Carbon-Based Life: Questions & Answers

[Stephanus]

Dear PF Forum,
I have questions about carbon based life and molecule back bone.
Is it true that all life on Earth are carbon based?
If it is true, why?
Is it because carbon is halfway in periodic table? 4 valence?
What about Silicon, Tin and Germanium? They have 4 valence, why life is not based on them?
Is it because Carbon the simplest atom then Silicon, Tin and Germanium?
Why polymer backbone are mostly carbon? Can polymer be constructed from silicon, tin and germanium?
Perhaps these are too many questions for one thread, my point is all these questions lead to carbon based life. Is carbon based life because of all of those question?
Thanks for explaning to me.

Steven.

 

[Bystander]

Hit the forum search for "non-carbon life." Read those 187 posts on the subject that have accumulated over the past 10 years.

 

[mfb]

Is it true that all life on Earth are carbon based?

It is.

If it is true, why?

The first life was, and all current life evolved from that.
There are many arguments why carbon should be ideal, but other options might be possible - we don't know. Those wikipedia articles shouldn't have been hard to find.

 

[rootone]

One problem with Silicon is that it has a strong affinity to Oxygen.
While Silicon can make long chain molecules as Carbon does, any free Oxygen in the environment would be lethal to a lifeform based on that.

 

[OmCheeto]

Is it true that all life on Earth are carbon based?

It is.
...

Doh! I just told someone this last week that there are sulphur based lifeforms.
Thank god it was on Facebook.

Perhaps I don't understand the term "carbon based". Can it have different meanings?
If all you eat to survive is sulphur and hydrogen, are you carbon based?

Earth Life May Have Originated at Deep-Sea Vents
...Hydrogen sulfide is a poison gas that’s lethal for humans even in very low concentrations. Yet, this compound — two parts hydrogen, one part sulfur — turned out to be the food source for bacteria that drive an entirely new ecosystem.
...

also

NASA announcement: Arsenic-based life form discovered on Earth

Or are they just being sloppy in their terminology.
But the article continues:

...
It had long been the assumption that without six certain essential elements -- carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur -- life could not exist.
...

So would it be more correct to say that most life on Earth is carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur based, rather than just "carbon based"?

 

[Drakkith]

Perhaps I don't understand the term "carbon based". Can it have different meanings?
If all you eat to survive is sulphur and hydrogen, are you carbon based?

Possibly. I think it depends on what the organism is composed of. Bacteria that use hydrogen sulfide as an energy source still require carbon to form lipids, sugars, and other complex molecules.

So would it be more correct to say that most life on Earth is carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur based, rather than just "carbon based"?

Not that I can see. Carbon is the primary element in almost all complex molecules used by life. Everything from DNA to Proteins to even vitamins are based upon chains of carbon atoms connected together. The other elements you listed are important, but don't form the base from which to build complex molecules.

 

[Bystander]

"NASA announcement: Arsenic-based life form discovered on Earth"
http://www.nature.com/news/arsenic-life-bacterium-prefers-phosphorus-after-all-1.11520

more correct to say that most life on Earth is carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur based,

Yes, plus other "trace elements." H, Li, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Co, Cu, Zn, Se, Br, Mo, Cd, I, ... give or take ... have been identified in assays of healthy organisms, or identified as necessary to health of some organisms.
"Carbon based?" Lipids/fats/oils. proteins/enzymes, carbohydrates/sugars/starch/cellulose, DNA/RNA cell nuclei --- all necessary, and all carbon chemistry. Various S reactions can be observed, both oxidations and reductions, as energy sources to drive the reactions of C based organisms.

 

[Stephanus]

Doh! I just told someone this last week that there are sulphur based lifeforms.
Thank god it was on Facebook.

Ahh, the holder of the 2014 humor award. Okay, let's see how funny it can be!

Perhaps I don't understand the term "carbon based". Can it have different meanings?
If all you eat to survive is sulphur and hydrogen, are you carbon based?

Earth Life May Have Originated at Deep-Sea Vents
...Hydrogen sulfide is a poison gas that’s lethal for humans even in very low concentrations. Yet, this compound — two parts hydrogen, one part sulfur — turned out to be the food source for bacteria that drive an entirely new ecosystem.
...

Then you'll smell stink! But your body still consists of carbon right. A stinking carbon based I supposed. I think H₂S contains energy, and you'll burn it to become CO₂ and H₂O. The Sulphur? It exits as residue.

also

NASA announcement: Arsenic-based life form discovered on Earth

I'll lookup arsenic in Wiki...
Well, perhaps...

