Horizon (1964) s39e15 Episode Script

The Secret Lives of Caves

Down in the depths of the earth, lies a secret so intriguing that scientists are willing to risk their lives to find it.
They brave an assault course of lethal obstacles, and fumes that kill in seconds.
And then we realise, it's carbon monoxide that's going off.
Our respirators don't protect against carbon monoxide.
I mean, this cave is just full of good ways to die.
What lured them here was a simple puzzle, to figure out what form these fabulous caves.
But in trying to solve this mystery, they have made a far greater discovery, because hidden within these caves may be an explanation of how life on earth began.
These are the Guadalupe Mountains of New Mexico in the United States.
Deep beneath them lies a spectacular secret worid.
It's such a different environment and it's almost like going to another planet.
In a sense it is another planet.
It's part of our own planet that we have not explored, just like the deep oceans or something that's only become accessible to us in the last century or less.
Now we're finding that kind of pioneering effort going on in caves.
Scientists are drawn here by some of the worid's most magnificent limestone caves, the Carisbad Caverns, and in particular Carisbad's 'Big Room'.
When I first walked through this cave in the early 1970s I was just amazed at the size of this room.
The size alone made it unusual.
Its ceilings tower as high as a 30 storey building, and it covers a space larger than six football fields.
But the 'Big Room' is more than just an underground wonder.
It is also a geological puzzle.
There were a number of mysteries in the cave that we couldn't figure out.
One is: Why are these caves so big? And: Why was there no place that looked like the water had entered the caves and had gone out of the caves? Geologists had always believed that limestone caves like these were formed by water.
Rain would penetrate cracks in the rocks, absorb carbon dioxide from the air and turn into carbonic acid.
Slowly, over millions of years, this mild acid would dissolve away the rock.
It had always been assumed that the vast labyrinth at Carisbad had been formed in this way.
But the puzzle was that no matter how hard they looked, they couldn't find any trace of water.
And a further discovery was about to deepen that mystery.
A corner of the Big Room was littered with massive 100 ton blocks of rock.
No one had paid them much attention until Dave Jagnow came along.
He discovered they were made of a mineral that is almost never found in caves gypsum.
In most caves you wouldn't expect to find gypsum because it's so easily dissolved and I would have expected it to be flushed out of the cave here long ago.
So if water had formed Carisbad, these giant blocks should not be here.
Their very presence testify to the fact that the caves had been shaped without water and without carbolic acid.
So why were they here at all.
The hunt for answers began further into the Guadalupe range, three miles from Carisbad at Lechuguilla Canyon.
Following the sound of the wind to the bottom of the pit, three cavers uncovered a magical place.
Deep underground their lights illuminated another worid.
Passageways twisted through tunnels encrusted with snow white gypsum.
In contrast to Carisbad, every inch of the cave was covered with these exquisite gypsum formations.
The most dazzling were found in the chamber they christened the 'Chandelier Ballroom'.
Lechuguilla had been sealed from the surface for millions of years so its gypsum had remained utterly untarnished.
The gypsum is just beautifully preserved in Lechuguilla cave, but gypsum is a rare mineral to find in any cave and yet these caves were fully of these unique formations, and so that was another one of the clues that made us think these caves must have a very unique origin.
Dave and Carol were now faced with two immense subterranean networks.
Carisbad and Lechuguilla that they couldn't explain.
The only clue they had to go on was the gypsum itself.
It was telling them something but they couldn't work out what.
Gypsum occurs naturally on the plains at the foot of the Guadalupe range, so perhaps, over time, this gypsum had somehow seeped into the caves and been deposited on their walls.
What occurred to us then is to test the gypsum to see if there was a correlation between the gypsum in the caves and the gypsum outside in the gypsum plain.
If the cave gypsum was the same as that on the plains, it would share the same chemical structure.
Carol tested both samples for the mineral sulphur because it exists in two forms.
One heavy and one light.
She started with the cave gypsum.
I found out that the sulphur was very, very light, whereas the gypsum out on the gypsum plain was very heavy, so it couldn't possibly have come from the source on the gypsum plain.
In other words, the gypsum must have somehow been made in the cave itself.
There is only one way that this could have happened with sulphuric acid.
If you poor this acid on limestone it dissolves out carbonate, releases carbon dioxide gas and leaves behind gypsum.
Dave wondered whether at some point the limestone cave walls had been carved out by sulphuric acid.
Sulphuric acid is much stronger and rarer than the carbonic acid that usually forms caves.
It can dissolve out about eight times the volume that a normal cave would be as a result of carbonic acid solution, so it's much more powerful.
