This is geology B with all of us trampled.
The fossil record goes back through the phanerozoic.
Eon about, 540 million years, and even earlier into the
ediacaran period. But while the fossils, provide
incontrovertible evidence of ancient life, the fossils
themselves are certainly not alive in fossils.
The original organic matter belonging to the fossilized life
form. Has been replaced by inorganic
materials cast into the shape formerly occupied by the life.
Form. However, in some situations the
original organic material does survive.
For example, original spores, as old as 350 million years have
been identified using their original organic material and
DNA can survive for as much as a million years.
But in 2019 bacteria that had been buried.
A hundred million years with barely any access to nutrients
were not only identified, but shown to be a I've had they been
in suspended animation for all that time or where they managing
to eke out a living using much less energy than was previously
thought to be necessary. Steve don't is a professor of
oceanography at the University of Rhode Island.
He studies life beneath the seafloor and was on the team
that discovered the bacterial cells living in a hundred
million year old sediment. Steve, don't welcome to geology
B. Thank you very much Oliver.
It's a pleasure to join you here today where where the hundred
million year old sediments. Containing these ancient
bacteria? The sediment was in the middle
of the South Pacific. Civic gyre.
It's this extensive area of a Bissell clay that carpets the
middle of the South Pacific Ocean.
And why did you focus on that area?
We focused on that area because the sediment accumulates very
slowly. It accumulates as slowly in some
places is a few centimeters per million years.
And why was it important to study an area?
That had? Such very low deposition rates
my colleagues and I wanted to study the microbes That had the
lowest access to energy anywhere in the ocean and we wanted to do
so in an environment where we could quarter them with
relatively little contamination. So that meant relatively easily
penetrated sediment relatively, close to the sea floor and that
Clay is very low in organic matter.
It tiny amount of organic matter and the amount of organic matter
is relatively constant for tens of millions of years in the
sediment. So it's not eaten very quickly.
So these elements are below about 6 kilometers of water.
How does one go about recovering sediments from that depth?
Well we're fortunate to have access to the Joy.
These resolution, which is a drill ship operated on behalf of
the international ocean Discovery program, which is a
multinational collaboration to core of the sediment and rock of
the world ocean. I'm fascinated about how you
actually go about doing that. Do you have a rigid drill that
goes down that enormous distance?
Is a rigid drill from your, in my perspective, it's drill pipe.
And when we stand next to it, if we lean on it, it's not going to
bend. But when you have six kilometers
of pipe out, it's a little bit more like, soft spaghetti.
I'm so it dangles from the ship and then when it hits the
bottom, it then starts spinning to drill a call it dangles from
the ship, there's a driller and the driller controls the rate of
spin. So this drill ship is somewhat
like oil and gas drilling vessels.
But the rig is set up very differently with an oil or a gas
vessel. They have a really wide outer
pipe to prevent blowouts, so we don't use that outer pipe.
We use an inner pipe and we make sure that we drill where there's
no chance of oil or gas. And that allows us to work in
much deeper water because we don't have the way to that big
outer pipe and how far below the surface.
Did you have to go to get these bacteria that we're talking
about here? This sediment is really thin out
there because this Sedimentation rate is really slow.
So even where the basement is 100 million years old, we might
have only 70 meters of sediment. This is a really different
situation than people usually think of when they think of
drilling the deep sea other Expeditions have gone out and
drill as much as two and a half kilometres beneath the seafloor.
But our Target wasn't depth, our Target was age.
So we chose this region where we knew the sediment accumulates,
very, very slowly and we could get hundred million year old
sediment roughly. Eeyore 70 meters, beneath the
seafloor. Wow!
So you only have to drill a few tens of meters.
Really not very much at all. Exactly.
So when you got down to those bacteria, to the 100 million
year old age, how many bacteria were actually present in the
core samples? And how does that compare
roughly to the bacterial population?
On the sea floor surface. So we have roughly 1,000 cells
per cubic, centimeter of sediment in the old sediment.
At the sea floor in that region, we might have more like a
million cells per cubic centimeter or 10 million cells
per cubic centimeter. And in environments on
Continental shelves we might have like a billion cells or 10
billion cells per cubic centimeter.
So at some level of thousand individuals is a lot, right?
You give you can imagine a room full of a thousand people but
compared to what you would have living at the seafloor, even at
the same site, almost all the cells that were and at the
seafloor are gone. So this is a pretty unlikely
environment to see something that could survive for this
length of time, but I'd like to understand why it was unlikely
in by altering. That question would be good if
you could explain what it is. That a bacterium?
