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How difficult is it for life to start?


RichIsnang
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I suppose it is quite easy for life to start if the conditions are right. And that it is quite difficult if the conditions are wrong.

 

A better question might have been "How difficult is it for the right conditions for life to exist?" Or "How difficult is it to determine what the right conditions for life are?"

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the most likely place for life to start is in a giant molecular cloud.

 

GMC's are so large that even if life is very unlikely to form it is bound to happen eventually.

 

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

 

 

 

Polycyclic aromatic hydrocarbons are the most common and abundant of the known polyatomic molecules in the visible Universe, and are considered a likely constituent of the primordial sea.[4] PAHs, along with fullerenes (or "buckyballs"), have been recently detected in nebulae.[5] (Fullerenes are also implicated in the origin of life; according to astronomer Letizia Stanghellini, "It’s possible that buckyballs from outer space provided seeds for life on Earth.”[6])

 

PAH's are not normally very soluble in sea water, but when subject to ionizing radiation such as solar UV light, the outer hydrogen atoms can be stripped off and replaced with a hydroxyl group, rendering the PAHs far more soluble in water.

 

These modified PAHs are amphiphilic, which means that they have parts that are both hydrophilic and hydrophobic. When in solution, they assemble in discotic mesogenic stacks which, like lipids, tend to organize with their hydrophobic parts protected

Edited by granpa
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I'm thinking that the initial discotic stacks of PAH's werent held together by chemical bonds but rather by much weaker forces.

 

cold temperatures would help that

There is plenty of bonding going on in distotics, and it is generally agreed that it can get quite hot as time goes on. Also, as time goes on, movement increases.

 

But very often, bonds are broken when it gets to closing time, showing that these are indeed quite weak forces.

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While we only have a data point of one it is possible to assert that life forms very easily. The Earth had hardly cooled when we start to see the first signs of life. If signs of life begin to show up. Some estimates put is at just a few million years some think it was far faster. but it is demonstrable that life formed very quickly on the cooling earth.

 

PAH's do form in space but to say that actual living organisms were formed in space is... somewhat less than reasonable, no working fluid is the most difficult thing to get around, extremely low temperatures is also a big problem. PAHs might been deposited on the earth and almost certainly were but not actual living organisms.

 

Personally i sit in the metabolism first camp, i think it was a synergy of several different factors that allowed life to form. Hypercycles of organic chemicals exchanging chemical energy with in the earth and was probably a big factor but there are others. large organic molecules forming in certain types of clay probably has big impact as well, organic molecules being pounded aprt in surf zones into the tiny organic bubbles that resemble cells and their ability to take up other organic molecules and then break apart and grow again almost certainly contributed to the early stages of life...

Edited by Moontanman
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you dont need a fluid medium in space. Space itself is the medium

 

even if living organisms formed in space they would not survive on earth.

 

I am only postulating that organic molecules formed (by self reproducing molecules) in space and were deposited by comets in great amounts on the early earth.

Edited by granpa
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you dont need a fluid medium in space. Space itself is the medium

 

even if living organisms formed in space they would not survive on earth.

 

I am only postulating that organic molecules formed (by self reproducing molecules) in space and were deposited by comets in great amounts on the early earth.

 

 

I think there can be little doubt that organic molecules on the earth came from space, in fact all organic molecules came from space... organic is just a molecule containing carbon, it has no special-ness apart from that...

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you dont need a fluid medium in space. Space itself is the medium

 

even if living organisms formed in space they would not survive on earth.

 

I am only postulating that organic molecules formed (by self reproducing molecules) in space and were deposited by comets in great amounts on the early earth.

 

It should be noted that solvent effects are a huge consideration in organic chemistry. I also think that the molecular collision frequencies in these low temperature gas clouds must be extremely low. Photochemical reactions dominate space chemistry to a large degree. Life as we know it needs a polar and or nucleophilic solvent to make biochemistry "go".

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While we only have a data point of one it is possible to assert that life forms very easily. The Earth had hardly cooled when we start to see the first signs of life. If signs of life begin to show up. Some estimates put is at just a few million years some think it was far faster.

This is eqaully, or indeed better, evidence that life must have been seeded from space. The complexity of even the simplest imaginable cellular lifeform is much more removed from prebiotic chemistry than from the first eukaryote and that transition took a billion years plus.

