What's the chance of life didn't happen at all?

[arabianights]

all the information points to that life started on Earth by pure chance

what are the chance that life didn't happen at all on planet earth

 

[phinds]

68.993121 percent.

 

[Ryan_m_b]

What do mean life started by pure chance? There is no comprehensive theory of abiogenesis yet but we know enough to know that there was a probability of life forming eventually. Other than the we can't really say what the percentage chance was, there are too many variables (most of them unknown).

 

[epenguin]

But there has been life on Earth for most of its history, in fact last i heard you can't really identify a time when there wasn't, which suggests the chance is high.

 

[neerajareen]

Sooner it later. Given enough time, the the random permutations of protein molecules will eventually form DNA. So there are going to be life forms on other planets too. It's inevitable.

 

[jackmell]

But there has been life on Earth for most of its history, in fact last i heard you can't really identify a time when there wasn't, which suggests the chance is high.

That's not bad I believe. Mostly so. Had to cool first but soon after, I believe a few tens of millions of years, early forms of life began to appear. And I also agree the relatively quick appearance of life on Earth suggest the chance of life evolving on similar planets is high.

 

[Ryan_m_b]

Sooner it later. Given enough time, the the random permutations of protein molecules will eventually form DNA. So there are going to be life forms on other planets too. It's inevitable.

What are you basing this on? Proteins and DNA are not made from the same components. Are you suggesting that proteins alongside nucleic acids will eventually build DNA because that isn't how it works. Indeed abiogenesis was likely to be dominated by RNA rather than proteins or DNA.

 

[jackmell]

"RNA world" makes sense to me:

http://en.wikipedia.org/wiki/RNA_world_hypothesis

Here's an interesting quote:

since proteins large enough to self-fold and have useful activities would only have come about after RNA was available to catalyze peptide ligation or amino acid polymerization

Keep in mind nucleic acids are made of rings of cyanide (carbon-nitrogen bonds) and I believe cyanide is a common compound found in meteoroids. You may want to investigate that.

 

[HallsofIvy]

all the information points to that life started on Earth by pure chance

what are the chance that life didn't happen at all on planet earth

Surely that is not what you meant to ask? I am living proof that "the chance that life didn't happen at all on planet earth" is 0!

 

[Pythagorean]

When I attended college, all science majors were required to take metaphysics and epistemology, the branches of philosophy that examine the basics of what we know and how we know it. "arabianight's" question is interesting and valid, but not in a science forum. He/she is asking a question more basic then we ask in science. This questioner needs a philosopher, so here we go.
Life is defined as self-generated, self-sustaining action that can potentially replicate itself. So, yes, THERE IS LIFE, you asking the question is the proof. Many posters tried to answer you with ideas in molecular biology and statistics, and there are many interesting threads in those areas. For example, I marvel at the fact that while the original organic process may have been subject to random influences, and while nucleotide mutation may, in part, be random due to flaws in the mechanism itself, the overall genetic process that struggles with habitat influences to arrive at the summation we know as population biology, takes my breath away. The system is such a small part of the universe but yet so simple/complex. EVOLUTION is wonderful. That people figured it out is outstanding.

Scientists are philosophers: they can follow branches of philosophy like empiricism, scientific reailsm, platonism. Physicsforums tries to stick to empiricism for the most part. Currently, I don't think we have enough empirical evidence to posit the probability of life "in general". It would essentially be a long chain of Bayesian conditionals like the Drake equation.

If we specify that we mean the probability of life given we already had an Earth (as the OP seems to suggest) then there's many aspects of basic chemistry and geology (both in terms of mechanisms and molecules) that provide many of the basic building blocks for life that it might have been hard to avoid.

 

[Jupiter60]

Has life originated on Earth more than once, and if it hasn't, would that suggests that life happened by chance?

 

[Pythagorean]

Has life originated on Earth more than once, and if it hasn't, would that suggests that life happened by chance?

You can design a deterministic system that has a single saturation event.

"originated more than once" is kind of loaded. In the RNA world hypothesis it seems it would be a more 'global' event (not necessarily Earth-wide, but encompassing the whole system of emerging lifiness). So it was happening more than once both spatially and temporally. And it was (is still?) a process, not a singular event. If life is more of a spectrum thingy than an switch thingy, then maybe we want to look at the continuous lifiness value over time rather than a step function.