Normally needs in order to be alive and well, well, bacteria
and need nutrients, and they need energy microbiologist who
work in Labs often think about nutrients, but when they discuss
that they're often lumping in the sources of energy, G.
And in my mind, I separate these things because I think a little
bit more like an oceanographer and so classical oceanographic
nutrients. Are elements like phosphorus and
nitrogen, and sulfur and iron. And then we need a source of
energy. When normally, when people think
about bacteria, they think of bacteria eating organic matter,
whether they're attacking our bodies or whether they're
attacking something in the world around us.
And in that case, they're getting their nutrients in their
energy from the same. Place in a way that getting the
nutrients from the organic matter that they eat and they're
getting energy from oxidizing, the organic matter just like we
do just like we do and if you think about that for a second
you realize is that the energy really doesn't come from the
food. It comes from the oxidation of
the food so it comes from the combination of the oxidant in
the food source and in the broader world of bacteria, there
are many, many categories of bacteria that use oxidants in
the world around them, Like Oxygen or nitrate or sulfate.
And then use reduced compounds in the world around them like
methane or hydrogen or organic matter and they get their energy
from combining those two things. So you need both things, you
need the nutrients, which would be the reduced matter and you
need the oxygen to supply, but you need to have the energy
generating reaction that then keeps the organism alive, right?
For the energy. You need something reduced and
you need. Something oxidized and for you
and me and our listeners, the thing that we use to oxidize is
oxygen itself and the reduced matter that we eat is our food,
okay? So what was extremely scarce
than in this environment for these bacteria?
So it's extremely scarce. In this environment is food, one
of the things we discovered on this Expedition is that.
So little organic matter is consumed in the sediment that
oxygen is present all the way from the sea.
E floor down to, and into the basement below.
So even where the sediment is 100 meters thick, there's oxygen
in the sediment all the way down.
How does it get that it diffuses in from the ocean above?
It takes a long time for oxygen to make it 100 meters into
sediment is probably a few hundred thousand years.
So the process of Organic oxidation in this sediment is
incredibly slow, very little organic matter is eaten, in any
cubic centimeter or even any vertical, 70 meters of sediment.
But nonetheless, they did have oxygen, but they had virtually
no nutrients. So, what was previously known
about the ability of bacteria to survive under these sorts of
conditions? People have found bacteria in
sediment in Marine sediment up to around 35 million years and
it should mention that people have pulled bacteria out of gold
mines in Canada and in South Africa where the rock is more
than a billion years old. And so those bacteria and those
gold mines are living in the water in the fractures of The
Rock. And they've been isolated from
the surface world for probably most of that billion years.
But it's not a very analogous. Situation to the sediment that
we're talking about because the bacteria can move around in the
fractures and their oxidants and their reductants can move
through the water of the fractures.
We've previously found microbes living in sediment from the
eocene little over thirty four million years ago and we were
trying to push back deeper into time here, but they're thing
were really interested in wasn't finding the oldest living back
heel communities. It was Finding bacterial.
These were challenged by so little access to energy in until
this Expedition people really had not looked at bacteria from
environments that have been exposed to oxygen for tens of
millions of years where there was too little organic matter
around for them to use up all the oxygen.
So let's get back to the experiment that you did what was
done to the sediments that were taken out of the coal.
Once you got them back into the lab.
So with the experiment that you and I are talking about today,
our colleague Yuki Morano took little pieces of the sediment
using sterile, sampling. And he'd set one piece of side.
So we could use DNA sequencing to determine what was in it and
then splits of that same little piece he would put in different
vowels with different food sources and in some he would put
amino acid mixture in others, he would put ammonium as a reduced
molecule, he put carbon dioxide and some, which could be a
source of carbon but not a source.
Produced material and he put lactate in some.
So, a variety of very simple, organic molecules carbon bearing
molecules and nitrogen bearing molecules and then he waited to
see what would grow. And what he found was that,
after a few weeks, he had growth in all of the vials where there
was reduced, material, added where there was a monia added or
acetate or amino acids. And the growth can be measured
in terms of the number of cells per cubic centimeter.
Liter of fluid in the vial. He went from 1,000 cells per
cubic centimeter in the sediment to having something like 100,000
cells per cubic centimeter of culture.