Arsenic is a chemical element with symbol As and atomic number 33...
A pnictogen[1]/ˈnɪktədʒɨn/ is one of the chemical elements in group 15 of the periodic table. This group is also known as the nitrogen family. It consists of the elements nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) and the synthetic elementununpentium (Uup) (unconfirmed).

Frankly, I don't know. Arsenic is in the neighborhood with Carbon group. May be, may be not that life can be based from Arsenic.

Or are they just being sloppy in their terminology.
But the article continues:

...
It had long been the assumption that without six certain essential elements -- carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur -- life could not exist.
...

So would it be more correct to say that most life on Earth is carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur based, rather than just "carbon based"?

Even if it's been more than 30 years since Junior High School. I still remember my biology teacher, Pak(Mr.) Airbanoe said, CHON for fat and CHONSP for protein. But carbon still the most occurence element in many molecules or compounds or polymer. Life can be formed without six essential elements? I don't know. I"m no chemist for sure, but the probability is very, very small I suppose.

 

[Ygggdrasil]

Doh! I just told someone this last week that there are sulphur based lifeforms.
Thank god it was on Facebook.

Earth Life May Have Originated at Deep-Sea Vents
...Hydrogen sulfide is a poison gas that’s lethal for humans even in very low concentrations. Yet, this compound — two parts hydrogen, one part sulfur — turned out to be the food source for bacteria that drive an entirely new ecosystem.

Perhaps I don't understand the term "carbon based". Can it have different meanings?
If all you eat to survive is sulphur and hydrogen, are you carbon based?

Most organisms need two types of food: one type to provide energy and another type to provide the building material for cellular components (for more information see https://en.wikipedia.org/wiki/Primary_nutritional_groups). For chemoheterotrophs like humans, we derive both our energy and building materials from the foods we eat. However, for plants, these nutrient sources are different: they derive energy from light and building materials from carbon dioxide. For the chemoautotrophic bacteria that the article describes, although they derive their energy from the oxidation of hydrogen sulfide, they still derive their building materials from carbon dioxide.

NASA announcement: Arsenic-based life form discovered on Earth

Or are they just being sloppy in their terminology.

It's worth noting that the "Arsenic life" paper has been debunked
http://news.nationalgeographic.com/...rsenic-space-nasa-science-felisa-wolfe-simon/
https://www.physicsforums.com/threa...than-anything-else.453117/page-2#post-3746064

However, the general point that all life uses C,N,O,S,H,P, and various other trace elements is valid.

 

[rootone]

Of those though, only Carbon has the ability to form complex chains, loops, and other structures, and it easily combines in a nearly infinite number of ways with all the other elements in that group.
I'd say that's the reason we give the name 'carbon based' to life that we know of.

 

[Ygggdrasil]

Yes, plus other "trace elements." H, Li, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Co, Cu, Zn, Se, Br, Mo, Cd, I, ... give or take ... have been identified in assays of healthy organisms, or identified as necessary to health of some organisms.
"Carbon based?" Lipids/fats/oils. proteins/enzymes, carbohydrates/sugars/starch/cellulose, DNA/RNA cell nuclei --- all necessary, and all carbon chemistry. Various S reactions can be observed, both oxidations and reductions, as energy sources to drive the reactions of C based organisms.

Speaking of the elements required for life, here's a really nice infographic about the elements found in living organisms:

http://astrobiology.com/2015/07/the-astrobiological-periodic-table.html

 

[OmCheeto]

Ahh, the holder of the 2014 humor award. Okay, let's see how funny it can be!
Then you'll smell stink! But your body still consists of carbon right. A stinking carbon based I supposed. I think H₂S contains energy, and you'll burn it to become CO₂ and H₂O. The Sulphur? It exits as residue.
...

Well, I saved my best joke for last:

From the hydrothermal vent life form article I posted:

...
Chemosynthesis is the biological conversion of carbon molecules and nutrients into organic matter — the stuff of life. Whereas photosynthesis uses energy from sunlight to convert carbon dioxide into that organic matter, giving off oxygen as a byproduct, chemosynthesis uses inorganic molecules (such as hydrogen sulfide) or methane and combines them with an oxygen source (in this case seawater) to create simple sugars.
...

Where do they say the bacteria get the carbon from?
Are there little tiny bottles of "One a day, multiple elements, for bacteria" floating around down there?