But you very rarely find it in nature.
But if Dave's hunch was right, it posed a new problem.
What could be producing sulphuric acid in such enormous quantities as to eat out chasms the size of Carisbad's Big Room? They went looking all over the Guadalupe range.
Then they remembered that thousands of feet beneath these mountains lay major deposits of oil and gas.
When they examined the oil they found the first clue.
They realised that it was tainted with a particularly smelly chemical.
These deposits are what we call sour because they contain hydrogen sulphide, and any time you drill a well around the Guadalupe Mountains, you smell this rotten egg smell.
This hydrogen sulphide gas.
Hydrogen sulphide instantly drew Carol's attention.
I knew that if hydrogen sulphide mixed with oxygen it would create sulphuric acid.
So that had to be the source.
It seemed the hydrogen sulphide from the oil fields was leaking into the caves and becoming sulphuric acid.
But again, this discovery raised more questions than it answered.
What could be converting the oil into hydrogen sulphide deep underground? Hints at what must be going on beneath the Guadalupe range were found thousands of miles north at Yellowstone National Park in Wyoming.
Water boils in Yellowstone at 93°C.
I don't dare touch this hot water because it's so hot, it's.
temperature's fluctuating but it's about 180°F, that, in Celsius, is 83°C - that's really hot.
Scientists had always believed that such extreme conditions would destroy all living things.
But despite these boiling temperatures, they discovered bacteria in the hot springs that were thriving.
It's pretty surprising to think that microbes can actually grow under these conditions and these high temperatures.
The microbes were nicknamed 'extremophiles'.
Scientists have learnt that they can live in the harshest environments on earth, even worse than those at Yellowstone.
We discovered organisms living at temperatures well above boiling - 230, 240°F.
So it really proved the point that indeed life could thrive under some rather extreme conditions.
These extremophiles have one other very peculiar property.
They feed off chemicals and make gases.
And some were making the very same gas that Carol and Dave had isolated in the oil deposits under Carisbad hydrogen sulphide.
Extremophiles appeared to be implicated in the mystery of the caves.
Dave and Carol suspected that if they can tolerate the most severe conditions on earth, then surely they could live deep beneath the Guadalupe Mountains.
So they proposed a simple but radical theory biology, not just geology, was at work in making the caves.
They suggested extreme-loving microbes had fed on oil deep underground making hydrogen sulphide.
This seeped up into the mountain, mixed with oxygen to form sulphuric acid, which then melted away the limestone walls leaving behind the caves.
Although it was only an idea, this seemed to make sense.
But the scientific community was sceptical.
Everyone for a hundred years had just assumed that was only carbonic acid which carves out caves.
Nobody had even thought of sulphuric acid being the agent by which this cave and the other caves in the Guadalupe Mountains could have formed.
It was a completely new idea.
But it was just a theory.
To show beyond doubt that caves could be shaped and formed simply by acid from microbes, they were going to need living proof.
So a team of biologists returned to the gypsum caves of Lechuguilla.
They were embarking on a hunt for life.
It would take them underground for four whole days.
Just to reach the opening to the cave they first had to face a dizzying drop.
First in was Diana Northup.
For some people it's easy.
For me its an incredibly difficult cave to go into because I'm afraid of heights and Lechuguilla is pits.
It's just one hole after another.
But what draws me is the fact that there is incredible science to be done in this cave.
It is full of scientific mysteries.
At the bottom of the pit Diana climbed through the hatch door that protected the cave's entrance.
As the air pressure changes, winds whistled through the tunnel at up to 50mph.
Once inside she would be plunged into absolute darkness, and totally dependent on battery powered lights.
Alright, I'm going to close the gate behind you so it's a little easier to get down.
When the door slams, all the wind shuts off.
Instead of this wind tunnel that you've been in, just comes down to a murmur, and then as you move away from it, the cave becomes completely silent.
So you get no concept of what's around you because you're just sort of sitting in there in a bubble of blackness.
Next down was Diana's colleague, Penny Boston.
I had done a lot of extreme environment work in surface environments, but I had never caved before in a wild cave.
And so Lechuguilla was my introduction to caving.
And the first couple of times I went on trips there, I kept thinking, all I have to do is live long enough to get out, and then I never have to come back, and that's what kept me going long enough to actually sort of endure it.
And after those first couple of trips, when all I wanted to do was get out, the beauties of the cave, in the sense of.
of other woridliness that I got, really soaked into my soul.
Lechuguilla is the deepest known cave in the United States, and one of the longest in the worid.
Since the cave was discovered, over 100 miles have been mapped.