So after a few weeks essentially these organisms that have been
trapped or this community that have been trapped for 100
million years, they woke up and they said, wow, food.
And then they reproduced. And that didn't happen to the
samples. Why he just added oxygen.
It didn't happen to the samples where he just added CO2 and it
didn't happen to the samples where He did not add any Oxygen,
he did some control samples without oxygen to see what would
happen and they didn't have growth.
So, this confirms that it was the nutrients they were really
lacking, not the oxygen in a sense, it's the food.
That was really lacking. Yes.
So from this result, we can say that some bacteria from the
sample had survived a hundred million years of food starvation
and they started to behave like normal bacteria.
Does this mean, they were alive, IE dividing or repairing?
Or be it at an extremely slow rate all along or where they
essentially Frozen or hibernating, and just started
Living again, when they had access to a supply of food?
This is a really good question because we're faced with a
conundrum here. These microbes on average had so
little access to energy that they really had barely enough
energy to keep repairing. Molecules as they broke just
like you or I might get a muscle tear if we strain ourselves.
So they had enough energy to repair their equivalent of a
muscle tear but they didn't have enough energy formally to
reproduce as we know it if they weren't reproducing though this
meant that the individual cells and survive something like 100
million years. So we're left with two
ridiculous Alternatives, one that individual cells have lived
for 100 million years or to population has turned over over
the course of that hundred million years.
But Much much, much slower rates on much less energy than our
current understanding allows. And I think that the answer
probably lies somewhere in between that these cells
probably are living much longer than the bacteria in the world
around us. But they're probably reproducing
over those hundred million years.
There have actually been some recent Studies by a group at the
Technical University of Munich. Looking at microbes from parts
of the North Atlantic. They've shown that at least some
bacteria. Multiply over the first few
million years of burial. So that's not quite the same
thing as showing that something's been multiplying
over a full hundred million years and it's not the same
thing as showing that every lineage that survives is
multiplying. But they've been able to show
that at least a couple of lineages.
Do multiply it in the subsea floor environment so that
provides I think reasonable evident that at least some of
them can reproduce on much less energy than we've previously
believed realistic. So you said that, there was an
Impulsivity of nutrients, which was what the limiting factor was
down there in those sediments, but if they were at least eking
out a very sparse living but nonetheless dividing does that
mean they had access to a key, some form of nutrients of some
reducing agent that could just keep the processes ticking over.
That's another really good question and they really have
accesses to two sources of energy if you will.
The First Source is that the organic matter is being a
Oxidized at very low rates, we can tell that because as we go
down in the sediment we find slightly higher nitrate
concentrations as we go and slightly lower oxygen
concentrations as we go. And we can tell from the ratio
of those things that oxygen is being used to oxidize Marine
organic matter, it very very slow rates, the other source of
energy in there in the form of reduced compounds and oxidized
compounds is natural radioactive splitting of water.
So In all natural environments, there is some concentration of
naturally, radioactive material. So even in our bodies, we have
radioactive potassium, radioactive carbon, for example,
and deep sea sediment, has radioactive uranium radioactive,
thorium radioactive potassium in it.
And as those radioactive elements, in the minerals Decay,
they release radiation that strikes.
The water around them in the sediment and striking that water
breaks. It up and then it can recombine
into hydrogen and various oxidized chemicals.
So hydrogen peroxide is one. But if you've got reduced metal
around the oxidized products of the radioactive breakage will
oxidize the metal and then they can use that as an oxidant.
We've done some basic calculations that suggest in
this settlement where organic matter is so scarce there may be
70 times as much energy available from radioactive
splitting of water as from the Mission of organic matter.
Wow, that's amazing. But if that is the primary
source of the nutrients and that presumably is pervasive
throughout the crust and the mantle, in fact, so with this
kind of survival mechanism be viable at arbitrary depth this
kind of survival mechanism should work in any mineral
environment where there's water. So it's the survival mechanism
that the people who study the gold mines believe supports the
microbes in their fractures It's the mechanism that we believe
supports life in deep sediment and as you can surmise, it's a
mechanism that might support life on mars or Europa or
extrasolar planets. All the bacteria that survived
those thousand per cubic centimeter versus the million or
10 million that you would get on the sea floor.
Surface, are they a special subset of the population?
A kind of extremophiles specially adapted to living
under such energy. Poor conditions, their
extremophiles in the sense that they've survived the burial for
100 million years but they're not typically thought of as
extremophiles because they're part of the standard.