During the RNA world, there were no cellular organization has we know it but live wasn't just free floating either. However, the molecules of life probably form some type of organized structure called supramolecular aggregates. These were structures that could easily exchange genetic information and had some similarities to the cellular structures that we know today. So any new information that would arise from random chemical not-associated with supramolecular aggregates could potential be integrate in the system. Also the supramolecular aggregates do not leave a Darwinian-like lineage.

Those supramolecular aggregates gave rise to the three cell type we know today and each event was likely independent. Each cell type had to pass the Darwinian threshold and became more organized and were able to leave a lineage. Bacteria were the first to pass the Darwinian threshold from the supramolecular aggregates and the archea and eucaryotes then followed.

I think another question that should be ask is when should we consider that life began.

https://www.physicsforums.com/showpost.php?p=1377146&postcount=11

 

[epenguin]

Has life originated on Earth more than once, and if it hasn't, would that suggests that life happened by chance?

No, it is first-comer takes all. Newcomers don't stand chance against established life forms.

 

[Mytacist]

No, it is first-comer takes all. Newcomers don't stand chance against established life forms.

Would separate forms of life occupying completely different niches still interfere? e.g. if creatures initially developed using a form of photosynthesis, would it be possible for a separate type of life utilizing chemosynthesis to flourish?

 

[Khantazm]

No, it is first-comer takes all. Newcomers don't stand chance against established life forms.

Not necessarily. We don't know that we came from first-comers. We could have easily been the second-comers at the dawn of life, but outcompeted all the other comers.

Also taking competition into account, you first have to become an organism at all, and that's a long way from a self-replicating molecule. There's a good chance both types of life in their separate areas would have the same kinds of habitat and adapt to those, so when a bridge between the areas appeared, there'd still be competition, with both kinds having their own chemosynthesizing life, as an example. The fact that one side didn't fit into the balance of the other, which was more fecund or more developed, could have easily driven one side into extinction, just like marsupials in South America.

 

[Pythagorean]

Agreed that we might not have been the first. However, I think epenguin's statement still holds water, now that our lineage(s) (the only surviving lineage(s) on Earth) have saturated the environment. Macromolecules that would become new lifeforms (from scratch) don't stand a chance; they are food to already-established populations.

 

[Jupiter60]

Agreed that we might not have been the first. However, I think epenguin's statement still holds water, now that our lineage(s) (the only surviving lineage(s) on Earth) have saturated the environment. Macromolecules that would become new lifeforms (from scratch) don't stand a chance; they are food to already-established populations.

Is it also possible that when life first originated on Earth, it changed the environment to where it wouldn't be possible for life to originate again?

 

[Pythagorean]

I don't think origination is such a simple topic that you can talk about it as some instance that occurred. As iansmith's quote about RNA world implies, life "originated" 3 times independently depending on where you define something as living vs. not living.

There's also this additional potential confusion:

The endosymbiotic theory states that several key organelles of eukaryotes originated as symbioses between separate single-celled organisms. According to this theory, mitochondria and plastids (e.g. chloroplasts), and possibly other organelles, represent formerly free-living bacteria that were taken inside another cell as an endosymbiont. Molecular and biochemical evidence suggest that the mitochondrion developed from proteobacteria (in particular, Rickettsiales, the SAR11 clade,[1][2] or close relatives) and the chloroplast from cyanobacteria.

In it's most simplest form, endosymbiotic theory suggests one single celled bacteria ate other bacteria and instead of digesting them, entered into an advantageous relationship... many cells became part of one (a possible explanation of why mitochondria have their own DNA or why cynaobacteria look so much like chloroplasts).

I don't know whether the precursor bacteria would be of the same lineage or not, or whether we should include that as an event of new life. It would be a new level of life, I think: emergent consequence of two organisms is they become one more complex organism.

In the next step of life, instead of consumption, there was cooperation between cells, role assignment (differentiation) which lead to multicellular life which, as far as I know, is limited to eukaryotes (the cells that contain mitochondria).