Names of places like: 'Freak Out Traverse', 'Death Pit' and 'Chasm Drop' spell out the dangers awaiting the team.
One of the most treacherous obstacles is 'Boulder Falls'.
Correct rigging says that you rig it so that you have to get onto the road at the very edge of this pit.
You know you have a safety to help you but for me who's afraid of heights, that's not a lot of comfort, and that's 150ft drop that is against the wall for a little way and then free, so as you come down this, you are just hanging out in space.
'Boulder Falls' is named after all the rocks that came loose the first time explorers ventured down.
They lowered themselves on a single rope tied to an anchor, and controlled their speed with a handbrake.
If they didn't apply enough friction they would spiral into an uncontrollable deadly descent.
The team continued their climb down.
They were entering a worid where many had always believed nothing could be alive.
When you go into a cave and shut that door and get beyond the entrance, there is no sunlight.
So the normal system that we think about fuelling life is not there.
Now in other caves they have rivers that run through them that bring in carcasses or dead leaves or twigs and things like that, that can fuel microbial processes.
That doesn't occur in Lechuguilla.
And so it's a very low nutrient environment, and that makes it more extreme.
It had long been thought that Lechuguilla was entirely dead, that it had stopped forming long ago and was now too hostile to support life.
But Penny and Diana hoped that if microbes had been involved in its creation, they might have left traces.
I assumed that if the ideas we have about how Lechuguilla was formed are correct, that at the time it was forming it would have been inhabited by hydrogen sulphite bacteria.
But, whether or not those would have persisted over a very long period of time remained a question and so recently went on a fishing expedition for organisms to see whether or not our hunch about that was correct.
After six exhausting hours they were getting near the bottom of Lechuguilla.
And then they came across a small lake.
The water was so pristine that at certain angles it seemed invisible.
Everything about the team's presence risked contaminating this purity.
We have a huge impact on caves by the very fact that we go in and bring ourselves.
Now this may seem like a foreign concept but as we walk through a cave we shed tens of thousands of skin fragments a minute.
So you're a veritable little snow storm and around you is this pile of debris.
Your hair is falling out and littering the cave.
Now, over a mile in and a thousand feet down, every step was taking them into new territory.
Then, turning a corner, they found something peculiar.
The walls were covered in rust coloured patches, and around the patches the caves seemed to be crumbling away.
They had never seen anything like it before.
Could it be evidence of the extreme microbes that had once formed the cave? Back in the lab Penny and Diana used an electron microscope to examine the rust covered patches searching for signs of life.
Scanning electron microscopy allows you to see incredibly tiny things, and we spend hours and hours lost among the sand grains, you know as we just sort of cruise with the electron beam from particle to particle hunting, and its very hard sometimes because there are minerals that look like micro organisms.
For over three months they looked through one sample after another.
But eventually their patience paid off.
We found a really exciting thing when we looked at some samples and saw what looks like a string of pearis .
These are actual cells, and these are shapes consistently found in all the corrosión residues.
These tiny circles were remnants of microbes, suggesting that organisms had once lived in Lechuguilla's barren darkness.
And they found something else.
Originally we thought that perhaps many of the organisms that we might find would be either dead or just shut down metabolically.
But what we have found is that there are very large numbers of these guys actually active metabolically and reproductive.
And so to me that was one of the most amazing things.
But what was not yet clear, was whether these microbes had actually carved out the cave.
Then they looked at another of their rust coloured samples.
This one rich with the mineral manganese.
What we're able to see is a very unique cell shape with an elongated tail that is associated with some bacteria that eat manganese, and manganese eating bacteria are able to produce acid which could be part of the corroding of this rock, possibly as they pull the manganese out of the rock wall to eat it, they're also leaving holes in the crystal lattice.
So these two pieces together provides some of the evidence that we have that microbes are actually eating the rock walls.
It seemed not only was Lechuguilla home to living and breathing organisms but they were actively eating away at the cave walls.
But further examination revealed that these rock eaters were extremely slow.
They would need millions of years to gnaw away just a few millimetres.
Even if their efforts were combined with the sulphuric acid bacteria they would still not be able to carve out massive chambers.
Something had to be missing.
To find it they decided to look for a cave that was still in the process of being created.
With the year news of such a cave drew Diana and her colleague, Louise Hose, to the rain forests of Southern Mexico.
As they approached they noticed the stream flowing from the cave was milky white, rich with sulphur and telltale gypsum.
Large amounts of hydrogen sulphide bubbled up in the water, a danger sign to anyone wanting to go further.
