Tiny Organisms in Earth’s Most Unlivable Places May Help Us Find Alien Life
Luke McKay, an astrobiologist and microbial ecologist, is probing the extreme limits of life on Earth to answer bigger questions about the universe.
Image: Lindsay Blatt/Motherboard
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.
“I really set myself up for failure here, but okay,” Luke McKay says jokingly.
I had asked the scientist how he would explain his work to a child. McKay is an astrobiologist and a microbial ecologist. The 35-year-old Alabamian studies microbes: diverse life forms that exist invisible to the naked eye. Over the past several years, McKay has trekked across the globe probing colonies of microscopic extremophiles, or unique organisms that thrive in Earth’s least habitable places: Hot springs, Antarctic ice, deep sea hydrothermal vents, and other hostile environments where humans daren’t go.
By looking at the remarkable existences of extremophiles, we may better understand the origins of life—here at home, and perhaps on far-off worlds.
“I would probably start with a question like, ‘Where did you come from?’” McKay tells me.
“The child might say something funny like, ‘Mommy and Daddy,’ or ‘I came from my house,’” McKay continues. “But I would drive that line of thinking to the basic idea of what made you? What caused your body to exist? There are things that, if you don’t have them, you can't live. And if you understand how prevalent they are [throughout the universe], you start to think, ‘Oh, extraterrestrial life isn’t improbable. It actually seems probable because there’s so many energy sources.’”
McKay is one of nine scientists featured in Motherboard’s experimental documentary, The Most Unknown, which explores some of humanity’s most vexing questions. (“What is dark matter? What is consciousness? Where did life come from? Is there life elsewhere in the universe?”) All have forged careers by examining the fundamental building blocks of life, and how they’re needed on Earth, around the solar system, and elsewhere in the universe. Things that, together, create a wide constellation of knowledge about our complex existence.
What does it mean to be alive? What is living? What caused all of this to be? These are the questions, simultaneously simple and exceedingly complex, that fuel McKay’s infectious brand of curiosity. While others peer into space or manipulate the human brain, McKay is rewinding the course of life, all the way back to primordial Earth when everything was “just chemistry,” he says.
“Those are big, big, huge questions, but those are hard,” McKay admits. And in order to test such broad questions, it’s often necessary to break them down into smaller concepts, which brings us to methane.
Methane, or CH4, is one carbon atom surrounded by four hydrogen atoms, and is “basically the coolest molecule,” exclaims McKay. It’s a potent greenhouse gas that’s both colorless and odorless, and abundant on Earth. Lots of things release methane into our atmosphere, like cow farts, melting permafrost, and the consumption of fossil fuels, which directly contributes to climate change—methane is responsible for 20 percent of current global warming. Much of this methane comes from biological sources, chiefly the microbes that McKay studies, and its presence on Earth is a signpost for life.
And, maybe—just maybe—its presence on other planets could be a sign of life there, too.
This is partly why McKay is obsessed with funky, ancient organisms that produce or consume methane gas through metabolic processes and, along the way, are able to convert chemical compounds into biological energy. Some use hydrogen, carbon dioxide, or carbon monoxide for energy. They belong to the Archaea, one of the three domains of life together with the Bacteria and Eukarya. These single-celled microorganisms evolved more than 3.5 billion years ago and many of them are also extremophiles, found in animals’ guts, swamps, or in unthinkably hot and cold environments.
For roughly the last 40 years, McKay explains, scientists believed that microbial metabolisms involving methane, like methanogenesis, which these tiny organisms perform to survive, were isolated to a narrow branch on the tree of life: a single archaeal phylum called Euryarchaeota. (Life as we know it falls under three big domains— Eukarya, Bacteria, and Archaea—and each is further divided into phyla.)
Then a 2015 study found the genes responsible for performing methanogenesis on a very different branch of life: Bathyarchaeota. And one year later, another group of scientists discovered them in Verstraetearchaeota. To people like McKay, who are tracing the origins of existence, this was huge. Today, even more groups are unearthing these ancient genes across Archaea.
“We're starting to realize that, not only is methanogenesis thought to be an early way of life, but that the process is evolutionarily diverse,” he adds. On his website, McKay describes this as a paradigm shift. “Many more organisms may be involved in producing or utilizing methane than previously thought.”
A large portion of Earth’s methane is made by these organisms, but other sources, such as geological processes like volcanism, can produce methane, too.
So what does it mean when scientists find methane on, say, Mars? Did it arise from life, or was it created non-biologically, deep within the planet?
In 2003 and 2004, three independent groups of scientists announced an incredible finding: the presence of atmospheric methane on the Red Planet. Several years later, in 2013 and 2014, NASA’s Curiosity Rover detected methane plumes on the surface of Mars. And earlier this year, Curiosity provided even more Martian data, suggesting seasonal changes in methane activity, though still not answering the question of where it was all coming from.
The exciting possibility that these lifeforms on Mars, past or present, created its methane is a real one. And various studies are now investigating their ability to survive conditions similar to the subsurface of Mars. Elsewhere in the solar system, Saturn’s moon Titan, which also harbors methane, is another candidate for life.
