Episode 2: The alien underground

Half a mile below the surface of the earth, in a cave too hot to explore without an ice-packed suit, NASA scientist and Nat Geo explorer Penny Boston clambers around glassy crystals that are taller than telephone poles and wider than dinner tables. But it’s not The Crystal Cave’s grandeur she’s interested in—it’s what may be hibernating inside the crystals.

Half a mile below the surface of the earth, in a cave too hot to explore without an ice-packed suit, NASA scientist and Nat Geo explorer Penny Boston clambers around glassy crystals that are taller than telephone poles and wider than dinner tables. But it’s not The Crystal Cave’s grandeur she’s interested in—it’s what may be hibernating inside the crystals. Astrobiologists like Penny Boston scour the Earth’s most hostile environments for microorganisms, to see if they hold clues to what life might look like on other planets—maybe even planets in our solar system.


PENNY BOSTON (ASTROBIOLOGIST): In the early 2000s, a fellow cave explorer sent me some images from the Naica Caves and I thought it was a photoshop hoax.

PETER GWIN (HOST): Scientist Penny Boston says she had to see these Naica Caves for herself. They’re nearly a thousand feet deep and they’ve been flooded for millennia. So really what these caves are an ancient time capsule. A National Geographic documentary crew followed her deep inside in 2008.

BOSTON: This passage just curves around to the left here, I think.

GWIN: And that’s where she saw them.

BOSTON: Ooh ooh – look at that! Giant crystals.

GWIN: Boston had seen crystals in caves before, but never like the ones in Naica. To picture it, imagine Superman’s Fortress of Solitude. There were these massive white crystals lined from floor to ceiling.

BOSTON: It’s like being on the inside of a cut gem, isn’t it? It’s just fabulous. I’m going to climb down through (FADES UNDER)

GWIN: The most spectacular cave is about two stories tall and the size of a football field. It’s crisscrossed with these massive crystal pillars the size of telephone poles.

BOSTON: You can't put your arms around them, they're so big.

GWIN: My own thought when I saw this documentary was, “Is this even real?” It looks other-worldly. In the midst of these beautiful, massive crystals there are these tiny little people wearing what looks like orange hazmat suits. Boston says that’s because it’s extremely hot.

BOSTON: Parts of the caves uh, up to 140, in some cases 150 degrees Fahrenheit. Uh, so, not survivable. And so they put together these spacesuit-looking things, although they're in a rather shocking shade of orange and the main features were an ice vest underneath which was heavy as the dickens because ice is, is really, really heavy. And then the suit goes over that. And then there is a um, ice pack in one's caving helmet to keep your brain cool and then a breathing backpack that sent air across very heavy frozen cylinders of ice.

GWIN: But even with the ice suits; Boston says she and her team could only survive in the cave for short periods of time.

BOSTON: We didn't have arms and legs protected from the heat and so we would get weaker and weaker and, you know, the heat effects would start to really affect our bodies. So we were not supposed to stay in longer than half an hour. We once pushed it, um, to 50 minutes and I nearly killed myself. It was a very bad idea.

GWIN: Killer heat, sharp crystals, no natural light. All this makes you wonder, what was she doing in that cave that was worth risking her life?

BOSTON: And the more important thing than the giant crystals to me — although they were spectacular — was that a fellow scientist, said, “I think we're seeing microbial shapes in little pockets within these crystals.” And I'm like, “Oh my gosh.”

GWIN: Microbial shapes. As in life. She was looking for life in the crystals. Microscopic fossils trapped within small imperfections. She found some, and then took them back to her lab to see if they would grow. And they did.

BOSTON: Lo and behold, on that first expedition I got a lot of things growing.


GWIN: I’m Peter Gwin and you’re listening to Overheard at National Geographic, a show where we eavesdrop on the wild conversations we have here at Nat Geo and follow them to the edges of our big, weird, beautiful world.