The hydrogen sulphide combines with the moisture and humidity in the cave and forms sulphuric acid and sulphuric acid is in the air and you breathe it into your lungs and it will start to deteriorate the linings of the lungs.
So we wear these gas masks to help filter out the hydrogen sulphide and that's protecting my lungs from the sort of damage that can be done.
Diana and Louise cautiously headed off into the heart of the poisonous cave.
It has been called "Cueva de Via Luz" or lighted house, after the few skylights that connect it to the surface.
But despite the influx of fresh air, the cave was full of hydrogen sulphide.
So they carried a gas monitor to alert them to danger.
Soon it started to detect other noxious fumes.
Like what? Well, sometimes you have hydrogen fluoride, hydrogen chloride.
Really! What do those do to you? Kill you.
But for the moment the levels were safe enough to carry on, and before long they found something.
Usually when you walk into a cave life is something that you have to look pretty hard to see, and so the thing that just strikes you, just slaps you in the face and in Via Luz is the fact that every where you look there's life.
A whole ecosystem was thriving despite the deadly air and the lack of sunlight.
As you go deeper into the cave and into the dark areas, there are rocks in the stream that are covered with this green coating.
It's not being driven by sunlight, it has to be driven by other things so you think about wow! what's really driving this system? And it wasn't just the life that was exceptional.
So were the walls of the cave itself.
When you look at this cave the walls are literally melting .
It's like a birthday cake left out in the rain that's sort of melted.
And so it just cries out to you that this is an enlargement process because the walls are literally being dissolved before your eyes.
Here at Via Luz for the first time they could actually watch a cave in the act of being formed.
As in Carisbad, the hydrogen sulphide from microbes deep underground was turning into sulphuric acid.
But the speed with which the walls were melting was a clue to what else was at work.
It was then that they noticed strange formations dangling from the ceiling.
They looked like stalactites but unlike stalactites, which are hardened limestone, these were soft, gooey strings of mucous.
For obvious reasons they named them snottites.
The liquid that was dripping off the end of each of the snottites, if you get it on your hands, I've had it drop in my eyes, it burns tremendously.
Clothing will tend to dissolve when we have it drip on our clothes.
But just as it seemed they were on the verge of a discovery.
The oxygen levels plummeted.
There's a 10% drop in oxygen.
We've seen it go from about 20.
5 … When you start to drop below 18 or 19 one worries.
When it gets down to about 9.
5% it'll kill you very rapidly.
So we have to evacuate the area.
The expedition had to end abruptly.
But on the way out Diana snatched a sample of sticky snottites.
It was a piece of quick thinking that would turn out to solve the mystery of what was forming these caves once and for all.
Their precious specimen was subjected to a barrage of tests.
We discovered many things when we looked at the snottites.
When you look at them with the microscope and look at them magnified many, many times, they're just enormous bacterial colonies.
They're just little weakly bacteria everywhere.
This abundance of bacteria explained why the Via Luz teemed with such life.
These bacteria are eaten by the gnats, by the fish, by various other organisms in the cave.
One of the coolest things that you see is in the stream there are these little diving beetles, and sometimes the males carry eggs on their back.
They're colonised by bacteria.
And then the fish come along and nibble on these bacteria.
And so you get this whole incredible food web that's developed, much of which is being fed by these snottites.
The snottites had one other surprise in store.
When I looked at the DNA from one of these snottites, it's just this thriving culture of a bacteria that is known to eat sulphur and produce sulphuric acid.
So it's as though little battery acid generators on the walls that are just cranking out acid, and you see these cave walls melting.
The snottites were the final piece of the puzzle.
Finally they explained how these mysterious caves had come into existence.
Via Luz had provided the answer.
Scientists now believe that millions of years ago the microbes waged a three pronged war on the Guadalupe range.
Bacteria deep underground feasting on oil reserves gave off hydrogen sulphide.
This seeped up through the mountain, turned into sulphuric acid and dissolved rock.
Meanwhile, armies of rock-eating bacteria moved in and coated the cavern walls, while snottites hung from the ceiling, oozing pools of sulphuric acid.
This triple attack explained how tiny microbes could be powerful enough to carve from solid rock vast underground labyrinths, from Carisbad to Lechuguilla to Via Luz.
We think of Via Luz as sort of a modern day analogue for what six million years ago Lechuguilla might have looked like, so you can imagine all that sulphuric acid being produced in the chambers, being enlarged and getting bigger and bigger and bigger.
We now know that microbes are not just along for the ride when it comes to caves and subsurface in general, but they're active agents and geological change over time.
