All life on Earth is surprisingly homogeneous from a biochemical point of view. Every organism known to us is primarily built with carbon-based molecules that also contain hydrogen and oxygen, mainly proteins, fats and carbohydrates; short-term energy storage occurs in the phosphate-phosphate bond of ATP, and long-term storage in the carbon-oxygen double bonds (C=O) of complex carbohydrates; information is stored in the sequences of nitrogenous bases of DNA and RNA; chemical exchanges occur through liquid water; of the 92 natural elements, only few others play a role in known biochemistry (sulfur in certain aminoacids, calcium in shells and bones, iron in blood, magnesium in chlorophyll, sodium in nerve cells, etc).

However, would it be possible for organisms that share a common ancestor, however old, to be wildly different? Could completely liquid or completely solid life forms evolve from more traditional ones? Could related organisms use different fundamental forces to control their internal chemical reactions? I know that this is a difficult question to answer, but I guess the bottom line is - can huge changes to biochemistry like this occur without a second genesis, such as the examples I gave above?

  • What does a "completely liquid ... life form" look like? More importantly, how does it keep it's structural integrity without cell walls? – RonJohn Nov 10 at 12:39
  • @RonJohn Surface tension? Alternatively, it could live only in a porous medium like pumice stone. – SealBoi Nov 10 at 12:47
  • "Surface tension?" Better hope it doesn't rain too hard. And how would the organism get into the pumice? – RonJohn Nov 10 at 12:55
  • "Use different fundamental forces": not really. From the scale of atoms to the scale of blue whales the electromagnetic force is the one and only fundamental force which is strong enought to count. The strong and weak forces are effective over much shorter distances, so at those scales they vanish; gravity is way too weak; and there is no fifth fundamental force. I'm afraid any kind of biology is an application of quantum electrodynamics. – AlexP Nov 10 at 13:18
  • Surface tension isn't actually all that out there (at least, compared to some of the more implausible creatures in published science fiction). If the creature's biosolvent is a) not the most common liquid in the environment, and b) immiscible with whatever constitutes rain, seas, etc., then it could work out fine. E.g., organisms whose biochemistry takes place suspended in oil drops / oil slicks surrounded by water. – Logan R. Kearsley Nov 12 at 20:01

However, would it be possible for organisms that share a common ancestor, however old, to be wildly different?

If they share a common ancestor, they necessarily share the same biochemistry. They might just differ in some metabolic path, like aerobic and anaerobic life form do.

If you want radically different biochemistry, you cannot have a common ancestor.

As you point out, life sorted out the basic mechanisms long ago. Competition between life forms mean the fittest survive and wildly different variants were outcompeted.

What you need is a refugium. Just as marsupials and giant land tortoises avoided being outcompeted by placental mammals by hiding in their refuges, so too your wildly divergent biologicals. These must have escaped the mass of their relatives at some point in very early evolution and made it to some place where they could live unmolested, and over the eons diverge.

Mars comes to mind, with primitive creatures traveling from Earth via asteroid impacts in the Hadean period of Earths history. Or perhaps there are refuges in the very deep earth, cut off from the surface for billions of years?

We already have things living in boiling underwater sulfide volcanoes (which also make use of tungsten btw) as well as others that can survive the radiation, temperature and vacuum of space.

Granted all of these still have high similarities in the most basic metabolic pathways (like ATP usage), but overall they do (need to) have vastly different and adapted biochemistry. If we'd put one of them in some sort of outer space enviroment and the other still in the deep sea volcanoes, I could imagine that with a few more million/billion years of evolution also these similarities can go away.

I doubt organisms with drastically different biochemistry can evolve from the same environment. One will be more efficient in the other, and win out the competition for some shared resource (sunlight, mineral nutrients, etc.).

I do think that organisms in same enviroment will compete for same resources. While there are 100+ elements in the periodic table, only a small subsets can co-exist in liquid form, and ultimately every lifeform will be using same or similar reactions to store or release energy.

You could have different form metabolisms evolve in different environments, and then have the lifeform using either metoabolism evolve to live in the "middle ground". Various outcomes are possible:

  • they live independently (carbon animals eat plants, rock animals eat rocks),

  • Symbiosis (rock trees provide shelter to carbon birds, bird poop provides minerals)

  • Competetion (both need calcium) until one side wins, or they hit an equilibrium.

  • When you say "carbon animals", do you mean carbon-based animals? – RonJohn Nov 10 at 19:52

once you have a scaffolding - cell structure, metabolic pathways, information-strorage - there isn't a need to reinvent them. there isn't an opportunity, because existing life will close those opportunities via predation.

the need is to adapt structurally & behaviorally - the scaffolding mediates those critical adaptations in competition with others for food, in predator/prey relations, in motility/sensory enhancements, etc., in the here and now. but for existing organisms there is no mechanism for altering its basal cell structure beyond slight tinkering with what's already there.

whatever winnowing, or selection, there was on the basic cell structure, biomolecules, etc., took place during abiogenesis, possible rna-world era, all leading up to the LUCA.

once there was a stable cell line, in fairly short order everything organic became food. this is also the reason we have no trace evidence of LUCA precursor material of any sort.

that game ran one time.

in a situation with closely situated habitable planets there might be some interesting scenarios where disjoint microbial biota were introduced to one another, say via meteorite, and then jousted for liebensraum.


All life on earth shares a underlying biochemistry because they evolved from the same chemical process, one that relies on water and its fairly unique characteristics. All life on earth exists withing the temprature range liquid water can exist at, (albeit in some cases under some very special circumstances). Water is one of the few naturally occuring polar liquids which allows for many useful reactions. A completely solid material would not allow for transport, diffusion, or many chemical reactions while a complete liquid has no separation from the environment, it can't collect or store materials, protect its reactions, or even stop its parts form diffusing away.

However keep in mind earth life ranges from algal sludge to trees, to echinoderms which can become remarkably rigid on demand. Earth life can give you a wide range of materials.

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