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  • It may seem like we're all standing on solid earth right now,

  • but we're not.

  • The rocks and the dirt underneath us are crisscrossed by tiny little fractures

  • and empty spaces.

  • And these empty spaces are filled with astronomical quantities of microbes,

  • such as these ones.

  • The deepest that we found microbes so far into the earth

  • is five kilometers down.

  • So like, if you pointed yourself at the ground

  • and took off running into the ground,

  • you could run an entire 5K race and microbes would line your whole path.

  • So you may not have ever thought about these microbes

  • that are deep inside earth's crust,

  • but you probably thought about the microbes living in our guts.

  • If you add up the gut microbiomes

  • of all the people and all the animals on the planet,

  • collectively, this weighs about 100,000 tons.

  • This is a huge biome that we carry in our bellies every single day.

  • We should all be proud.

  • (Laughter)

  • But it pales in comparison to the number of microbes

  • that are covering the entire surface of the earth,

  • like in our soils, our rivers and our oceans.

  • Collectively, these weigh about two billion tons.

  • But it turns out that the majority of microbes on earth

  • aren't even in oceans or our guts or sewage treatment plants.

  • Most of them are actually inside the earth's crust.

  • So collectively, these weigh 40 billion tons.

  • This is one of the biggest biomes on the planet,

  • and we didn't even know it existed until a few decades ago.

  • So the possibilities for what life is like down there,

  • or what it might do for humans,

  • are limitless.

  • This is a map showing a red dot

  • for every place where we've gotten pretty good deep subsurface samples

  • with modern microbiological methods,

  • and you may be impressed

  • that we're getting a pretty good global coverage,

  • but actually, if you remember that these are the only places

  • that we have samples from, it looks a little worse.

  • If we were all in an alien spaceship,

  • trying to reconstruct a map of the globe from only these samples,

  • we'd never be able to do it.

  • So people sometimes say to me,

  • "Yeah, there's a lot of microbes in the subsurface, but ...

  • aren't they just kind of dormant?"

  • This is a good point.

  • Relative to a ficus plant or the measles or my kid's guinea pigs,

  • these microbes probably aren't doing much of anything at all.

  • We know that they have to be slow, because there's so many of them.

  • If they all started dividing at the rate of E. coli,

  • then they would double the entire weight of the earth, rocks included,

  • over a single night.

  • In fact, many of them probably haven't even undergone a single cell division

  • since the time of ancient Egypt.

  • Which is just crazy.

  • Like, how do you wrap your head around things that are so long-lived?

  • But I thought of an analogy that I really love,

  • but it's weird and it's complicated.

  • So I hope that you can all go there with me.

  • Alright, let's try it.

  • It's like trying to figure out the life cycle of a tree ...

  • if you only lived for a day.

  • So like if human life span was only a day, and we lived in winter,

  • then you would go your entire life

  • without ever seeing a tree with a leaf on it.

  • And there would be so many human generations

  • that would pass by within a single winter

  • that you may not even have access to a history book

  • that says anything other than the fact that trees are always lifeless sticks

  • that don't do anything.

  • Of course, this is ridiculous.

  • We know that trees are just waiting for summer

  • so they can reactivate.

  • But if the human life span

  • were significantly shorter than that of trees,

  • we might be completely oblivious to this totally mundane fact.

  • So when we say that these deep subsurface microbes are just dormant,

  • are we like people who die after a day, trying to figure out how trees work?

  • What if these deep subsurface organisms

  • are just waiting for their version of summer,

  • but our lives are too short for us to see it?

  • If you take E. coli and seal it up in a test tube,

  • with no food or nutrients,

  • and leave it there for months to years,

  • most of the cells die off, of course, because they're starving.

  • But a few of the cells survive.

  • If you take these old surviving cells

  • and compete them, also under starvation conditions,

  • against a new, fast-growing culture of E. coli,

  • the grizzled old tough guys beat out the squeaky clean upstarts

  • every single time.

  • So this is evidence there's actually an evolutionary payoff

  • to being extraordinarily slow.

  • So it's possible

  • that maybe we should not equate being slow with being unimportant.

  • Maybe these out-of-sight, out-of-mind microbes

  • could actually be helpful to humanity.

  • OK, so as far as we know,

  • there are two ways to do subsurface living.

  • The first is to wait for food to trickle down from the surface world,

  • like trying to eat the leftovers of a picnic that happened 1,000 years ago.

  • Which is a crazy way to live,

  • but shockingly seems to work out for a lot of microbes in earth.

  • The other possibility is for a microbe to just say,

  • "Nah, I don't need the surface world.

  • I'm good down here."

  • For microbes that go this route,

  • they have to get everything that they need in order to survive

  • from inside the earth.

  • Some things are actually easier for them to get.

  • They're more abundant inside the earth,

  • like water or nutrients, like nitrogen and iron and phosphorus,

  • or places to live.

  • These are things that we literally kill each other to get ahold of

  • up at the surface world.

  • But in the subsurface, the problem is finding enough energy.

  • Up at the surface,

  • plants can chemically knit together carbon dioxide molecules into yummy sugars

  • as fast as the sun's photons hit their leaves.

  • But in the subsurface, of course, there's no sunlight,

  • so this ecosystem has to solve the problem

  • of who is going to make the food for everybody else.

  • The subsurface needs something that's like a plant

  • but it breathes rocks.

