This says geology bites with Oliver.
Strimple stromatolites are thought to represent evidence
for life on Earth as far back as about 3 1/2 billion years ago,
which would be far and away the oldest life we know about.
They are the LED structures left behind in rocks by the interplay
between communities of microbes and their environment.
But the interpretation of these structures as biological in
origin is controversial, and several non biological
mechanisms have been proposed that can generate stromatolite
shapes. Martin van Kralendonck has
devoted his long and prolific research career to the study of
the early Earth. One major theme of his work has
been to use detailed mapping and lab research to develop
geological models for the environments of Earth's oldest
fossils. This has helped establish the
biological origin of many ancient fossils.
His recent work on a newly discovered find of exceptionally
well preserved 3 1/2 billion year old sedimentary rocks in
the pillbrocratin of WA has provided the strongest evidence
to date. The structures of this great age
were indeed produced by the earliest forms of life.
Martin van Crellendonck is a professor in the School of
Biological, Earth and Environmental Sciences at the
University of NSW in Sydney. Martin van Crellendonck, welcome
to Geology Bites. Hello Oliver, it's a pleasure to
be here and nice to have a chat with you.
What do stromatolites look like? Stromatolites look like layered,
wrinkly structures in rocks that are different from their
surrounding geology. Their structures preserved as
fossils, just like a fossil elephant bone or a trilobite,
that are preserved in rocks and then surrounded by the
geological matrix, the sandstone, the silt, the shale,
the shirt, which is made by processes that don't involve
life. And they're entombed within that
matrix for, in some cases, many billions of years.
So roughly how big are the structures that you're talking
about? Stromatolites can be very large
indeed. They could be up to 5 meters
high, and they look like rocket cones and some exposures.
They're packed side to side, but those are in slightly younger
rocks than what we're talking about.
Those are already 2 billion years old, but the very ancient
ones, they're quite a bit smaller.
They're about a centimeter scale to sometimes up to 30
centimeters. But even 2.7 billion years ago,
they're stromatolites that are the same height as me, almost 2
meters tall. Before we talk about how
stromatolite like structures can be formed biologically, how do
proponents of a non biological origin explain them?
So you have to be clear that stromatolites are regarded by
the entire community as evidence.
For life through much of the fossil records.
So there are stromatolites that are living today.
There's stromatolites that are a couple of million years old.
There are stromatolites that are one and 2 billion years old, and
nobody has any doubt that those are made by biology.
It's really only the very most ancient ones, these ones that
are 3.5 or beyond, because there is one claim in Greenland at 3.7
billion years old, once they get to that great antiquity.
People are a little bit more cautious just because the rocks
are so old that in many cases they've had quite a long history
of alteration movement, you know, by tilting and folding and
cracking. And because the structures are a
little bit more cryptic, people are rightfully cautious about a
direct interpretation of biology.
Extraordinary claims need extraordinary proof.
That bar is raised for the most ancient type of life, to be able
to really document very carefully that it was made by
biology and not by something else.
There have been proposals, and the main one is that they could
just be the crusts of minerals that have accumulated over time.
And we know that happens in a variety of different settings.
We can see beautiful sometimes shrub like shaped mineral
growths. Some beautifully layered smooth,
some a bit more regularly textured, and those are
structures that can sometimes look like stromatolites.
So people are rightfully cautious to say, well, how can
you absolutely determine that that structure is not a mineral
crust without the influence of biology?
That's a perfectly valid question.
If you think about it, we as humans are living.
But we're also a chemical system and we also produced minerals.
So if you tap your teeth, you're tapping a mineral.
We make minerals, we make bones, we make teeth, we make
fingernails. And so that divide between life
and just chemistry or just geology is in some cases really
fine and really hard to define. What is the mechanism whereby
these intricate layered structures, as much as 5 meters
tall, can be formed by? Well, by biology?
And what kind of biology? Yeah.
So the great thing is that we have living remnants of these
microbial communities that are still making stromatalites
today. So we can study those and
understand very clearly how these rock structures are formed
because they are forming in front of our eyes today.
