One of the great grey areas of astrobiology
is just how alien biochemistry might work. Conventional wisdom would be to look at life
on earth, we know for a fact it can exist, and then imagine how that might apply to life
in the universe. And while there doesn’t seem to be any reason
to doubt that carbon-based biochemistry couldn’t be common in the universe, it’s also possible
that other types of radically different biochemistry could exist. So here are 10 ways alien life could be radically
different from that of earth. Number 10. Alternative Chirality One odd aspect of life on planet earth is
that everything is apparently of one variety when it comes to chirality, effectively how
biomolecules can exist in mirror configurations. But there doesn’t appear to be any good
reason why life couldn’t also function in alternative chirality, and that examples of
it just happen to be missing here on earth. Or at least appears to be missing, as amino
acids of opposite chirality have been found here, and while they are thought to be a product
of the decay of normal organisms, it also can’t be ruled out that life of opposite
chirality does indeed exist here and we simply haven’t detected it. Given what we know, it could be possible that
life on other worlds might be based on some configuration of alternate chirality. While different in a chemical sense though,
these type of configuration wouldn’t be all that alien, at least in the sense of it
being markedly different from what we see on earth. In short, we would recognize it as life. But it would be alien in the sense that it
would have no relation to life on this world, so far as we know. Number Nine. Different Solvents We often discuss the search for life in the
universe on the presence of liquid water on the surface of an exoplanet. There’s a reason for this, it’s crucial
to life here on earth. But, our planet is a sampling of one. But water isn’t the only liquid that life
might use as a solvent and we have to be careful of water bias when evaluating the possibilities
for life. Perhaps the strongest alternative to water
would be ammonia. Like water, there is no shortage of it in
the universe. Ammonia can support a wide range of chemical
reactions, and can dissolve organics. Other possible alternatives to water include
formamide, hydrogen flouride, and even hydrocarbons opening the way for very low temperature life,
and also liquid in low temperatures is nitrogen. But, as with anything, there are tradeoffs
and the alternative solvents seem more limited for life than liquid water, but even water
actually does have some disadvantages, one being that it has high albedo, contributing
to the severity of earth’s ice ages. Also possible are a few possible mixes of
water and other liquids, such as ammonia and water. This is thought to be possible at Saturn’s
moon titan, where a subsurface mix of ammonia and water could remain liquid at much lower
temperatures than water alone. The solvent in which alien life is based would
also profoundly affect things like evolution, for example water being transparent to sunlight
helped guide the evolution of oceanic creatures, and ultimately the formation of eyes. In other conditions in other fluids, the equations
can change and life based in an alternate solvent could be very different from that
of earth indeed. Number 8. Arsenic Life Even though arsenic is usually considered
poisonous, at least to humans, it’s thought that phosphorus and arsenic are chemically
similar enough that it may be possible that alien life could use arsenic in its biochemistry
and even its DNA. And, arsenic might figure prominently as far
life in the universe at large because phosphorus has somewhat of a problem. Astronomers studying the abundance of phosphorus
in the universe have found that it’s actually not that common, due to differences in how
it’s created in supernovas. If this is the case, life, at least as we
know it on earth, wouldn’t be able to get started in some areas of the universe just
from a lack of phosphorus. This is enough of a problem, that the idea
of phosphorus simply being rare and unevenly distributed in the galaxy could be a solution
to the Fermi Paradox. While contentious, if arsenic can indeed function
similarly to phosphorus in biochemistry, then there may well be more arsenic based life
out there than phosphorus based life. Number Seven. Non-Green Photosynthesis Plant life on earth is predominantly green
in color due to the plants inability to absorb some of the green wavelengths of light, yet
the sun emits strongly in green light. Rather plants tend to absorb red and blue
light, and it could be that green isn’t absorbed simply because the plant has all
the light it needs, at least those on land. But when you start looking at the classes
of stars that might also be suitable for alien life, the profiles of their light emissions
change. As a result, photosynthesizing plant analogues
on exoplanets may not tend towards green, rather yellow, red or even black. It’s also possible that alien photosynthesizing
analogues might not even be based on chlorophyll, but rather retinal. If so, this kind of life would appear purple. Number Six. Azotosomes It’s possible, perhaps even likely, that
the very simplest microbial forms of life in the universe will tend to look a lot alike
no matter where it’s found. Some very likely will be similar to organisms
present on earth. But looks can be deceiving, if functionally
similar, their biochemistry could still be radically different. Take Titan, the only other body in the solar
system to sport large amounts of liquids on its surface other than earth that could support
some kind of biology. The problem being, Titan also happens to be
extremely cold, far colder than anything life on earth can withstand. But what of a different configuration of microbial
life. Researchers envisioned what this might look
like by thinking about different kinds of chemistry, in this case nitrogen compounds
that could be used to create a kind of cell membrane that could function on Titan. Called an azotosome, this hypothetical cell
membrane could function at temperatures where methane is liquid, about 292 degrees below
zero fahrenheit. Such a microbe could use the nitrogen, carbon
and hydrogen that are present on Titan in its biology, and use no oxygen at all. Number Five. The Long Sleep With planet earth, we essentially got lucky
as far as stable climate conditions. Mostly. Our planet undergoes seasonal changes that
make certain periods harder on some animal life than the rest of the year. But this could actually get much worse on
exoplanets where life, at least as we envision it, might come to a near standstill for long
periods of time. Life on earth has proven resilient to cold
periods, for example there are species that can completely dry out, freeze, and then effectively
