Last summer, Zac Peterson was on the adventure of a lifetime.
The 25-year-old teacher was helping archaeologists excavate an 800-year-old log cabin, high above the Arctic Circle on the northern coast of Alaska.
They had pitched tents right on the beach. Over the course of a month, Peterson watched a gigantic pod of beluga whales swim along the beach, came face-to-face with a hungry polar bear invading their campsite and helped dig out the skull of a rare type of polar bear.
But the most memorable thing happened right at the end of the trip.
"I noticed a red spot on the front of my leg," Peterson says. "It was about the size of a dime. It felt hot and hurt to touch."
The spot grew quickly. "After a few days, it was the size of a softball," he says.
Peterson realized he had a rapidly spreading skin infection. And he thought he knew where he might have picked it up: a creature preserved in the permafrost.
Nano-zombies or red herrings?
In the past few years, there has been a growing fear about a possible consequence of climate change: zombie pathogens. Specifically, bacteria and viruses — preserved for centuries in frozen ground — coming back to life as the Arctic's permafrost starts to thaw.
The idea resurfaced in the summer of 2016, when a large anthrax outbreak struck Siberia.
A heat wave in the Arctic thawed a thick layer of the permafrost, and a bunch of reindeer carcasses started to warm up. The animals had died of anthrax, and as their bodies thawed, so did the bacteria. Anthrax spores spread across the tundra. Dozens of people were hospitalized, and a 12-year-old boy died.
On the surface, it looked as if zombie anthrax had somehow come back to life after being frozen for 70 years. What pathogen would be next? Smallpox? The 1918 flu?
The media took the idea of "zombie pathogens" and ran with it.
"Climate change ... could awaken Earth's forgotten pathogens," The Atlantic wrote in November. "Many of these pathogens may be able to survive a gentle thaw — and if they do, researchers warn, they could reinfect humanity."
"Scientists are witnessing the theoretical turning into reality: infectious microbes emerging from a deep freeze," Scientific American wrote.
But something is a little fishy about these "zombie pathogen" stories: The evidence presented is as holey as Swiss cheese.
The key researcher cited is a biologist who studies amoeba viruses, not human viruses. These so-called monster viruses have evolved to live in cold soil, deep underground, not in warm, human flesh above ground.
And in terms of zombie bacteria, anthrax is a red herring. Anthrax has been "rising up" from soils all over the world for millennia, even longer. The bacteria survive by hibernating in the ground until conditions are right and then spring back to life. Back in the Middle Ages, it was common to see fields of dead sheep in Europe, wiped out by "zombie" anthrax. The French called these fields champs maudits, or the "cursed fields."
Now there are some tantalizing hints that the Arctic is, indeed, a frozen champ maudits, filled with pathogens even more dangerous than anthrax. Across the permafrost — which covers an area twice the size of the U.S. — there are tens of thousands of bodies preserved in the frozen soil. Some of these people died of smallpox. And some died of the 1918 flu — a strain of influenza that swept the globe and killed more than 50 million people.
But is there actually any evidence that these deadly viruses could survive a "gentle thaw" and then start a new outbreak?
To figure that out, I headed up to the top of the world, where Zac Peterson was last summer, to see exactly what type of creatures — and diseases — are hiding in the permafrost.
I was not disappointed.
"We've got a head right here"
Up on top of an ocean bluff, Zac Peterson and a few students are on their knees, digging inside a hole that's about the size of a Volkswagen minivan.
In 2013, a severe storm ripped off a big chunk of the bluff. Now the 800-year-old cabin is teetering on the edge of a cliff, near the town of Utqiagvik in Alaska. The team is trying to pull off an emergency excavation before the cabin crumbles into the ocean.
Hunters have been using this spot for thousands of years. At one end of the house, somebody was storing fresh kills.
"We've got a head right here, and a main body right there," says Peterson, as he points to two mummified seals, lying face up in a soup of thawing permafrost and decaying sea mammal flesh inside the cabin.
The seals are starting to warm up. Their organs are seeping out of their bodies and beginning to decay. The whole area smells like a rotting tuna fish sandwich. Peterson's pants are covered in black, oily goo.
The seals have been buried in permafrost for about 70 years. They are incredibly well-preserved. You can see their skin, their whiskers and even something that looks like a flipper.
