The Case For Non-Carbon Life
The periodic table currently has 118 known elements on it, with more possible ones to
be discovered.
Yet out of all these possible elements, astrobiologists still consider carbon necessary for life and
look for signs of it when searching for extraterrestrial life forms.
Despite our carbon fixation, however, there are alternative elements that could feasibly
support life.
This is Unveiled, and today we’re asking the question: Is there a Case For Non-Carbon
Life?
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All life as we know it is based on carbon, and there’s a reason that scientists think
that it’s the likeliest candidate for alien organisms as well.
Carbon is the main element in organic compounds here on Earth and no life could exist if it
weren’t for carbon’s unique abilities.
Carbon is able to form stable bonds with other elements, including itself.
In fact, it’s able to form more compounds than any other element known, with nearly
10 million carbon-based compounds found in living creatures here on Earth.
Carbon is the building block of carbohydrates, lipids, proteins, and nucleic acids, all of
which are essential to life.
If there exists an element that can form the basis for life elsewhere, there are a few
conditions that it has to meet.
Carbon is considered the king of the elements because of its enormous versatility in forming
compounds.
If alien life forms are to be based on another element, that element will have to form stable
bonds with a variety of different elements.
All elements have electrons orbiting their nucleus, and bonding occurs when they share
that electron with another element.
This element would also need to be abundant enough in the universe so that it’s not
completely out of the ordinary for it to be found on a random planet.
In addition, it should be able to recycle itself in some way, the same way carbon does
in the carbon cycle on Earth.
Living organisms need a way to expel excesses of that element back into the environment.
The best alternative to carbon appears to be silicon.
Scientists mainly think this because it’s extremely similar to carbon.
Carbon has four electrons in its outermost shell, and elements tend to bond so that each
atom has eight electrons; this makes carbon the perfect pair-up partner, ideal for covalent
bonds in which it shares four of its own electrons with other atoms, while they share four of
their electrons with it.
Silicon also has four electrons, and like carbon is abundant in the universe - among
the top ten most abundant elements in the universe, and 135 times more prevalent on
Earth than carbon.
Silicon can also bond to oxygen and form long chains with itself, much as carbon does.
For these reasons, silicon seems to be the most likely candidate for non-carbon life.
But why, then, isn’t life on our planet silicon-based?
Well, despite the similarities between silicon and carbon, silicon does have some downfalls.
While silicon does have four electrons, these reside in its third orbital and not its second
as with carbon, which basically means that it requires more electrons to be satisfied,
thus tending to form weaker bonds.
Carbon’s bonds are so strong that when it pairs with other carbon atoms it can become
diamond, the hardest known material on Earth.
Silicon also acts differently when bonded to oxygen, an essential element to many life
forms.
Carbon becomes carbon dioxide, a gas that is easily expelled by living beings and recycled
into the atmosphere.
Silicon, however, becomes quartz, which is a solid and forms sand.
Organic beings would be hard pressed to expel sand from their system easily, or indeed any
solid.
But one of the main reasons that we consider lifeforms based on other elements to be improbable
is just the fact that carbon-based life is all we’re familiar with.
Astrobiologists look for signs of carbon as a potential sign of alien life because every
life form that we know about comes from Earth - and every life form on Earth is built from
carbon.
Scientists can look at the reasons why this is the case, but that doesn’t mean that
alternatives are impossible.
When we evaluate the likelihood of life on other planets, we look to see if they have
similar conditions to Earth.
But planets that are far hotter than our own would actually give silicon the advantage
in forming life, as it can withstand far higher temperatures than carbon.
Scientists didn’t think that life could survive in such harsh conditions until they
discovered extremophiles that thrive in the volcanic vents as the bottom of the ocean,
with temperatures of around 249 degrees Fahrenheit.
Scientists too assumed that planets have to be in the so called goldilocks or habitable
zone around their star to have liquid water and the temperatures associated with life,
but that notion too was thrown into question with the discovery of probable subsurface
oceans inside moons like Europa and Enceladus, and Titan’s hydrocarbon lakes.
So when considering alternative forms of life, scientists have to be open minded and imaginative.
Some researchers have even gone so far as to consider the possibility that Dark Matter
is a form of alien life!
Sure, non-carbon life might be very weird compared to what we’re used to.
But there are a variety of other elements that could spawn life in the right conditions,
and we can see some examples of this on Earth.
Take arsenic, for example!
Arsenic is poisonous to most life, but some marine algae on our own planet incorporate
arsenic into complex organic molecules, like arsenosugars and arsenobetaine.
Other small life forms use arsenic to generate energy and to assist in growth.
Sulfur too is capable of forming very long chains of molecules similar to carbon, and
some bacteria survive off sulfur rather than oxygen by transforming it into hydrogen sulfide.
Even phosphorus is a possible alternative, as it too can form long chains with itself,
and when combined with nitrogen, another common element in the universe, it can form a wide
range of possible molecules.
Phosphorus is already a very important element that’s essential to life on Earth, so it
could be essential to life forms elsewhere as well.
There’s even a case for chlorine and nitrogen.
Because these ideas are so foreign to us, there’s a concern that researchers might
miss potential signs of life even if they were staring them in the face.
One experiment asked participants to look for signs of life on Mars.
While the subjects were busy studying photos of terrestrial surfaces, a majority failed
to see a little waving gorilla in one of the pictures.
The purpose of the experiment was to show that humans develop tunnel vision when tied
up in their own biases and will often miss blatant signs if they’re not actively looking
for them.
Our fixation on carbon may prevent us from recognizing alternative forms, so we have
to be open to new possibilities.
Assuming otherwise means we might very well miss them.
And that’s the Case for Non-Carbon life.
What do you think?
Is there anything we missed?
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