Season 5: Episode 1

The Slime of Life

For most of our planet’s existence, the Earth was quiet. The boisterous sounds of life we know today are a recent development, one that the growing field of bioacoustics is helping us understand and interpret. In this episode, we travel to Australia to listen to dolphins and meet the microbes that helped usher in life on the planet.

Guests

Extras

Credits

Transcript

[00:00] INTRODUCTION

AMY: Hi. I know you just pressed play on this episode, but I'm about to ask you to stop listening to me. Yes, this is a strange way to start a new season of our show, I know. But this is my request—or my invitation. If you're so inclined, in just a moment please press pause and spend ten or fifteen seconds listening to whatever you can hear around you. All the voices, anything making any sort of noise at all. And then press play again. That part is crucial: please come back. OK, are you ready?

Three.

Two.

One.

SILENCE

AMY: What did you hear?

Could you hear any sounds that weren't made by people

SOUND: SLOW CRESCENDO OF HUMAN-MADE NOISE

AMY: If so, consider yourself lucky. Because human beings have become very very loud.

SOUND: NOISE

AMY: This relentless noise we make? It’s not normal. For most of our time on this planet, we humans have been very good listeners. Tuning in carefully to the movements of water, changes in the weather, the voices of other animals. 

SOUND: NOISE

AMY: But now, many of us move through our days—or even our entire lives—hearing almost nothing but the sounds of just one species.

SOUND: NOISE

AMY: Our own.

SOUND: NOISE

AMY: If the planet is a dinner party, we are the guests who are ruining the conversation. Talking over everyone, assuming that our voices are the most important ones in the room. We’re drowning out essential communication between other creatures, forcing them to spend their lives shouting to each other in order to be heard. Or worse, we're silencing them forever. 

And our noise doesn't only threaten other beings—we're endangering ourselves. We know things are out of balance. We feel isolated and cut off, because we are. With multiple ecological crises mounting around us, many of us feel desperate to help. And there is, unquestionably, so much work to be done. 

But maybe the first step is slowing down and letting the voices of our planet mates back in.

SOUND: PIED BUTCHERBIRD

AMY: What if being useful starts with being quiet?

What if saving the world begins with listening to it?

SOUND: MEDLEY OF CRITTERS AND PLACES

AMY: What changes when we remember to listen to the more-than-human-world? That’s the question at the heart of this season of our show.

MUSIC

AMY: Despite all the damage that’s already been done, there is still a vast planetary choir singing around us. It’s right there waiting for us if we turn our attention to it.

All over the world, people are hearing those voices, and responding. We are in the midst of a listening emergency, but also a listening renaissance. This season, we'll meet people who are devoting their lives to listening—reconnecting with old listening traditions, or creating new ones, and building tools that might someday allow us to comprehend what other animals are saying in ways we’ve only dreamed of in the past. 

It’s going to be a fun journey, and a fascinating one. But I'm going for something deeper than the wow factor of cool nature sounds. I chose to make this season now because I think all of our ecological crises—climate, extinction, pollution—are essentially breakdowns in relationship. And the first step in healing any broken relationship is listening. So what happens when we do that? 

SOUND: BLACKBIRD

AMY: Welcome to Threshold, I'm Amy Martin,

SOUND: BLACKBIRD

AMY: and this is season five. Hark.

INTRO MUSIC

[05:56] SEGMENt A

SOUND: boat

AMY: It's seven o’clock on a sunny morning, and I'm on a boat heading into Shark Bay—a huge marine reserve off the Western Australian coast. This is Malgana Country, one of hundreds of Aboriginal groups in Australia. In Malgana, the name of this place is Gathaagudu, which means “two waters.”

STEPHANIE: Dolphin straight ahead.

AMY: We've barely left the jetty, and Dr. Stephanie King has already spotted a dolphin. It surfaced and disappeared again in a flash, but that was enough time for her to identify it. It was a female named Gindy.

AMY: You knew who it was that fast?

LAURA: Yeah she does.

AMY: Wow.

LAURA: She's great.

