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If life can start from scratch, and the earth's condition is suitable for life to start from scratch, logically every day brand new simple life form could be starting from scratch somewhere on earth independently of all life forms on earth, right? New life form could've started 4 billion years ago, 3.9 billion years ago, 3.8 billion years ago... and so on, and evolved on separately.
Good question and the answer shows how probabilities are so important in evolution.
The conditions that allowed the first proto life form(s) to start were changed by those life forms, so they were no longer present. ...It would seem that there's a fairly narrow window of conditions that would be favorable for de novo biogenesis.
Maybe new life forms are occurring all the time de novo-- but being in low numbers, the odds are great that they'd be quickly wiped out...Ever play the card game "War?"--- if you started out with only 3 cards (all low denominations) and your opponent had the other 49 cards (including all the aces & face cards), the game would end quickly, You wouldn't have a chance against those odds.
BTW- "War" is also a good example of why no two species can occupy the same niche in the biome for long-- one will inevitably be wiped out just by chance., leaving the other to continue without competition.
If life can start from scratch, and the earth's condition is suitable for life to start from scratch, logically every day brand new simple life form could be starting from scratch somewhere on earth independently of all life forms on earth, right? New life form could've started 4 billion years ago, 3.9 billion years ago, 3.8 billion years ago... and so on, and evolved on separately.
Why is there only one evolution tree on earth?
1) Just because life can start on Earth does not mean that it was ever likely to start on Earth. What were the odds? We just don't know.
Think of it this way. If we could 'replay the tape' of Earth's early conditions, how often would the result be life? Maybe it would be 9 times out of 10. If the odds are that high, we can expect that life (or proto-life) arose multiple times. On the other hand, maybe it was 1 time out of 10 (or 1 in 1000, or 1 in 1,000,000,000,000,000,000,000,000 - who knows?), in which case we would not expect it to happen more than once.
2) Even if the odds were such that life developing on Earth was not at all unusual, nascent life (or, again, its precursors) occurring after life had already come to exist could well prove extremely vulnerable - it would have been nutrient rich and utterly defenseless - and thus been quickly devoured by earlier life.
3) Life version 2.0 simply might've been out-competed - in ways other than by predation - by the life we know (or, we could be life 2.0, and life 1.0 went down to defeat), leaving just one life of universal common descent.
If life can start from scratch, and the earth's condition is suitable for life to start from scratch, logically every day brand new simple life form could be starting from scratch somewhere on earth independently of all life forms on earth, right? New life form could've started 4 billion years ago, 3.9 billion years ago, 3.8 billion years ago... and so on, and evolved on separately.
Why is there only one evolution tree on earth?
To which "earth" are you referring?
On this Earth, there are three evolutionary trees: archaea, bacteria and eukarya.
You should seriously consider filing a lawsuit against your school district, because they failed to teach you properly and you have been harmed.
Furthermore, there could literally be dozens of other trees neither you nor I nor anyone else who has lived, is living or will ever live knows anything about.
Dozens of different life forms could have started and then died out immediately or started and evolved briefly before going extinct.
There could be others that started, evolved and existed for a Million to a Billion years before going extinct and there is no law that requires any organism to leave trace evidence of its existence for others to find in the Future.
We don't even know how many species of bacteria exist today. How are we supposed to know how many species existed a Million or a Billion years ago? There's no way to know.
Your definition of "life" is also highly suspect.
Life did not form, rather chemicals bonded together. Huge difference.
Had you been watching the news a few months back, you'd know the chemicals to create DNA exist on asteroids and comets, because they successfully landed a space probe on one and found them.
The two Nobel Prize-winning scientists who discovered DNA (Crick & Watson) never believed life formed on Earth. They believed that life, well, at least eukarya, formed in Space and came to Earth where it evolved further. That's something else your teachers should have told you but obviously didn't.
You are nothing more than a complex series of chemical reactions simultaneously occurring 24/7 until those chemical reactions cease and you expire (or die, if you prefer).