"That's what's so amazing about Arctic sites," says Anne Jensen, an archaeologist with the Ukpeavik Iupiat Corp. who is leading the excavation. "The preservation is amazing," she says. "It's like the animal just keeled over and died right then."
Then something even creepier appears in the ice: a human molar.
"It's just a tooth," Jensen says. "People lose them all the time. And then just throw them out."
Now, this hunting cabin isn't built on a burial ground. Jensen doesn't think any bodies are buried near here. But Jensen is a world expert on excavating human remains from Arctic permafrost.
"I've probably dug up as many burials as anybody, " she says. "I would prefer not to be excavating burials. But I've spent a lot of my career doing that."
She has excavated everything from individual body parts — one time, she found just an upper arm in the ice, she says — to a massive cemetery, right here along the coast.
In the late 1990s, the graves in the cemetery started washing into the sea because this stretch of the Alaska coast is eroding. The local government called Jensen in to save the bodies. She saved dozens. But a few hundred remain, threatened by erosion.
Sometimes these mummified human bodies — which can be centuries old — are just as well-preserved as the seals in the log cabin, Jensen says.
"The little frozen girl from Uquitavik, she was actually better preserved than the seals," Jensen says. "She was about the age my daughter was at the time, so it was really sad."
Buried in the meat cellar with a little sled
Back in 1994, erosion exposed the body of a 6-year-old girl completely encased in ice for about 800 years. "Water had seeped into her burial," Jensen says. "So we took her out as a block of ice."
The little girl was carefully wrapped in a duck-skin parka with a fur-trimmed collar. Her parents had buried her with a little sled inside their meat cellar.
Her body was so well-preserved that Jensen shipped her to Anchorage so doctors could do a full autopsy. One of those doctors was Michael Zimmerman, a paleopathologist at the University of Pennsylvania who has been studying mummified bodies for 30 years.
"When you open up frozen bodies from Alaska, all the organs are right in place and easily identified," Zimmerman says. "It's not like Egyptian mummies where everything is shrunk and dried up."
Doctors can easily see why a person died. For the little frozen girl, it was starvation. But Zimmerman has seen infections in bodies excavated from permafrost. In one case, a mummy from the Aleutian Islands seemed to have died of pneumonia. When Zimmerman looked for the bacteria inside the body, there they were, frozen in time.
"We could see them under the microscope, inside the lungs," Zimmerman says.
But were these "zombie" bacteria? Could they come back to life and infect other people? Zimmerman tried to revive the bacteria. He took a smidge of tissue from the lungs. Warmed it up. Fed it.
"But nothing grew," Zimmerman says. "Not a single cell."
Zimmerman says he wasn't surprised the bacteria were dead. Pneumonia bacteria have evolved to live in people at body temperature, not cold soil.
"We're dealing with organisms that have been frozen for hundreds of years," he says. "So I don't think they would come back to life."
But what about viruses — like smallpox or the 1918 flu? "I think it's extremely unlikely," Zimmerman says.
In 1951, a graduate student decided to test this out. Johan Hultin went to a tiny town near Nome, Alaska, and dug up a mass grave of people who had died of the 1918 flu.
He cut out tiny pieces of the people's lungs and brought them back home. Then he tried to grow the virus in the lab.
"I had hoped that I would be able to isolate a living virus," Hultin told NPR in 2004. "And I couldn't. The virus was dead.
"In retrospect, maybe that was a good thing," Hultin added.
A good thing, yes. But here's the disturbing part. Hultin tried to capture the 1918 flu virus again, 45 years later.
By this time he was a pathologist in San Francisco. He heard scientists were trying to sequence the virus's genome. So at age 73, Hultin went back to Alaska. And he took a piece of lung from a woman he named Lucy.
"Using his wife's pruning shears, Hultin opened Lucy's mummified rib cage. There he found two frozen lungs, the very tissue he needed," the San Francisco Chronicle reported.
"Her lungs were magnificent, full of blood," Hultin told the paper.
At the same time, a Canadian team of scientists went hunting for the 1918 flu virus in Norway. They dug up seven bodies. But none of them were frozen, and the team failed to recover any virus particles.
In the 1990s, Russian scientists intentionally tried to revive smallpox from a body in their permafrost. They recovered pieces of the virus but couldn't grow the virus in the lab.