AMY: That's Laura Palmer, she’s working on her PhD. And the other person with us is research assistant Amelia Clark. All three of these scientists are from the University of Bristol in the UK. Stephanie is the leader of the expedition and the current captain of the boat.

AMY: How did you know?

STEPHANIE: Because of the markings on the dorsal fin. She has an uncle who has a similar fin to her. You can see the three small nicks, the little break marks at the top.

AMY: Ah ha!

STEPHANIE: Each nick is kind of similarly spaced along the fin, almost equidistant from each other. So each dolphin has a unique dorsal fin. Like...we say like a fingerprint, but it's far more obvious than that, I guess. Like a human face. So they're very distinct. If you've been working with them a long time then you recognize all the individuals.

AMY: Shark Bay and its surrounding coastal areas are listed as a UN world heritage site, and it's easy to see why. The water is a clear, turquoise blue, and huge seagrass meadows provide food and shelter for an abundance of wildlife. Sea turtles, dugongs, and more than 300 species of fish, including the namesake sharks. But the superstars here are the dolphins. The scientists of Shark Bay Dolphin Research have been studying them continuously since 1982, making this one of the most carefully observed communities of dolphins on the planet. Stephanie is one of the current co-directors.

AMY: Do you know how many dolphins are here, roughly?

STEPHANIE: Two to three thousand. There's about eighteen hundred that we have in our catalog that we work on. And that's just in a core study area in the Eastern Gulf. There's far more than that.

AMY: And of those eighteen hundred how many of them can you identify on sight, like you just identified that in two seconds?

STEPHANIE: I've never tested myself, but maybe we could do that. I know a lot.

AMY: Like, two hundred?

STEPHANIE: Way more than 200.

AMY: When did you first come here?

STEPHANIE: I first came to Shark Bay in 2014. So ten years ago now.

AMY: And have you been coming almost every year since then?

STEPHANIE: Every year. I think 2020 was the only year because of covid. But I come every year. And it's a really important part of my...I guess just part of my life coming here. Spending time with the animals, being inspired for the next questions that we want to answer, seeing who's still around, who's had a calf, how the males are doing, who's allying with who. I think this is certainly where I'm at my most happiest, a s a field biologist. It's where I'd like to be most of the time if I could.

AMY: Stephanie studies these dolphins using every non-invasive tool she can find: drone videography, DNA sampling, and especially bioacoustics. Recording and analyzing the sounds the dolphins make.

STEPHANIE: Sound is the primary way that they communicate. And a lot of our research now is starting to uncover exactly what some of these sounds mean and how they’re used.

AMY: Bioacoustics is the name for a fast-growing field of science—or really, an approach to scientific research that's being used across many fields. Sometimes it's also called ecoacoustics, or acoustic ecology. All of these labels have slightly different meanings, but they're all based around listening to the more-than-human world. And they’re all booming right now. Over the course of this season, we’re going to meet bioacoustics researchers working with all kinds of different creatures. But we’re going to dive deep with dolphins. Pun intended. We’ll be returning to Shark Bay in several episodes, in hopes of really getting to know this team and the way these remarkable animals are using sound. Stephanie says that starts with learning about the dolphins’ world overall: their habitats, their relationships, their needs and preferences. 

STEPHANIE: So we look at behavioral complexity in bottlenose dolphins, and that can take the form of foraging specializations and to use, which is a great example of animal culture, but we also spend a lot of time looking at cooperation. This is really where my passion lies—understanding how animals use communication to mediate complex social behaviors like cooperation.

AMY: Highly social animals like dolphins, elephants, and people have special needs for communication. We make decisions together, like where to find food, or how to respond to a threat. We maintain long-term relationships that we depend on in times of need. And we pass on information to our young. All of this cooperation demands that we develop complex communication skills.

STEPHANIE: And in Shark Bay, we have male dolphins that form long term alliances. So these are really significant relationships for these animals that are investing heavily in these cooperative relationships with each other. And I'm really fascinated by the ways that they do that. So what vocal signals are they using to mediate these relationships? How do they keep track of each other? How do they coordinate their behavior? So these are all the types of questions that we aim to answer in our work in Shark Bay.

