When we envision the end of life on earth, the inevitability of it, we tend to think
in terms of catastrophes like asteroid impacts, wars and so on.
But the reality is that they can’t actually do it.
In recent years, several papers have come out that actually have established that the
real true final extinction of all life on earth will only come at the hands of the sun.
There’s actually nothing else that can do it, especially on the microbial scale.
At least nothing that’s currently known.
And that’s a problem, though.
What you don’t know, can hurt you.
It was once thought that the end of life on earth would come in the distant far future
when the sun swells into its red giant phase and swallows the earth.
It’s actually uncertain however, based on much more recent work, whether the sun actually
will reach out far enough to engulf earth, or will just closely roast it, leaving a cinder
earth behind to permanently orbit the sun as a cooling white dwarf.
If not engulfed, the history of earth is somewhat melancholy.
The earth started as molten, then its surface cooled to what we have now, but it will go
molten again in the future only to finally and permanently solidify again in orbit of
the white dwarf with no traces whatsoever of the living planet it once was.
But that overall view has changed over the years, we have far less time than 4.5 billion
years.
Rather there is only about 1.1 billion years left at most before the increasing luminosity
of the sun dramatically changes earth into a hot house Venus like planet due in part
to the evaporation of the oceans, then as it bakes earth, it eventually turns back to
a surface molten state not unlike it was when it first formed.
The sun is gaining about ten percent luminosity for every billion years it ages.
But hidden within this are still wildcards that are unknowns, and sometimes they surface.
One such wildcard surfaced in 2022.
A big one, that before that year, no one knew was even happening.
In a paper by Motohiko Murakami and colleagues, link in the description below, they found
something unexpected and somewhat shocking.
The finding involves the cooling of the earth’s core and the convecting dynamo in the outer
core that is creating earth’s protective magnetic field, something surface life on
this world very much depends on in a variety of ways.
It’s been known for a while that earth’s core mantle boundary bears large amounts of
the enigmatic mineral bridgmanite, more on that in a bit.
This area of the earth’s interior is unlike anywhere else on the planet.
The boundary between the outer core and the mantle resides about 2,900 kilometers deep
in the interior of the earth.
The liquid outer core is extremely hot, about 4200 degrees celsius, or 7600 degrees fahrenheit.
But the solid bridgmanite rich mantle just above it, is significantly cooler by about
400 degrees celsius.
This zone is also subject to extreme pressure, which leads to interesting geology that happens
nowhere else on the planet.
A very common mineral in the solar system is olivine, a compound of silicon, magnesium
and iron.
But under that intense pressure, it actually is forced into becoming other mineral arrangements,
which are things like bridgmanite, but also ringwoodite and an unusual mineral called
wadsleyite.
But of specific interest here is bridgmanite, and to a lesser degree the mineral ferropericlase.
Together these two minerals in the lower mantle determine how fast the outer core can cool.
Bridgmanite is the most common mineral in the earth’s lower mantle and in fact this
mineral might actually be the most abundant mineral in earth’s overall internal make
up.
Because of the conditions in which it forms, it is not found on the surface of the earth.
This led to a sort of odd situation in that it’s existence was from a prediction, meaning
it wasn’t an actual mineral until recently, rather it was just a hypothesis.
Tiny crystals of it however have been found in the Tenham meteorite, so it now is officially
a mineral.
The problem here is that bridgmanite transfers heat, and the recent paper has shown that
at the core-mantle boundary, the bridgmanite is actually transferring heat out of the outer
core 50 percent faster than what was previously thought.
This is spooky.
What this means is that earth’s outer core is cooling significantly faster than we previously
knew, and this in turn means that at some point, once the core cools enough, the dynamo
of the outer core shuts down and with that, so does the earth’s magnetosphere.
Why this was not previously known is that it’s actually somewhat difficult to experiment
with Bridgmanite.
It needs the immense pressure of the interior of the earth to even form.
You can synthetically make it, but it’s really difficult given the heat and pressure
needed, which generally inhibits direct lab study of this mineral and its heat transfer
properties at the pressure and temperatures of the lower mantle.
That was until this paper came out.
Murakami and colleagues did just that however, they synthesized bridgmanite and encased it
in a diamond anvil at extreme pressure, and then heated it with a laser to the core-mantle
boundary temperature.
Then they measured how efficiently heat can transfer through it, and it was much more
efficient than what had been predicted.
There’s also another effect at play.
The mantle is solid, but also in a way plastic.