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My interested-layman impressions: 1. We don't have a secure theory; 2. We don't have an understanding of the bottlenecks involved in the leading hypotheses. Estimating the probabilities of life emerging from a given set of theoretical conditions is a dubious task.

 

The following is the best thing I've seen lately, but again, I'm merely an haphazardly interested layman.

 

http://www.ibioseminars.org/lectures/chemicalbiologybiophysics/jack-szostak.html

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Your remark about the ignorance of bottlenecks is spot on and suggests that you have a superior grasp of the issues compared to some of the speciliasts in the field who allow their enthusiasm to overwhelm their scepticism circuits.

Edited by Ophiolite
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Good points, I rephrase my question.

Given a planet revolving at the optimum distance around a star that is capable of supporting life, what is the probablility that life will start? How likely is it that the correct atmosphere and other factors will be in place for organisms to be able to start reproducing themselves?

The origins of my question of course come from wondering if life is on other planets, it seems to me that there will be several planets at the correct distance from the correct stars with the correct distribution on the correct elements on the planet for maybe life to start? My thinking is that it takes cells/molecules of several thousand/million/billions atoms to be able to reproduce themselves and maybe therein lies the difficulty for life to start?

Thoughts?

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Good points, I rephrase my question.

Given a planet revolving at the optimum distance around a star that is capable of supporting life, what is the probablility that life will start? How likely is it that the correct atmosphere and other factors will be in place for organisms to be able to start reproducing themselves?

The origins of my question of course come from wondering if life is on other planets, it seems to me that there will be several planets at the correct distance from the correct stars with the correct distribution on the correct elements on the planet for maybe life to start? My thinking is that it takes cells/molecules of several thousand/million/billions atoms to be able to reproduce themselves and maybe therein lies the difficulty for life to start?

Thoughts?

 

 

I honestly think that life will form spontaneously on any planet that forms, I think it was Thomas Gold that said that life was a natural aspect of the formation of almost any world. He suggested that any body in the solar system that had liquid water would probably have life and at some point all planets have liquid water, how long it actually takes life to develop is the $64,000 question. Mars, three moons of Jupiter and the larger moons of the outer planets almost certainly have water and life.

 

On many bodies of the solar system under the crust exist liquid water and given water and enough time this means life. Even very cold planets like Pluto might have liquid water deep within them and therefor have the conditions for life. One of the small moons of Saturn, due to tidal stress, is not only shooting water out into space but complex organics as well.

 

Some have suggested that life might form inside of comets but the internal conditions of comets is not well enough known to be sure.

 

Given an earth like planet life almost certainly forms at some point in the evolution of the planet. that life might be snuffed out as conditions change but the conditions that exist on all planets big enough to hold an atmosphere at some point probably develop life.

 

This idea suggests that life is just a naturally occurring chemical reaction that forms in places where there is an energy surplus and organic chemicals.

 

Complex life is however something else, there are no primitive life forms on the earth, the first life on earth must have been much simpler than what we see today, even archea are vastly advanced compared to what the first life forms would have been. We look at bacteria and think primitive simple life forms but in fact bacteria are quite complex and advanced, not primitive. traces of life go back more than 3.8 billions years, this is just after the earth is thought to have cooled enough to allow liquid water. The swiftness of the development of life would indicate life forms easily and swiftly.

 

Complex Eukaryota life took at least 1.5 to 2 billion years to develop, this might have been due to conditions on the earth not being conducive to complex life or it could be simply because it took that long to develop.

 

http://www.nature.com/nature/journal/v384/n6604/abs/384055a0.html

 

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

 

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

 

Stromatolites were much more abundant on the planet in Precambrian times. While older, Archean fossil remains are presumed to be colonies of cyanobacteria, younger (that is, Proterozoic) fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). One genus of stromatolite very common in the geologic record is Collenia. The earliest stromatolite of confirmed microbial origin dates to 2.724 billion years ago.[3] A recent discovery provides strong evidence of microbial stromatolites extending as far back as 3.450 billion years ago.[4][5]

 

The bacteria that form stromatolites had already developed photosynthesis almost 3.5 billion years ago.

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IIRC the claim that photosynthesis could be placed 3.5 billion years ago was only weakly supported and is rather disputed. See Rasmussen et al 2008 (Nature 455, 1101-1104 (23 October 2008), for example.

Edited by CharonY
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  • 3 weeks later...

Watching this talk made me recall this thread.