All these attempts — and all these failures — make you wonder: Maybe it isn't melting permafrost we should worry about when it comes to zombie pathogens, but what scientists do in the lab.
It's not over until the fat seal sings
When I finished writing this story in December, I ended it with a faint warning about the dangers of human curiosity. I was convinced that the only way "pathogens" would rise up from the permafrost was if a scientist bent over backward to resurrect the creatures in the lab. The chance of it happening naturally seemed infinitesimally small.
But then I received an email from Zac Peterson: "After kneeling in defrosted marine mammal goo ... doctors treated me for a seal finger infection," Peterson wrote. A photo showed a purplish-red infection covering the front of his knee.
Seal finger is a bacterial infection that hunters contract from handling the body parts of seals. The infection can spread rapidly into the joints and bones. Sometimes people lose fingers and hands.
The doctors never tested Peterson's infection to see if it really was seal finger. It responded well to simple antibiotics — the treatment for seal finger.
The only seals Peterson had handled were those in the log cabin. Those seals had been frozen in permafrost for decades.
"Even if there's a possibility it was something else," Peterson wrote, "I still tell people that I got infected by an 800-year-old strain of a seal hunter's disease that was trapped in ice."
Peterson just might be the first victim of "zombie bacteria" rising from Alaska's thawing permafrost.
AILSA CHANG, HOST:
Now we take you to the top of the world, to the northern coast of Alaska where a cliff is crumbling and exposing an ancient hunting site.
MICHAELEEN DOUCLEFF, BYLINE: Oh, there's another head back there.
ZAC PETERSON: Yeah. We got a head right here, a head right there, main body right here.
CHANG: Across the Arctic, these prehistoric settlements are being unearthed. And the reason why is climate change. As NPR's Michaeleen Doucleff reports, scientists are worried about something that could be lurking inside these settlements - zombie pathogens.
(SOUNDBITE OF WAVES CRASHING)
DOUCLEFF: Up on top of an ocean bluff, a team of archaeologists is trying to pull off an emergency excavation.
DOMINIC TULLO: Coming out of here, we have ribs and vertebrae and other long bones.
DOUCLEFF: That's Dominic Tullo, a student helping to dig out a hunting cabin. He's found a stash of animal bones.
UNIDENTIFIED WOMAN: Say that one more time.
DOUCLEFF: At the other end of the house, Glenys Ong shows me where someone was storing fresh kills.
GLENYS ONG: And so this is - this looks like skin right here.
DOUCLEFF: Right at my feet are two mummified seals, and these seals are incredibly well-preserved. You could see their skin, their whiskers.
ONG: And this - oh, it's a little paw.
DOUCLEFF: Oh, it is a little paw.
Everywhere they dig, there's another surprise.
ANNE JENSEN: Holy Moses, this is ridiculous.
DOUCLEFF: That's Anne Jensen, the archaeologist leading the team. They're at a coastal site near Utqiagvik, the town once known as Barrow. They're rushing to save a piece of history before it falls into the ocean. The cliff where the cabin is buried is thawing and breaking apart because of climate change.
PETERSON: It's that a bird?
JENSEN: It's just bird after bird after birds stacked up in there - skin there - ay-ay-ay (ph). Oh, yeah - yeah, there is - oh, my goodness.
PETERSON: It's the whole leg.
PETERSON: Oh, boy...
DOUCLEFF: Things are getting super stinky. The birds are thawing and rotting.
ONG: Oh, that's ripe.
DOUCLEFF: One student's hands are covered in black, decaying bird flesh.
JENSEN: Oh, no, oh, (laughter) her hands - oh, my gosh, oh...
DOUCLEFF: Now Jensen starts worrying about something we can't see.
JENSEN: Avian flu...
COLINE LEMAITRE: The norovirus...
JENSEN: Oh, norovirus, yes.
DOUCLEFF: The team realizes there could be bird flu hidden in these carcasses. You see, all across the Arctic, climate change is causing the ground to warm, soften like butter. And there are a lot of things buried in this ground - not just animals but also their diseases.
JENSEN: Take a break. Take a break, Coline. You're going to drive yourself - go nuts. Seriously, you need a break (laughter).
DOUCLEFF: Colin Lemaitre (ph) is a student. She puts on gloves.
JENSEN: Yeah, you should probably do that rather than go barehanded 'cause, I mean, there's a lot of gunk in here that...
