One of the strangest episodes in the field of exobiology is that of the meteorite Allan
Hills 84001, a rock thought to have originated on Mars.
While this story is obscure now, it wasn't in 1996 when a NASA researcher discovered
evidence of what he believed was fossilized alien microorganisms contained within the
meteorite.
This claim was considered so credible at the time that United States President Bill Clinton
made a public announcement that we had indeed discovered proof of alien life.
The research was later called into question during peer review, but the possibility that
we may have evidence for ancient microbial life on Mars remains open to this day.
Allan Hills 84001 was found in Antarctica's Allan Hills on December 27, 1984 by a team
of American scientists.
Antarctica is an interesting place to hunt for meteorites because its landscape can be
quite ancient and undisturbed, this particular meteorite is thought to have fallen about
13,000 years ago, but also for it's general lower possibility of earth contamination because
Antarctica is, well, basically a giant freezer.
Plus, given that we're dealing with ice sheets, most rocks that melt out of glaciers on that
continent tend to be meteorites rather than terrestrial rocks because the meteorites fall
on top of the ice and get buried.
So, to recover meteorites in Antarctica one simply goes to the termination point of melting
glaciers to find a bonanza.
Most of the meteorites found in Antarctica are pedestrian nickel-iron or stony iron meteorites
originating from asteroids.
Rocks in the asteroid belt crash into each other and send material flying off that eventually
smacks into Earth.
But under certain conditions, such as a giant impact, rocks from the smaller moons and planets
in the solar system can also be blasted into space.
This includes our moon, and in fact all moons, but Mars is also just small enough for material
to be ejected from it during large impacts.
The Martian meteorites are a small group of meteorites found mostly in Antarctica that
appear to be from the surface of Mars.
Called SNC's after the first letters of the names of the first three meteorites of this
type to be identified, they contain chemical elements that match Mars's geological and
atmospheric makeup.
They tend to be less interesting volcanic basalts of the types that the various Mars
rovers ignore on the surface of Mars, but the 4.3 lb Allan Hills 84001 meteorite is
very different.
For one, it's unbelievably old.
It's considered to be one of the oldest objects in the solar system at 4.091 billion years.
While it is a basalt, it's a really early one from a time when Mars had abundant liquid
water.
This is interesting because most of the Martian meteorites, some of which also have odd life-like
structures in them which could be contamination or something else, date from the current dry
period of Martian history.
Though, even that is in question as briny liquid water springs still appear to exist
on the surface of Mars.
We also have a possible idea of where on Mars this meteorite is from, the largest canyon
in the Solar System: Valles Marineris, or the Valleys of Mariner after the Mariner 9
probe that first saw it in 1971.
As an early basalt rock, isotopic analysis showed that the carbonates contained within
the meteorite appear to have precipitated out of water and contained the characteristic
carbon dioxide of Mars' atmosphere.
It appears that the rock might have once been part of an aquifer located a few meters beneath
the surface of Mars.
It's thought that the rock was blasted from Mars about 17 million years ago and spent
millions of years wandering the solar system before falling in Antarctica.
Under a scanning electron microscope, tiny structures were found that appeared to be
fossilized bacteria.
But there was a problem, they were much smaller than their earth counterparts.
Orders of magnitude smaller.
There is a theory in microbiology that unbelievably tiny bacteria called nanobacteria might exist.
They are problematic, with most researchers agreeing that they seem to exist but probably
aren't alive.
Yet most also agree that they seem to reproduce in some way leading to the whole mess being
dubbed the "cold fusion of microbiology".
That aside, even their presence on Mars would be of great interest due to the fact that
the nanobacteria question is still open and that the structures contained within the meteorite
do not resemble microbial contamination found in the other Martian meteorites.
In fact, they appear to be integrated in the matrix of the meteorite itself in such a way
that Earth contamination does not do.
But it's not conclusive.
And that's the problem.
This all comes down to morphology.
Interpreting the structure of something like the proposed fossils in the meteorite's interior
is often prone to error.
You need more, and that's where we start hitting walls.
But there are other tantalizing hints that the structures may be the product of life,
such as the carbon isotopes contained within them.
But pinning everything down has proven maddeningly elusive.
And it gets worse.
There's another meteorite that seems to show potential evidence for life on Mars.
This meteorite fell in Egypt about a century ago, and reportedly vaporized a dog in the
process, that is believed to have Martian origins.
Within this meteorite, named Nakhla after the town it fell in, tiny structures were
found along with abundant carbonaceous material contained within cracks inside the basalt
rock.
This material resembled the traces left by bacteria in the same kinds of rocks found
on Earth.
The trouble is, carbon is the fourth most abundant element in the universe, so it's
presence doesn't necessarily mean life.
Even more interesting though, amino acids were found inside this meteorite, the building
blocks of life.
But it's not clear if they are contamination or original to the rock.
Once again, it can't be pinned down conclusively.
So did Mars once harbor microbial life?
Well, we know it had the conditions for it in the distant past.
In fact, it was actually more hospitable to life in the past than Earth was when life
first arose here.
That's led to a theory called panspermia which suggests that life originally arose on Mars
but was deposited here by a meteorite.
That's right, it's possible that we, and all life on Earth, aren't native to this world.
But that's a subject for another video.
But the only way to know for sure that Mars once had life, it seems, is to simply go there
and find out.
With the discovery of the briny springs, that would imply that active aquifers still exist
on Mars and might still harbor life to this day.
If not, returning pristine samples of the type of rock that composes Allan Hills 84001
would go a long way in laying the fossil question to rest.
Thanks for listening.
I am futurist and science fiction author John Michael Godier, a day late with my latest
video due to a misbehaving laptop computer, and be sure to check out my books at your
favorite online book retailer and subscribe to my channel for in-depth regular explorations
into the interesting, weird and unknown aspects of this amazing universe in which we live.