Jump to content
Science Forums

How Complex Chemical Reactions Emerged On Earth? A Scenario


minus

Recommended Posts

At the primordial earth we had many geological phenomena, such as volcanos etc, etc. Temperature was higher, sun energy was stronger and the atmosphere was different. Many chemical reactions were happening at the atmosphere, so a wide variety of chemicals were created. Eventually all these different chemical molecules fell on the ground due to gravity. So the surface of earth and the floor of the oceans and seas were the place were many different chemicals were collected. In fact, an inch of this “carpets” collects everything that comes from above i.e atmosphere and underlying water. So at every tiny inch of the surface, a huge variety of chemical molecules were collected. All these chemicals, with the help of strong external energy (e.g. solar energy, heat etc), started to react with each other due to close proximity. (Probably that would have been invisible our eye). Many different substrates were produced this way, so they started to react with each other as well, plus they reacted with all the previous chemicals and so eventually equilibrium was avoided and instead further complexity was created. Repeatable systems of reactions sustained themselves and prevailed.

 

However, terrestrial reactions, despite gaining significant complexity, equilibrium would have eventually occurred everytime. On the contrary, marine reactions were buoyed by water and so reactions and chemicals were stuck together for more time, and so complexity was promoted, as well as the creation of hydrophobic membranes that made the process multi-local rather than diffuse. This complexity was constantly increasing through the eons.

After trillions of years, the end result would be a tremendously complex system of reactions near the surface of earth. Interestingly, these reactions will be composed of repeated sub-systems (reproduction?) and the reactions that will be eventually present at the end would be those whose systems selected due to survival capacities.

 

Ok!! This is the scenario.

And lets see what scientific evidence from fossils found tells us about the istory of life on earth. The story in general goes something like…

Life on earth was first evolved 3,5 billion years ago. The first organisms with structure to create fossils were marine prokaryotes. First bacteria performing photosynthesis appered 3,4 billion years ago. 2 billion years ago appeared cmplex cells, and 1,2 billion years appeared sexual reproduction. Around 1 billion years appeared some bizarre multicelluar organisms such as skolithos, diplocraterion, cruzianna, ichnotaxon, spriggina, sinotubulites, namacalathus, etc, with elusive properties. Until 500 million years ago, all life was marine. Around that period the first terrestrial life-forms appeared. Soon after, Cambrian explosion happened and the rest is history….

Link to comment
Share on other sites

Welcome to hypography, minus! :) Please feel free to start a topic in the introductions forum to tell us something about yourself.

 

And lets see what scientific evidence from fossils found tells us about the istory of life on earth.

As you note, the first fossils are about 3,500,000,000 years old, and are of marine bacteria that photosynthesize – Cyanobacteria. Since fossils don’t have sufficiently high spatial resolution to show molecular features, this tells us only that something very similar to modern cyanobacteria was around then. Assuming, as most biologists do, that these ancient organisms couldn’t have existed without the DNA and RNA of their modern look-alikes, this tells us that complex, DNA-using organisms appeared very soon – about 500,000,000 years – after the Earth’s surface solidified from its early, usually melted, state, prior to which organisms like bacteria couldn’t have survived, that is, after the Hadean era.

 

So the picture I get of abiogenesis is an Earth that had the necessary conditions for life far before it was cool and hospitable enough for it to survive long enough to evolve the complexity necessary to have the orderly replication that pretty much distinguishes biological from non-biological chemical reactions, which appears to be managed by RNA, then later, DNA.

 

This is the most accepted consensus - that life began when a “replicator” system of molecules, RNA, then DNA, appeared via more-or-less trial-and-error, gene-free, pre-biological evolution. There is a family of alternative theories, however, that hold that biological-like chemical reactions, moderated by non-biological materials such as clays, occurred first. I find these “metabolism first” theories fascinating, and have a hunch that the truth involves a combination of “replication first” and “metabolism first”. I think that the pre-biological evolution of the first replicator molecules was much less trial-and-error than many imagine, due to the influence of non-biological moderators.