I googled "food without carbon" yesterday, and the only two things people could come up with were salt and water.
Hardly what I would call "food".

I also googled "sugar" as I've never taken a biology class in my life, and I did very, very badly in college chemistry, which was 30 years ago, btw.
Wiki claims that sugars have the general form C_nH_2nO_n.
Now I know that NaCl is not the only salt in the sea, so maybe there are other forms of sugar. (I really am this stupid.)
But googling "carbonless sugar" only yielded the obvious: "Carbon free sugar is called water".
Ha!

But kidding aside for a moment, I read a very good article yesterday, which was written in very simple language, and I think I may have understood it:

Could silicon be the basis for alien life forms, just as carbon is on Earth? [Scientific American 1998]
...
But when carbon oxidizes--or unites with oxygen say, during burning--it becomes the gas carbon dioxide; silicon oxidizes to the solid silicon dioxide, called silica. The fact that silicon oxidizes to a solid is one basic reason as to why it cannot support life.
...

I thought that was very interesting. If we were silicon based, we would breath in air, and exhale sand! But that only explains why "we" can't be transmutated into silicon based beings. The bacteria either eat or breath, or perhaps both, hydrogen sulphide, and poop out sulphur. hmmmm... Perhaps that's how we could do it, breath in air, exhale nitrogen, and have sandy poop. hmmm...

Anyways, the article kind of concludes:

...
It is possible to think of micro- and nano-structures of silicon; solar-powered silicon forms for energy and sight; a silicone fluid that could carry oxidants to contracting muscle-like elements made of other silicones; skeletal materials of silicates; silicone membranes; and even cavities in silicate zeolites that have handedness. Some of these structures even look alive. But the chemistries needed to create a life-form are simply not there. The complex dance of life requires interlocking chains of reactions. And these reactions can only take place within a narrow range of temperatures and pH levels. Given such constraints, carbon can and silicon can't.
...

 

[Ygggdrasil]

Where do they say the bacteria get the carbon from?
Are there little tiny bottles of "One a day, multiple elements, for bacteria" floating around down there?

They get the carbon from dissolved carbon dioxide in the ocean water. There is 50x more carbon dioxide in the oceans than there is in the atmosphere (https://en.wikipedia.org/wiki/Carbon_cycle).

 

[OmCheeto]

They get the carbon from dissolved carbon dioxide in the ocean water. There is 50x more carbon dioxide in the oceans than there is in the atmosphere (https://en.wikipedia.org/wiki/Carbon_cycle).

Excellent! You should write up an "Insights" piece on the little buggers.
Easy enough for me to read though. I look at some most of the titles, and just shake my head.

Something like the following:

Chemoautotrophs, aka freakish little buggers, in addition to having hydrogen sulfide for lunch, top it off with a nice tall glass of carbonated sea water.

Is it safe to assume that the nitrogen and phosphorus are condiments?

 

[Bystander]

nitrogen and phosphorus are condiments?

N, P, and K.

 

[OmCheeto]

N, P, and K.

I was supposed to be somewhere an hour ago.
I'll be back.

 

[Alcathous]

The term 'food' means nothing, or is really confusing, when we start to talk about autographs. They need to fixate carbon, which is in a low energy state as part of CO2, to form complex molecules to actually build the molecular machines that we call life.
They need energy to drive processes in directions that are normally thermodynamically unfavourable, as CO2 is a low energy level and any organic molecule, that can be a machine of life, needs to be lifted up to a higher energy.

For us humans food is both the carbon source and the energy source, as well as the course of all trace elements and organic molecules we cannot synthesis ourselves.

Carbon-based chemistry means chemistry where carbon is the backbone of the complex molecules. Sulfur cannot be a backbone of complex molecules, because it cannot form enough bonds.

Take vitamin b12 or DNA and try to replace the carbon with something else. That is the challenge of finding an alternative to carbon and that is what it means for life to be carbon-based.

There's many reasons why it is hard to postulate an alternative to carbon. Carbon being abundant, having 4 valence electrons and the energy levels/strength of the bonds it can form, are all important. If carbon-carbon bonds are too weak, the molecules are too reactive. If they are too strong, it will form an inert molecule and not do anything else.
As it is now, photosynthesis can provide enough energy to break CO2 apart. But one can also put some organic molecules on a table with oxygen around, and it won't spontaneously explode back into CO2.

