I’ve heard that life emerged on the earth about 1 billion years after it was formed and began cooling.
Based on the circumstances of that time, as well as the timing of the event itself, do we have any hypothesis on whether “life generation” seems to be a quick and necessary occurrence under the proper conditions?
Of course there is such a hypothesis. The problem is testing it, and we’re a long ways from doing that, if we ever can. It’s one thing to be able to detect life on a distant planet, but it’s quite another to be able to understand the history of life on such a planet.
Life on earth probably emerged more than once - that is, it’s unlikely that all life, through the major extinctions, evolved from a single proto-lifeform. It’s even unlikely that all life stems from ancestors that survived the Permian wipeout.
Consider that the ability to fly evolved separately at least four times. There’s no reason to think that billions of years of early biohistory has only one thread, like elementary school history.
This seems about as wrong as it is possible to be. I do not think you will find any biologists or paleontologists who will agree with it. It is, in fact, essentially universally accepted that “all life, through the major extinctions, evolved from a single proto-lifeform” (i.e., the one referred to in the OP, that emerged about 1 billion years after the Earth first formed). It is overwhelmingly likely that all life around today stems from ancestors that survived the Permian “wipeout”.
None of the “major extinctions”, certainly not the Permian one, involved anything remotely close to extirpation of all life - many species became extinct, but many others survived - and I have never heard any serious scientist even hint that that there is any evidence or reason to think that new episodes of abiogenesis followed any of them.
It is possible that, in the original period when abiogenesis occurred, it happened more than once, in more than one location, but, almost certainly, the descendants of just one of those events soon became dominant and wiped out any others, and all life today is descended from that one original lineage (if, indeed, there ever was more than one -we are unlikely ever to find actual evidence of others).
Actually, it seems that the first evidence of life may be from only 200-300 million years after conditions had stabilized enough for it possibly to exist. (Before that the crust was too hot, or the surface was being bombarded by debris.) And life probably existed for some time before leaving geological evidence.
And I have read of scientists speculating that given how little time geologically speaking it seems to have taken that life may have evolved more than once, only to be destroyed when another major impact sterilized the planet again.
No direct evidence; but the short time that life apparently takes to appear combined with the fact that early Earth had repeated oscillations between being survivable and non-survivable for life is evidence it may well have happened.
I’m aware of that, and of the consensus on the matter. If it pleases you to think of that first proto-cell as being a vanishingly rare phenomenon, unduplicated anywhere in the vastness of Earth’s soup - in that same short era or over the billions of years to follow - be my guest.
Given the extraordinary “will” and robustness of life, I find the notion laughable. I find it much more likely that proto-life formed in multiple and many times over before multicellular life became dominant.
It’s not about what pleases me or not. Speaking as a scientist, I’m simply stating what the consensus is at this point. If and when there IS evidence to the contrary, then the consensus will change. You can laugh at the way science works if you like, but you are operating in the world of folk-science, not actual science.
ALL extant forms of life share a rather large number of features that seem to be what are termed “frozen accidents” - that is, features that don’t seem to be necessary, and have alternatives that could have worked equally well. If life arose more than once and produced descendents that survive to today, it would be exceedingly unlikely that ALL of these “accidents” would have “frozen” into the same state in each and every line. This is the strongest evidence for a single origin of life.
This actually makes a great deal of sense when you think about it. I don’t think even the most optimistic chemist would dispute the claim that getting from a primordial soup to life takes a lot of time and perhaps some amount of luck. Thus, we’d expect abiogenesis to be a relatively rare event. However, once that first life arose, it would spread. Quickly. Very very quickly.
So let’s imagine abiogenesis happening twice. The first time it happens, the new life form finds a big ol’ earth, completely free of life and competition. By the time the second abiogenesis event happens, the descendents of event 1 would have spread through all of the available environment and be competing like made. The new, feeble, unadapted lifeform from event 2 wouldn’t stand a chance. It’d probably be eaten almost instantly.
The search for a shadow biosphere is a niche field. It’s not completely absurd, since most microorganisms are undescribed and it’s possible some of our current detection methods would miss really weird critters from a second genesis. But whether it’s at the bottom of the ocean, in the upper atmosphere, or a mile under the ground it seems like everything is related to everything else.
Unless it was a different chirality, lived in an inhospitable environment, or if its alternative chemistry was poisonous. Like if it excreted arsenic or something. Although there are some specialized bacteria that can eat arsenic.
FWIW, here is my speculation. First, it does appear that life emerged more or less as soon as it was geologically possible. To me, that makes it seem likely that there were probably a number of life forms early on, but one of them outcompeted the others, perhaps because its genetic code was superior, perhaps for some other reason. Since all extant organisms use the same genetic code (that is, using 3 letter codons as well as the mapping between 3 letter codons and amino acids) it seems overwhelmingly likely that all the current life forms trace back to one origin. Life didn’t start over after extinction events.
Here is another similar question. Life percolated along as single unnucleated cells (prokaryotic) for about 2 billion years before some cell swallowed another cell and, instead of munching on it, incorporated it into its cellular machinery and thus created eukaryotic cells. From that point, multicelluar life followed fairly quickly and eventually vertebrates, mammals, primates, great apes, hominins, H sapiens, came along relatively quickly. Now what I have long wondered is whether that nucleation event was inevitable or unlikely. Maybe on average it happens in 200,000,000 years, but earth was unlucky. Maybe on average it takes 20,000,000,000 years and we were just lucky.
Here’s another such question on which we do have two samples. Dinosaurs were around for 165,000,000 years and never developed human type intelligence. Were dinos unlucky or is there something in the lizard line that makes it impossible. But it seems that human intelligence developed on the basis of some lucky events. The right kind of climate change, a particular hunting strategy, etc. It is for reasons like this that I always found the Drake equation silly, if not fatuous.