 

You could say I subscribe to a form of the “clay hypothesis”, since reading about it in a 2007 article. We discussed it in this thread, which I recommend.

Link to comment
Share on other sites

Simple chemical compounds don’t fossilize easily, but instead some criteria must be fullfiled for this to happen. Hence, life-related compounds and/ or chemical reactions could have existed long before 3,5 billion years ago.

 

If I had to select between the “metabolism first” and “replication first” scenario, I would be strongly in favor of “metabolism first”, for the following reasons:

a)Self-replicating molecules (such as DNA or RNA) by themselves don’t ensure the creation of life.

b)It is highly unlikely to my opinion that suddenly some non-reacting complex molecules managed to self-replicate in high accuracy. It is not impossible, but I would be inclined towards a simplier scenario.

c)”Metabolism first” is more easy to occur, as it is easier to get some complex systems of chemicals that were reacting with each other. These chemical reactions could have been subjected to some sort of evolution of chemical reactions and selection of reactions most capable of sustaining themselves.

d)Replication can be included inside metabolism. For instance, repeatable reactions are a form of primitive reproduction. Repeatable reactions can sustain themselves in the long term, and can be slowly evolved into sophisticated complex self-replicating systems.

Link to comment
Share on other sites

The most important molecule of life is H2O or water. Modern experiments have shown that life on earth, at any level, from large animals to enzymes, will not work properly without sufficient water.  At the same time, experiments have also shown that no other solvent be used as a replacement for water for life on earth at any level. 

 

What this means is water was the basis for all chemical selection for life on earth. Water selected what will be used by life; these selections only work in water. Water provided an environment, at the nano-scale, for chemical selection. It did do in an orderly way based on energy and entropy. 

 

Chemical selection is not much different from selecting an animal to live in the arctic circle or an amazon jungle. The environment sets many criteria, which define which animal will be more optimized and therefore selected. Water is like a very specific nano-jungle, that differs from all other solvents. Water pre-defines what chemicals will work in water and thrive. 

 

With abiogenesis, even from day one, one needs to think in terms of water and what would be selected by water. For example, all the important biomaterials form hydrogen bonds, which is also what water does, with water doing this more than any other material; highest hydrogen bonding density. Hydrogen bonding materials  will be selected and even induced to synch with water. 

 

This is just Darwin's theory of evolution and natural selection, but used at the nano scale where the solvent is the jungle and not all nano-critters; molecules, will be selected. Those nano chemicals that are selected, will form a close connection and symbiosis with their water environment. This is why no enzyme will work properly without water. 

 

The complexity of life is in the organics, not in the water.  Water has fewer needs and wants allows us to infer the order of complex events. 

Edited by HydrogenBond
Link to comment
Share on other sites

I agree! Our life is an example of life that was water-dependent even from its own creation. Water was a basic element from the very beginning. You cannot separate water from life on EARTH AS WE KNOW IT. However, water alone does not create life. It was found in other planets as well, but obvious signs of life are lacking.

The question is if another solvent can as well support life. If yes, it is obvious that this life would be very different from what we see here, with totally different composition. To me, the direct question is not whether DNA or RNA can be created under these solvents, but rather if complex systems of chemical reactions can be created and sustained…

Link to comment
Share on other sites

The most important molecule of life is H2O or water. Modern experiments have shown that life on earth, at any level, from large animals to enzymes, will not work properly without sufficient water.  At the same time, experiments have also shown that no other solvent be used as a replacement for water for life on earth at any level. 

 

What this means is water was the basis for all chemical selection for life on earth. Water selected what will be used by life; these selections only work in water. Water provided an environment, at the nano-scale, for chemical selection. It did do in an orderly way based on energy and entropy. 

 

Chemical selection is not much different from selecting an animal to live in the arctic circle or an amazon jungle. The environment sets many criteria, which define which animal will be more optimized and therefore selected. Water is like a very specific nano-jungle, that differs from all other solvents. Water pre-defines what chemicals will work in water and thrive. 