It can move and even convect and allow hotter material to rise, and cooler material to sink,
albeit very, very slowly.
This process however is transferring heat upward, and this too is happening faster than
was thought.
But there is an issue here, Earth’s core has two sources for its heat, its original
leftover heat from its formation, and radioactive decay.
It may have to be adjusted in the models as to just how much heat is there, or if more
radioactive decay is happening than originally thought, to account for the temperatures at
various levels inside the earth.
It’s unclear what this means for earth’s magnetosphere’s longevity, but also its
geologic processes such as plate tectonics, also thought to be crucial for life and abiogenesis
through the carbon cycle.
Once the magnetosphere shuts down, this world will face the full fury of the sun unprotected,
including its solar storms and that in turn will result in the gradual stripping off of
the earth’s atmosphere.
At this point however, it’s difficult to predict when all of this will occur, there
are still too many unknowns, all we know is that it’s happening much faster than we
realized.
One thing that is set to happen is that as the cooling process happens, the bridgmanite
will slowly turn into a different mineral, known as post-perovskite.
That’s a worse problem because that mineral actually conducts heat even faster than bridgmanite,
which should further accelerate the cooling of the outer core and the mantle itself, and
as the slow plastic convection in the mantle halts, so does plate tectonics.
Given the uncertainties, it’s unknown whether all of this will occur early enough to cause
the wholesale extinction of all surface life on earth, nor is it clear what effect it will
have on subsurface microbial life on earth.
If it happens sooner and overtakes the increasing luminosity of the sun, then it’s a new and
very efficient mass extinction event above and beyond what an asteroid can do.
If it happens later, then the mass extinction event will still happen, but will be brought
about directly by the luminosity of the sun, which is ultimately the more likely scenario
here, and it would result in the complete extinction of all life on earth anyway.
But this is also the point where all of this gets weird.
Back to bridgmanite, which is responsible for the enhanced outer core cooling problem
here.
This is not all that bridgmanite is implicated in.
It also seems that we needed bridgmanite for life to arise on earth at all.
And It’s even conceivable that this mineral plays a role in both bringing about life on
a planet, and ending it.
In a paper by Michael Russel and Adrian Ponce, link below, they hypothesize that there are
six minerals that are required to be present for life to arise, above and beyond those
that we know chemically from life.
So in addition to mineral sources of all the elements needed for biology, there actually
appears to be more that are solely geological in action.
According to the authors, these minerals are olivine, serpentine, fougerite, pyrrhotite,
Machinawite and bridgmanite.
In a nutshell, for life to arise, these minerals seem essential in the overall makeup of a
planet.
This all has a very curious, and potentially very important effect however and it’s specifically
because of bridgmanite.
If your planet or moon cannot, due to size, produce enough pressure through mass to reach
the pressures needed to create bridgmanite, it may mean that life cannot arise on that
planet or moon.
This would severely restrict the potential for life in the environments of the solar
system to just Earth, Venus and Mars.
It could knock out Europa and Enceladus and presumably all of the ice shell moons and
minor planets, which actually are strangely low on carbon dioxide as far as we can tell,
though recent JWST observations of Europa do show it is present on the surface, though
oddly it’s very localized.
Further, Venus and Mars do not have magnetic fields, or plate tectonics, further limiting
what life can do on those planets, even though Mars once had liquid water, and Venus may
have.
It’s uncertain whether Venus or Mars once had tectonics and magnetic fields, just that
both of them have long ago shut down if they were ever present.
This is unsurprising for Mars due its smaller size, it would have cooled faster.
But Venus is a total unknown.
There’s something a bit spooky about this sort of extinction event, if that’s what
this results in, because previous to just a few years ago we had no idea it was even
happening, even though it could represent one of the most wide reaching and profound
extinction events ever in the history of the earth.
The shutting down of the magnetosphere would dwarf all other mass extinctions in scale
and might leave earth as a subsurface microbial only planet.
But in the end, the sun will win, and that will be the one extinction event we so far
know of that will end all life on earth forever.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently pondering Titan.
It’s actually on the table for very low temperature life based on liquid hydrocarbons
as a solvent.
It definitely doesn’t have the pressures to form bridgmanite, but that would also be
a form of life that may not require it.
Life finds a way indeed and be sure to check out my books at your favorite online book
retailer and subscribe to my channels for regular, in-depth explorations into the interesting,
weird and unknown aspects of this amazing universe in which we live.