I have heard it proposed that life arose from a series of atoms/chemicals/compounds fortuitously coming together, aidied by zaps of lightning or other energy sources, progressing through increasingly complex formations until something resulted we could call ‘life’.
My question; is there any evidence this is still going on? Is new ‘life’ constantly being generated? Is anyone even looking at this?
I recognize the chemistry of the oceans/atmosphere etc may have changed, but we do still have lightning and other energy sources (thermal vents)
The usual answer I’ve seen is that current, highly-adapted life decisively outcompetes/feeds on any organic chemical compounds that might be randomly forming before they can develop into true life. That is, life can only develop in an empty world where there’s no pressure from pre-existing, entrenched life.
We also have a lot more free oxygen around now, which breaks down complex molecules quickly. Much less opportunity to gain in complexity when the environment is so corrosive nowadays.
Also, any molecule that could become complex enough to be considered proto-life is also complex enough to be considered food for something.
Probably not. Even if there are conditions today that would perhaps lead to a new origin of life, I don’t think any new pre-life conditions would survive against currently established organisms. The various conjectured “primordial soups” are basically solutions full of nutrients and organic molecules; current life forms call that “lunch”. And the current batch of organisms has a three billion year evolutionary head start.
And across all of evolutionary history, there is no evidence for multiple origins of life. If there have been other origins, the resulting organisms did not survive, or they are hidden well enough that we haven’t yet discovered them. So if life hasn’t successfully re-originated over the course of the last ~3 billion years, I’d say that the chances of it happening currently are approximately zero.
Then why are scientists so quick to say that life will almost certainly evolve given the right conditions? They usually state this when talking about life on other planets like Mars. They make it sound that any planet that is close to Earth like will have life.
If the origin of life on Earth is singular, why are they so optimistic about life elsewhere?
The origin of life is singular on Earth because once life appeared it prevented a second appearance of life, since the organic chemicals required were now bound up in living things and any new lift that might have appeared would immediately be eaten by the already existing life. Life will almost certainly appear given the right conditions, but the right conditions include not already having pre-existing life taking up all the available ecological niches.
I’m not sure that scientists ARE so quick to say that life in inevitable in certain conditions. Maybe they hope it is, but it certainly hasn’t been proven, so I’d expect most of them to hedge. Science WRITERS, now, are more likely to leap to certainties.
Scientists are still picking at the possibilities. The link is just one possibility being explored. As an example of the way that scientists try not to overstate things, when Niles Lehman (in the link) describes his results, he says: " . . . My overall sense is that this is interesting but probably too clean and tidy to be really meaningful in any realistic early earth setting.”
On the contrary, even the most omnivorously versatile have greatly restricted dietary requirements.
Therefore it would be much easier to stipulate that a second appearance would likely be unpalatable
to enough already exiting life to have a good chance of survival.
This clause appears unconnected with the surrounding.
Question: How do you know that all availabe niches are too crowded to permit a second appearance
of life to survive?
Answer: You don’t know, and you can’t know.
However, given the likley microscopic size of a second appearance there ought to be plenty of room,
and even a large species could get by if its diet did not require other living matter and if it did not
taste good to other living matter.
This is not really true when you consider such things as bacteria, archaea, and other single celled organisms.
You are right that it is not absolutely impossible for there to have been a successful second (and third, fourth, etc.) origin of life on Earth, but there are indeed very good reasons to think that it is very unlikely, and there is absolutely no evidence to suggest that it has happened.
All life uses the same DNA code. Since there appears no objective reason for that, the default explanation is that life had one origin (or, at any rate, one that outcompeted all others). Since there has never been a successful new origin in 4 billion years, it seems unlikely to go an ongoing process. The point about oxygen is also important. In fact the appearance of oxygen (a byproduct of photosynthesis) was the first ecological catastrophe. But it happened slowly enough that many organisms were able to adapt (and a few found anaerobic niches).
To expand on what Hari Seldon said: The genetic code refers to the way that the information encoded in DNA is translated into proteins. Every “word” (called a “codon”) of three “letters” (base pairs) in DNA corresponds to some particular amino acid (there are some duplicates, since there are 64 “words”, but only 20 amino acids). So, for instance, the codon GAU gets translated into aspartic acid, as does the similar codon GAC, while GAA and GAG both correspond to glutamic acid.
But the thing is, there’s a combinatorically large number of different ways you could set up this correspondence. If life arose twice by random chance, even if it happened to be based on DNA both times, the probability is as close to certainty as you’ll ever encounter that they’d end up using different genetic codes. But every single life form we’ve ever found, from blue whales to the tiniest viruses, from the archae that live in boiling hotsprings in Yellowstone to the bacteria that live in the deepest rocks, from the molds that live off of the radiation in Chernobyl to us, all of it uses GAU and GAC to represent aspartic acid, and GAA and GAG to represent glutamic acid, and so on. Ergo, we conclude that all of the life we know has some single common ancestor, and it all came from the same origin event.
Any of this is speculation. I personally dislike any theory that requires specialness or uniqueness to our being. As long as I have seen, the standard answer to biological development has been “it was first, therefore we all succeeded from it”. While I’ll admit that this likely occurred in many instances, the idea that at no time, our biology developed toward a thermodynamic minimum is rediculous. Mutation is at its very heart a chemical process that, like every other chemical process, is governed by thermodynamics and to say that over the course of 4 billion years a thermodynamic minimum was never chosen is just plain wrong.
Which is why I disagree with statements like this.
With 4 billion years of reaction time, it doesn’t take a huge difference in reaction energy for a minimum to develop. We certainly know that chirality can develop spontaneously in auto catalytic systems, and life is the ultimate auto catalytic system. Would DNA on another planet look like ours? Probably not, but if I had to bet on a type of DNA, I wouldn’t bet against the one we already know works.
WarmNPrickly, you fail to appreciate just how huge the number of possible genetic codes is. If you counted up the total number of organisms that has ever existed on Earth, and assumed that every single one of them had a novel mutation that caused it to use a different genetic code, you still wouldn’t sample all of them.
Irrelevant. Evolution can only go to work on a mutation once that mutation has already arisen. Even if our genetic code really is the absolute optimal one, and would be guaranteed to outcompete any other code given the chance, a new life origin would almost certainly never even try it to give it that chance.
First of all, it’s not irrelevant if the mutations themselves are disproportionate which, as chemical reactions, they should be. Second, in the early phase of abiogenesis, I have no doubt that a chemical natural selection was taking place before anything that we would even call life existed. There were billions of years for this to occur. In non self replicating systems these mutations would be reversible and thermodynamics prevail. When self replication becomes a factor, then autocatalytic kinetics take over, but still the rate of self replication will have an effect on the outcome.
I’m not stating that an exact duplicate of our own genetic code is likely, but if there were a billion possibilities, the probability might be as high as two out of a billion instead of one. Some of the other more likely possibilities might have very similar characteristics, but not knowing what those are, I’d have to bet on the two out of a billion that I know work. FTR, a billion is not meant to be the actual number of possibilities.
I’m sure what you say is true in the context of emerged lifeforms, but is it also true for the probable precursors to living organisms? Are there, for example, amino acids that nothing currently alive is interested in.
Any number of them. But since Life As We Know It doesn’t incorporate those compounds into proteins, they are just “Random compounds with an anime and a carboxylic acid functional group” and not amino acids.
You’re still not getting it. A billion is tiny. I said combinatorically large, not merely astronomically (and really, a billion isn’t even astronomically large). As in, 10^77, or so.