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from the out-with-the-old-priors-and-in-with-the-new dept.
New Theory Concludes That the Origin of Life on Earth-Like Planets Is Likely:
Does the existence of life on Earth tell us anything about the probability of abiogenesis — the origin of life from inorganic substances — arising elsewhere? That's a question that has confounded scientists, and anyone else inclined to ponder it, for some time.
A widely accepted argument from Australian-born astrophysicist Brandon Carter argues that the selection effect of our own existence puts constraints on our observation. Since we had to find ourselves on a planet where abiogenesis occurred, then nothing can be inferred about the probability of life elsewhere based on this knowledge alone.
[...] However, a new paper by Daniel Whitmire, a retired astrophysicist who currently teaches mathematics at the U of A, is arguing that Carter used faulty logic. Though Carter's theory has become widely accepted, Whitmire argues that it suffers from what's known as "The Old Evidence Problem" in Bayesian Confirmation Theory, which is used to update a theory or hypothesis in light of new evidence.
[...] As he explains, "One could argue, like Carter, that I exist regardless of whether my conception was hard or easy, and so nothing can be inferred about whether my conception was hard or easy from my existence alone."
In this analogy, "hard" means contraception was used. "Easy" means no contraception was used. In each case, Whitmire assigns values to these propositions.
Whitmire continues, "However, my existence is old evidence and must be treated as such. When this is done the conclusion is that it is much more probable that my conception was easy. In the abiogenesis case of interest, it's the same thing. The existence of life on Earth is old evidence and just like in the conception analogy the probability that abiogenesis is easy is much more probable."
Journal Reference:
Daniel P. Whitmire. Abiogenesis: the Carter argument reconsidered [open], Int J Astrobio, 2022. DOI: 10.1017/S1473550422000350
(Score: 3, Interesting) by oumuamua on Wednesday October 05 2022, @01:35PM (17 children)
Life on Earth emerged, literally, just after the molten ball cooled off. Molten ball: 4.5 billion years ago, life emerges: 3.7 billion .
https://naturalhistory.si.edu/education/teaching-resources/life-science/early-life-earth-animal-origins [si.edu]
If abiogenesis was difficult, you'd expect life to show up billions of years after ideal conditions appeared.
It is like someone making a half court basketball shot on their first try.
(Score: 0) by Anonymous Coward on Wednesday October 05 2022, @01:56PM
Well, put even more simply, it is thermodynamically favorable. Therefore it happens everywhere all the time, as certain as planets revolving around stars.
(Score: 3, Interesting) by mcgrew on Wednesday October 05 2022, @07:06PM (10 children)
Those were almost certainly the conditions necessary. Note that as far as is known, life only began on Earth then and never afterwards. My question is, how old did the universe have to be for the right stars to go supernova to produce the nevessary elements that fused into various substances that are necessary for life?
mcgrewbooks.com mcgrew.info nooze.org
(Score: 3, Interesting) by Immerman on Wednesday October 05 2022, @08:32PM (5 children)
As far as we know, there's absolutely no reason to expect later-spawning life to survive. New life could be spawning every day on Earth, but it would have no chance to survive in competition with life that's already been optimized by billions of years of evolution.
And that'd be just as true after a thousand years of evolution. The only way a new form of protolife that just barely figured out imperfect self replication could compete with life that's been around for a while is if it had a *huge* innate advantage. And if it had such a dramatic advantage, then it would be reasonably expected to rapidly outcompete all pre-existing life once it had time to start evolving a few improvements. Resulting in exactly the same fossil record as if life had only arisen once.
(Score: 2) by mcgrew on Thursday October 06 2022, @04:07PM (4 children)
There was a billion years of life on Earth before evolution started 750 million years ago.
mcgrewbooks.com mcgrew.info nooze.org
(Score: 2) by Immerman on Thursday October 06 2022, @04:34PM (3 children)
What?
The first (definite) animals evolved around 750M years ago, but evolution started immediately after the first self-replicating pre-biotic systems started replicating 4+ billion years ago.
There's nothing magical or animal-specific about evolution - it's just the inevitable result of imperfect replication and death due to environmental factors.
(Score: 2) by mcgrew on Tuesday October 11 2022, @06:04PM (2 children)
Not according to that scientist, who studies ancient organisms. Life began, according to her, one billion seven hundred fifty years ago and didn't start evolving until life had been here for a billion years. Note by "life" it's not viruses, which aren't really alive, since they need a host to replicate. Oh, and if it's not alive it can't die, even if, like an automobile, it can seem to be alive ("it's dead, Jim." "Well, hold on... try it now).
mcgrewbooks.com mcgrew.info nooze.org
(Score: 2) by mcgrew on Tuesday October 11 2022, @06:26PM (1 child)
Correction: one billion seven hundred fifty MILLION years.
mcgrewbooks.com mcgrew.info nooze.org
(Score: 2) by Immerman on Tuesday October 11 2022, @08:57PM
Citation?
Here's one of mine, with a links to many others: https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life [wikipedia.org]
If one scientist says something, they're probably wrong. Something like 80-90% of all published studies are later disproven - that's the whole point of peer review. And why you should take everything with a grain of salt until a concsensus of scientists agrees that something is true after it has withstood extensive challenges by experts in related fields.