So the most famous ones are in Shark Bay, WA and they're large
structures up to a meter tall and they're made of rock.
For 99% of the structure, they are made of rock, but the very
top most layer is green and squidgy.
And so if you press on it, it's a little bit slimy, it's goopy,
it moves. So that's where we can see the
life is. And of course when we take a
microscopic view, we can see the microorganisms.
But what these communities do is they make their structures in
three different ways. One is that because they are a
bit sticky, they actually trap sediment that's loosely in the
water. Just think about the piece of
sticky tape on your dining room table with the sticky side up.
Any dust that's floating through the air will stick onto that
sticky tape. And so stromadolites grow the
same way. They trap and then they grow
over and bind the sediment and make a layer that way.
But they can do other things as well and because of their life
force, their metabolism. They actually change a very
small volume of seawater. They change its composition and
seawater has dissolved minerals in it.
When you evaporate the water, it leaves behind those minerals.
And so limestone reefs are one example of that.
Limestone is dissolved in water and we know that salt is
dissolved in seawater and So what microbes can do is they
change the composition of the seawater.
And that will induce the precipitation of minerals
behind. And the microorgans always stay
one step above, they deposit the minerals below and they keep
growing upwards. And so you build up these
layered kind of apartment buildings, if you like from the
ground floor up over time. And then the 3rd way is that you
can get a biological mineral precipitation so.
The presence of those microbes just induces the minerals to
precipitate on them because they have a charged surface.
So there's been interplay of three different mechanisms that
allow for stromatolites to grow. Some only grow by trapping A
binding sediment, some grow really primarily by
precipitating materials as a result of metabolism.
And then there's any combination in between, and that's caused
some of the confusion in the geological literature.
How can we prove that these are made by life?
If you can also have a biogenic mineral crust precipitation, so
it is a tricky game. Are the labs analogous to growth
rings and trees? Each successive wrinkle, if you
like, in this tramatolite. It's very, very tempting to
interpret the layers as annual growth links, but the reality is
that a colleague of mine has sat on a beach in the Bahamas and
watched tramatolites grow for years on end.
And it turns out it's not very regular at all.
That depends a lot more on changing environmental
conditions and storm events turn out to be really important
markers and then they grow very slowly and not much happens for
a long time in between. So it's not as easy as saying
their annual layers, but they do accrete over time if the
conditions are right. Okay.
So let's talk about the recent find of these exceptionally well
preserved 3 1/2 billion year olds from Atalites.
Where exactly were they found and what do they?
Look like so. These ancient structures were
found in the Pilbara region of WA, which is right up in the
northwest corner of the continent, but they weren't
recently discovered. They were actually found in the
very late 1970s already, and they've been looked at for a
long time using mostly just quite simple techniques.
Their shape in the outcrops some thin slices of rocks.
But it's only recently that we've been able to really
penetrate deep inside them into fresh materials and that's the
recent advances that have been made by our group.
So all the previous studies have been worked on from surface
deposits. And the problem is, is that the
surface of the Earth is exposed to weathering.
It's exposed to sun and rain and drying and oxygen.
And in very old rocks, that causes the minerals to get
altered by those surface processes.
And so even though the textures are really well preserved at the
surface, what made the minerals and what the fine kind of
textures were preserved, we couldn't determine until we were
able to retrieve samples of fresh, unaltered material from
deep below the surface through diamond drilling.
Just like the way that exploration companies will take
a drill rig to explore for mineral deposits deep beneath
the ground, my group in two different studies were able to
take a drill into the Pilbra and penetrate below the level of the
surface alteration and extract fresh materials.
And it's by studying those fresh materials that we've learned so
much more about these ancient structures.
How do you know where to dig? Yeah, well, that takes a long
time. So I've been chomping around
that country for about 30 years now, and I'm finally starting to
get a bit of understanding about it because you're right, there
are places where the structures might be faulted away.