 

With abiogenesis, even from day one, one needs to think in terms of water and what would be selected by water. For example, all the important biomaterials form hydrogen bonds, which is also what water does, with water doing this more than any other material; highest hydrogen bonding density. Hydrogen bonding materials  will be selected and even induced to synch with water. 

 

This is just Darwin's theory of evolution and natural selection, but used at the nano scale where the solvent is the jungle and not all nano-critters; molecules, will be selected. Those nano chemicals that are selected, will form a close connection and symbiosis with their water environment. This is why no enzyme will work properly without water. 

 

The complexity of life is in the organics, not in the water.  Water has fewer needs and wants allows us to infer the order of complex events. 

 

HB you know you cannot draw a trend from one data point, in many ways other possible solvents are better than water in fact Titan has the signs of possible life that would be dissolved in liquid methane, hydrogen it's self is a possible replavement for water and ammonia is superior to water in some ways.

 

 https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

 

Ammonia, like water, can either accept or donate an H+ ion. When ammonia accepts an H+, it forms the ammonium cation (NH4+), analogous to hydronium (H3O+). When it donates an H+ ion, it forms the amide anion (NH2), analogous to the hydroxide anion (OH).[32] Compared to water, however, ammonia is more inclined to accept an H+ ion, and less inclined to donate one; it is a stronger nucleophile.[32] Ammonia added to water functions asArrhenius base: it increases the concentration of the anion hydroxide. Conversely, using a solvent system definition of acidity and basicity, water added to liquid ammonia functions as an acid, because it increases the concentration of the cation ammonium.[42] The carbonyl group (C=O), which is much used in terrestrial biochemistry, would not be stable in ammonia solution, but the analogous imine group (C=NH) could be used instead.[32]

 

Link to comment
Share on other sites

I was limiting myself to life on earth, because this is the only life that has been proven to exist by science. This choice is based on the philosophy of science. I am not arguing against other possible solvents, other than the fact that none of these possible solvents can replace water, for life on earth. This has tried done in the lab, and even enzymes get bogged down. The reason is, all the features of the cell evolved in water, with water selecting materials that complement water. 

 

If we used ammonia to start life, ammonia would do the nano-selection with no other solvent tuned as well to ammonia's chemical selections for life. If we know the needs of water or ammonia, we can guess steps of the organic materials. 

Edited by HydrogenBond
Link to comment
Share on other sites

In protein folding, it is hydrophobic interactions along the protein, which help drive the folding process. Hydrophobic means water fearing. Folding due to water fearing is one reason other solvents don't work when used to replace the water for life on earth. The hydrophobia proteins side groups are not as phobic of organic solvents, so the drive is much less, and the final protein is not folded properly.

 

Ammonia, alcohols, etc., are considered organic so the hydrophobic repulsion with water, which drives earth based protein folding, would be replaced by attraction, making the folding happen differently. If life evolved in ammonia, the protein side groups would need to be different, so a push away from ammonia; ammonia-phobic, would dominate. 

 

Water is easier to complement is this way, since water and many organics do not mix. I am not sure of what phases separate from ammonia and could be used as raw materials for polymers that can pack and separate out. 

Edited by HydrogenBond
Link to comment
Share on other sites

The system of water and oil is a useful way to explain how complexity can form from simplicity, in an orderly fashion, using water as the solvent for life. A similar analysis would work for other solvents but would need an alternate counter phase. 

 

If we mix water and oil, with agitation, this will increase the entropy/disorder of the oil and water. If we then let the emulsion stand, it will slowly lower entropy all the way back to two layers or water and oil. This spontaneous lowering of entropy is not a violation of the second law of entropy, because entropy is a state function. A state function means there is given value of entropy for any given state of matter with specific conditions; eq. water at 25C and 1 atmosphere pressure has a specific level of entropy that can be measured in any lab. 

 

The emulsion state is water, oil, blade and energy, which can support higher entropy, but the settled state of water and oil cannot support that same level of entropy. Since the amount of entropy of the universe needs to increase, the only way the second law can be satisfied and entropy can increase is by defining a new state. This new state might mean adding some unsaturated bonding to the oil or the attachment of phosphate to polarize one end. If we do nothing, the entropy would need to stop at that state.