AMY: Is the cooperation that they're engaged in—how much of that is happening through sound?

STEPHANIE: It's mostly happening through sound, and that's because it's a species that lives underwater. Right. So vision is restricted because light doesn't travel that far. They have good visual acuity. They got good vision, but they don't rely on vision because they can't see that far underwater. But sound travels really far. 

AMY: Dolphins use other forms of communication too, of course.

STEPHANIE: They can be quite tactile with each other, so they'll spend time petting and rubbing each other. And that's a way of reaffirming or establishing or maintaining relationships.

AMY: But Stephanie says sound is central.

STEPHANIE: They use sound for all important aspects of their life—to navigate their environment, to find food, and importantly, to communicate with each other. So it's their primary modality. It's sound. It's not vision, it's not gestures. And by sharing information through vocal signals, they can let each other know where they are. Maybe if they plan to move, if they want to reunite, this type of information.

SOUND: BOAT

AMY: When I visited them in May of 2023, they were just getting started for the year. Amelia, who goes by Millie, is a recent master's graduate, who's here to get experience as a research assistant. Laura is a PhD student, collecting data for her thesis work.

LAURA: This is my first time in Shark Bay, so I've only been here a week now. We've had lots of amazing days on the water, so certainly very lucky. It was a good time to come.

AMY: Laura and Millie are under some pressure, because they only have a few weeks with Stephanie. Then she has to leave, and they'll do everything on their own. One of the key things they need to learn is how to take a survey of every dolphin they meet.

STEPHANIE: By survey I mean we photograph the group and we stay with them for at least five minutes, and we write down their predominant behavior. So are they socializing, traveling, resting. And then we look at who are they with. And by doing that throughout the season over multiple years—and we've been doing it for 40 years now—we have this incredible picture of who associates with who, who has strong friendships, which dolphins avoid each other. And we can map the social network if you like. And we can look at the structure, and maybe link some of that information to fitness measures. Like, does being more sociable mean that you're more successful and you have more offspring, for example?

STEPHANIE: You got dolphins Laura?

LAURA: No, not yet. But there's splashing basically at zero degrees.

AMY: While I've been peppering Stephanie with questions, Laura and Millie are scanning the water for anything that looks remotely dolphin-ish. Laura said she saw some splashes at zero degrees, meaning straight ahead, so she moves to the bow of the boat to get a better look.

STEPHANIE: If we see splashes, we'll check just to make sure it's not dolphins foraging. Anything that looks like it could be a dolphin or indicate dolphin behavior, we'll check with the binos and maybe even go a bit closer.

AMY: I quickly got obsessed with dolphin spotting myself—which was a little dangerous. Stephanie told me that if someone says they see a dolphin and it turns out to be a bird, they have to bake something for the rest of the group back at the research station.

LAURA: (from a distance) Yeah. Yeah.

STEPHANIE: Yeah?

AMY: But then Laura calls from the bow—there's definitely dolphin activity up ahead.

AMY: We're in business!

MUSIC

AMY: The dolphins are constantly in motion and they are fast. Stephanie needs to move us quickly or we'll lose them. But she also want to maintain some distance, so we don't disturb them. It's a bit of a dance to find that just-right spot.

AMY: Ooo I just saw a fin!

AMY: Everyone has a job to do. Stephanie is in the captain's chair. Laura will try to get clear photographs of every dolphin we see. Millie will write down notes. And I'll just try to stay out of the way.

STEPHANIE: We have Zeppelin and Blimey.

AMY: Hands on the steering wheels and eyes on the water, Stephanie calls out the name of each dolphin to put into the notes.

STEPHANIE: Z-E-P, and B-L-M. Yeah, you got them!

MILLIE: (quiet laugh)

LAURA: (off mic) Good work.

STEPHANIE: They might come again they're still just beneath the surface. Coming up, maybe, coming up, yep…

AMY: (laughter) They're so close!