And so one of the best places where we take visitors to come
and see. We didn't drill there because
there's a little fault structure and we weren't sure how deep it
might have offset the units, so we went somewhere else where the
conditions were much better preserved.
And we were able to drill there first in 2007 and we retrieved
really good materials. And then more recently in 2019,
we drilled in that similar locality but in a couple of
different places and we retrieved really good material.
And listen, sometimes it doesn't always work out.
One of our drill holes in 2019 completely missed.
And another one got stuck in a fault that was full of clay and
we lost the drill a stem. And you know, it's a risky
business, but the success is worth the effort.
And we got 3 drill holes that were really perfect right
through the sequence. And we actually had one piece of
drill core that we pulled out of the ground and it had
stermatolites exposed on the edge of the core.
We could see it come out of the ground.
It was just incredible how far down was it?
8090 meters down, the depth of alteration can extend down to
about 70 meters. And so we purposely drilled down
till about 80 or 90 meters to be below the effects of surface
oxygen. So what exactly did you look at
in these pristine rocks from this formation then that you
were able to recover from the core to try and clinch the
biological origin of these very, very ancient rocks?
So on the surface, these stromatolites appear rusty red
and black. And they're wrinkly, textured.
And the wrinkly texture is the signature of biology, because
that doesn't happen so easy with just geology.
But then, at depth, these structures that looked exactly
the same were bright yellow, made out of what's commonly
known as fool's gold or pyrite, iron sulfide.
And when that's exposed at the surface, the sulfur combines
with oxygen and it weathers and it makes rust, basically.
So we were looking at the rusted equivalents.
And we couldn't see the fine scale texture.
But down under the ground we found that perfectly preserved
pyrite. And when we pulled those
structures out, we could see these lovely little Dome shaped
columns, in some cases only one centimeter high, but very
clearly growing off of the ancient sea floor 3.5 billion
years ago. And below that we could see
ripples in the sandstone. You know, we could see where the
beach environment was. We could really reconstruct the
environment from these fresh materials, but most importantly
to be able to look inside the layers.
So remember when I talked about livingstromatolites at Shark
Bay, how there's that sort of green squidgy layer at the top
that's the growth material. Well, as the minerals
precipitate, they sometimes grow around the organic matter that
those communities produce and they trap it inside and.
And a colleague of mine of Raphael Baumgartner devised the
way of etching away some of the iron sulfide and revealing what
was buried and tombed within the stromatolites and he found
remnants of organic matter. And so that was a real aha
moment, because if they were just non biological mineral
crusts you wouldn't expect to see organic matter.
It shouldn't be there. And so we found this material
preserved inside the iron sulfide, this wrinkly lamination
that made the structure of the stromatolites.
And that was, Oh my goodness, there's something unexpected
here in terms of a biology. But there's a feature that's
consistent with these structures being made by ancient life.
When you say organic matter, did you actually find biomolecules
like lipids or something? No.
So these very ancient rocks have been heated up by metamorphic
processes, by temperatures, and really just heat coming through
the crust for so long. So they've been up to about 300
degrees Celsius. They've been cooked, and that's
too hot for biomolecules to be preserved.
What we did find were two features that were of great
interest. One is that the type of carbon
preserved in the rocks was consistent with that heating.
One of the options that the skeptics would say is, oh, that
organic matter could have been brought in later and has nothing
to do with the material and the texture that you're looking at.
But there were two features we could argue against that.
One is that it had been heated to the same temperature as the
rocks around, so we knew it was very early.
It had to be there at the same time as the layers were formed.
And the second was that the isotope ratio of carbon.
So carbon forms in a couple of different types, 12 and 13
carbon, the isotopes of carbon and.
In just normal organic matter, that's fractionated at a certain
degree, but then life changes that dramatically because it
prefers the lighter carbon, the 12 carbon.
And this organic matter, it turned out, was fractionated in
the same way that life fractionates carbon down to
about -27, -, 30 per mil. It's a very strong
fractionation. And so again, that was
consistent with life. The other really important
textural observation was that there were no veins, so later
cracks that could have allowed the caravan to come in.