This week: a journey to shed light on the secrets lurking in ancient caverns hidden deep inside our planet and how that work could help us better understand the potential for life in the most hostile environments in the universe.


More on that, after the break.

BOSTON: My name is Penny Boston and I have spent my career looking for weird organisms in unusual places.

GWIN: Penny has hunted for microbes in exotic caves all over the world. She wants to uncover how they’ve survived without the luxuries of sunlight and nutrients from organic matter.

BOSTON: Well, the ones that I am personally the most interested in are the ones that eat rocks and minerals.

GWIN: It turns out that surviving on a rock-diet isn’t easy. Especially when compared with the diet that most microbes get.

BOSTON: So you know if I were to swab your tongue for example, those microorganisms living on you are used to a very fat and happy fast food existence. Right? So they've got lots of stuff to eat and so they grow really fast. But if you're a little microorganism in a mineral environment where you have to work like the dickens to get every little erg of energy, you don't waste it. You don't grow fast. There aren't a lot of you and you're very small. And in many cases you're not motile; you don't move around.

GWIN: Okay, so these are tiny, immobile workaholic bugs that eat rocks. I can’t even imagine what they look like.

BOSTON: Oh, they're so cute. There are wild, fanciful shapes. Things that look like beads on a string. The shape we call hairy sausages. There are some that look like little micro chrysanthemums. We have star-shape guys. We have cubes. We have tiny guys that are so small that at first, we didn't believe that they were independently living organisms. We have giant things with lots of appendages sticking off them that we call “death stars.”

GWIN: Microscopic death stars. These microbes sound totally weird.

BOSTON: That may be because there are fewer grazers and predators in the subsurface and they can afford the luxury of having complex shapes that may serve some other function. So that's why they're particularly cute as microbes go.

GWIN: They may be cute but they’re not easy to find. Boston says you can’t just put them on a slide and look at them under a microscope to tell if they’re alive.

BOSTON: Oh, things don't just wiggle under a microscope. The size of the microorganisms that we're interested in are minuscule and they're also at very low concentrations. And so, um, finding them, when many of them are actually coated in minerals as part of their um, you know, their life processes, makes a very, very cryptic, very, very secretive, and very, very hard to detect and prove that they're living.

GWIN: She says you have to be very patient.

BOSTON: I have some experiments that have been going for 20 years uh, or more. And, you know, that maybe the organisms take years to actually even show up in some kind of culture setup and even longer to do something of interest to me like turn one mineral into another mineral.

GWIN: There’s a name for these slow-growing creatures: extremophiles. They make their home in extreme conditions: boiling and frigid temperatures, in pools of acid, without oxygen, in the dark. Pretty much the last places you’d expect to find anything living.

Boston says she’s interested in them because if they can survive here on Earth, then maybe we can find something like them on other planets. And that’s Boston’s ultimate goal, because what I haven’t told you yet is that Penny Boston is not your average caver. She’s the director of the NASA Astrobiology Institute.

BOSTON: Astrobiology is a vast field of study that encompasses pretty much everything we think about life in the universe.

GWIN: Okay, so really vast.

VICTORIA JAGGARD (EXECUTIVE EDITOR): So astrobiologists are the people who were charged with saying, “How do we look for life elsewhere in the solar system slash galaxy and how do we know it when we think we've found clues?”

GWIN: Victoria Jaggard is the executive science editor at Nat Geo. She says some of these clues might look a lot like the weird extremophiles in Penny’s cave.

JAGGARD: The reality of the situation, I think, if you were to talk to a lot of astrobiologists, is when we do find that first hint of alien life? Gonna be microbes. Bacteria. Viruses. Little tiny bugs. Maybe something akin to a nematode.

GWIN: I don’t even know what that is. What's a nematode?

JAGGARD: Nematodes are these primitive worm-like things that exist on a microscopic level.

