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See the Ugly Beauty That Lives in a Toxic Cave

Norman Pace collects samples of a microbial mat.
Microbiologist Norman Pace collects a sample of a brainy-looking mat made of microbes (called a vermiculation) that coats the ceiling of Sulphur Cave.
Photograph by Norman R. Thompson

Lurking below the quaint ski town of Steamboat Springs, Colorado, lies a cave belching deadly gases. Its ceiling is dotted with snottites, dangling blobs that look like thick mucus and drip sulfuric acid strong enough to burn holes through T-shirts. And the whole place is covered in slime.

So why would anyone want to go there?

“Being in the cave reminded me of being inside a huge organism—as if I had been swallowed by some gigantic, alien monster from deep in the ocean or from outer space,” says photographer Norman Thompson.

Thompson joined a small group of scientists who are among the few people to ever explore Sulphur Cave, and who found it eerily beautiful, and brimming with strange life. As shown in National Geographic’s exclusive video below, along with spiders and insects, the cave holds sulfur-breathing microbes and a new species of blood-red worm.

EXCLUSIVE VIDEO: Clumps of newly discovered blood-red worms thrive in Sulfur Cave, which contains levels of toxic gases so lethal that any human who enters unprotected could quickly die.

“In a sense, we really were inside of an organism,” Thompson says, “or perhaps more accurately, an ecosystem. Because the cave is a colony of organisms, living together in a lightless ecosystem, powered not by sunlight, but by the sulfur coming from deep within the Earth.”

Inside the Belly

To enter the 180-foot-long (54 meters) cave, the intrepid scientists had to squeeze into a pit entrance, a hole in the ground that skiers might glide right past. And if you happen to visit without special equipment, you ought to glide past. Otherwise, the cave’s gases could knock you unconscious in a jiffy.

“It’s sort of foreboding,” says David Steinmann, a cave biologist at the Denver Museum of Nature and Science. “You have to climb and crawl down a wet muddy slop that’s stinky and smells like rotten eggs.”

A snottite found in a sulphur cave.
Snottites are thick, mucus-like blobs formed by bacteria growing in a sulfur cave.
Photograph by Norman R. Thompson

“It’s belching toxic gases,” Steinmann says, “and in the winter you can see steam coming out. You have to stoop down and squeeze through to get into the first room. Once you’re in there, it’s totally dark.”

But when the team brought in lights, they found that the cave is also lovely, in its own way. Crystals made of gypsum glitter on walls, and a small stream washes across the floor. Long tendrils made of more microbial colonies wave in the water’s flow.

Thompson photographed the cave twice, entering only after scientists had aired out the crevice using large fans—appropriately, the kind normally used to flush out underground sewers. “Even with the poisonous air flushed out by the fan, the cave still stunk of sulfur,” he says.

Such sulfur-filled caves are rare, with some found in Mexico and Italy. The high levels of sulfur that create the gas in Colorado’s Sulphur Cave come from deep within the earth. The cave is formed in travertine, a type of stone formed by deposits from streams and mineral springs.

Hydrogen sulfide gas, which gives the cave its rotten-egg smell, can be deadly at high concentrations. Yet life thrives inside the cave despite both the hydrogen sulfide and carbon dioxide up to four times levels that could kill a human.

Wormy Wonders

The biggest surprise was the blood-red worms found in the cave. “There’s a hell of a lot of worms in there!” says Norm Pace, emeritus professor of microbiology at the University of Colorado Boulder.

Worms in Sulphur Cave, Steamboat Springs, Colorado. These worms are believed to live on the chemical energy in the sulfur in the cave, similar to the way tube worms live in a world without light at the bottom of the ocean. Also visible on the left side of the image are streamers—colonies of microorganism, similar to those seen in hot springs in Yellowstone National Park. Photograph by Norman R. Thompson
These worms in Colorado’s Sulphur Cave are believed to live on the chemical energy in the sulfur in the cave, similar to deep-ocean tube worms. On the left are streamers—colonies of microorganisms similar to those in hot springs in Yellowstone National Park.
Photograph by Norman R. Thompson

The small worms live clumped together on the cave floor, where they’re probably making a living by grazing on the bacteria growing in wet spots, Pace says.