It actually sat within these very, very small, and I'm
talking nanoscale here, so extremely tiny, much, much,
much, much, much thinner than the width of a human hair.
These kind of pores within the sulfur.
And that showed again that the material was present as that
pyrite was being precipitated, which we think was actually
induced by the microbial activity.
So that organic matter, then, is carbon, a certain kind of actual
carbon that came out of this skeletons of these
microorganisms? It's a material that's called
kerogen and it's a complex mix of carbon bearing molecules, but
it's attached to oxygen and hydrogen.
And because it's been cooked up, it's quite a structured
material. The most structured type of
carbon is graphite that we use in our pencils, and that comes
from much higher temperatures. That's got to be up at about 500
degrees. But Keragen is an intermediate
step. So there's no indications of the
primary organisms, the microbes, because it's all been heated up
so much, but it's the decayed remains of microbes.
And a material that microbes make called extra polymeric
substance EPS. And what that is, it's kind of a
sugary goo that microbes make so that they can move around their
environment. Microbes need to be able to move
towards sunlight, towards food sources, and they do that by
gliding through the sugary goo. This EPS.
And in fact it turns out that in stromatolites.
The EPS goo is actually much more in volume than the microbes
themselves. They make quite a soup that they
can move around in, and it's this soup that actually gets
preserved most commonly. And when we dissolve that pyrite
away with a little bit of nitric acid, where we found ropy
remnants, sometimes curling back on itself and knotted and then
breaking into strands all entombed within that pyrite.
And that looks exactly like the EPS of modern microbial
communities and it was that kind of feature that really sealed
the deal. So in addition to the carbon,
the kerogen being preserved in the pores, having the right
carbon isotope value and then this rope remnant EPS, that was
a triad that showed that yes, these were formed by biology.
You also looked at the concentration of certain other
trace elements in these formations, didn't you?
That's. So we were able to take a very
thin slice of one of these centimeter tall stromatolites
down onto the synchrotron in Melbourne, which is a source
that generates high energy particles.
And we use the X-ray analytical facility and we were able to map
changes in element concentrations through those
layered pyrite stromatolites. And it turns out that pyrite can
absorb different elements as it grows, and so it can be rich in
arsenic. It can be rich in copper, zinc,
lead, etc. And what we found was this very
gorgeous microscale lamination of changes between arsenic rich
pyrite, zinc rich pyrite and nickel rich pyrite.
And the exciting thing there was that it demonstrated there were
textures of the layering. That showed it wasn't just
regular a biological growth, but highly irregular with cutoff
structures, growths like you see in trees, some layers that grow
regularly and then they get over printed by another layer,
whereas middle growth is very simple and continuous.
So there was a good textural contrast.
But what we also know is that there's a very early type of
primitive type of microbe that prefers using zinc and nickel,
and those are called sulfate reducing bacteria.
They take sulfate that's dissolved in the seawater in
very early earth conditions and changing that to sulfide.
So, so four goes to S2. Most of it binds with iron, but
because microbes of that type need nickel and zinc, they leave
behind traces of enrichments in nickel and zinc.
And that was another smoking gun to say, wow, this fits exactly
what we predict. And there it was, looking us
straight in the face. It was very cool.
Wow, so. These metals are byproducts or
part of the metabolism of these anaerobic microbes.
That's right, they need these trace metals to just enhance the
chemical reactions between these major elements, sulfur and iron
and stuff. So that's known by studying
modern sulfate reducing bacteria.
They always find enrichments of zinc and nickel and here we
found them 3 1/2 billion years ago so. 3 1/2 billion years ago
was before the Great Oxidation Event and when the Earth's
atmosphere became rich in oxygen as it is today.
And so did these early microbial communities then have different
anaerobic metabolisms to those that are around today in Shark
Bay. So that's something we're still
trying to tease out of these ancient structures.
It's very difficult to be able to prove a type of metabolism.
Now we think that the zinc and the nickel combined with
fractionated sulfur isotopes that previous groups have
documented strongly suggests that there was sulfate reducing
bacteria alive at that time. But there may have been other
microbes present in those communities as well.