AMY: Stephanie is mindful of keeping some distance, but the dolphins aren't as concerned about the rules. They swim close to the boat, zipping around and seeming to check us out. When they swim over dark patches of sea grass, they can all but disappear. And then all of the sudden they pop up again to grab a quick breath.

STEPHANIE: Coming up!

AMY: (laughter)

AMY: Even though I can see them coming, it's delightfully startling every time they crest the surface. These are Indo-Pacific bottlenose dolphins, smaller than some other species, but still – big. They average around two-and-a-half meters long, or more than eight feet, with a maximum weight of about 230 kilograms, or around 500 pounds. But their bulk doesn't limit their grace. It's hard to call what they do swimming. It looks more like dancing, or flying. Their smooth, shiny bodies roll past us in a heartbeat, as Laura tries to get a clear portrait of each.

LAURA: I'm going to try to get Blimey one more time.

AMY: As if she heard Laura's request, Blimey pops up and looks right at us, and Laura presses down on the shutter.

LAURA: (laughing) Thanks Blimey!

AMY: (laughing)

LAURA: Cool!

AMY: With the visuals taken care of, it's time to move on to sound.

AMY: So Laura's pulling out her recorder, plugging in the hydrophones.

AMY: A hydrophone is just a waterproof microphone attached to a long cable. This team has four of them. As Laura gets everything connected and ready to record, Stephanie keeps the boat following the dolphins from a distance. They seem to be on the move toward something—or someone.

STEPHANIE: We have another dolphin up ahead, I think it's Juicy. Blimey's on the bow. Hey guys! Both on the bow.

AMY: Oh, wow. Right under the surface.

AMY: And then they're gone again. It's shocking how quickly a group of five-hundred pound animals can just disappear.

SOUND: WAVES

AMY: The four of us stand in the boat, looking in four different directions. Waiting. Watching. We know they're nearby. But we don't know exactly where or when they might pop back up to take a breath.

SOUND: WAVES

AMY: Stephanie uses the temporary pause in activity to look over Millie's notes and tell her what needs to be added.

STEPHANIE: So the five minute information would be travel—there are two other animals here.

AMY: They're back. Stephanie interrupts herself to call to Laura, telling her that Juicy is not the only dolphin that has joined this group. There's another one, so far unidentified. Then, she quickly turns back to Millie.

STEPHANIE: Ahh... travel regular, ah regular, straight, slow, tight.

MILLIE: Ahm, regular, straight…

AMY: There's a lot happening all at once, with dozens of these teachable moments every hour. Stephanie has to find a balance between making sure the data get collected correctly and giving the younger researchers freedom to do things themselves.

LAURA: Ok, so there's just going to be cables running around the back here as well.

AMY: OK.

AMY: Laura is about to start recording.

STEPHANIE: Blimey just ahead. Juicy's here.

LAURA: Yeah!

AMY: So are there four here?

STEPHANIE: Yes. So that's Juicy. She's got a really gnarly peduncle, like an old shark bite wound, makes it very scarred.

LAURA: Love Juicy. Juicy showed up on a few days now, she's becoming a firm favorite.

AMY: How old is she, roughly?

STEPHANIE: Juicy was born in 2001. So she's about 22 years old, and her calf is about three and a half. She's still quite young, you know.

AMY: Yeah. Twenty-something.

(laughter)

AMY: Oh wow, three just all came up.

AMY: Young dolphins like this calf, named Jungle, usually stay with their mothers for around four years. At first they depend on mom for milk, but even after they're weaned, they usually stick around, perfecting their hunting skills, and learning how to fit in to dolphin society. I can't help but notice some parallels between the animals in the water and us humans up in the boat. All together, we're a total of eight mammals, working in two teams, using acoustic communication to learn from our leaders.

SOUND: speaker crackling on, dolphin sounds coming through for the first time

AMY: And then, for me, came one of the more magical moments of this experience.

SOUND: DOLPHIN BUZZES

AMY: You have a speaker!?

LAURA: Yeah yeah.

AMY: So we're hearing the hydrophone!