You can think only because chemical reactions take place among highly evolved and specialized cells unique to the brain.
In the most general terms, an evolutionary tree—also known as a phylogenyFootnote 3—is a diagrammatic depiction of biological entities that are connected through common descent, such as species or higher-level taxonomic groupings. An overwhelming body of evidence supports the conclusion that every organism alive today and all those who have ever lived are members of a shared heritage that extends back to the origin of life some 3.8 billion years ago. One might therefore expect it to be possible, at least in principle, to reconstruct the Tree of Life, branch by branch and bough by bough, from the current diversity residing at the outermost twigs to a universally shared root.
On this Earth, there are three evolutionary trees: archaea, bacteria and eukarya.
You should seriously consider filing a lawsuit against your school district, because they failed to teach you properly and you have been harmed.
Furthermore, there could literally be dozens of other trees neither you nor I nor anyone else who has lived, is living or will ever live knows anything about.
Dozens of different life forms could have started and then died out immediately or started and evolved briefly before going extinct.
There could be others that started, evolved and existed for a Million to a Billion years before going extinct and there is no law that requires any organism to leave trace evidence of its existence for others to find in the Future.
We don't even know how many species of bacteria exist today. How are we supposed to know how many species existed a Million or a Billion years ago? There's no way to know.
Your definition of "life" is also highly suspect.
Life did not form, rather chemicals bonded together. Huge difference.
Had you been watching the news a few months back, you'd know the chemicals to create DNA exist on asteroids and comets, because they successfully landed a space probe on one and found them.
The two Nobel Prize-winning scientists who discovered DNA (Crick & Watson) never believed life formed on Earth. They believed that life, well, at least eukarya, formed in Space and came to Earth where it evolved further. That's something else your teachers should have told you but obviously didn't.
You are nothing more than a complex series of chemical reactions simultaneously occurring 24/7 until those chemical reactions cease and you expire (or die, if you prefer).
You can think only because chemical reactions take place among highly evolved and specialized cells unique to the brain.
All life is just chemical reactions.
Of the four possible spontaneous chemical reactions, three of them produce byproducts with increased entropy and are not likely to contribute to complexity. The fourth produces byproducts with lower entropy, but requires an external heat sink. I’m always puzzled when the claim is made that “life is just chemical reactions” because the probability for chemical abiogenesis is based on a factor less than one. Multiple iterations of N^(.25) tends toward zero rather quickly. There is obviously something else at play.
1) Just because life can start on Earth does not mean that it was ever likely to start on Earth. What were the odds? We just don't know.
.
Your line of thinking is correct, but your conclusion wrong: there are basically two ways of determining "the odds"-- we can guess based on apparent complexity (like you're suggesting) or we can go by past experience. In the case of Earth, we have one system and one result (life did form) ie, odds are 100% certain....The odds on the tote board are meaningless after the race has finished.
Quote:
Originally Posted by Mircea
To which "earth" are you referring?
On this Earth, there are three evolutionary trees: archaea, bacteria and eukarya.
.
...but all three are based on DNA/RNA and have miraculously common metabolic pathways...What are the chances that all three developed the same very complex systems de novo independently?
Quote:
Originally Posted by TimAZ
Of the four possible spontaneous chemical reactions, three of them produce byproducts with increased entropy and are not likely to contribute to complexity. The fourth produces byproducts with lower entropy, but requires an external heat sink. I’m always puzzled when the claim is made that “life is just chemical reactions” because the probability for chemical abiogenesis is based on a factor less than one. Multiple iterations of N^(.25) tends toward zero rather quickly. There is obviously something else at play.
That "something" is called Self-Organization....While looking at it from strictly a physical chemistry POV, the tendency to increase entropy would seem to make it unlikely that life would persist, but add in the concept of "eating"- ie- continually taking in fresh sources of energy--and the energy expenditure makes the highly organized state (lower entropy) more likely to persist. Cf- formation of a fat globule in water- tendency towards increased entropy (dispersal) is over shadowed by the lower energy state of an organized, spherical globule....We see it in economics too: "It takes money to make money."