And we think that because in modern environments, sulfate
reducing bacteria are quite a small volume of the overall
community within a stromatalite. And when I say a community at
Shark Bay, there are more than 10,000 different types of
microbes in a stromatalite, but there's usually one dominant
type of bacteria. And in modern stromatalites,
that's cyanobacteria, what used to be called blue-green algae.
It's actually bacteria, and that harnesses light energy and it
gives off oxygen as a byproduct. And they're the ones that
changed our planet about 2 1/2 billion years ago to this
beautiful blue marble that we live in today.
But prior to that, there were almost certainly oxygenic
photosynthesizers, as we call them, the cyanobacteria present,
but we don't know how far back in time they went.
And certainly in the very early Earth, there's no evidence for
free oxygen in the atmosphere. And so the question is, what was
the primary producer? What was the big volume of
microbes that could build these structures that even though
they're small at a microbial scale, are still very big,
right? Like a microbe is maybe 10
microns in diameter, 100 microns in diameter.
And these stromatolites we're looking at are centimeters to
some case, 30 centimeters. So that's a lot of microbial
activity and we think, but we haven't been able to prove that
there were probably anoxygenic photosynthesizers.
So bacteria that had been able to harness the energy from
sunlight but gave off a different byproduct from oxygen.
It's actually a much more complicated metabolism to give
off oxygen and to break those molecular bonds than it is by
using photosynthesis to metabolize without producing
oxygen, And that's known to be a much more primitive lineage.
And so it's likely that there were an oxygenic
photosynthesizers. But we haven't been able to show
the definitive proof for that. And that might be beyond our
science at the moment, something we're still working on.
But it's. Interesting that, even though
the conditions could have been radically different back then
from what they are today and therefore that the Community.
The population, if you like, of the microbes would be quite
different from those that are around today in Shark Bay.
Nonetheless, you have structures that are very reminiscent and
morphologies that are very reminiscent of what we see
today. So it's kind of interesting that
the same microfilm and columnar branching and all the things
that you described would be so closely analogous across the
billions of years. I guess in some ways it's not so
surprising because what stromatolites do is they
actually of course they want to survive and out compete the
other aspects of their environment.
Now in the very early Earth there were no competitors like
crabs or snails or seashells that would eat them today, but
they were competing against the environment.
Their environment was introducing sediment into the
area where they were trying to grow and sediment kills them
off. If there's too much sediment,
they can't grow, and so stromatolites compete against
this by growing upward to stay above the sea floor.
And so that kind of aspect is common throughout time.
If you only cover a flat surface, you can only grow so
much. Just like humans build apartment
buildings to fit more people into a small area, so
stromatolites grow upwards because they're increasing their
surface area can fit more microbes into that volume of
space. It's just a common survival
technique. And so it's maybe not surprising
that even the oldest remnants of life show that battle to
survive. You've.
Been heavily involved in the search for life on Mars with the
Curiosity and Perseverance Rovers.
Is that because if there was one's life on Mars, it might
have resembled to rescue stromatolites?
Or because we think that Mars may once have had an environment
similar to that of the Archaean on Earth.
It's for both of those reasons all of us.
We have an example of 1 here on Earth.
Everything that we do in our exploration for the search of
life elsewhere is based on our understanding of early life on
Earth, particularly around Mars. Because Mars is a smaller
planet, it became geologically dead much earlier in its
history. Most of the rocks exposed on the
surface of Mars are between 4:00 and about 3 billion years.
And so really the Pilbara in WA, one of the few places on the
globe that has rocks 3 1/2 billion years with evidence of
life, is the place that everybody goes to, to not only
see the textures that life preserved, but also to
understand the habitats where life lived.
If you have a whole planet to explore, like Mars, where would
you go to maximize your chance of success, to look for life?
