The development of life in the Universe has been an overarching question form most of
human history.
Why are we here?
How did life evolve on Earth?
And what would life be like if it had developed on another planet, instead?
These existential issues have boggled the minds of scientists and science fiction writers
alike.
However, according to a new theory proposed by a pair of Harvard astrophysicists, when
we do make first contact with an alien species, we may find that the life we encounter may
not be that alien at all.
That it may, in fact, have terrestrial origins.
This is Unveiled, and today we're answering the extraordinary question; did alien life
escape Earth?
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The transfer of life between planets was first theorized by the ancient Greek philosopher
Anaxagoras, in a process he termed as Panspermia.
In the centuries since, the theory has evolved to claim that life could feasibly exist throughout
the universe, traded between planets as micro-organisms within space dust, meteoroids, comets, and
other interplanetary travellers.
Many have then speculated that if this theory were to prove accurate, it would suggest that
life as we know it didn’t originate here on Earth.
Instead, the key building blocks of life may have arrived here from another planet via
a collision event.
According to some, this origins story should even be considered statistically most likely…
but, regardless, theories on panspermia have remained mostly speculative, due to the lack
of direct evidence that micro-organisms would be able to survive the harsh conditions of
travelling within space.
That was until the Tanpopo Project.
Headed by Akihiko Yamagishi, the Tanpopo Project saw a team spanning multiple institutions,
including various Japanese Universities and Japan’s National Space Agency, JAXA, set
out to test the survivability of deinococcus bacteria in space.
The experiment saw the bacteria, which is known for its resistance to radiation, placed
on exposure panels outside of the Kibo module of the International Space Station.
The dried samples were of different thicknesses, and were left on the side of the ISS for one,
two, or three years.
When their allotted time was up, they were removed and analysed.
As the experiment was started in 2015, this means the final samples were brought back
down to Earth in 2018.
In 2020, after two years of study, scientists reported that some of the bacteria had survived
for at least three years in space.
Specifically, it was found that while the outer layer of all the samples didn’t survive,
those outer layers did serve to protect the bacteria located underneath.
Therefore, the thicker samples generally held more surviving bacteria.
Thanks to the Tanpopo project, then, it’s now been hypothesized that a bacteria colony
just one millimetre in diameter could potentially survive up to eight years in space - which
is potentially enough time for it to make the transit between Earth and some of our
nearest astronomical neighbours.
And, theoretically, it could then make a similar trip again, and again, spreading further and
further afield as it goes.
Perhaps the most famous case of possible panspermia from another planet to Earth came in 1996,
when a team from NASA's Johnson Space Center claimed the discovery of microbial fossils
on the Allan Hills meteorite, officially logged as ALH84001.
Having been discovered in Antarctica in 1984, the meteorite is said to have landed on Earth
some 13,000 years ago… but it’s also believed to have formed on Mars approximately four
billion years ago.
Back then, liquid water is thought to have been present on the Martian surface, with
some theories that early lifeforms may have thrived there.
And so, the Allan Hills meteorite was rigorously tested, and was found to be a potentially
viable host for transporting potential Martian bacteria between the two worlds.
It remains a highly controversial conclusion to draw, however, as there is still no definite
proof that the apparent fossils found in the rock really do have origins on Mars.
They may have more simply formed on the meteorite in the time after it had landed here on Earth,
instead.
But still, if nothing else, ALH84001 stands as prime example of how panspermia could theoretically
work.
While theories regarding Panspermia more typically suggest how life came to Earth, however, another
suggests that ancient life may have actually escaped Earth (to other systems) in the same
way.
In their paper titled "Possible Transfer of Life by Earth-Grazing Objects to Exoplanetary
Systems", the Harvard astrophysicists Amir Siraj and Avi Loeb suggest that several panspermia
events should have happened throughout Earth's history that would have carried microbial
life away from our planet.
According to the paper, the frequency of comets and meteorites grazing through our atmosphere
- particularly, during the early stages of the solar system - make it likely for tens,
perhaps hundreds, or more of these brief visitors to have picked up colonies of airborne microbes
as they passed.
This process could have therefore sent terrestrial life out into the universe.
While the theory has been met with some scepticism, it’s generally been accepted by the academic
community as a possibility.
We’ve known for decades that there are colonies of bacteria living in our planet's upper atmosphere,
miles away from the ground… and so, it perhaps isn’t too much of a stretch to imagine those
bacteria hitchhiking on a passing piece of space rock.
It’s an idea which has opened a whole new area of study, though.
For example, by combining Siraj and Loeb's paper with the results of the Tanpopo project,
it might be possible to tentatively map where (and how far) life from Earth may have travelled…
if, indeed, it did ever escape in the first place.
Considering again the Tanpopo Project's estimate - that a one-millimetre colony of bacteria
could potentially survive for eight years in space - we know that there wouldn’t be
enough time for any meteorite or comet host to leave the Solar System before the bacteria
dies.
So, if ancient life did escape Earth, it likely only escaped to the closest planets or moons
around us.
Which takes us to Venus, for example, a world that certainly falls into that category.
In September 2020, a team of researchers announced the detection of the potential biosignature
for phosphine gas high in the Venusian atmosphere.
One interpretation of this discovery is that it could suggest the existence of microbes
- of effective alien life - generating phosphine gas emissions.
There’s ongoing debate as to what’s really happening, though.
And, while it’s yet to be confirmed that there are tiny, living organisms on Venus,
or that those organisms could somehow have arrived there direct from Earth… if panspermia
has taken place, then there could be no limits to where else it could spread.
Again, we have an example of the potential for panspermia, but no concrete proof that
it has happened.
Of course, these potential, hypothetical developments still mean very little in terms of the arrival
of complex life to somewhere else in the solar system, as the likes of Venus still lack all
the other atmospheric and environmental conditions needed to turn tiny microbes into bigger creatures.
Nevertheless, there are further considerations to take into account.
What if, for example, a bacteria sample much larger than one millimetre across is picked
up by a passing rock?
Could it then survive for a much longer time than eight years, and potentially long enough
to exit the solar system?
Or, what would happen if it somehow became buried extremely deep into a meteorite or
comet?
Would that grant it greater longevity, too?
Amir Siraj and Avi Loeb’s paper, for one, floats the possibility that, under certain
conditions, bacterial life may be able to go beyond our solar system, after all.
Perhaps then, were bacteria to continue living in a rogue comet that falls out of the solar
system, it would head for another star system entirely.
Once there, what if it just so happens to crash into a planet around a different star,
but within that star’s habitability zone?
Could the evolution of life start anew once the microbes were redispersed?
If even all of that was physically possible, the chances of such an event taking place
are clearly extremely low.
But arguably they’re not zero.
We’d perhaps be talking of a time frame of billions of years, and distances of perhaps
thousands of lightyears, but in the infinite expanse of space that’s not a problem.
What’s evident is that there’s so much more work left to do, as we try to understand
the implications of how microbes could potentially move through the universe.
But, also, if material from this world ever were to make it to another, then the eventual
discovery of alien life could well end up feeling very familiar.
We could, after all, share a much-travelled chemical history.
What do you think?
Is there anything we missed?
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