 

[Stephanus]

Well, I saved my best joke for last:

Good

Where do they say the bacteria get the carbon from?
Are there little tiny bottles of "One a day, multiple elements, for bacteria" floating around down there?

Ygggdrasil has answered that. He answers me, too. See his post below.

I googled "food without carbon" yesterday, and the only two things people could come up with were salt and water.
Hardly what I would call "food".

It depends on what the definition of food is, don't you say. Thanks for googled me.

I also googled "sugar" as I've never taken a biology class in my life, and I did very, very badly in college chemistry, which was 30 years ago, btw.
Wiki claims that sugars have the general form C_nH_2nO_n.
Now I know that NaCl is not the only salt in the sea, so maybe there are other forms of sugar. (I really am this stupid.)
But googling "carbonless sugar" only yielded the obvious: "Carbon free sugar is called water".
Ha!

. Is this a science joke? We have C₆H₁₂O₆ then you remove C, and it becomes 6H₂O?

Could silicon be the basis for alien life forms, just as carbon is on Earth? [Scientific American 1998]
...
But when carbon oxidizes--or unites with oxygen say, during burning--it becomes the gas carbon dioxide; silicon oxidizes to the solid silicon dioxide, called silica. The fact that silicon oxidizes to a solid is one basic reason as to why it cannot support life.

I thought that was very interesting. If we were silicon based, we would breath in air, and exhale sand! But that only explains why "we" can't be transmutated into silicon based beings. The bacteria either eat or breath, or perhaps both, hydrogen sulphide, and poop out sulphur. hmmmm... Perhaps that's how we could do it, breath in air, exhale nitrogen, and have sandy poop. hmmm...

Anyways, the article kind of concludes:

...
It is possible to think of micro- and nano-structures of silicon; solar-powered silicon forms for energy and sight; a silicone fluid that could carry oxidants to contracting muscle-like elements made of other silicones; skeletal materials of silicates; silicone membranes; and even cavities in silicate zeolites that have handedness. Some of these structures even look alive. But the chemistries needed to create a life-form are simply not there. The complex dance of life requires interlocking chains of reactions. And these reactions can only take place within a narrow range of temperatures and pH levels. Given such constraints, carbon can and silicon can't.
...

I think it's a matter of mathematic then. Carbon with 4 valence can easily be combined with other atoms. And from your quote, Silicon is more difficult. The other atoms in Carbon group are Silicion, Germanium, Tin and Lead and they are heavier than Carbon. Perhaps it makes them more difficult to join other atoms than Carbon. I read in Wiki that Germanium is heavier then Iron, and also Tin and Lead.
So they must have been created in supernova process. Silicon burning is the last stage before iron burning, perhaps that what makes carbon more abundance than Si, Ge, Sn and Pb. Carbon is created in triple-alpha process and in CNO cycle
That's why carbon is the fourth most abundance element in the universe?
https://en.wikipedia.org/wiki/Abund...lements#Abundance_of_elements_in_the_Universe

But that's according to mass. We have to multiply hydrogen by 16 and helium by 4.
Luckily Carbon is the fourth most abundant element. And also Hydrogen and Oxygen, they are the most reactive element. Do you think the universe is better without Helium? What good is Helium for life?
As Brian Green once said, "Our universe is so fine tuned for life"
It has "just" enough mass to form the galaxy. Not scattered so that galaxy can't be formed. Not too heavy that not long after big bang it collapse again. It's been 13.8 billions years and the universe is still going fine. Many galaxies and we know that our universe can contain life. At least on Earth!.
So my question is this.
Why all (if not almost) life on Earth is carbon based? Because mathematically carbon is the easiest way to form life?
Most abundance, easiest reacted, has 4 valence?

 

[Stephanus]

For us humans food is both the carbon source and the energy source, as well as the course of all trace elements and organic molecules we cannot synthesis ourselves.

Good point. Carbon source. I thought food is just energy source.

Carbon-based chemistry means chemistry where carbon is the backbone of the complex molecules. Sulfur cannot be a backbone of complex molecules, because it cannot form enough bonds.

I suspect that! But I never read someone wrote that. Now I'm certain that other elements not in Carbon group is more difficult to form bonds because of its valence.

Take vitamin b12 or DNA and try to replace the carbon with something else. That is the challenge of finding an alternative to carbon and that is what it means for life to be carbon-based.

