Origin of life

[kingkong]

imho, we know next to nothing about how multicells organisms are formed to know how unlikely it's. however, if the argument over the likelihood of planets, esp those capable of supporting life, is any thing to go by, i'm inclined to believe that it's not by some magical equations at all.
i can imagine how some people will want to hold on to the hope that complex organisms particularly intelligent life like human is still very unlikely. but imho it's, like previous ones, just dashing hope...

[acc]

There are more than a billion billion stars out there... so the odds are we are not the only "intelligent" beings around...

[Tachyon]

Well, we all have to come to our own conclusions after examining the current evidence.

What I can say is this - that after been in the biosciences for 18 years, I am not convinced that life arose spontaneously. How it arose I do not know, and I can only say that all the conjectures currently out there do not give me confidence to believe in one theory or another.

Even if one can create a cell from scratch, it does not mean that is how life arose in this planet. Even the early conditions of earth is in dispute.

Short of creating a time machine and traveling back through time and observing it happening, everything else is just theory and extrapolation.

The key is to keep an open mind and not commit to any one theory until the evidence is unequivocal. For me, I am not convinced. Maybe I'm just skeptical in nature, but I need solid evidence, not hypotheses, to be convinced.

But that's just me...

p.s. The only theory that is convincing right now is that parallel universe theory, but even then, where are the facts?

[ChaosKnight]

Spontaneous means a self-generated event, typically requiring no outside influence or help.
http://en.wikipedia.org/wiki/Spontaneous

I'm going out on a limb here, but i hope by this statement:

I am not convinced that life arose spontaneously.

you do not mean you believe in some form of creationism.

Even if one can create a cell from scratch, it does not mean that is how life arose in this planet. Even the early conditions of earth is in dispute.

Lets put it this way:

1. Some researcher managed to create a cell from scratch
2. He/she used only simple techniques that are "spontaneous", or some sort of "self-assembly" process, like some aspects of Irene Chen's experiments
3. We think the lab conditions reasonably could have existed on early Earth

Given all 3, is it reasonable to say it is possible life was created in a similar way to the experiments?? Yes or no.

I need solid evidence, not hypotheses, to be convinced.

Well...you did ask for a hypothesis. But since you're now asking for evidence, i'll give you some to back my hypothesis.


This is an image seen under an ordinary light microscope of common NaCl mixed with some natural polymers then dried. Instead of forming crystalline blocks, you get dendrites.


The black clumps are cell aggregates adhered to the dendrites.

[kingkong]

I am not convinced that life arose spontaneously.

you do not mean you believe in some form of creationism.

uh oh! back off gently now... back... back...

[Tachyon]

Spontaneous means a self-generated event, typically requiring no outside influence or help.

Now, the definition of 'outside influence' is rather vague. So if we increase the temperature from 0K to 293K in order to get the reaction going, is that not considered 'outside influence or help'?

Providing the right physical conditions, chemical mixtures in the right proportions, with the right catalyst and appropriate laws of thermodynamics (as you see, I am not discounting the parallel universe theory where other universes will have different laws of thermodynamics), and then life will 'spontaneously' develop? It seems like a lot of 'help' to me.

Anyway, I know what you mean but there's no point discussing about it - been there, tried that - there's just no end when the facts are not sufficient.

you do not mean you believe in some form of creationism.

Creationism is about faith. Science is about facts. Let's keep the two separate.

1. Some researcher managed to create a cell from scratch
2. He/she used only simple techniques that are "spontaneous", or some sort of "self-assembly" process, like some aspects of Irene Chen's experiments
3. We think the lab conditions reasonably could have existed on early Earth

Given all 3, is it reasonable to say it is possible life was created in a similar way to the experiments?? Yes or no.

That's inference, not proof. It's the same logic that earned super-symmetry the criticism in the first place. Science works this way (at least practically):

1. Observe
2. Hypothesize (usually the null hypothesis)
3. Experiment
4. Exclude null hypothesis

In the scenario which you described above, the order is:

1. Hypothesize
2. Experiment
3. Search for observations to substantiate the hypothesis

Super-symmetry was a pure mathematical construct - there was no observational fact to substantiate it. Same here - the hypothesis was that 'given the right combination of physical factors and chemical compounds, life will spontaneously develop'. Was there any evidence to suggest that this was the case, or was just just a mental scenario on what might have happened?

The danger with proceeding with mental hypotheses is that there are very many, all probable, but not all possible. Given enough scenarios, if you test every one, you will find one that works, statistically. But is that the ONE that caused this life here on earth?