(Score: 3, Interesting) by Immerman on Thursday October 06 2022, @05:16PM (3 children)
As to how old the universe had to be for life to form? First off, we can only talk about life-as-we-know-it - but that's built entirely out of light elements, so it could theoretically have formed as soon as the light elements were present in the universe, shortly after the first stars exploded at least 13 billion years ago.
The first generation of stars were formed from pure hydrogen (and possibly a bit of helium), somewhere between 100 and 400 million years after the big bang which was all that existed in the early universe. Fusion in their cores created lighter elements up to at least oxygen (the C-N-O cycle being the tail end of stellar fusion, though there's probably lots of incidental production of heavier elements), and the heavier elements (including the transuranics) were created in their death-explosions, which mostly happened a few million to a few hundred million years after the big bang for all the giant and hyper-giant stars. Even the smaller stars
The second generation stars formed from their remnants, and their dust clouds would have contained all the elements necessary to form rocky planets and life, though possibly not in great enough concentrations for either to be common. (Their spectral lines show their atmosphere is less than 0.1% "impurities" - aka everything heavier than helium). They produced even more light elements, and their death explosions created even more heavy elements.
Our sun, along with most visible stars, is a third generation star, whose atmosphere contains ~1% impurities, and whose pre-stellar dust cloud contained plenty of raw materials to produce rocky planets and life. They started forming about 9 billion years ago, while our own is about 4.5 billion years old (with Earth, and earth-born life forming within the next 500 million years).
So 9 billion years ago is probably a good ballpark guess as to when the probability of life forming on new planets reached approximately the level it would have been at when our sun formed.
The Fermi paradox exists because of the fact that millions if not billions of Earthlike planets in our galaxy were already as old as Earth is now before Earth even formed, and there's likely hundreds of billion more that formed in the billions of years in between.
(Score: 2) by Immerman on Thursday October 06 2022, @05:21PM
Bah - I hate catching editing errors after hitting submit.
>and the heavier elements (including the transuranics) were created in their death-explosions, which mostly happened a few million to a few hundred million years after the big bang for all the giant and hyper-giant stars. Even the smaller stars
Should be
>and the heavier elements (including the transuranics) were created in their death-explosions, which mostly happened a few million to a few hundred million years after their formation for all the giant and hyper-giant stars. Even the smaller stars were free of impurities, and thus would have burnt much hotter and faster than modern stars
(Score: 2) by mcgrew on Tuesday October 11 2022, @05:58PM (1 child)
Boron, Cadmium, Copper, iron... how old was the universe when these were produced? If it was 7 billion years ago, we could be the first, life on Earth started one billion seven hundred fifty million years ago, the sun about two or three billion when the Earth formed. You need the sun and the Earth for Earthian life to start.
mcgrewbooks.com mcgrew.info nooze.org
(Score: 2) by Immerman on Tuesday October 11 2022, @08:41PM
I just gave you the timeline. When the first generation hypergiants started exploding is when the first *everything* became available - from lithium to uranium and beyond. About 100M years after the big bang, or 13.7 billion years ago. But the amounts were pretty low.
Third-generation stars like ours, whose planet systems probably have element ratios similar to our own, started forming about 9 billion years ago, though the concentrations of heavier elements might not be quite as high as here, depending on the specifics of the protostellar cloud formation.
Where are you getting your numbers from?
Life started on Earth at least 3.42 billion years ago - the age of the oldest fossils, and it's suspected that the last common ancestor of all Earth (LUCA) life actually lived between 3.71 and 4.41 billion years ago - as early as a hundred million years of the formation of Earth, and about the same time liquid water began to form. https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life [wikipedia.org]
Meanwhile, the sun is roughly the same age as the Earth and other planets, between 4.5 and 4.6 billion years old. Planets form from the same protostellar cloud as their suns, and once the sun ignites most of the remaining cloud is blown away by the photon pressure. Though the gas giants may have caught much of it as it blew out past them - the process likely took several million years.
https://en.wikipedia.org/wiki/Sun#Formation [wikipedia.org]
https://www.worldatlas.com/articles/how-old-is-the-sun.html [worldatlas.com]
(Score: 2) by captain normal on Wednesday October 05 2022, @08:54PM
Well there's a 100 billion first shots just in our galaxy.
When life isn't going right, go left.
(Score: 2) by legont on Thursday October 06 2022, @01:56AM (3 children)
Life did not emerge. It simply came here from somewhere else.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by Immerman on Thursday October 06 2022, @05:46PM (2 children)
And when did it emerge there?
(Score: 2) by legont on Friday October 07 2022, @12:25AM (1 child)
Perhaps, even before the big bang.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by Immerman on Friday October 07 2022, @03:44AM
Not unless it's high tech enough to have hopped into the universe from elsewhere hundreds of millions of years after the big bang - prior to that the universe was too hot for atoms to exist. And if you're hopping universes, then you run into the problem that there's absolutely no reason to believe the laws of physics are the same between any two universes. It's quite possible that out of an infinite number of universes, this is the only one in which atoms as we know them can exist. Kind of hard to colonize another universe when your constituent atoms cease to exist upon entering.
And even assuming it's possible - all your insanely magi-science equipped universe-hopping aliens have accomplished, from our perspective, is to push the origins of life back a little. At some point in the past life had to emerge from somewhere - unless you want to argue that life somehow predates not just our universe, but all of existence? And... that's a bit of a problem, as it certainly seems that life has its roots in physical reality.