AMY: Laura has flipped on a speaker in the boat, so we can hear in real time the conversations the dolphins are having in the water around us. Suddenly, we’re with them in a completely different way.

SOUND: DOLPHIN BUZZES, WHISTLE

LAURA: Yeah!

STEPHANIE: Whistle.

LAURA: Eeee!

SOUND: DOLPHINS

LAURA: Oh, I love these guys!

AMY: I'd heard recordings of dolphins before this trip, and you probably have too. But this was the moment that I learned the enormous difference between hearing a random recording of some anonymous dolphins and being with actual living individual creatures and hearing their voices as they fly through the water all around me.

SOUND: DOLPHIN buzzes

STEPHANIE: Juicy.

LAURA: Juicy. Juicy is at 230 degrees.

SOUND: DOLPHIN whistles

STEPHANIE: That might be the calf!

LAURA: Woo-hooo!

AMY: That high-pitched, swoop is called a whistle, and it's one of the most important sounds in dolphin communication. Laura is overjoyed to hear it, because whistles are at the center of her research for this trip. She wants to learn more about how they are  used between mothers and calves—like Jungle and Juicy are doing right now.

LAURA: Juicy at 20 degrees. With calf in BP.

AMY: BP stands for “baby position,” meaning right next to mom and moving in tandem with her. It's a quick way of noting how the dolphins are grouped and relating to each other.

AMY: This is so cool, you guys, it's making me cry!

ALL: Ohhh….

AMY: It's so amazing!

LAURA: I could cry with joy as well. This is a great recording for me!

AMY: I brought my own hydrophone on this trip, and I’m eager to get it into the water. But soon, this group of dolphins disperses, and Laura pulls her gear back up into the boat.

AMY: What do you call those kinds of sounds, that uhh…..

LAURA: Oh, so they were buzzes. So when they're foraging, it's very rapid, right. Echolocation. They're basically using it to gain a lot of information on their environment. Right. And potentially the prey items that they're tracking. We've also heard a lot of whistles, which are predominantly social signals as well. So it's likely they're communicating with each other or, you know, potentially the other animals that we've initially saw but are not with us right now.

AMY: We head off to a new spot across the bay, and as the boat picks up speed it's harder to talk, so I settle in and watch the waves for a while. This team has been gracious enough to let me tag along for several days, so there will be time for more of my questions later. And I have a lot of them. I want to know everything about these whistles—what they mean, why they matter. I want to ask Stephanie a lot more about these male alliances that she’s studied, and how they use sound. But right now, it’s time to take a deep breath, and appreciate where I am, and what I’m getting to witness.

AMY: I don’t have to understand it all to know that I have just been visited by wondrous beings. Creatures full of beauty and power and intelligence. And they’ve survived on this planet for millions of years by listening to each other.

AMY: We’ll have more after this short break.

Break

[25:18] SEGMENT B

AMY: Welcome back to Threshold, I'm Amy Martin, and for the rest of this episode, we’re going to do some time travel. We’re going back to a world long before dolphins, before dinosaurs, before there were any animals, or plants.

MUSIC

AMY: If we could transport ourselves back to the very early Earth, we would find a barren world, blanketed in toxic gas. The atmosphere had almost no oxygen in it. There was no life at all.

SOUND: KALAMARK ICE

SOUND: TWO MED THUNDER

AMY: The only thing making sound was the planet itself: storms, earthquakes, ocean waves, volcanoes.

SOUND: BRUBOODJOO WAVES

AMY: And that’s how things were for a really long time. The Earth is around four-and-a-half billion years old, and for about 90 percent of those years, nothing existed that was capable of intentionally making a sound, or receiving it.

SOUND: IOWA THUNDER

AMY: So how did we get from that world to this one? How did the Earth transform itself from a place of such unfathomable quiet into a nonstop symphony of sound? We're going to spend the rest of the season telling that story, tracing the sonification of the Earth roughly in the order in which life evolved. It all started with a silence too long for us to truly comprehend—but I wanted to try. And it turns out one of the best places to do that is just down the Western Australian coast from where I met the dolphin researchers.