Your line of thinking is correct, but your conclusion wrong: there are basically two ways of determining "the odds"-- we can guess based on apparent complexity (like you're suggesting) or we can go by past experience. In the case of Earth, we have one system and one result (life did form) ie, odds are 100% certain....The odds on the tote board are meaningless after the race has finished.
There is no way to determine 'the odds'. Period. The only thing we know is that they are not zero. I suggested nothing 'based on apparent complexity'. The question is about the appearance of life, not its subsequent development into increasingly complex forms.
And, no, the odds are not meaningless. A person buys a lottery ticket and wins the jackpot. What does that tell us of the odds (ie, the number of potential combinations)? Nothing. Nothing at all. That single data point does tell us anything about whether the odds of such a win are one in ten or one it ten octillion. Any lottery winner who thinks the odds of them winning the lottery are 100% should have their graduation from 6th grade revoked. No meaningful extrapolation can be made from that single data point, be it the lottery winner or the Earth.
We don't know due to an obvious lack of data, regardless of the math-challenged who think otherwise.
There is no way to determine 'the odds'. Period. The only thing we know is that they are not zero. I suggested nothing 'based on apparent complexity'.
You claim we can't know the odds of de novo biogenesis. As I said, there's only two ways to attempt a guess-- one based on our estimates of complexity, the other on actual experience....Our only actual experience is for our own planet. Here the probabilities are 1.0. Certainty.
If you go to the race track and see seven thoroughbreds prancing around the paddock before the race and one mule also entered, you'd be a fool to place a bet on the mule. You certainly have some knowledge of the value of long legs and sleek muscles in producing running speed, as opposed to the short legs and bulky muscle of a mule. You'd have to guess the mule has very slim hopes of winning this race..
If you're a good handicapper, you may even be able to make further evaluations and narrow the odds of the other seven to winning...That's BEFORE the race is run...But AFTER the race has been won and the winner is known, the a priori evaluations are meaningless (They may have been right, but they're still meaningless at this point. Who cars if #4 was 5:1 favorite, but lost out to #6?)
So it is with the probabilities of life starting on Earth: the odds may be against it on another, similar planet without life right now, but on Earth the probability is 1.0-- It happened. The race has been won and the winner is known.
In regards Watson & Crick's suggestion that DNA must have started elsewhere: that's quite a stupid comment, if indeed they said it. It merely adds a layer of complexity to the question- how & when? Why not here? Why would another place be more favorable?
What are the odds of cutting a deck of cards and getting the Ace of Spades?-- 1/52
What are the chances of cutting a deck of card twice and getting the Ace of Spades on both? -- 1/52 x 1/52.(much smaller chance)
OK, so let's all agree the odds of DNA appearing anywhere in the universe is really small....What does that do to the odds of DNA forming elsewhere, travelling thru God knows how long a journey to just happen to bump into Earth, surviving a fiery descent thru the atmosphere to crash in a huge explosion on the surface and still reman intact to evolve into life here?... I'd say next to nil.
Chances of forming here -- 1 in alot; chances of forming elsewhere and getting here- 1/alot x 1/even more = much closer to zero than 1/alot by itself.
Last edited by guidoLaMoto; 09-07-2020 at 10:13 AM..
Indeed.
G- and K-Class Stars are the most abundant in the Universe.
Do G-Class Stars support life? This one does. Our own Sun is a G-Class Star. K-Class Stars are slightly smaller and burn a tad cooler, but all that means is that if our Sun was a K-Class Star then both Venus and Earth would have life.
Once life is found elsewhere, and it will be found, the point is moot.
Quote:
Originally Posted by TimAZ
Of the four possible spontaneous chemical reactions, three of them produce byproducts with increased entropy and are not likely to contribute to complexity.
Increasing entropy creates complexity. You should try reading modern science instead of the McGuffey Reader.
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