come back to life when conditions allow for it. Essentially, this isn’t just dormancy, but
a period of death and resurrection, and it’s not just simple life, there are species of
frog that can do this. As to what’s possible elsewhere in the universe,
there may even be intelligent species that have evolved in harsher conditions than earth
that hibernate, or even outright die in order to survive periods of adverse conditions only
to rehydrate when times get better and effectively come back to life. Such a species might even use that to their
advantage, making long journeys across space in a state of natural suspended animation
or even temporary death. Number Four. Silicon Based Life Most elements on the periodic table are not
good candidates for life due to their chemistry. An element like gold for example doesn’t
have the ability to react with other elements to create the complex chemistry needed to
sustain an analogue of biology. But there are a few that might, and chief
among these is silicon. Silicon is in the same group as carbon on
the periodic table and can form complex molecules that could conceivably be a basis for life. But it’s much more limited than carbon is,
but on the other hand it’s been suggested that silicones could be more stable than hydrocarbons
in atmospheres rich in sulfuric acid, such as venus-like worlds. And while carbon is extremely common in the
universe, more so than silicon, terrestrial planets like earth are very rich in silicon,
yet poorer in carbon, yet despite that, life on earth is carbon based and we have not found
any strictly silicon based life on this planet, though plenty of life uses it, such as diatoms
and one hypothesis holds that the presence of silicon may have been necessary for carbon
based life to have its genesis. Silicon based life might also be well adapted
for very low temperatures, or high ones, and it has to be said that it may be the case
that silicon ends up being the basis for intelligent life, not in a biological context, but a technological
one as species may choose to transition to become machine civilizations. But silicon isn’t the only possibility,
boron-based life is also in principle thought possible, though it’s somewhat rare in the
universe. Sulfur also has hypothetical scenarios where
life based on it might be possible, but perhaps most interestingly are some of the metals. Life might also, under very strict conditions,
exist using metal oxidation, even at very high temperatures where carbon based life
probably cannot exist. Number Three. Neutron Star Life One of the biggest problems when discussing
the possibilities of alien life are biases. Carl Sagan once stated that he was a carbon
chauvenist, and to a degree a water chauvenist when speculating about what alien life can
be like. But it could also be surprising, and nothing
like what we’re used to. One possibility, though a long shot, would
be life based on a neutron star. First proposed by Frank Drake, and explored
in the books of Robert Forward, this speculative form of life would exist on the surface of
a neutron star. They would be very tiny, sub-microscopic,
existing based on a kind of alternate type of molecule where tighly packed atomic nuclei
form random molecules of sorts. It’s a complete unknown if this is even
possible, neutron stars are made up of extraordinarily dense material. But what can be said is that if this type
of life indeed does exist, it might exist in fast forward due to the speed at which
nuclear reactions occur. They would experience their lives conceivably
millions of times faster than you do. Number Two. Plasma Life So far, we’ve taken the subject of alternative
life mostly from the standpoint of straightforward chemistry, but that may not be the only possibility
for life. In 2003, researchers were able to create plasmas
that exhibited life-like behaviour, in that they could grow, replicate and even communicate
to some degree with each other. This plasma phenomenon featured a distinct
layer, much like a cell wall, that separated it from its outside environment, a key feature
of biological cells. They could also replicate by splitting in
two, again like living cells. And they demonstrated the ability to grow
under certain circumstances. The communication came in the form of electromagnetic
emissions. If this can indeed be considered a form of
life, which is fully open for debate, we may already have seen an alternative form of life. Number One. The Shadow Biosphere and RNA life While speculative, the concept of panspermia,
the idea that life could hitch a ride on rocks blasted off a planet and then fall on another
planet and survive to colonize it, isn’t all that far-fetched and may well have occured
within our own solar system. Indeed, life on earth might have originally
been seeded here from some other body, such as Mars, where conditions in the distant past
may have made it an easier place for life to arise, than earth was at the time. But the idea of panspermia can be extended
to interstellar scales. While carbon based life as we know it may
not have great chances of surviving interstellar travel, it’s possible that some of the hypothetical
alternate life on this list might fare better, such as silicon based life. If this is indeed possible, it might be here
undetected, or if silicon-based simple indigenous life could have formed on earth, then would
we even know about it? The answer is not necessarily. The shadow biosphere is a hypothesized second
biosphere, or even a second separate genesis of life on earth based on some other biochemistry. Given that our methods of studying microbial
life typically depend in some way on familiar means of biochemistry, it’s possible that
an entirely different microbial world could, at least in principle, exist alongside our
standard microbial biosphere undetected. Another variant on this theme is that it’s
possible that there were once organisms on earth that may have been based on RNA instead
of DNA. If so, the methods typically used to detect
microorganisms wouldn’t detect them, should they still be living among us. While the shadow biosphere is hypothetical,
there is a phenomenon in geology known as desert varnish that’s not well understood. It forms as deposits on the surface of rocks
and its origin is more likely to be geological rather than biological. But one odd feature of this material is that
it’s very high in manganese, about 50 times more abundant than is normal for earth’s
crust. One possibility that’s been advanced is
that a shadow microorganism could be depositing it. Thanks for listening! I am futurist and science fiction author John
Michael Godier currently eyeing my office suspiciously wondering if there’s a shadow
biosphere in here and what it’s currently doing. It’s all very cloak and dagger, the microbial
world 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.
Hello wonderful people my name is not Anton.