SOUND: driving

SOUND: van door closing, chiming wedgebills in Hamelin Pool parking lot

AMY: OK, I'm just in the parking lot—

SOUND: RAVEN, Crawww craww crawww!

AMY: Pardon me. I'm just in the parking lot for the Hamelin Pool.

AMY: I leave behind one talkative Australian raven and a small flock of chiming wedgebills, and walk the short distance out to the edge of Hamelin Pool—a big bay with a surface smooth as glass.

SOUND: walking

AMY: I just want to try to listen here for a little while.

AMY: The water is so still. There's not a ripple, there’s not a…there's no birds landing on it. There's no bubbles or any sign of movement.

AMY: It’s early, and I’m alone. But those aren’t the only reasons this place is so silent. Hamelin Pool has an inner stillness. It’s extremely salty—twice as salty as the open ocean—which means it's hard for plants and animals to survive here. And against this canvas of quiet, every sound made by a living thing pops out.

SOUND: peep

AMY: A bird peep,

SOUND: buzz

AMY: a fly buzz.

AMY: For most of our planet's history, this kind of silence reigned supreme.

MUSIC

AMY: Just think about the entire Earth being that quiet. There was nothing. Breathing. Flying. Walking. Crawling. A whole planet with nothing that had a voice.

AMY: But although Hamelin Pool may be a profoundly quiet place, it isn’t actually as lifeless as it seems. There’s a lot of mysterious blackish gunk carpeting the beach in front of me, almost like a bathtub ring of slime growing where the water meets the shore. These are communities of microbes—they go by sexy names like gelatinous microbial mats or pustular sheets. And they built a bridge between the barren early Earth and the lush, loud, fruitful world we enjoy today.

MUSIC

AMY: Ancient microbes were the inventors of what is arguably the most important technology of all time: photosynthesis. A couple of billion years ago, they started to tap into the Sun's energy and produce oxygen. And that changed everything. Bit by bit, they pumped that oxygen into the sea…

ERICA: You know, and after a while, then all that oxygen created by photosynthesis from microbes eventually saturates the ocean, the ocean can't hold any more. Where does the oxygen go? It goes into the atmosphere.

AMY: This is Dr. Erica Suosaari.

ERICA: The atmosphere becomes oxygenated, which essentially that allows for evolution, which then...here we go. And finally you get to us.

AMY: The slimy mats I saw growing at Hamelin Pool were microbes still performing these ancient rituals—doing the work that led to all other life on Earth. They don’t look like much at all, but they hold the origin story of every call, cry, squawk, or song ever heard. 

ERICA: This is a living system, still doing this, still doing these same processes that were happening billions of years ago. That is...there is no place else on the planet that represents that in its entirety. It is really this window into the ancient.

AMY: I'm curious about you. What stage in your development did you realize. 'I really want to learn a whole lot more about goo?

ERICA: I guess technically I'm a marine geologist. I'm a carbonate sedimentologist, but I look at marine rocks.

MUSIC

AMY: Erica is based at the Smithsonian Institution's National Museum of Natural History in Washington, D.C. She first visited Hamelin Pool while working on her PhD, and she was so blown away by the glimpse it provided into the early Earth, that she moved to Western Australia and lived close by for several years, just so she could continue studying the place.

ERICA: So I have sort of this obsession with time. I've always had this obsession with time and kind of infinity and what it means, and the big picture, and how significant our lives are and what we do, because the time is so... big. And so I've just always been like fascinated with that. It's like figuring out the puzzle of what life means on huge scales.

AMY: And key pieces of that puzzle can be found in these communities of microbes at Hamelin. Erica is one of the world's leading experts on them, and the stony structures they create, which are called—

ERICA: Microbialites, which are basically rocks created by microbes.

AMY: We don’t tend to think of microbes as creating anything. Except infections maybe. But at some point, way back in time, they started to make rocks: clotted thrombolites, branched dendrolites, and layered stromatolites.The world's oldest fossilized stromatolites, found in Western Australia, are almost three-and-a-half billion years old. And the microbes at Hamelin Pool are still making these rocks today. It’s the largest known collection of living marine stromatolites in the world.

