, a completely new circumstance, and completely absorbing.”

The first “slimes” that are preserved in the fossil record are as old as 3.5 billion years. In caves like the Frasassi, geomicrobiologists get a glimpse of the earth’s earliest history through the slime they collect.

“There are lots of things we don’t understand and maybe can't even imagine about how a microbe-only ecosystem works, so one of the things we try to do is go places on the modern Earth where there are microbe-only ecosystems to try to study those, to learn about how the ancient Earth might have worked,” Macalady explained.


If we’re going to find life in space, it's likely to be microbial, because that’s what our own planet’s life looked like for billions of years.

“It's about analogues: how life might be in the past on Earth, which is really like a different planet, or on other planets in the solar system or beyond,” she said.

These days, Macalady doesn’t get to spend as much time as she’d like in the field, chasing that awe that her astronomy students felt when she led them underground for the first time.

The first time Macalady ever went caving, her oldest son, Luca, was just eight months old, and still breastfeeding. She left him with his father, and went down.

“I was so absorbed by what I was doing, eight hours went by and it felt like five minutes,” she recalled, still awestruck at how that could have happened. “When I came out, there was my son's father walking back and forth across across the cave entrance with this crying baby. It was this shocking moment for me. It was the alien environment, a completely new circumstance, and completely absorbing.”

It was like time travel, she said.

It took years before she got to the point where she was making observations freely in the cave, letting go of the hesitation that our surface-senses try to cling to: Will I slip here? Is my foot in the right spot? What was that sound? All that uneasiness faded away over the months and years of expeditions, until all that was left was the exploration.



Conveying a love for the slime, and especially the kind of thrill Macalady and scientists like her feel when she finds a really good, really gooey specimen, isn’t always an easy task. Not everyone can get this hyped about microbial cities of cave snot.

That’s why a big chunk of her work, she tells me, is devoted to outreach: teaching students and young scientists how to speak to the rest of the world about their work. “One of the things lots of scientists don't understand—especially students but also grown-up scientists—they think that you're either good at outreach or you're not,” she said.

Jenn Macalady. Photo credit: Xavier Aaronson

The trope of the introverted, antisocial scientist toiling away in their lab is so pervasively embedded in popular culture today that scientists have to actively fight against it.

“Really, the truth is that you have to practice,” Macalady said. “Nobody is good at translating what they do for different audiences, and the more you practice that, the better you get.”

Macalady told me that she’s seen a recent shift in how universities treat outreach. It’s a higher priority now, as students have to be jacks-of-all-trades in their fields, and act as public advocates for their own work.

“I think the more root cause is scientists as a group have figured out that people don't have it loaded in their minds anymore that science works,” Macalady said. “That used to be something that everybody had loaded into their memory every day.”


Legislation like that posed by creationists and conservatives to “teach the controversy,” around climate change and evolution , for example, undermine what scholars have proven as fact. From its start, the current administration led many scientists to say there is a “war on science” unfolding as hiring freezes and budget cuts struck vital scientific agencies.

”There's so much rhetoric that's anti-intellectual and anti-science, and I think people have just lost touch with the fact that science actually works, that it's useful, that it helps us, and I think scientists have caught on to that and realized they have to fight back a little bit,” she said.

Macalady’s research work includes nearly a decade of seeking solutions to toxic acid mine drainage in Pennsylvania’s streams, 10 years of studying the biovermiculations (microbial communities that live in extreme environments) within the Frasassi cave system, exploring how Mars’s briney waters could sustain life, and exploring Bahamian marine caverns, knows as “blue holes,” to see if they hold any clues that may help the search for life beyond Earth.

“We are curious about things that we are not even certain have to exist, but we want to find out, so we just keep observing.”

But there’s no single discovery or study that stands out to her as the most important of her career. Rather, she says the everyday moments of being a scientist and building on the work of others is what get her up in the morning.

“One of the things that astrobiologists do is they imagine telling somebody who’s not from Earth what Earth life is like,” she said. “It’s a little thought experiment that people do to boil down, well, what is Earth life? What is it? That boiling down exercise is really fed by the work of thousands of scientists who have been investigating minute aspects of Earth life for 200 years already.”


As part of the experiment of The Most Unknown, Macalady met Davide D’Angelo, a physicist at the Universita degli Studi di Milano in Italy, who is studying dark matter and all the mysteries that come with it. She asked him where he hopes scientists will someday find dark matter, and his response is that of a classic physicist: As scientists, they can’t hope and guess at these things, he says. They just have to keep doing the work.

“All the scientists in the film, we all are doing this process,” she told me, recalling that moment with D’Angelo. “And the process is, you try to make observations that will answer your question with the least amount of doubt. Sometimes you can design an experiment or make an observation that leaves you very little doubt about the answer to your question, and sometimes the world is just made in such a way that you just have to keep observing and keep trying.”

“I think that's an amazing thing about scientists,” she continued. “We are curious about things that we are not even certain have to exist, but we want to find out, so we just keep observing.”

For her, that unknown is a big one: what is most of Earth's life is really doing here?

“If you asked me, ‘Do we really know what Earth life is like?’ In a certain sense I could say, ‘Yes, we all have DNA, we all have RNA, we all have ribosomes, we all make ATP,’ all that nerdy stuff,” she said. “But really we haven't met most of Earth's life forms yet. So that's a huge challenge. There might be three trillion microbial species, and that's about as many stars in the galaxy.”