DOUCLEFF: At this point in the excavation, something even creepier happens. A human molar appears.
PETERSON: Wait. It's really a human tooth.
DOUCLEFF: Now, the site we're at isn't a burial ground. There shouldn't be bodies right here. But the tooth does make them pause because it reminds them that there aren't just animal diseases buried in the Arctic but also possibly human diseases. There are tens of thousands of bodies hidden in the Arctic permafrost. Jensen knows this better than anyone.
JENSEN: I've done a lot of burials, yeah. I've probably dug as many burials as anybody.
DOUCLEFF: Some of the people buried up here - they died of smallpox, others from the 1918 flu.
Have you ever seen human remains, like, as well-preserved as this seal?
JENSEN: Oh, yeah.
JENSEN: Yeah, yeah. Well, the little frozen girl from Utqiagvik, (unintelligible) - yeah, she was actually much better preserved than the seal.
DOUCLEFF: The little girl was just 6 years old. She was carefully wrapped in a duck skin parka with a fur-trimmed hood. She had this little sled with her. She died about 800 years ago.
JENSEN: Water had seeped in around her burial I think, and she was - so she was basically encased in ice. We are able to take her out in a block of ice.
DOUCLEFF: Her body was so well preserved that Jensen shipped her to Anchorage so doctors could do a full autopsy. One of those doctors was Michael Zimmerman, a paleobiologist at the University of Pennsylvania.
MICHAEL ZIMMERMAN: I've done a number of studies on frozen bodies in Alaska. And when you open them up, the organs are all there, and they're easily identified. It's not at all like Egyptian mummies where everything is shrunken and dried up.
DOUCLEFF: So it's easy to see what a person died of. For the little frozen girl, it was starvation. But Zimmerman has seen infections in bodies excavated from permafrost. In one case, a mummy from the Aleutian Islands looked like it had died of pneumonia. And when he looked for the bacteria inside the body, there they were frozen in time.
ZIMMERMAN: We can see them microscopically in the lungs.
DOUCLEFF: There's this fear out there that once human bodies are exposed by melting permafrost, the pathogens in them could come back to life like zombie pathogens. It's not unheard of. Anthrax can do it. It happened just a few years ago in Russia. A massive reindeer burial ground thawed, and the anthrax that killed the reindeer woke up and started an outbreak. Were these pneumonia bacteria still alive? Zimmerman tested it. He took a smidge of tissue from the lungs, warmed it up, fed it and tried to revive it.
ZIMMERMAN: Nothing grew.
DOUCLEFF: Not one single cell.
ZIMMERMAN: No. (Laughter) I was happy (laughter) 'cause I didn't have to worry about catching anything.
DOUCLEFF: Zimmerman says he wasn't surprised the bacteria were dead. Anthrax is a special case. In general, bacteria that make people sick can't survive a deep freeze.
ZIMMERMAN: We're dealing with organisms that are hundreds of years old. At least in the stuff I worked on, they're frozen for hundreds of years, and I really don't think they're ready to come back to life.
DOUCLEFF: I ask him if the same is true for viruses.
ZIMMERMAN: I think it's extremely unlikely. We've never been able to culture any living organisms out of these bodies.
DOUCLEFF: In 1951, a pathologist from San Francisco, Johan Hultin, decided to test this out. He went up to a tiny town near Nome, Ala., and dug up the bodies of five people who had died of the 1918 flu, a virus that killed at least 50 million people. Hultin told NPR in 2004 that he cut out tiny pieces of the people's lungs and tried to grow the virus in the lab.
(SOUNDBITE OF ARCHIVED BROADCAST)
JOHAN HULTIN: I hoped that I would be able to isolate a living virus, and I couldn't. The virus was dead. And in retrospect, of course maybe that was a good thing.
DOUCLEFF: Or a good thing - but here's the crazy part. Hultin tried to capture the virus twice. He went back to Alaska when he was 72. And Russian scientists like Hultin have intentionally tried to revive smallpox from bodies in their permafrost. They recovered pieces of the virus but couldn't get that to grow either. So maybe when it comes to zombie diseases, it's not melting permafrost we need to worry about but what scientists are doing in the lab. Michaeleen Doucleff, NPR News. Transcript provided by NPR, Copyright NPR.