ERICA: What Hamelin represents is...is...I don't even have a word for what Hamelin represents. It's just...it's is a really spectacular place. It's a living laboratory.

AMY: The stromatolites are kind of like the Machu Picchu or Egyptian pyramids of the microbial world—structures made by communities of living things with a story to tell. They grow close to the edges of Hamelin Pool in the shallow water, maybe a foot or two high. Some of them look a little bit like toadstools, others resemble stubby fingers, or brainy mounds. But whatever form they take, there’s something about them that signals life—you can see familiar organic patterns in them, you can sense that they grew. And this is how it all began. Even though the microbes themselves are very quiet, without them, there would be no voices to speak, or ears to listen.

AMY: Erica says one of the essential ingredients in this process is a coating the microbes make and cover themselves with.

ERICA: It's called EPS, it's exo-polymeric substance.

AMY: Exo-polymeric substance. I asked her to translate that into non-sciencey language.

ERICA: It's….the slime of life. You know...it's like a...it's a goo. (laughter)

AMY: (laughter) It's a goo. We've got a microbe that makes a goo.

ERICA: Yeah. (laughter)

AMY: As sediment in the water floats by, some of it sticks to this goo, kind of like dust sticking to flypaper. It builds up layer after layer into stone.

ERICA: And you build up, kind of this laminated structure. So that's a stromatolite.

AMY: The EPS can actually do all kinds of cool stuff. It helps the microbes communicate with each other. It acts as a sunscreen. It even changes the chemistry of the water, which helps in the stromatolite-building process.

AMY: So it's a self-produced goo that does chemistry.

ERICA: Yes. Or has chemistry happening, yeah, all around it.

AMY: U-huh, OK. There's like, a lot going on.

ERICA: Oh, yeah. There's a lot going on.

AMY: I like to think of these microbial communities as the world's first cities, with the bacteria in them bustling around, working as architects and engineers, carpenters and chemists. They farmed sunlight, and produced oxygen—the oxygen that led to me, talking to you, right now.

ERICA: These lineages of bacteria, life persisting for billions of years.

MUSIC

AMY: While everything changed around them, again and again and again, these microbes carried life forward, passing it on and on and on, one generation after another.

ERICA: It's not a timeline that I still think I can wrap my mind around. But I find it sort of comforting that there is this long stretch of time that these rocks represent, and I am drawn to that.

MUSIC

AMY: What do you think the world sounded like when the only living things were these microbes?

ERICA: (deep breath) Crashing waves. I don't know. A lot of water. But underwater...there's something about silence. I can't imagine. I mean...silence. What does that sound like, for oxygen bubbles to rise to the surface, crashing waves... Kind of meditative and calm, which is crazy, because it's a time in Earth's history where it's very chaotic and...and yet, you know, there's like, the kind of peace that life brings.

AMY: As I stood on the beach at Hamelin Pool, I tried to imagine more than three billion years of that silence. Eons of ear-splitting emptiness.

MUSIC

AMY: And then, finally, the planet began to sing. 

SOUND: CREATURES

AMY: Every song or call or cry made on Earth happened in just the last tenth of the planet’s existence. The cacophony of life that we take for granted is actually exceptional—silence is the norm on our planet. Or any planet that we know of. Erica's work is being used in the search for life on Mars, and maybe someday we'll receive communication from some extraterrestrial being. But so far, we Earthlings are singing together into the void. The only voices we've ever heard are each others’.

CREDITS

AMY: This episode of Threshold was written, reported, and produced by me, Amy Martin, with help from Erika Janik and Sam Moore. Music by Todd Sickafoose. Post-production by Alan Douches. Fact checking by Sam Moore. Special thanks to Tim Lamont and Miles Parsons. This show is made by Auricle Productions, a non-profit organization powered by listener donations. Deneen Wiske is our executive director. You can find more about our show at thresholdpodcast.org