They’re also intensely red, much like the famous Riftia worms found at deep-sea vents, which are also rich in hydrogen sulfide. Pace has studied life in the vents and expected the cave ecosystem to be similar. It wasn’t, exactly. The ocean worms have special structures called trophosomes filled with bacteria that are able to live on hydrogen sulfide; essentially they “breathe” it. The worms rely on the bacteria to do this, so Pace was surprised that so far, the team hasn’t found a special home for bacteria inside the Sulphur Cave worms.

As for the cave worms’ bright red color, it probably comes from high levels of hemoglobin and related compounds that protect the worm from hydrogen sulfide. Steinmann and his colleagues described the worms this year in the journal Zootaxa.

They named it Limnodrilus sulphurensis, in honor of the sulfur that powers the base of the food chain in this otherwise deadly environment.

“It took over a year for the sulfur smell to gradually air out from my cave coveralls,” Thompson says. But would he go back? He’s still drawn by its strange beauty he says, so yes— “in a heartbeat.”


Correction: The cave is 180 feet long, not deep. This has been updated, and I  deleted a sentence about organic matter in the cave’s travertine—the cave’s sulfur comes mainly from geothermal activity, with microbial breakdown of organic matter as an additional, but minor, source. A clarifying sentence has been added. —EE (updated 6/15)

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Look Up! There’s an Invisible Zombie Highway Right Above You

Step outside on a clear day this summer and look up.

What do you see? Blue. Nothing more. Or so you think.

But surprise! In July and August, an enormous herd of animals is passing directly over our heads. There are so many creatures up there, creatures that are so busy, so athletic, so tiny, so invisible. I’m talking about three to six billion of them every month soaring through the air directly above us. You should meet them. They are insects. High-flying insects. When I read about them in a science paper five years ago (I was at NPR at the time), I made this video, which provides a short introduction:

And now for the update.

It turns out, as you just saw, that the highest flying insect made it to 19,000 feet above sea level. That’s almost the height of Mount McKinley in Alaska. But more recently scientists have found another, even higher zone that’s also home to live critters that soar way, way up—miles higher, to the upper edge of the Earth’s atmosphere.

They are Earthlings that spend days, even weeks, practically in outer space.

What Are They?

According to David J. Smith and his team at the University of Washington and Kostas Konstantinidis and his team at Georgia Tech, there are thousands of species of very small, simple Earth life—bacteria, fungi, viruses—that get swept up by storms and make it to where there’s hardly any oxygen, where the temperatures are fiercely cold, and where they’re no longer protected from solar radiation by the Earth’s ozone layer.

And yet, write Peter Ward and Joe Kirschvink in their new book A New History of Life, most of these microbes will eventually come back down to Earth no worse for wear. They’re teeny. You can’t see them without a microscope. Typically, it would take almost 40,000 of them laid end to end to make it around your thumb.

Drawing by Robert Krulwich
Drawing by Robert Krulwich
Drawing by Robert Krulwich

But there are lots of them up there, so many that Ward and Kirschvink say this zone is becoming “the most newly discovered ecosystem on Earth,” a vast territory (many, many times greater than our oceans) where microbes routinely spend time dancing in the air.

Drawing by Robert Krulwich
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Some bacteria have been in this high zone so regularly or for so long that they’ve adapted to life in the sky. Some species develop pigments that mimic sunscreen; some, says the New York Times, feed only on cloud water; and some can reproduce within clouds.

Drawing by Robert Krulwich
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Scientists call this new family of creatures-in-the-sky “high life,” and it is a biological zone with its own rules. Up there is not like down here.

How Do They Survive Up There?

For one thing, scientists differ about how microbes at the upper end of the zone stay alive. When deoxygenated and freezing, do they slow way, way down like a hibernating bear? Or do they go dormant and essentially suspend their lives until they return? Or, as Ward and Kirschvink suggest, do they spend a brief period being dead?


