Is there any scientific evidence that abiogenesis occurred on our planet?

[Ahu_Ha]

Thank you to everyone for the responses.

[levdrakon]

I like Stephen Hawking’s answer to the God question. Paraphrasing: “it’s useless to speculate about what God could do. We need to discover what he did do. He created the laws of physics, set the universe in motion and hasn’t intervened since.”

It’s about at the nine minute mark on this youtube interview video.

As an agnostic, I’m okay with God having snapped his fingers and set the universe in motion. I just wish the various religions would shut up and quit trying to tell me what else God might have been thinking.

[Musicat]

@ralph124c

My question: why isn’t primative life constantly being created? i mean, evolution has advanced the DNA-we now have millions of animal and plant species. But why arent new primative life forms continuing to appear? are they out-competed by more advanced forms?

Your question prompted my thought process, so here goes.

It is often argued that if life began and evolved on totally different planets with no contact, that it would likely have nothing in common. One form of life might even be silicon-based instead of carbon.

So let’s suppose that every billion years, life began from scratch here on earth, then progressed and evolved. That would give us about 3 biological streams, and if these are so different (as they would be if they originated on different planets), they might conflict, but probably couldn’t interbreed.

So the next question is, does ALL life on Earth have enough in common that multiple, independent beginnings are ruled out? Are we confident that there is only one ancestor to ALL life forms, not two or three or more?

Then, to restate ralph124c’s post, did other forms begin/evolve, then die, or never began/evolved at all? And if so, why or why not?

[ITR_champion]

@Strassia

Your second and third questions have similar answers. In both cases they are testing for what is possible, not what actually happened. They are also working in labs, not the world. In some conditions many or even most of the molecules may have disintegrated. Remember that the experiment took place in a box in a room over a short period of time. The real thing had a large number of varied environments over a large period of time. It may be that the in the wild the conditions to let the chemicals reach a stable steady state was rarer than the conditions to create them in the first place. It may also be that thousands of systems of replicating chemicals were formed and either destroyed or eaten over time. The bottom line is we will probably never know for sure what did happen, we can only try and isolate what is could have happened, and possibly what is most likely to have happened.

Let me focus on the recent discovery of a self-replicating RNA enyme. By itself, the fact that humans can build such an enzyme does not mean that such an enzyme could form automatically, just as humans building a computer doesn’t prove computers can form automatically. The question is what process did they build the enzyme by and under what conditions?

I know nothing about RNA enymes but I assume–and the articles on the topic seem to support–that they built this enzyme by stitching together several fragments of RNA of shorter length. If so, it would be highly relevant to this discussion to ask how complex those fragments were. If they could really just dump RNA nucleotides in a test tube and have them form this enzyme, that points towards the possibility of abiogenesis. On the other hand, if they needed complex fragments of RNA to begin with, then this finding really says nothing about abiogenesis.

Like I said, the articles currently available are not detailed enough to tell which case it is, so I hope more details are presented soon.

[ITR_champion]

@Musicat

So let’s suppose that every billion years, life began from scratch here on earth, then progressed and evolved. That would give us about 3 biological streams, and if these are so different (as they would be if they originated on different planets), they might conflict, but probably couldn’t interbreed.

Every life form on earth has exactly the same set of transcription RNA molecules, which are the molecules that match codons of DNA to specific amino acids. Since there’s no reason why organisms from seperate beginning would have the same sets of tRNA molecules, we believe that there’s common descent for all organisms.

[Busy_Scissors]

@ITR_champion

A few questions.

First, I’ve heard the Miller-Urey experiment called into question on several grounds. First, the experimental setup was not actually based on our best estimation of what chemical conditions on the early earth were like. Rather, it was based on what chemical conditions were needed in order to form amino acids. Scientists now believe that the early earth atmosphere was not dense in methane and ammonia, the chemicals used the Miller-Urey experiment. Rather, it was dense in sulfur compounds, carbon dioxide, and nitrogen. Is this true?

Second, they also claim that the conditions of the Miller-Urey experiment were not actually a simulation of natural processes. In particular, the experimental setting used a “cold trap” that artificially separated out different vapors. Without this device, all of the amino acids would have disintegrated immediately. Is this right or not?

Third, the self-replicating RNA enzyme that they designed at Scripps does not emerge from amino acids. It emerges from RNA, obviously. The New Scientist article doesn’t give the details, but I presume they formed it by joining together shorter molecules of RNA. Is there are evidence of RNA nucleotides forming by themselves from an early-Earth environment?

Questioning the Miller-Ure experiment is interesting in microcosm, but it’s not an important question at the conceptual level of abiogenesis. It’s thought provoking to think about whether the atmospheric conditions were accurately replicated, or whether electrical discharge is the key pre-biotic reaction condition etc. but the bottom line is that there are so may reasonable syntheses of basic building blocks, under so many reasonable conidtions, that no one working in the area is particularly exercised about this question these days.

#3 is where you should be directing your sceptical energies. You are quite correct to wonder about the origin of RNA - it is demonstrated to have self-replicating properties but where does it come from? It’s a relatively complicated molecule, and establishing a viable pre-biotic synthesis of RNA from simple ribose and nucleobase building blocks has consumed careers - a definitive answer has yet to be forthcoming and is the nub of the replication versus metabolism debate.

[Musicat]

@ITR_champion

Every life form on earth has exactly the same set of transcription RNA molecules, which are the molecules that match codons of DNA to specific amino acids. Since there’s no reason why organisms from seperate beginning would have the same sets of tRNA molecules, we believe that there’s common descent for all organisms.

Then that would argue towards a rare, one-time event and not a commonly repeated occurance.

[begbert2]

@Musicat

Then that would argue towards a rare, one-time event and not a commonly repeated occurance.

Or it would argue towards there never having been a later event in an area not dominated by the hungry and/or dominatingly more competetively effective offspring of a prior event. Which is to say, that there is only one surviving strain now doesn’t mean that there haven’t been ten thousand other varying strains that didn’t last long.

[Chronos]

Or it would argue towards there never having been a later event in an area not dominated by the hungry and/or dominatingly more competetively effective offspring of a prior event. Which is to say, that there is only one surviving strain now doesn’t mean that there haven’t been ten thousand other varying strains that didn’t last long.

Put another way: Living things tend to taste good, to something or other at least, but they also tend to put up a fight against getting eaten. Almost-living proto-things also tend to taste good, but they’re not as good at keeping from getting eaten.

As to the abiogenesis experiments currently being performed, keep in mind that those experiments are all done in tanks a few meters in size, in a few widely-scattered labs, and over timescales comparable to a human lifespan or less. If you increase the size of your laboratory to cover the entire planet, and let it run for hundreds of millions of years, the odds go up considerably.