GWIN: And they’re important because scientists found microscopic things that look like them on the surface of a rock that broke off of Mars millions of years ago. This rock landed in Antarctica during the last Ice Age and scientists thought, this is it! We found it. Evidence of life.

JAGGARD: In the summer of ’96, a group of scientists from NASA's Johnson Space Center put out a paper and according to them, they had evidence for traces of fossilized life from early Mars.

GWIN: It wasn’t just the strange microscopic shapes that caught NASA’s attention. Victoria says that there were chemicals in the meteorite, chemicals that are produced by living things on Earth.

JAGGARD: This was taken to such an extreme that then-president Bill Clinton went out on the South Lawn of the White House and announced to the American people that we have this evidence in hand and that he is making it a priority that we continue our studies of Mars, continue our studies particularly of this meteorite, and continue to look into the validity of these claims. Let me read you a statement from his, the transcript of his speech:


PRESIDENT BILL CLINTON: If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered. Its implications are as far-reaching and awe-inspiring as can be imagined. Even as it promises answers to our oldest questions [FADES UNDER]

JAGGARD: Now imagine yourself turning on your TV and listening to the president of the United States speak those words.

GWIN: You know, I’m a little embarrassed to admit this, but I don’t remember Bill Clinton ever making that speech. And there’s probably a reason for that. Because after careful study of the meteorite, scientists determined it actually wasn’t proof of alien life.

JAGGARD: And so, at the end of the day, what they did say is, look, you can get these particular spiral structures just from basic geology. No life required.

GWIN: No life on the actual meteorite itself.

JAGGARD: Correct.

GWIN: Okay, total bummer. But that excitement wasn’t all for nothing. It brought together a lot of scientists and energized the field of astrobiology. The organization that Penny Boston directs, the Astrobiology Institute, was founded two years later to help answer some of the questions raised by the meteorite.

JAGGARD: Even though the answer at the end of the day may be a little womp womp, no life. What it did do by having this moment was saying to scientists that they really need to be more careful and more creative, I think, in their approach to understanding what potential life could be out there on other worlds. How do we find this stuff in the first place? What kinds of environments can it live in? And what honestly are the traces it’s going to leave behind that are going to be unequivocally life? Big red flashing neon sign, "life here."

GWIN: Okay, but how do we know where do we look for the neon sign?

JAGGARD: One of the tricks that NASA has been using has been the strategy of "follow the water."

KEVIN HAND (ASTROBIOLOGIST): Of all of the ocean worlds out there of which I think there are at least six, possibly many more. I like to point to Europa, Enceladus, and Titan as the most tantalizing in our search for life that could be alive today.

GWIN: Kevin Hand is also a NASA scientist. He works at the Jet Propulsion Laboratory. And he’s particularly interested in exploring one of Jupiter’s moons, Europa.

HAND: Ah. What does Europa look like? It's sort of an icy white that is a mixture of water ice and then some salts that have kind of been concentrated out of the, the ice. And then, there are regions that are kind of a, kind of like an egg yolk yellow and that I think is irradiated salt. And then there are regions that are a bit more reddish and that's sulfur compounds. And then I hope that there's also some brownish goo that might be organic material that could be indicative of life within the ocean.

GWIN: Yes, it’s all about the ocean.

HAND: If we've learned anything about life on Earth, it's that where you find liquid water, you generally find life. And Europa has got two to three times the total of, total volume of all the liquid water found in Earth's ocean.

GWIN: So another huge liquid water ocean in our solar system. So if there's so much water out there, then maybe there's life out there too.

HAND: We just don't know but I definitely side more towards: if the conditions are right and if they are similar to what we think happened on Earth, then I think the origin of life is probably pretty easy.

GWIN: Okay, hold on a second. So what did happen on Earth? Okay, evolution. I understand: organisms compete with each other. Over time they change, they get more complex, branch off into different species. You eventually get nematodes, dinosaurs, platypuses, and modern humans. The so-called tree of life. But how did the whole thing get started in the first place? I mean, to have evolution you need to start with a living thing. So how did that first thing get started?