This is one of the most provocative passages in Ward and Kirschvink’s book. “Most of us would agree,” they write, “that for mammals, and perhaps all animals, dead is dead.” You don’t come back from “dead.” But then they go on:

“… in simpler life, such is not the case. It turns out that there is a vast new place to be explored between our traditional understanding of what is alive and what is not.”

What if, in this new airy realm high above the planet, there could be “a place in between,” where bacteria might take wing, arrive in that freezing, irradiated zone, lose their life-giving machinery, and then, somehow, on the trip back down, build it back again?

Ward and Kirschvink are both well-respected senior scientists. Ward studies mass extinctions, Kirschvink magnetofossils. Neither is given to overstatement, which is why when I hit this line in their book, I put down my copy, stared out the window and thought, What?

How can anything be undead?

In the chapter I was reading, Ward and Kirschvink explore how life came to be four billion years ago. They suggest that instead of a single Genesis-like event (a bag of inert chemicals suddenly sparks into living chemistry), maybe “in the beginning,” chemistry switched back and forth, sometimes alive (on), sometimes not (off), and maybe, just maybe, in the simplest creatures, this may still be a habit—in fact, it may be happening to this day. Very simple creatures high in the sky, they say, might be alive, then not, then alive again, or as they put it:

“Life, simple life at least, is not always alive.”

Woah! This is a new idea to me. I tried to talk more with Peter Ward, but he’s in Papua New Guinea doing ocean research in a dugout canoe and doesn’t have a good internet connection, and Kirschvink is not answering email at Caltech, where he teaches. But I’m curious: Have any of you readers bumped into this notion? Life de-animating, then reanimating? It seems wonderfully preposterous—and very intriguing.

Let me know …

Peter Ward and Joe Kirschvinck’s new book “A New History of Life: The Radical New Discoveries About the Origins and Evolution of Life on Earth” goes after the hardest questions in life’s history, how did we begin, how simple life grew more complex, the origin of sex; they attack these puzzles carefully, feasting on the latest and especially the wildest research, so if you want an up-to-date primer guaranteed to keep your inner-college-sophomore up all night arguing, binging on ideas, going “no way”—this is a pretty good book. I also relied on David Montgomery and Anne Bikle’s “The Hidden Half of Nature, The Microbial Roots of Life and Health,” to get my head around itty bitty bits of life, the fungi, the bacteria, the archaea, the viruses, the protists. Their book took me into intestines, soil, and, yes, to the sky. It comes out in November. Also, my artist for the video, Benjamin Arthur, is about the most elegant, sly, multi-talented illustrator around; give him a tale, he’ll give you a perfect look to tell it with. Each of our ventures has a completely different visual style. Check out Why Can’t We Walk Straight? Last year he even turned in a piece (not with me, alas) on microbes. You can find it here.

Editor’s Note: This post has been updated to correctly reflect the spelling of Anne Bikle’s name.

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Noah (and his ark) Updated, Improved for Our Time

Instead of the Noah you know, the one who built the ark, sheltered all those animals, sailed for 40 days and 40 nights and got to see God’s rainbow, instead of him, I want you to meet a new one. An updated version.

This Noah shows up in a tough little essay written by Amy Leach, of Bozeman, Montana, who knows her science, knows there’s a flood coming—a flood of humans, seven billion and counting, already swamping the Earth, crowding the land, emptying the sea, and her more modern Noah—informed, practical, not inclined to miracles—has a different plan. He announces,

water color painting with text reading ''unfortunately, animals. we are not going to be able to bring all of you with us this time.''
Illustration by Robert Krulwich

The old Noah, you may remember, squeezed eight humans (wife, kids, their spouses) and at least two of every critter, big and small, onto his crowded ship. But the new Noah, being more practical, feels he can winnow a little. “Everybody” is a lot of animals, more than you know. Back in the day, Amy Leach writes,

pink watercolor background with two drawings of frogs peeking up over the text, which talks about what it would be like to bring two of every creature onto noah's ark
Illustration by Robert Krulwich

And, honestly, (I’m thinking to myself), if the world lost a scorpion or two, would anyone notice? Or want them back? And blotchy toads, biting little flies—some animals are hard to keep going on a tight, crowded ship. On the last voyage, dormitory assignments were beyond difficult.