This is really new perspective that the organisms and the geology cannot be separated and to understand caves, we have to understand the life that they contain, and that if we had a planet with no life on it, the caves that would form would be very different from the ones that we have on this planet, and that magic ingredient that we have here that has to be figured out is life.
But the discovery that subterranean life had carved out Carisbad and Lechuguilla turned out to be only part of the story.
The secret life of caves was about to lead to one final revelation.
An insight into one of sciences great unresolved mysteries.
How life on earth first began.
Four and a half billion years ago, our planet was a raging inferno.
The surface conditions were so hostile.
The earth was being bombarded by meteorites, there was a heavy UV radiation load on the earth because there was no ozone shield at that time.
Volcanic eruptions… Yet scientists had always believed that life somehow took hold around this time and that the very first creatures, our ancestors, were microbes that lived in vast colonies oozing over the surface.
We have very clear even fossil evidence of microbial life existing three and a half billion years ago, so life had originated from earth's first billion years.
But back then, the surface of the earth seemed too harsh for even the hardiest bacteria to exist; too inhospitable for even the extreme - loving inhabitants of Yellowstone.
Yet apparently, in the primordial soup, life had not only got started, it had thrived, and actually giving rise to the worid around us.
It just didn't add up.
How could life have got going in such violent conditions? But a seemingly ordinary cave in Wyoming was about to offer an explanation.
Hidden on a rocky embankment is the entrance to Lower Kane Cave.
When scientists first approached, the familiar rotten egg smell hit them hydrogen sulphide.
But the gas levels here were much lower than at Via Luz.
They originally came here on a routine missión to survey all the caves in the area.
At first site Cane looked like nothing special.
It had none of the exquisite mineral formations of Carisbad or Lechuguilla.
It had none of the abundance of life of Via Luz.
The ceilings lacked even the humblest stalactite.
But the droplets gleaming in the light turned out to be sulphuric acid.
Just as in Via Luz, Kane was coated with microscopic life, busily eating away at the cave walls.
Everything about this cave seemed to reaffirm their theories of how caves formed.
But as the scientists probed deeper, they discovered something wonderful.
Just below the surface the springs stretched tapestries, woven by trillions of microbes added together in lurid, coloured mats.
It's unusual to see bacterial materials in a cave at all.
When we found these extensive communities and different colours and different positions, we were flabbergasted.
And then the second surprise was how complex the communities are.
We're finding in these mats after studying them for several years that they're composed of a wide range of micro organisms using iron, using sulphur, using carbon in different ways.
And we never really thought that that would be possible, and each one the mats has a different assemblage of micro organisms doing specific things for the cave.
They recognised the microbes that eat hydrogen sulphide making sulphuric acid and dissolving limestone.
And they found those that were living off the waste of the rock eaters making gas and new minerals.
But there were others that were completely new to science.
And closer examination revealed something truly exceptional, because a few of the microbes had extraordinary DNA.
It was very primitive and appeared to have remained unchanged for billions of years.
These microbes had been caught in a time warp unaltered by evolution since the dawn of life on earth.
Kane Cave is a window into early life and how life first evolved, and it's a window into how early life on earth existed.
I think some of the organisms that existed on the earth 4 to 3.
5 billion years ago could be fairly similar to what we find today living in these deep subsurface environments.
Looking at them was like looking back to that mysterious era when life on earth began.
Suddenly scientists realised the true importance of these cave microbes.
Not only did they explain how the caves themselves were formed but they also shed light on how life first got a foothold and our planet was at its most inhospitable.
There is a growing consensus that life probably began in these subsurface environments where organisms would have been safeguarded from the rather horrendous conditions going on at the surface at the time.
So anything that might have come up to the surface and tried its hand at the struggle for existence would have probably had its evolutionary path nipped in the bud.
So really the deep subsurface was probably the safest place to be.
So the secret worid of caves seems to tell a new story of how life on earth began.
Billions of years ago, when the surface of our planet was at its most violent, one refuge remained.
Here, deep underground, our microbial ancestors hid away in safe, still nooks and crannies.
These primitive creatures, just like the cave microbes today, didn't need sunlight or plants to survive.
They just ate rocks and minerals.
Over the years they would give rise to all living creatures and would leave in their wake a lasting monument, a place we are only just beginning to discover, another universe beneath our feet.
We can't see microbes and so therefore we tend to dismiss them.
But they are not only active, they're powerful, they carve out caves.
They're why we're not up to our necks in dead trees and plants.
They produce even the very air that we breathe.
Without them we'd be nothing.
They actually really are the engineers of our planet.
They are worthy of our respect.