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.

Which makes you wonder:

If these subsurface processes
are so good at sucking up

all the carbon dioxide
coming from below them,

could they also help us
with a little carbon problem

we've got going on up at the surface?

Humans are releasing enough
carbon dioxide into our atmosphere

that we are decreasing
the ability of our planet

to support life as we know it.

And scientists and engineers
and entrepreneurs

are working on methods
to pull carbon dioxide

out of these point sources,

so that they're not released
into the atmosphere.

And they need to put it somewhere.

So for this reason,

we need to keep studying places
where this carbon might be stored,

possibly in the subsurface,

to know what's going to happen to it
when it goes there.

Will these deep subsurface microbes
be a problem because they're too slow

to actually keep anything down there?

Or will they be helpful

because they'll help convert this stuff
to solid carbonate minerals?

If we can make such a big breakthrough

just from one study
that we did in Costa Rica,

then imagine what else
is waiting to be discovered down there.

This new field of geo-bio-chemistry,
or deep subsurface biology,

or whatever you want to call it,

is going to have huge implications,

not just for mitigating climate change,

but possibly for understanding
how life and earth have coevolved,

or finding new products that are useful
for industrial or medical applications.

Maybe even predicting earthquakes

or finding life outside our planet.

It could even help us understand
the origin of life itself.

Fortunately, I don't have
to do this by myself.

I have amazing colleagues
all over the world

who are cracking into the mysteries
of this deep subsurface world.

And it may seem like life
buried deep within the earth's crust

is so far away from our daily experiences
that it's kind of irrelevant.

But the truth is
that this weird, slow life

may actually have the answers
to some of the greatest mysteries

of life on earth.

Thank you.

(Applause)