 

The two phase water-oil system, sets a fairly low base state for entropy for such a complex system where there should be more variety of interaction, if they could blend, but they can't. The second law requires that the entropy of the universe needs to increases, but with entropy being a state function, this cannot happen with that system. The system has to change into another state, that allows for more entropy.

 

With billions of years to work and entropy has to increase, each level of entropy increase is associated with specific state functions. 

 

 

Link to comment
Share on other sites

If we had a semi-permeable membrane; osmosis, water will spontaneously diffuse in the direction of higher solute concentration. It will diffuse from the pure water side toward water plus solute. This is driven by an entropy increase; randomize all the moieties with each other. This direction will also increase entropy even for water and oil, if these were ideal. But in this is not ideal and will increase surface tension. 

 

Free energy G = H-TS where H is enthalpy, T is temperature and S is entropy. The increase in surface tension is connected to H, which causes G to increase faster than what can be gained by S; move toward the ideal solution. 

 

If water and oil were fully soluble, like oil and alcohol, maximizing mutual contact will increase entropy; solution. But because of surface tension H, this is not allowed since G becomes positive due to H. The spontaneous S direction is not large enough to offset H. The S does not dominate like in an ideal solution. 

 

In terms of water, hydrogen bonding is both polar and covalent, with the covalent state of hydrogen bonding more stable. The surface tension between water and oil, induces the covalent state in water's hydrogen bonding near the oil surface. This will help  lower energy slightly because the surface contact has increased energy; tension.  

 

This does a create a layer of ordered water close to the oil surface. This layer does have less entropy than the bulk water. This lowers energy but not enough to zero this out. The residual higher energy, due to the forced oil and water contact is conserved and is transmitted into the aqueous continuum that exists beyond the surface contact. This extra energy is reflected by more polar hydrogen bonding in the bulk water to reflect higher H.  The polar hydrogen bonding defines higher entropy, than does the covalent hydrogen bonding. This is the higher entropy offset. 

 

As we reverse the emulsion, the lowering of surface tension will give off energy. This energy releases will increase the hydrogen bonding energy at the surface, so the covalent order becomes more disordered; polar. The polar absorbs this energy. Since there is less surface tension energy transmitted into the water, the bulk water shifts equilibrium away from a much polar. 

Edited by HydrogenBond
Link to comment
Share on other sites

In protein folding, it is hydrophobic interactions along the protein, which help drive the folding process. Hydrophobic means water fearing. Folding due to water fearing is one reason other solvents don't work when used to replace the water for life on earth. The hydrophobia proteins side groups are not as phobic of organic solvents, so the drive is much less, and the final protein is not folded properly.

 

Ammonia, alcohols, etc., are considered organic so the hydrophobic repulsion with water, which drives earth based protein folding, would be replaced by attraction, making the folding happen differently. If life evolved in ammonia, the protein side groups would need to be different, so a push away from ammonia; ammonia-phobic, would dominate. 

 

Water is easier to complement is this way, since water and many organics do not mix. I am not sure of what phases separate from ammonia and could be used as raw materials for polymers that can pack and separate out. 

 

 

Ammonia is organic? Really HB?

Link to comment
Share on other sites

Ammonia is organic? Really HB?

 

Technically, you are correct since you need a carbon atom to be called organic. However, unlike water, ammonia is highly soluble in oil. This is why it a good household cleaner. Nitrogen (in ammonia) is less electronegative than oxygen (in water) so the hydrogen of ammonia act like they are in the middle between water and organics. This bridge between water and oil, makes it harder to find an appropriate nemesis pair with ammonia, like water and oil. 

Link to comment
Share on other sites

Technically, you are correct since you need a carbon atom to be called organic. However, unlike water, ammonia is highly soluble in oil. This is why it a good household cleaner. Nitrogen (in ammonia) is less electronegative than oxygen (in water) so the hydrogen of ammonia act like they are in the middle between water and organics. This bridge between water and oil, makes it harder to find an appropriate nemesis pair with ammonia, like water and oil. 