BOSTON: My mental picture of early Earth is a gigantic laboratory the size of a planet with zillions and quajillions and other -illions of little tiny experiments going on all the time in many, many different environments. That there was no single "a ha, a cell appears!" kind of moment.

GWIN: Both Boston and Hand think that if you get all of the basic ingredients for life together, with enough time and energy those basic ingredients could start to mix.

BOSTON: This interacting system of chemistry got more and more complicated over time, got more and more life, lifelike. Um, pre-biotic, um, life-y, life-y-ness index went up.

GWIN: Life-y-ness. So it’s like a group of instruments all making noise at the same time. You got tubas, violas, percussion, a random clarinet. It sounds chaotic. But then over time they start playing together and it becomes music.

BOSTON: And that, gradually out of that beautiful symphony, that soup of life — maybe not only soup but crunchy bits — um, that proto organisms arose from that and that many different flavors of proto organisms probably existed.

GWIN: Proto organisms: the things that come before organisms, all mixing in a primordial soup. And that’s when natural selection kicks in and the tree of life starts adding shoots and branches.

BOSTON: The minute you get different things in an environment that are competing for something like nutrients or space or water or I don't know what. Uh, sunlight. You get selection. This is the beauty of selection. And so the minute you have that, there are going to be some proto-organismic-like things that are going to do better than others and they're going to gradually, uh, you know, winnow out who's the most successful.

GWIN: And so maybe, in an environment like Europa with just the right combination of energy, nutrients, and time, Kevin Hand says, life could emerge.

HAND: If we do find life on Europa, I would be happiest with even the tiniest microscopic little microbe.

GWIN: He’s looking for tiny microbes because as Boston told us, that’s what grows in extreme conditions.

HAND: And even though that's not as exciting as a giant Europan squid, it's still profound from the standpoint of changing the way we think about life and biology. For all of the diversity of life on Earth from a giant squid to Mick Jagger to extremophile microbes, we're all connected by the same tree of life. We all run on DNA, RNA, proteins, and ATP. And if we were to find even a simple microbe on Europa, I would be curious, what makes it tick? Does it have DNA or does it run on some other genetic compound? Is it connected to some other tree of life that's completely independent from life on Earth?

GWIN: And the only way to find that out is to go there. Hand says plans for a mission are underway. It’s called the Europa Clipper.

HAND: That mission will hopefully get to the launchpad in 2023ish and then out to Jupiter and Europa in the mid to late 2020s. And it'll fly by Europa some 45 times and send back all sorts of stunning images and spectra and ice-penetrating radar and lots of great stuff.

GWIN: “Great stuff” that may have a lot in common with stuff we’ve seen before.

HAND: An environment that I like to imagine might be relevant to Europa's sea floor is our deep ocean. Just by a curious serendipitous quirk of our solar system, the pressure at the deepest regions of our ocean. The pressure down there is roughly equivalent to the pressure near the seafloor of Europa’s ocean. And so I think these environments on Earth can be extremely informative in serving as a guide for how we assess whether or not the deep ocean of Europa could be habitable or possibly even inhabited.

GWIN: So there are places here on Earth that have similarities to environments on other planets. Certain parts of the ocean, beneath Antarctica, or at the bottom of the world’s deepest caves.

Penny Boston says that when she was a kid, she was taught there couldn’t be life down there. But later on as an adult, she found her first cave microbe. Well, that’s its own story and it all started with an idea Boston had while watching a certain documentary.

BOSTON: Well, you know, it was… It was a National Geographic special and it was about Lechuguilla Cave in New Mexico.