And all those supplies? Amy Leach writes how the first Noah would have had …

a yellow watercolor background covered with text about collecting food for animals
Illustration by Robert Krulwich

This doesn’t mean we don’t care, new Noah says to the animals. We definitely, absolutely want to bring a bunch of you with us. But, we’ve got to be practical.

Even if our ark has grown to the size of a planet, carrying everybody through is not going to be logistically possible, which is why, he says,

blue watercolor background with black text on it about being in charge of a future noahs ark where not all animals are included
Illustration by Robert Krulwich

And anyway, that first Noah? He lived in a different age, a time they call the Holocene, before humans began to dominate and crowd out the other species. Back then, there weren’t as many people. And there were more kinds of animals, closer by, hiding in the woods, clucking in the yard, so the world was more various then, more intimate, more riotous, and thinking about it (a little wistfully, if only for a moment), the new Noah quietly recalls that on that first ark …

yellow watercolor background with text on top related to how noahs ark would be different today than it was in the Old Testament
Illustration by Robert Krulwich

And now, animals, it’s time for many of you to step away. You’ve had your unruly eons. They were wild, unplanned, noisy, great fun. Natural selection ran the world. Crazy things happened. Those were good times, Amy’s essay concludes …

blue watercoor with black text on top that reads''But the future belongs to us.''
Illustration by Robert Krulwich

Amy Leach is a writer living in Bozeman. Her collection of very short pieces—about jellyfish, beaver, salmon, plants that go topsy turvy and stand on their heads—are collected in a wonderful little book called “Things That Are.” In this column I do to Amy what the new Noah is doing to our planet: I edited her down, sliced, diced, slimmed (lovingly, I hope), trying to give you a taste for her fierce, crazy prose. But like the planet, she’s wilder in the original, so I hope you go there and sample the unedited version.

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An Alien Origin for Life on Earth

This is the second of three blog posts associated with this week’s episode of Cosmos: A Spacetime Odyssey, which addresses life in the universe. Read the first one here.

Whether the universe is filled with alien beings who wish upon stars, struggle to understand the subatomic realm and argue over who’s paying for dinner is not yet known. We’re looking for them.

But in the search for life, there’s another fundamental question that has gone unanswered for millennia. Step one in the development of any civilization is life itself. How, exactly, does life get going?

“The essential message of life has been copied and recopied for more than three billion years,” says Neil deGrasse Tyson, on this week’s episode of Cosmos: A Spacetime Odyssey. “But where did that message come from?”

Even on Earth, the origin of that on-switch is murky. We don’t know how a pile of organic molecules, their atoms arranged in intricate rings and bridges, gained the ability to survive and replicate, to wall themselves off from a young Earth’s iron-rich seas and oxygen-free air.

Some ideas suggest that life’s first gasp came from shallow ponds, warmed by a sun still in its childhood; others point to bubbling hot springs, clays, ice, or to warm, energy-rich vents erupting from the deep ocean floor.

For decades, scientists have tried to replicate the planet’s primordial recipe for life. They’ve mixed salty brews, spiced them with metals and smelly gases, and jolted the mixes with electricity, or sunlight, or heat, then reset the timer and started all over with a new handful of ingredients and instructions. These experiments have taught us a lot. Among other things, we’ve learned that amino acids are sort of easy to make from scratch, that complex metabolic pathways can emerge from a seemingly random mix of ingredients, and that single-stranded, ribonucleic enzymes can replicate themselves indefinitely.

But none of these experiments have produced the secret sauce that sparked the first single-celled organisms. Each time, when the oven timer chirped, there was no life.

Enter: Another theory that’s been simmering for years (millennia, even). What if, it asks, instead of being baked from scratch on Earth, life came from the stars?

“If life can withstand the hardships of space, and endure for millennia, then it could ride the natural interplanetary transit system from world to world,” Tyson says. “What this means is that life doesn’t have to start over again.”

