The universe we live in is incredibly
vast. As human technology and knowledge expand over the years, our search for
other living species outside our own planet has increased and intensified. So
with all of this increase in our technologies and instruments, why haven’t we
found any sign of life elsewhere?
Even using our lowest and most
pessimistic estimates, there should be billions upon billions of intelligent
civilizations running around in the universe. With so many alien civilizations
running around, it stands to reason that humans should have been contacted. Or
at least we should have found promising evidence by now, perhaps some radio emissions or other
signs of intelligent life.
We should have seen them. But we
haven’t.

To get a bit more specific, there are
some 100 billion planets in the Milky Way, and even if just a mere fraction are
habitable (a modest estimate), that still means that there should be millions
of planets with alien life and hundreds of thousands that have intelligent
alien life.
Why this life seems to be missing is
the very heart of Fermi’s paradox, which addresses this apparent
contradiction—the difference between our estimates and the evidence (or lack
thereof) for alien life.
Now, new research from the Australian
National University proposes the possibility that we have not been able to find
aliens because they are all dead.
The hypothesis is based on what we
know about the first billion years or so after a new planet forms – its
environments are extremely unstable, fluctuating in temperature and atmospheric
composition so wildly that the chances of a new life form evolving quick enough
to cope are very slim.
“The Universe is probably filled with
habitable planets, so many scientists think it should be teeming with aliens,”
said lead researcher, Aditya Chopra from the Australian National University.
“Early life is fragile, so we believe it rarely evolves quickly enough to
survive.”
SO HOW DID THE EARTH SURVIVE?
The research team points out that 4
billion years ago, Venus and Mars were fairly habitable when they first formed
and may have indeed been home to life beyond Earth. However, evidence shows
that a billion years after they formed, these two planets may have killed off any
existing life forms due to its changing temperature.
With all of these in mind, why has
our planet continued to nourish its inhabitants?
Apparently, the answer is the
inhabitants themselves. It was suggested that the Earth’s success is causes by
the stabilizing effect the inhabitants had on the environment. “Most early
planetary environments are unstable,” says Chopra. “To produce a habitable
planet, life forms need to regulate greenhouse gases such as water and carbon
dioxide to keep surface temperatures stable.”
The researchers simulated this
scenario using a model they call the “Gaian bottleneck,” which basically means
that if life can’t evolve fast enough to stabilize its environment, it dies
out. If we’re looking at examples such as Venus and Mars, the Gaian bottleneck
states that if you don’t make it through that brief period of rough but
possible habitability, you’ve probably missed your chance.
From previous research, it is a known
fact that life on Earth managed to evolve so fast, it ended up regulating
greenhouse gas emissions on a planetary scale, and this appeared to have a
favorable effect on what’s known as our planet’s albedo – the ratio of
reflected radiation to absorbed radiation. This is important because when Earth
was just forming, the Sun was up to 25 percent less luminous than it is now,
but all the evidence points to the oceans being liquid, or at least not
completely frozen. This scenario is also known as the faint young Sun paradox.
The interaction between these large
patches of frozen and liquid water on the surface of Earth interacted with the
radiation, and established the planet’s albedo, which ultimately determined its
surface temperature.
“In extremely rare cases – like on
Earth – the relatively rapid evolution from single- to multicellular organisms
to complex life forms did not produce enough greenhouses gases to cause runaway
negative feedback and heat the planet enough to evaporate all its liquid
water,” explains Campbell Simpson at Gizmodo. “It’s that particular and so far
unique quirk that has kept us alive, if the Gaian bottleneck explanation is
accurate.”
If this hypothesis is proven to be
true, it will answer the problem posed by the Fermi paradox: if the Universe is
a colossal space, filled with trillions upon trillions of potentially
life-sustaining stars and habitable planets, why haven’t we found any aliens?
“The mystery of why we haven’t yet
found signs of aliens may have less to do with the likelihood of the origin of
life or intelligence and have more to do with the rarity of the rapid emergence
of biological regulation of feedback cycles on planetary surfaces,” says team
member astronomer Charles Lineweaver.
The research has been published in
the journal Astrobiology.
If their hypothesis turns out to be
accurate, it is quite saddening that we will never meet other life forms
outside of our own planet. At the same time, this gives us more reason to
appreciate our planet and work together to ensure its existence by focusing on
the environment.
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