And while the primitive microbes that McKay studies may not be an exact analog for otherworldly life, they certainly give us a headstart on where we should be looking for it.
“DNA is my jam,” McKay says. “I love DNA.”
The stuff containing our genetic information, and that of nearly every other organism on Earth—deoxyribonucleic acid—is what draws McKay to extreme environments. Places that resemble the chaotic, boiling conditions where life may have first emerged. A hydrothermal vent, or a terrestrial hot stream, he explains. Here, McKay hunts for extremophiles that are associated with methane. By looking at their DNA, he can infer their genetic potential, and better understand how they derive energy from such environments.
“Virtually every single environment hosts new DNA, which means it also hosts brand new, undiscovered life forms that we don't understand completely yet,” McKay tells me. “And I think discovering new life is pretty freaking cool.”
McKay’s expeditions take him from islands in Antarctica to hydrothermal vents in the Gulf of California at depths of more than a mile. But most recently, he’s been poking around the famed hot springs of Yellowstone National Park, and even received funding from NASA to do so. Here, the microbial ecologist samples organic material that’s potentially brimming with microscopic life. McKay has used robotically operated vacuums to collect samples from water pushing 320 degrees Fahrenheit, which he takes back to the lab on dry ice.
In the lab, he performs DNA extractions to see exactly who makes up these unique microbial communities. This process involves centrifuges for spinning, “super stronger shaking machines,” and different chemical reagents to shear cells, spilling their DNA so it can be purified in a tube. Once the DNA is isolated, it can be sequenced and “read” to understand how these particular extremophiles get energy and carbon from exotic environments.
McKay notes that even microbiologists are just beginning to understand the enormous diversity of bacteria and archaea, and it wasn’t until the advances of DNA sequencing that this was possible.
Looking back on his relationship with science, McKay, now an assistant research professor at Montana State University, calls it a journey. “I'm from a really intelligent and curious family, but also I'm from a very religious background,” he says. Including graduate school, he’s spent a decade studying microbial ecology.
“From being born into this idea of knowing the answers to all of the questions, because it's in the Bible or because God said this or that,” McKay tells me. “To being like, later in life, ‘I don't think that is necessarily true. Then coming full circle around to, "Okay, so now I don't know the answers to these questions, and I'm gonna dig deep and find the answers.’”
After everything, McKay has decided that not knowing is perfectly okay, and that the absence of answers can be a catalyst for curiosity, perhaps even new discoveries.
Over the course of The Most Unknown, McKay spends time with two other scientists: cognitive psychologist Axel Cleeremans and astronomer Rachel Smith. Their shared perspectives are fascinating to behold because, while a psychologist might be unfamiliar with sequencing DNA, for example—as Cleeremans was—the fundamental questions they pursue are, at times, stunningly similar. “All these unknown bits that nobody sees,” Cleeremans says at one point, comparing the uncharted depths of consciousness with the vast, unexplored swaths of the evolutionary tree.
Smith, who teaches physics and astronomy at Appalachian State University, looks through a telescope and sees “a bajillion” stars. When McKay looks through a microscope, he says, what he sees are a bajillion tiny organisms that look like stars.
McKay remembers thinking: “‘Oh, my God, we kind of do the exact same thing. But you look way the hell out there, and I look way deeply into here.’”
“Axel and Rachel,” he adds, “I miss you both dearly. I loved hanging out with you and it was so fun. I can't wait to see you again.”
McKay is somewhat of an extremophile himself. The suffix phile denoting love—which is how McKay feels about the rugged terrains he explores. It’s paradoxical to love environments that would rather destroy human life, but “it puts us in our place,” he admits. “We think of ourselves as beings that can terraform any environment to suit us. But maybe not these.”
When he’s not adventuring, McKay is a pretty regular dude. He likes backpacking, snowboarding, playing guitar, and listening to rap and hip-hop.
He also loves science fiction—but good science fiction, which “is based on science, its potential, and legitimate possibilities that we haven’t yet arrived at.”
McKay remembers a talk given by San Diego State University biologist Forest Rohwer, after which a student asked: “What do you read?” Rohwer replied that he reads instrument manuals and science fiction. Because instrument manuals list the tools needed for doing things, and science fiction stimulates your curiosity for doing all of those things.
Which is perhaps why McKay adores the the science fiction trilogy The Three-Body Problem by Chinese author Liu Cixin. It’s a book that’s a bit manual-like itself, and has been lauded for its meticulous and original treatment of the classic extraterrestrial theme: What happens when humans make contact with alien life?
“There's biology, molecular biology in there, astrophysics, computer sciences, nanotechnology,” McKay exclaims. “It's so cool. It's such a good book!”
It’s easy to love these zoomed-out questions. What is life—here on Earth and elsewhere in the universe? But it takes a certain person to zoom in and deal with the minutiae. To peer back in Earth’s history so that humanity may chart its future. And yes, it would be awesome if that future also included aliens.
Even McKay admits that would be a good selling point.
“Yeah,” he says, reflecting on my original question of how he’d describe his work to a child. “Somewhere in there I would use the term ‘aliens’ because that would probably get them excited.”