Illustration of the 1833 Leonid Meteor shower. Could meteorites have carried life to Earth? (Edmund Weiss/Wikimedia)
Illustration of the 1833 Leonid Meteor shower. Could meteorites have carried life to Earth? (Edmund Weiss/Wikimedia)

Called panspermia, the theory suggests that organisms hitchhiking from one world to another can spread the organic seeds of life throughout the cosmos. Launched into space aboard blasted out bits of planetary debris, these space-faring life-forms could, upon arrival at an alien planet, survive and thrive – perhaps evolving into spiders, sharks (or spidersharks?), dandelions and elephants.

Obviously, no one knows whether panspermia actually happens. For years, the idea failed to gain strong scientific traction. But recent pieces of circumstantial evidence suggest that in some environments, such as the inner solar system, versions of panspermia aren’t so farfetched.

For starters, fragments of other planets have made their way to Earth. We have pieces of Mars and Mercury (maybe), and (probably) Venus on our planet. Pieces of Earth have undoubtedly made their way to our neighbors. This exchange of crusty planetary material, if it harbored the right kind of hardy organism, could conceivably transfer life from one world to the next, says astronomer Caleb Scharf of Columbia University.

“I’d say that a plausible, but entirely unproven, mechanism exists for the transfer of viable organisms,” Scharf says.

There are creatures on Earth that would probably consider an interplanetary trip a worthy challenge. Take tardigrades, for example, the tiny, tough invertebrates that have survived 10 days in space. Lichens have survived the same freezing vacuum for more than two weeks. Some microbes, like Deinococcus radiodurans, are especially tolerant of the levels of radiation they’d likely encounter during a trip to Mars. And organisms frozen for centuries beneath the ice in Antarctica have been revived in labs.

“We have no reason to believe that some microbes can’t survive interplanetary journeys inside of meteorites,” says astrobiologist David Grinspoon of the U.S. Library of Congress.

But, he says, spending two weeks in space and living to tell the tale is different from crash-landing after a decades-long interplanetary voyage and setting up shop in a new world. It isn’t enough to simply arrive – organisms have to thrive.

“We tend to separate the possibility of exchange of viable organisms between planetary bodies and the possibility that they can ‘seed’ a world,” Scharf says. “It’s just not clear that even the hardiest Earth microbes, dumped supersonically onto Mars (for example), are going to get a foothold. The Martian surface is nasty for terrestrial biology.”

Interplanetary panspermia as a dispersal mechanism seems fairly plausible, then, if unproven. Is it possible that young Earth, Venus, and Mars traded life-forms for a few hundred million years? (See Scharf’s treatment of a panspermic paradox here.)

Cosmos also introduced the idea of interstellar panspermia, which magnifies all the challenges associated with the inner solar system’s planets playing meteorite ping-pong. In other words, it’s a bit trickier to transport life from stellar system to stellar system. Distances are much greater, and the time it would take for a meteorite bearing life-forms to arrive on another world is substantially longer. To some scientists, it seems unlikely that such a thing is possible.

“Eventually, cosmic radiation would shred the genetic material beyond any ability to self-repair,” Grinspoon says.

On the other hand, he notes, stars are born in clusters. And at the age when young stars are busy assembling their planetary systems, the distances between them are much smaller. Our solar system would have exchanged material with these systems, Grinspoon says. Perhaps it’s during this period of stellar infancy that stars stud their sister systems with seedlings.

And there’s a third version of panspermia waiting in the wings, one proposed by Francis Crick and Leslie Orgel in 1973: Directed panspermia, or the idea that intelligent beings intentionally send life to other worlds.

“It now seems unlikely that extraterrestrial living organisms could have reached the earth either as spores driven by the radiation pressure from another star or as living organisms imbedded in a meteorite,” they wrote. “As an alternative to these nineteenth-century mechanisms, we have considered Directed Panspermia, the theory that organisms were deliberately transmitted to the earth by intelligent beings on another planet.”

But the pair concludes that there’s feeble evidence supporting the deliberate seeding of Earth with alien life, and similarly feeble evidence supporting the abiotic emergence of life on Earth. “Both theories should be followed up,” they wrote.

The idea that faraway, intelligent beings – or perhaps the bored teenagers of the species – might be intentionally hurling life at planets is truly science fiction. But it’s a universe of infinite possibilities, right?