Immunity at the seafloor. And so, this leads us to this
curious thought that, although they dominate subsea floor
sediment. They may not be very happy.
There, there are a normal part of the seafloor Community, but
unlike most of the seafloor Community, they can survive
burial for up to 100 million years or more.
So, we would not normally think of them as extremophiles.
If we weren't collecting them from the sediment beneath the
seafloor, we would think of them as just part of a normal Marine
community. Wow, so the same bacteria that
manages to survive under these extreme conditions are also
viable like in normal conditions.
Yeah. But if this ancient population
represented the bacterial population of 100 million years
ago, when we expect it to be different from a modern-day
population that has been evolving at a normal Pace.
Continuously, since that time, I think it's reasonable to expect
that, you'll have some mutation that would Operate say this
individual cell from that individual cell over a hundred
million years. The subsea floor populations are
probably not accumulating mutations very fast and the
populations in the surface world.
Like at the sea floor they've got a lot of mutations, I'll say
two things with regard to this. The first is that there's
undoubtedly been some mutation in both the surface World.
A lot of mutation in the surface world and perhaps some mutation
in the subsurface world since they've been separated.
But the richness of mutations if you will in the surface World,
populations is already so great. It wouldn't be very easy to pick
out the differences. We do know that the mutation
rates are low enough that we can still assign these microbes to
the same categories of bacteria. So we know which family in which
genus they belong to. And if we wandered around the
world exhaustively sequencing everything, we'd probably find
lineages that we would Call the same species in fact, in other
studies in my lab is done in a shorter time.
Scales looking at things over a few million years, we actually
find that to a first approximation.
What we see in the subsea floor is not just a subset of a
seafloor Community, but a subset of the local sea floor
community. And what I mean by that is that
if we see something that we might call a separate species,
in the subsea floor, at some site in million-year-old
sediment or three million year old settlement, we typically
have the same Species at the sea floor, but it's important to
bear in mind that definitions of things like species and genus
for bacteria and archaea, which are other very simple one-celled
organisms are numerical. So in the world around us, we
think, oh, horses and zebras are different species because they
can't have fertile offspring but bacteria don't reproduce by
having sex with each other. They just divide so our sexual
definition of a species, doesn't apply to bacteria.
And what my Microbiologists do instead is they say, oh if it's
97 percent similar or more similar to some other thing in
its gene content, we're going to call it the same species and
what that basically means then is that for the genes that are
used for identification. It's for like a barcode.
We take a chunk of the genome. We always take the same chunk of
the genome over and over again. If that chunk of the genome is,
like 400 bases long, then they've got to be more Than 12
mutations, separating it from another one for us to call them
different species, because we have that three percent we can
play with. So, I've wandered a little bit
on this explanation, but the basic point is, you can
accommodate mutation, and still call it the same thing, and
that's what we basically do. We see that as we go deeper and
deeper in the sediment, we're still calling them the same
thing, but they can be separated by some number of mutations over
time. But just from a naive point of
view, it seems a bit surprising that over 100 million years of
the population. That's been subject to this very
extreme selection pressure. If you like to survive with
virtually, no food should still be represented in the
population. That's on the seafloor surface,
which is had none of that pressure and could have evolved
quite happily in other directions.
You know, one of the curious things about selection is it
applies differently to different Gene's ultimately what you
select against is the organism, right?
The actual living thing, not the individual Gene, but this is
something again, that oversees lab in.
Munich is looked at recently, and what Bill finds is that
again over just a few million years which is what the depth of
sediment that he's looked at in the North Atlantic that you can
see mutations accumulate in the genomes of the organisms that
live beneath the seafloor, but the mutation is preferentially
accumulating in Is associated with functions that the bacteria
probably aren't using. So the genes for motility for
examples for swimming are accumulating mutation and the
genes for reproduction or not the remaining more stable.
One Thing Worth bearing in mind is that something like only one
in five thousand mutations are so, as positive right most
mutations are negative or neutral?
And so, essentially what bill is seeing, accumulate are mutations
that are basically neutral because these things aren't
swimming anymore. If you had a mutation in those
Gene sequences that are used for reproduction, almost all of the
time that would be negative and The Offspring just wouldn't
survive. So there's a lot of positive
pressure to keep their core genes from not changing very
much. And then, once that pressure is
released from genes that are used for functions that the
microbe no longer uses, then we start to see the mutations
accumulate, it would be fun to look at evolution in the context
of a hundred million year old community.