Oh

There's many reasons why it is hard to postulate an alternative to carbon. Carbon being abundant, having 4 valence electrons and the energy levels/strength of the bonds it can form, are all important. If carbon-carbon bonds are too weak, the molecules are too reactive. If they are too strong, it will form an inert molecule and not do anything else.
As it is now, photosynthesis can provide enough energy to break CO2 apart. But one can also put some organic molecules on a table with oxygen around, and it won't spontaneously explode back into CO2.

Very good point. And also to the point, too for my question.

 

[Stephanus]

Speaking of the elements required for life, here's a really nice infographic about the elements found in living organisms:

http://astrobiology.com/2015/07/the-astrobiological-periodic-table.html

Thanks for your picture. But it doesn't match with this.
https://en.wikipedia.org/wiki/S-process

At the second picture Germanium is synthesized all in supernova process. Should bring this in Astrophysics forum when I get time.

 

[OmCheeto]

...
. Is this a science joke? We have C₆H₁₂O₆ then you remove C, and it becomes 6H₂O?

Not really a joke. But a handy way to remember what the heck sugar is. Water is about the only molecule I've memorized.
Methane is another. It's pretty simple.
I learned another one the other day. <searches>
Formaldehyde!
Wait!
Formaldehyde is a sugar? (CH₂O) hmmmm... <searches>
Wait!
Sugars: C_nH_2nO_n (where n is between 3 and 7)
This is probably why I did so poorly in chemistry. I never pay attention to the details.

 

[DaveC426913]

Did a survey of my atoms a while back.

 

[Stephanus]

Formaldehyde!
Wait!
Formaldehyde is a sugar? (CH₂O) hmmmm... <searches>
Wait!
Sugars: C_nH_2nO_n (where n is between 3 and 7)
This is probably why I did so poorly in chemistry. I never pay attention to the details.

So sugar is C_nH_2nO_n. I thought sugar is only C₆H₁₂O₆. Thanks. I'll read about sugar. That's a new knowledge for me.

 

[Stephanus]

Did a survey of my atoms a while back.

Wow, a good software. You're 145 pounds, Dave?Is the calculation is correct?No, no. Don't answer it. It's too personal question. Btw the height is in the number of atoms not in mass. I see that Oxygen is 33.5 cm³ and Hydrogen is 46.2 cm³. The numbers somewhat confuse me. Why Oxygen is only 33.5cm cubic. It's gas isn't it. If the body is made of water 70%, than the oxygen weight must be at least 63% of body weight. And for someone about 70 kg, the Oxygen should be around 45kg. And in gas, 45 Kg O2 would fill more than just 3 litres as shown in the figure. 33.5 cm cubic. It should be around 3.5 metres x 3.5 metres x 3.5 metres cubic, roughly.

 

[mfb]

So my question is this.
Why all (if not almost) life on Earth is carbon based? Because mathematically carbon is the easiest way to form life?
Most abundance, easiest reacted, has 4 valence?

All known life on Earth has a common origin. It's not just the carbon atom as base - all life uses RNA and/or DNA and very similar decoding schemes to read them. Took some time until that evolved, but it was so successful that it replaced all other life.

A cube with a side length of 33cm has a volume of 3.3³ or roughly 36 liters. Probably liquid oxygen.

 

[Alcathous]

Not just carbon? You can't make RNA without carbon.

It would be perfectly possible to have completely independent strains of life on earth, even with a different molecule to store the genome, but they would all be carbon based.

RNA coding for different AA's in different strains, that's several levels above a carbon strain of life and a silicon strain of life.

 

[mfb]

Not just carbon? You can't make RNA without carbon.

Right, RNA/DNA show that the similarities are much more than "just carbon based". That was my point.

 

[DaveC426913]

Wow, a good software. You're 145 pounds, Dave?Is the calculation is correct?No, no. Don't answer it. It's too personal question.

Heh. No.

Btw the height is in the number of atoms not in mass. I see that Oxygen is 33.5 cm³ and Hydrogen is 46.2 cm³. The numbers somewhat confuse me. Why Oxygen is only 33.5cm cubic. It's gas isn't it. If the body is made of water 70%, than the oxygen weight must be at least 63% of body weight. And for someone about 70 kg, the Oxygen should be around 45kg. And in gas, 45 Kg O2 would fill more than just 3 litres as shown in the figure. 33.5 cm cubic. It should be around 3.5 metres x 3.5 metres x 3.5 metres cubic, roughly.

You got me. I shamelessly stole the numbers from here:
http://web2.airmail.net/uthman/elements_of_body.html