“If you imagine that intelligent, technological life exists on other worlds – which I do imagine,” Grinspoon says, “Then what would lead you to conclude that nobody anywhere in the galaxy has ever tried such a stunt?”

Looking toward the stars for our origins seems, perhaps, like the kind of explanation one ought to turn to when all other attempts to flick life’s on-switch have failed. It’s more than plausible that the building blocks of life – amino acids, nucleobases, sugars – were delivered to Earth by asteroids or comets. We know that asteroids in the solar system are carrying complex organic molecules. And not only that, complex organic molecules have been spotted wafting through interstellar space.

Put more simply, the galaxy is littered with the building blocks of life. But it could also be littered with life itself. And maybe, from across the interstellar sea, some of those organisms came to Earth, crawled out of their space rocks and flourished on their new cosmic shores.

NASA researchers have found the building blocks of DNA in a meteorite. (NASA's Goddard Space Flight Center/Chris Smith)
NASA researchers have found the building blocks of DNA in a meteorite. (NASA’s Goddard Space Flight Center/Chris Smith)


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Galápagos Monday: Southern Inhospitality

This is the second installment of a six-week series about my recent trip to the Galápagos. You can read my first post, about tortoises and donkeys, here.

At dawn on June 6, more than 30 years after Lynn was chasing tortoises at the top of Alcedo, our boat anchored near the volcano’s base in Urbina Bay. By 8 a.m., I was fully breakfasted and eager to begin the scheduled 2-mile hike, on which we were likely to see giant tortoises and land iguanas.

My mood dampened after disembarking on the beach. Even at this early hour, and even doused ear-to-toe with 100-SPF sunscreen, I felt an unrelenting solar assault. (Turns out it’s hard to concentrate on nature’s glories while obsessively imagining your skin cells morphing into irregularly shaped cancerous moles.) The beach was narrow and surrounded by foreboding gray rocks. Maybe this, I thought, is what Darwin meant when describing his first visit to these islands: “Nothing could be less inviting than the first appearance.”

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Galápagos Monday: Lynn’s Tortoises

Every Monday for the next six weeks I’ll be posting about my recent trip to the Galápagos. After a week on a big boat, hopping from one imposing volcanic island to the next, I saw most of the odd creatures that Charles Darwin famously wrote about: century-old tortoises, finches with beaks of all sizes, swimming iguanas. But most of what I learned was new to me — like how the Ecuadorian government hired expert hunters from New Zealand to shoot down thousands of goats by helicopter, or how, in 1954, a massive geological uplift almost instantaneously raised one island’s coast 15 feet, taking with it mounds of coral that have since blackened with dust. Many of the stories converge on what’s, for me, a perplexing theme: that people can be sources of both ecological destruction and impressive restoration. As the climate changes, and population and tourism rates continue to skyrocket, it will be fascinating to see how the economic-political-scientific ecosystem of the Galápagos evolves.

I kick off the series (below, after the jump) with a story about one of my naturalist-guides, Lynn, who has lived on the islands since 1978.


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Dear Mom

My mother is spunky and smart and I love her very much. But she’s got this one trait that drives me crazy: she believes everything she sees on The History Channel.

I visited her in Michigan a few weeks ago. One night at a local brewery, with my sister, Charlotte, and her boyfriend, Greg, in tow, Mom began telling us about why she believes humans came to earth from another planet. “Your evolution theories can’t explain the pyramids,” she said triumphantly.

“How does that have anything to do with aliens?” I asked triumphantly.

Charlotte, who goes out to eat with Mom much more often than I do, looked at Greg and smirked.

“How else would the Egyptians have known how to build them?” Mom said.

“And what evidence, exactly, do you have to support our alien origins?” I said.

“Geometry!” she said.

She then went on and on about latitudes and longitudes and the Maya and alien images in cave paintings. I understood little of what she said, but knew enough to proclaim, too loudly, “That’s such bullshit, Mom!”

For the sake of continuing an otherwise pleasant meal, we dropped it. But I resolved to find out what nonsense she was talking about and eventually set her straight.

So I found out. And it’s as crazy as I thought.