The Artifact Redux: Stone Mushroom Clouds

In this classic episode of STBYM’s The Artifact, Joe talks about mind-boggling prehistoric mineral formations. (originally published 2/10/2021)

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind, a production of
I heeart Radio. Hi. My name is Joe McCormick, and
this is the Artifact, a short form series from Stuff
to Blow Your Mind, focusing on particular objects, ideas, and
moments in time. On the western coast of Australia, there's

(00:24):
a place called Shark Bay, and within Shark Bay there's
a nature reserve known as Hamlin Pool. Today you can
walk out over a wooden jetty at Hamlin Pool to
see the shallows up close. Down below, there are hundreds
of strange, bulbous mineral formations peeking up over the water

(00:44):
line or sitting just below it. It's hard to describe
exactly what they look like. Black stone broccoli perched upright
in the still water, atomic mushroom clouds frozen in place,
or dark pebbly brains flocking out of the Indian Ocean.
These are stromatolites. If you stand on the jetty at

(01:06):
Hamlin Pool looking out at this army of mineral bulbs,
you're getting a pretty close approximation of what most visible
life on planet Earth looked like for something like eighty
percent of its history. Because while these are mineral formations,
They're not just dead rock, they're alive and growing. Stromatolites

(01:28):
are one type from a class of mineral formations called microbiolites,
natural stone monuments that are built by microscopic organisms, and
not all of them look like the columns of mushroom
brain broccoli at Hamlin Bay. Some microbiolites are flat, some
are domed, and some form ascending pillars with different shapes

(01:50):
and contours. Though there are lots of microbiolites in the world,
there are only a handful of places left where you
can find true marine stromatolites growing in the wild. So
what makes us stromatallite special. The word stromatallite means layered rock.
If you look at a cross section, you can see

(02:10):
banded strata within them extremely thin layers of mineral deposition,
kind of like a stone puff pastry, with the layers
sometimes alternating between light and dark. And these layers actually
tell us something about the process that created them. Stromatallites
are built by microscopic organisms like photosynthetic cyanobacteria also known

(02:33):
as blue green algae. These are single celled life forms
that can be found almost everywhere on Earth, especially in
the water. Cyanobacteria like plants, survived by using energy from
the sunlight to convert carbon dioxide from the environment into food.
Though cyanobacteria existed for billions of years before the first

(02:55):
plants evolved, without them, you never would have been born.
As Earth's first photosynthesizers, microbes like cyanobacteria converted the planet's
early atmosphere into what it is today by polluting it
with their metabolic waste product, which is oxygen. Every animal
that ever lived could only evolve because of what the

(03:17):
early photosynthesizers did to the atmosphere. So for billions of years,
these microbes dominated planet Earth, changing the composition of the
air and leaving behind their stromatolite mineral formations in the
fossil record. But to come back to the question about
how they form, where do these layers of strata and

(03:38):
the stromatalite come from. Microbes like cyanobacteria don't just float
around by themselves. When they're able, they glom onto other
micro organisms to form what are known as biofilms or
microbial mats. Think of a kind of thin, sticky carpet
in which billions of microbes glue themselves both to one

(03:58):
another and to an underlying surface with the help of
a class of biological cement known as extracellular polymeric substances
or e p s s. These microbial mats, being sticky
by evolutionary design, don't just stick to the underlying substrate.
They also act kind of like a glue trap, catching
hold of tiny grains of sediment and sand that wash

(04:22):
over the surface of the mat due to the tide
or other mechanical forces. Over the years, layer by layer,
these sticky mats of biological material trapped sediment and also
calcium carbonate harden into solid mineral formations like the columns
at Shark Bay, always climbing up higher like the crown

(04:42):
of a tree in the forest, to move towards the
sunlight that feeds them. If you look at the history
of earth life in the fossil record from roughly three
and a half billion years ago until about one billion
years ago, stramatallites absolutely dominate the scene, gathering in shallow
sea ease and across continental shores around the world. But

(05:03):
around a billion years ago, the finally layered stramatallites start
to vanish from the geological record, and they've remained rare
until today. What happened to them. There are several possibilities,
but one interesting investigation into this question was a study
published in in p N A S by Joan M.

(05:26):
Bernhardt at All. This study picks up from the observation
that at around the same time stramaatellites began to decline
in the fossil record, they seem to be replaced with
a different kind of microbial matt formation called a thrombo lighte.
Whereas stramatolites are layered rocks, thrombo lights are clotted rocks

(05:47):
with a microstructure to match their name. So did most
of the world stromatallites become thrombo lights and if so why?
The researchers behind this study suggest that thenswer to the
question may lie in the evolution of another organism known
as foraminifera. Foraminifera, often shortened to four ams, are a

(06:09):
type of single celled eukaryotic organism from the Kingdom of
life known as the protests. Along with organisms like amibas
and the Plasmodium parasite that causes malaria. You can find
for Aminifera throughout the ocean, often in seafloor sediments, where
they use amazing and fantastically creepy, shape shifting tendrils called

(06:30):
pseudopods to reach out into their surroundings and snatch up food.
For Aminifera build tiny shells for themselves called tests, and
they first evolved roughly around the time the stramatallites were
declining and the thrombo lights began to rise, so it
makes sense to wonder if they had something to do
with the change in Earth's microbial lites. The authors of

(06:54):
study wanted to see if the presence of for Aminifera
in a living stormatellite would have a noticeable effect on
how new mineral layers were accumulated, so they took modern
living stormatellites from a place called high Born Key in
the Bahamas and seeded them with foams. Some of the
test samples were treated with a drug that would inhibit

(07:14):
the function of the forum pseudopods, while others were left untreated.
After about six months, they found that the presence of
functional forums could absolutely affect the structure of the stormatallites.
In samples where the foreams had been drugged, thin layers
were visible. In the samples where the forearms were allowed
to do their thing, the stramatallites had assumed the clotted

(07:37):
structure seen today in thrombolites. Altogether, this is taken as
evidence that the forum and if um may have had
something to do with the stormatellites decline. Today, you can
only find living stramatallites in special places, usually places with
water that has a very high salinity, like evaporating salt
water pools and tidal areas. I kept thinking about how

(08:00):
in this way stramatollites have something in common with sauerkraut.
Lacto fermented foods like sauerkraut and kimchi are made by
salting vegetables and packing them down in a wet, anaerobic environment.
The reason the vegetables turn nice and sour instead of
simply rotting is that the salty wet conditions in the
jar inhibit the growth of microbes and mold that cause spoilage,

(08:23):
but allow the growth of salt tolerant lactic acid bacteria.
As the lactic acid bacteria thrive, they produce acid as
a byproduct of their metabolism, which lowers the pH of
the fermentation, further preventing other microbes from surviving and creating
the sour flavors we love. Wild stramatollites today tend to

(08:44):
survive in high salinity environments where organisms that would otherwise
graze on the exposed mats and eat them up just
can't tolerate the salt. Tune into new editions of the
artifact Free Wednesday, hosted either by Robert or myself. As always,
you can email us at contact at stuff to Blow

(09:06):
your Mind dot com. Stuff to Blow your Mind is
a production of I Heart Radio. For more podcasts for
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