BOSTON: And I saw this television special and several of my colleagues also saw this and it said several really important things. It said that the cave had only recently been dug into. That it was massive and huge and unexplored and pristine; and that there were a great richness of sulphur minerals. And the last thing that really caught our attention was the fact that one of the U.S. Geological Survey scientists had seen what he thought were microorganisms present in some of these spectacular mineral formations there. And so, I called him up the very next week and I said, "You don't know us, but we're from NASA and we’d like to go into your cave." And we had no training and I had only ever been into show caves as a kid. And so we did the first NASA-sponsored trip in to Lechugilla cave in April of 1994 and, uh, it nearly killed us.

GWIN: Hmmm, this seems like a theme for Boston. In the Nat Geo documentary, Lechuguilla is described as “The Mount Everest of Caves” so the going was pretty tough.

BOSTON: I happened to be looking up and a blob of this brown and orange stuff fell into my eye and it completely made my eye swell up within a matter of minutes. And I had to then back out of the cave with my eyes swelled shut. So then I didn't even have my three-dimensional vision. So the whole time I was in there, I was just thinking, “I have to live long enough to get out of here.”

GWIN: She got out and the light at the end of that tunnel came with an unexpected surprise.

BOSTON: When I did get out though, the cool thing — even though I was covered with bruises and my foot was swelled up like a giant tree ball and so forth — was that the eye — once I got to the surface with light and dryness, it cleared up within about four hours and I thought, “You know that seems very suspicious. I think that that seems like a biological signal.”

GWIN: A biological signal, as in the blob might be alive. And once they got out of their dark cavernous world, the microbes that had gotten into her eye died.

BOSTON: The material that had fortuitously flopped into my eye actually was a very exotic and very amazing microbial mineral community.

GWIN: That close encounter was a revelation for Boston. And Victoria Jaggard says, that’s the kind of thing that could teach us something about life elsewhere in the universe.


JAGGARD: The search for life beyond Earth is, in my mind, question number two of the top three most profound questions we can ask ourselves. Where did we come from? Are we alone? And how are we going to thrive in our future? And it, it would be a really profound moment when I think we are able to say it's possible for life to exist somewhere that is not here. We are not alone and/or we don't have to be alone anymore.



GWIN: And if you’re going to dream, why not dream big? Penny Boston and Kevin Hand are looking for microscopic things, but they’re open to other possibilities.

HAND: I also think that there is a chance that Europa's ocean could support larger organisms. Why is that? Oxygen seems to be the key to complex life on Earth and some of the calculations that we've done indicate that Europa's ocean could potentially have enough oxygen to support some of the smaller organisms that we see in our ocean like polychaete worms and jellyfish, et cetera. So I would be happy with the tiniest of microbe but, um, I hold out a bit of hope that maybe evolution has clicked even further along within Europa's ocean.

GWIN: Personally, I’m totally rooting for the giant alien squid. More after the break.

There’s so much cool information that we weren’t able to include in this episode, so if you’re in the mood to space out on astrobiology, we’ve got links for you in our show notes.

You can hear Penny Boston talk about all the ways she’s almost killed herself while caving.

You can find a report from Kevin Hand about all of the fascinating science behind the potential for life on Europa. And you’ll also find some reporting by Victoria and my other Nat Geo colleagues on the strange creatures living in the Crystal Cave. And of course, there are plenty of incredible pictures. Check it out in your podcast app.


Overheard at National Geographic is produced by Brian Gutierrez, Jacob Pinter, and Robin Miniter.

Our editor is Ibby Caputo.

Our fact checker is Michelle Harris.

Our Deputy Director of Podcasts is Emily Ochsenschlager.

Hansdale Hsu composed our theme music and engineers our episodes, with additional help from Jay Olszewski, Devin Ocampo, and Interface Media Group.

Special thanks to: NASA Ames Research Center, The Jet Propulsion Laboratory, The Clinton Presidential Library,and Galafilm.

This podcast is a production of National Geographic Partners.

Whitney Johnson is the director of Visuals and Immersive Experiences.

Susan Goldberg is our editorial director.

I’m your host, Peter Gwin. Thanks for listening, and see y’all next week.