And so a large part of the study that my group has done is to
understand the environments where life flourished on early
Earth. And one of the exciting things
is that we look at the Dresser Formation, these ancient 3.5
ones, but they're also Stromatal likes at 3.4, at 3.35, and
through the geological record we can build up a picture of where
life lived. What's extraordinary is that if
you talk about older than 3 billion, there are many
different niche spaces or environments where we find
evidence for ancient life. And that's incredible.
It just documents that life got started on Earth very early and
diversified into these different environments, also very early.
And that gives us hope about searching for life on Mars,
because Mars had that short history.
But if life got started on Earth and diversified very early, well
maybe it got started on Mars and was able to gain a foothold in
that very early record. So people come to look for the
geological traces. What should we be looking for on
Mars? What's the guide in terms of the
textures and the fabrics and the environments, rock types?
But then also what kind of habitat?
So would you go to a flowing river or a quiet lake or a delta
or a deep sea hydrothermal vent or a shallow caldera, where
would you look? So you've got all those choices
and our group has brought planetary investigators through
the Pilbara so that they can really see that evidence for
themselves. So we've had a little bit to do
with site selection and understanding textures and what
the search strategy should be if.
Microbial life does indeed go back to 3 1/2 billion years ago.
Do you think it was somehow facilitated by some particular
change in the environment at that time?
Or do you think there was no particular reason for the
emergence of life at that time? And if we just keep on looking,
we might find still earlier life, perhaps going back to near
the time the Earth first cooled enough to generate a hospitable
environment nearer to 4 billion years ago.
I would love that to be the case, Oliver, don't get me
wrong. But unfortunately the history of
Earth was that it had a very hot and almost cauldron like
beginning. And it's only until about 3.5
billion years ago that you get very well preserved ancient
rocks. So there are older rocks on
Earth going back to about 4.03 billion, but they've been really
cooked up. They've been brought down deep
into the crust. They've been heated to
temperatures above their melting point and then swirled around by
tectonic movements. And there's almost no primary
information left in the textures of the rocks, which is so
critical for understanding early life.
So the Pilgrim is one of these sort of geological anomalies,
just one of these fortunate places that have survived intact
basically from 3 1/2 billion years ago.
Most of the rest of the world, and we've looked now across a
lot of the rest of the world, has rocks that are either
younger or older but more strongly deformed.
And as I mentioned earlier, there is a record.
In fact, there's two different records of ancient life from
West Greenland in rocks that are 3.7 billion years old, and there
are little isolated pockets within that otherwise kind of
soupy mess where there are preserved some primary textures.
Now the community is not convinced by these older records
because it doesn't have all the different arguments like we've
described for the Dresser formation.
They have one or two features that are really compelling.
But because they're so heated and these are up to about 505
fifty degrees, they've got some big metamorphic minerals growing
around them. People are less convinced of the
fact that these were made by biology.
I am personally 100% convinced because I've been there.
I've seen them. I understand that setting.
And so getting that record of life back to older periods in
the geological record is really difficult.
And you mentioned about life emerging at 3.5.
So that story I just recounted actually suggests that life
probably emerged much earlier, but we just don't have a record
of it. And that's also part of the
exciting reason for going to Mars, because it doesn't have
that young history of cooking things up.
We can actually see a bit of our own early history on Mars
because it was frozen in time. And so there's value in going
back to Mars to learn about what our early Earth might have
looked like, and perhaps even get a better record of where
life might get started if it ever gained a foothold on Mars.
You're. Not suggesting a common origin
of life between here and Mars, are you?
No, that's just that. Both planets probably had a
similar very early start, and on Earth that early start has been
erased by younger events. But on Mars that's been
preserved, and so we might just be able to go and see what
happened in parallel there. So yeah, if we go and find signs
of ancient life on Mars, that might be a separate beginning.
That would have huge implications for our
understanding of the universe if it happened on 2 planets next
door to each other, Oh my goodness.
Just imagine how much life might be out there in the universe.
Unbelievable. Martin van Kerennock, thank you
very much. It's my great pleasure to talk
to you, Oliver, and thanks for the opportunity to talk about
stromatolites. To see pictures and
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