 

 

 

Great video, I have long supported the idea that life forms inevitably and is not some far fetched highly unlikely event. Thomas Gold also supported a similar view in his book The Deep Hot Biosphere...

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  • 5 months later...

In this video it is claimed all life is based on reverse citric cycle or citric cycle and all molecules are build up from this cycle. It is even stated explicitely that there are no (!) exections.

All those statements are not true. Since you can read this in every microbiology text book, you can only assume that this is also known to the speaker of this video (but somehow hurts his story :) ). That is not just simplifying for the non-scientific audience, that is misleading.

 

1) Lets just take one exception: Cyanobacteria and Plants (which use chloroplasts, which are related to cyanobacteria) produce glucose out CO2 without any involvement of of a citric cycle or reverse citric cycle. So one of the biggest part of all the biomass on earth (if not the biggest one) -- the cellulose in the cell walls of plants and cyanobacteria is produced outside those cycles.

2) Another one: Fatty acid synthesis also works wihtout the citric cycle.

3) In Chloroflexus there is neither the citric cycle nor the reverse one but another way.

....there are more examples in my text book ....

Just in general sugars can be converted into each other and their synthesis only very rarely has todo with the reverse citric cycle or with the citric cycle.

There are plenty of other ways to produce energy, most of which are either around glycolysis or at membrane gradients, and both are also very old, since there are common principles in all organisms.

 

But the bigger issue with the statements in this video are that there is not the slightest hint to explain how a metabolic cycle could actually evolve into something more complex (so he missed the whole point of life).

 

Wächtershäuser tried this. His theories are definitely worth discussing (even though I do not share them).

 

More on this the next days.....

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Among the theories of how to start life two common ones are:

a) RNA first

b) metabolism first

 

As a very simple summary you can say the main differences between the two are:

a) has an issue how this first self-replicating system started. This seems very unlikely (even though there are tons of different proposals). However, afterwards everything is easily explained by evolution. --> so the first step is the issue. The second is easy.

b) starts with something quite easy to imagine (a chemical metabolic cycle with a positive feedback loop). However, the issue here is who this ever can evolve and gain more complexity. --> so the first step is rather easy. The second is the issue.

 

This means, if somebody (like in the video) actually is in favour of b), he should talk about the critical second step (Wächtershäuser did.).

 

The video is a good example of convincing rhetoric:

- you mention accepted people (in science it should be nobel laureates or something similar).

- claim they did not have the complete picture (so not directly stating they were wrong but implying you are as clever as them) --> Warning: You should only use this strategy with dead people :) as otherwise you risk to get nailed in a hard discussion in the next symposium :). Actually, my personal impression is that F. Crick had a much more complete picture than the speaker.

- convince people by telling a lot of interesting but already very well known things. However, you can assume that for most people in the audience it is new information.

- claim that there are no exceptions. This is always very convincing (at least outside scientist community). Actually the principle of one simple rule and no exception is very much what most religions do to convince people.

- Make sure to show a lot of self-confidence and never the slightest hesitation.

So even though I admire the rhetoric skills (which help very much to make science more interesting to a broader audience), I prefer, if people do not go into black/white style of arguments. Science needs more open discussion and it is not helpful to promote religion-like convictions.

 

The metabolism-first theory is a fresh new way to approach the problem of start of life (to my knowledge mainly introduced by Wächtershäuser). You can learn a lot out of new approaches.

Personally I do not share the metabolism-first theory (but that does not prevent me to state, that there are some good arguments in it).

 

 

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Great video, I have long supported the idea that life forms inevitably and is not some far fetched highly unlikely event. Thomas Gold also supported a similar view in his book The Deep Hot Biosphere...

You may support the idea as much as you wish, but until you do so with considerable evidence you are merely expressing an opinion. You have every right to have that opinion, but the only valid sceintific position at this time is "We don't know."

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You may support the idea as much as you wish, but until you do so with considerable evidence you are merely expressing an opinion. You have every right to have that opinion, but the only valid sceintific position at this time is "We don't know."

 

 

Thank you for pointing out that it is my opinion... I guess mine is inferior to all the other opinions being asserted in this thread with no support what so ever...

 

http://www.nature.com/news/2006/061113/full/news061113-9.html

 

http://www.americanscientist.org/issues/feature/2009/3/the-origin-of-life/1

Edited by Moontanman
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