And see if what Bill sees over a few million years just carries
on. We haven't really tested the
cells that you keep brought back to life to see if they can swim.
For example, all that any special constraints than on the
nature of the geological environment that enables such
extremely long-lived, bacterial colonies to survive.
I mean, obviously, they won't survive passing into a
subduction zone. For example, one can imagine a
number of constraints, the usual constraints that People talk
about when they think about these natural environments,
revolve around temperature if it's too hot, everything dies.
And so, when people talk about extremophiles, there's a lot of
focus on temperature. One, could imagine more subtle
constraints. For example, the sediment that
these microbes are removed from has been continually exposed to
oxygen for 100 million years or more.
It's conceivable that anaerobic bacteria.
So bacteria that can't live In the presence of oxygen are
driven to Extinction in environments like that and in
fact, Yuki's control experiments suggest that, that's the case.
He wasn't able to grow anything in the vials without oxygen.
And in the case of subduction, which you mentioned, it's an
enticing thought that the combination of temperature and
pressure and subduction zones is extraordinary from a surface
World perspective. And if you think about the
temperature, you can also get deviations from a long-term
equilibrium like the core of the subducting slab.
Be cooler than the edges as it penetrates into the mantle.
So you could imagine a temporary refugium of even a few million
years in the core of the sinking slab.
That's what amazing thought, tens of kilometers down in the
middle of a slab, it just depends on when you break
through the temperature threshold, the known temperature
limit to life. Right now is about 120 degrees
Celsius under normal circumstances for the average or
that will take you down, you know, about 20 degrees per
kilometer. So that's six kilometers.
Down but where the geothermal is cooler, it can be deeper as for
example in a subduction zone. So if bacteria can survive for
100 million years is there really any upper limit as to how
long they might live from a practical perspective.
I really don't think so. The bacteria in our digestive
systems are living a few hours before they divided the bacteria
in this sediment have been living in isolation for 100
million years and so Over slowly.
They're dividing their dividing a lot more slowly than the
bacteria in our digestive systems orders of magnitude more
slowly. And the community has survived a
hundred million years as, you know, so to survive a billion
years on mars or even a billion years on Earth, that's only one
more order of magnitude. We took an extreme example and
thought of the community, in our digestive systems, is surviving
the durations of our lifetimes. If each of us lives 100 years,
this is the tiniest fraction of that. 100 million, right?
The ones in the settlement of the communities and settlement
of lived, a million times longer.
And so to pick up one more order of magnitude doesn't seem so
striking gosh. So you can really imagine
communities living for of the order of the age of the planet
or even the age of the universe. If you're up to about what 13
and a half billion, if you could retain the environment for that
long, you could in principle retain the community.
What we see on Earth of course, is that stuff that approaches
four billion years old has been massively heated.
Impressed and probably lost its bacteria long time ago.
But if you could somehow take a piece of ancient Greenland when
it was young and hold it, aside from the rock cycle, the
community, and it might reside there.
For four billion years, you touched on the space aspect.
When you mention the possibility of such communities, perhaps,
living below the surface of Mars.
And in fact, we had a podcast on the perseverance for over and by
looking just for that right now, but what about the implications
for life and perhaps that? Bacteria, traveling from one
planet to another, there are experiments, and a lot of
calculations that show that bacteria can survive relatively
small body impacts, right? So, if you have a chunk of Mars
that gets knocked out into space by a big impact, you probably
know that when you get a really big impact, the center of the
target is vaporized. And then, as you move farther
from the center, it liquefies, and as you move farther from the
center, it's just mechanically Erupted and that mechanically
disrupted stuff flies out of the crater area during the rebound.
So stuff that's mechanically disrupted, never reaches the
temperatures necessary to kill wife and people have shown with
vertical gun experiments at Nasa.
That you can essentially take the bacterium impregnated piece
of sandstone and fire it at a Target and it will survive.
So you certainly have the possibility for moving life
around on these timescales. So perhaps a potential support
for the pants. Bye, Mia, hypothesis for the
origin of life. It is potential support person.
I find panspermia hypotheses interesting because from my
perspective, the simplest explanation for the origin of
life on Earth. Is that it originated here?
Most of the people who talk about panspermia and the Earth.
Mars context, talk about it. Coming here from Mars, I think
it may be likelier that it's gone to Mars from here, Steve
don't thank you very much. Thank you very much Oliver.
It's been a pleasure to speak with you today. for more about
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