 

 

No HB, not technically, in the reality we both share organic means a carbon compound, if we are going to discuss this lets do it correctly, in fact in some ways ammonia is superior to water, the only reason water seems to perfect for life is that our life evolved in water, as I have said before if we had evolved in concentrated sulfuric acid CSA would seem far more perfect for life than water. You keep putting the cart before the horse. In fact as I pointed out earlier:

 

HB you know you cannot draw a trend from one data point, in many ways other possible solvents are better than water in fact Titan has the signs of possible life that would be dissolved in liquid methane, hydrogen it's self is a possible replacement for water and ammonia is superior to water in some ways.

 

 https://en.wikipedia...of_biochemistry

 

Quote

Ammonia, like water, can either accept or donate an H+ ion. When ammonia accepts an H+, it forms the ammonium cation (NH4+), analogous to hydronium (H3O+). When it donates an H+ ion, it forms the amide anion (NH2), analogous to the hydroxide anion (OH).[32] Compared to water, however, ammonia is more inclined to accept an H+ ion, and less inclined to donate one; it is a stronger nucleophile.[32] Ammonia added to water functions asArrhenius base: it increases the concentration of the anion hydroxide. Conversely, using a solvent system definition of acidity and basicity, water added to liquid ammonia functions as an acid, because it increases the concentration of the cation ammonium.[42] The carbonyl group (C=O), which is much used in terrestrial biochemistry, would not be stable in ammonia solution, but the analogous imine group (C=NH) could be used instead.[32]

 

 
Edited by Moontanman
Link to comment
Share on other sites

The value of ammonia ,in terms of life on earth, is since nitrogen has an electronegativity between oxygen and carbon, ammonia  provides a bridge between water and reduced organics. Ammonia can clean organic spills and dissolve in water. Protein, DNA and RNA use organic nitrogen to help bridge the gap between water and reduce carbon organics. The water and oil effect is moderated by ammonia. 

 

If we react two amino acids, to get a peptide linkage, there is a release of water. Not only is ammonia attached to the organic carbon  in amino acids, but water is also attached, with the H2O is distributed between the two polar ends. Proteins lose the attached water of amino acids and therefore drift slightly away from water, so the protein can phase separate out of water but stay connected. 

Edited by HydrogenBond
Link to comment
Share on other sites

The value of ammonia ,in terms of life on earth, is since nitrogen has an electronegativity between oxygen and carbon, ammonia  provides a bridge between water and reduced organics. Ammonia can clean organic spills and dissolve in water. Protein, DNA and RNA use organic nitrogen to help bridge the gap between water and reduce carbon organics. The water and oil effect is moderated by ammonia. 

 

If we react two amino acids, to get a peptide linkage, there is a release of water. Not only is ammonia attached to the organic carbon  in amino acids, but water is also attached, with the H2O is distributed between the two polar ends. Proteins lose the attached water of amino acids and therefore drift slightly away from water, so the protein can phase separate out of water but stay connected. 

 

All you are doing is stating the obvious, it has nothing to do with anything but how well earth life has adapted to water. 

Link to comment
Share on other sites

The molecular and phase bandwidth between water and oil, is higher than between ammonia and an unknown X, since ammonia is in the middle between water and oil. If you started with ammonia, your molecular and phase bandwidth becomes narrower, making life less likely than in water, which has a wider phase bandwidth. 

 

If you look in terms of energetics, which is critical to life, since you can burn ammonia in oxygen to make water and NOx, water also has an extra energy band width. Even if life did evolve in ammonia, any organic solvent or even hydrogen, life will evolve to use these solvents for food and burn them to water. Once it reaches water, it can't go lower and will have to stop there. 

 

An increase in entropy needs energy. The higher energy bandwidth of water, relative to organics, means water maximizes the energy output for entropy/change by being the lowest floor. All else equal, water will reach the finish line first; based on energy output, and will eat its slower competitors for energy. 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...