Panspermia is the theory that life on
our planet arose from other planets. The most plausible variant of
the theory is the hypothesis of directed panspermia, the idea that
life was seeded on our planet eons ago by some extraterrestrial
intelligence, which may or may not have been robotic.
Panspermia seems to be a useful
concept, because it may help explain something that is otherwise very
hard to plausibly explain. The problem with the origin of life is
that before you can have anything at all get started from an
evolutionary standpoint, a very high level of sophistication has to
be reached – in other words, a very high hurdle has to be jumped.
This threshold is apparently the simultaneous appearance of a
sophisticated genetic code and the existence of self-replicating
molecules such as RNA or DNA. There is a severe, unsolved problem of
explaining how that happened on the early Earth.
How can the panspermia concept help
with that? I can help explain it with an analogy. Imagine you robbed
$100,000 from a bank, and wanted to explain your new riches to your
girlfriend without raising suspicion. If you told her that you just
started playing the lottery yesterday, and won $100,000 on your first
try, she would never believe you. But if you told her you had been
playing the lottery every day for 10 years, and finally won $100,000,
she would be much more likely to buy the story. The panspermia
concept has pretty much the same effect. We can help “reduce the
miracle” of life appearing (making it seem like not quite so much a
miracle) if we imagine that there are billions of planets in our
galaxy on which life had an opportunity to arise, and that on one of
these life did arise, eventually evolving to some form that then
spread the seeds of life throughout the galaxy. The more trials or
chances there are for an improbable event to occur, the greater the
chance of eventual success.
Let's look at various possible findings
that may increase or decrease the plausibility of the panspermia
idea.
Things That Might Make Panspermia
Look More Likely
Below are some things that may add to
the credibility of the panspermia theory.
The existence of abundant planets
revolving around other stars. The more planets that exist in our
galaxy, the more attractive the idea of panspermia is, because the
more it accomplishes the effect of reducing an origin of life
“miracle” by increasing the number of trials or chances.
The existence of planets much older
than Earth. If there are planets in our galaxy billions of years
older than Earth, than panspermia becomes a more attractive theory,
because if allows us to say that even if life did not have enough
time to naturally arise on Earth four billion years ago, it might
have arisen on other planets during a much larger time window
spanning billions of years, and then spread to our planet. Also, the
earlier that life arose in our galaxy, the more likely that it may
have spread to other solar systems.
Possible breakthroughs allowing
interstellar travel.
If interstellar travel is impossible, then panspermia is ruled out.
But if there are breakthroughs that allow interstellar travel, then
the idea of panspermia becomes more popular.
Evidence of artificiality in the
genetic code. In this paper, some scientists have claimed to find evidence of
artificial features in the genetic code. If such claims are ever
confirmed, they would give weight to the hypothesis of panspermia
(although others might argue that some divine hand was involved).
Things That Might Make Panspermia
Look Less Likely
Below are some possible developments
that might decrease the credibility of the panspermia theory, making
it less likely to be true.
The artificial re-creation of
self-replicating molecules in conditions simulating the early Earth.
Imagine if scientists were ever to rig up some laboratory setup that
mimicked the conditions of our planet four billion years ago. If the
scientists were ever able to produce self-replicating molecules such
as RNA in such a laboratory setting, that would help show that the
origin of life wasn't such an improbable miracle. There would then
be much less need for any theory of panspermia.
The artificial re-creation of the
genetic code in conditions simulating the early Earth. Again,
imagine if scientists were ever to rig up some laboratory setup that
mimicked the conditions of our planet four billion years ago. If the
scientists were ever able to produce something like the genetic code
in such a laboratory setting, that would help show that the origin
of life wasn't such an improbable miracle. There would then be much
less need for any theory of panspermia.
Things That Would Not Make
Panspermia Look More or Less Likely
Below are some possible developments
that would not clearly either lend credibility to the panspermia
theory, or make it seem less plausible.
The discovery of life on a planet
revolving around another star. Imagine if scientists were to
find the tell-tale chemical signature of life in some planet
revolving around another star. No doubt some would claim that this
was proof that life will naturally arise wherever it gets the chance,
and that there is therefore no need for a theory of panspermia. But
such logic would be incorrect. We would have no idea of whether that
life discovered on that distant planet had naturally arisen on that
planet, or had been seeded on that planet through the same process
imagined by the panspermia theory.
The discovery of life elsewhere in
our solar system. Imagine if scientists were to discover life on
one of the moons of Jupiter, or in a comet in our solar system. No
doubt some would claim that this was proof that life will naturally
arise wherever it gets the chance, and that there is therefore no
need for a theory of panspermia. But such logic would be incorrect.
We have no idea how panspermia might have worked if it occurred
billions of years ago. Rather than it involving only a placement of
life on our planet, it might have involved a biological seeding of
large parts of our solar system, including a large part of our
planet's cometary system.
How is the Panspermia Theory
Standing Up These Days?
So far, the panspermia theory seems to
be holding up quite well. Little has come in recent decades from
scientists' attempt to recreate the key components of life in a
laboratory setting. When science writers write about such a thing,
they usually discuss the Miller experiments, but those experiments
occurred way back in the 1950's, and didn't take things very far,
producing only some of the building blocks of
proteins rather than self-replicating molecules. Attempts to get much
farther haven't been very successful. The origin of the genetic code
and the first self-replicating molecules is still a gigantic mystery,
a mystery that panspermia theorists hope to lessen.
In the past ten years astronomers have
discovered more than 1000 extrasolar planets, leading them to
conclude there are many millions or billions of planets in our galaxy
on which life can evolve. Last week astronomers announced the
discovery of five earth-sized planets in a solar system (Kepler-444)
that is 11.2 billion years old, almost 7 billion years older than
our solar system. That's exactly the type of finding that lends
weight to the idea of panspermia. If there were billions of planets for
life to evolve five billion years before Earth even existed, that increases the chance
that life may have been spreading throughout the galaxy while our
solar system was forming; and in such a case some of that life may be
the parent of all earthly life.
But it is an open question whether the
theory of panspermia eliminates the miracle of the origin of life, or
simply makes it seem somewhat less miraculous. There may be some
possibilities that still deserve to be called miraculous even if you
allow a billion trials and 10 billion years for their occurrence.
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