  • Luckily, such a thing exists,

  • and it's called a chemolithoautotroph.

  • (Laughter)

  • Which is a microbe that uses chemicals -- "chemo,"

  • from rocks -- "litho,"

  • to make food -- "autotroph."

  • And they can do this with a ton of different elements.

  • They can do this with sulphur, iron, manganese, nitrogen, carbon,

  • some of them can use pure electrons, straight up.

  • Like, if you cut the end off of an electrical cord,

  • they could breathe it like a snorkel.

  • (Laughter)

  • These chemolithoautotrophs

  • take the energy that they get from these processes

  • and use it to make food, like plants do.

  • But we know that plants do more than just make food.

  • They also make a waste product, oxygen,

  • which we are 100 percent dependent upon.

  • But the waste product that these chemolithoautotrophs make

  • is often in the form of minerals,

  • like rust or pyrite, like fool's gold,

  • or carminites, like limestone.

  • So what we have are microbes that are really, really slow, like rocks,

  • that get their energy from rocks,

  • that make as their waste product other rocks.

  • So am I talking about biology, or am I talking about geology?

  • This stuff really blurs the lines.

  • (Laughter)

  • So if I'm going to do this thing,

  • and I'm going to be a biologist who studies microbes

  • that kind of act like rocks,

  • then I should probably start studying geology.

  • And what's the coolest part of geology?

  • Volcanoes.

  • (Laughter)

  • This is looking inside the crater of Poás Volcano in Costa Rica.

  • Many volcanoes on earth arise because an oceanic tectonic plate

  • crashes into a continental plate.

  • As this oceanic plate subducts

  • or gets moved underneath this continental plate,

  • things like water and carbon dioxide and other materials

  • get squeezed out of it,

  • like ringing a wet washcloth.

  • So in this way, subduction zones are like portals into the deep earth,

  • where materials are exchanged between the surface and the subsurface world.

  • So I was recently invited by some of my colleagues in Costa Rica

  • to come and work with them on some of the volcanoes.

  • And of course I said yes, because, I mean, Costa Rica is beautiful,

  • but also because it sits on top of one of these subduction zones.

  • We wanted to ask the very specific question:

  • Why is it that the carbon dioxide

  • that comes out of this deeply buried oceanic tectonic plate

  • is only coming out of the volcanoes?

  • Why don't we see it distributed throughout the entire subduction zone?

  • Do the microbes have something to do with that?

  • So this is a picture of me inside Poás Volcano,

  • along with my colleague Donato Giovannelli.

  • That lake that we're standing next to is made of pure battery acid.

  • I know this because we were measuring the pH when this picture was taken.

  • And at some point while we were working inside the crater,

  • I turned to my Costa Rican colleague Carlos Ramírez and I said,

  • "Alright, if this thing starts erupting right now,

  • what's our exit strategy?"

  • And he said, "Oh, yeah, great question, it's totally easy.

  • Just turn around and enjoy the view."

  • (Laughter)

  • "Because it will be your last."

  • (Laughter)

  • And it may sound like he was being overly dramatic,

  • but 54 days after I was standing next to that lake,

  • this happened.

  • Audience: Oh!

  • Freaking terrifying, right?

  • (Laughs)

  • This was the biggest eruption this volcano had had in 60-some-odd years,

  • and not long after this video ends,

  • the camera that was taking the video is obliterated

  • and the entire lake that we had been sampling

  • vaporizes completely.

  • But I also want to be clear

  • that we were pretty sure this was not going to happen

  • on the day that we were actually in the volcano,

  • because Costa Rica monitors its volcanoes very carefully

  • through the OVSICORI Institute,

  • and we had scientists from that institute with us on that day.

  • But the fact that it erupted illustrates perfectly

  • that if you want to look for where carbon dioxide gas

  • is coming out of this oceanic plate,

  • then you should look no further than the volcanoes themselves.

  • But if you go to Costa Rica,

  • you may notice that in addition to these volcanoes

  • there are tons of cozy little hot springs all over the place.

  • Some of the water in these hot springs is actually bubbling up

  • from this deeply buried oceanic plate.

  • And our hypothesis was that there should be carbon dioxide

  • bubbling up with it,

  • but something deep underground was filtering it out.

  • So we spent two weeks driving all around Costa Rica,

  • sampling every hot spring we could find --

  • it was awful, let me tell you.

  • And then we spent the next two years measuring and analyzing data.

  • And if you're not a scientist, I'll just let you know that the big discoveries

  • don't really happen when you're at a beautiful hot spring

  • or on a public stage;

  • they happen when you're hunched over a messy computer

  • or you're troubleshooting a difficult instrument,

  • or you're Skyping your colleagues

  • because you are completely confused about your data.

  • Scientific discoveries, kind of like deep subsurface microbes,

  • can be very, very slow.

  • But in our case, this really paid off this one time.

  • We discovered that literally tons of carbon dioxide

  • were coming out of this deeply buried oceanic plate.

  • And the thing that was keeping them underground

  • and keeping it from being released out into the atmosphere

  • was that deep underground,

  • underneath all the adorable sloths and toucans of Costa Rica,

  • were chemolithoautotrophs.

  • These microbes and the chemical processes that were happening around them

  • were converting this carbon dioxide into carbonate mineral

  • and locking it up underground.