So what will it take to convince me? Here are some factors I will consider:

1. Consistent data on the early chemical composition of Earth
2. Based on this data (1), generate 'spontaneous' life in the lab (without over-optimization of parameters) using conditions with a reasonable range of values (I'm always wary when the experiment only works within a narrow range of values)
3. A marker that is found in this 'spontaneously' generated life that can be verified in ancient samples.

All three pieces must fit with no exceptions.

On your images of dendrites, we know that fractal dendritic networks are formed by many inorganic and organic processes, including blood vessel development, neuronal cells, rivers, etc. And when the branches confluences, you get aggregates. Pardon me, but I've been more skeptical since the ALH 84001 saga.


(Source: http://www.nature.com/nature/journal/v4 ... a-i1.0.jpg)

[ChaosKnight]

Now, the definition of 'outside influence' is rather vague. So if we increase the temperature from 0K to 293K in order to get the reaction going, is that not considered 'outside influence or help'?

Providing the right physical conditions, chemical mixtures in the right proportions, with the right catalyst and appropriate laws of thermodynamics (as you see, I am not discounting the parallel universe theory where other universes will have different laws of thermodynamics), and then life will 'spontaneously' develop? It seems like a lot of 'help' to me.

Interesting. So, can you name me one everyday example of an event you consider truly “spontaneous”? Something which requires no “help” at all.

…but there's no point discussing about it - been there, tried that - there's just no end when the facts are not sufficient.

But it’s fun to speculate, no? Otherwise why would threads like this
http://www.singastro.org/viewtopic.php? ... 9ed1#44437
exist?

That's inference, not proof. It's the same logic that earned super-symmetry the criticism in the first place. Science works this way (at least practically):

1. Observe
2. Hypothesize (usually the null hypothesis)
3. Experiment
4. Exclude null hypothesis

In the scenario which you described above, the order is:

1. Hypothesize
2. Experiment
3. Search for observations to substantiate the hypothesis

The 3 points I stated are conditions. They are not a scientific procedure. But since you want to see a strict procedure like some lab sheet, I’ll put it in that form:

1. Scientist noted the spectra of simple sugars in a comet (observation)
2. They noted the sugars are a precursor to forming ribose (observation)
3. Since the comets are out in space, they hypothesize simple sugars, and possibly nucleotides, can form naturally in space (hypothesis)
4. Scientists noted that vesicles form naturally in solution, and their structure is similar to the bilipid membrane in cells (observation)
5. Scientist hypothesize simple cells could be formed in a similar fashion (hypothesis)
6. From 3, scientists experiment on how nucleotides form (experiment+conclusions)
7. From 6, they observe nucleotides forming under a variety of conditions (observation)
8. From 5 and using results from 7, scientists create a very simple artificial “cell” in a lab, like what we are seeing (experiment+conclusions)
9. From 8, we say it is possible life on Earth was created in a similar way to the experiments (hypothesis)
10. Future work……

Would you object to such a procedure?

1. Consistent data on the early chemical composition of Earth
2. Based on this data (1), generate 'spontaneous' life in the lab (without over-optimization of parameters) using conditions with a reasonable range of values (I'm always wary when the experiment only works within a narrow range of values)
3. A marker that is found in this 'spontaneously' generated life that can be verified in ancient samples.

I’d say these are tall orders that may never be filled to your satisfaction. I can’t comment on 1, the people mentioned in the article are working on 2. As for 3, I could hazard a simple suggestion: the markers are your bilipid membranes.

Pardon me, but I've been more skeptical since the ALH 84001 saga.

You can rest a little easier here. We have a pretty good idea what we are putting in our test tubes.

[Tachyon]

Interesting. So, can you name me one everyday example of an event you consider truly “spontaneous”? Something which requires no “help” at all.

Precisely! There's no such thing as 'spontaneous' at the macro level. There is always 'cause and effect' - unless you are talking about quantum level, in which case I do not know enough to comment.

But it’s fun to speculate, no? Otherwise why would threads like this
http://www.singastro.org/viewtopic.php? ... 9ed1#44437
exist?

Which is why those threads exist - for pure speculation. Unless you want to turn this thread into speculation also. In which case, I will be happy to share with you my many theories of our existence - all without proof, of course!

Well, my comments would be:

1. Scientist noted the spectra of simple sugars in a comet (observation)
Are these multiple overlapping spectra or just one? How many simple sugars are detected in a single comet - all, or just a selected few? What percentage of comets have the exact same compositions? What about other compounds which are not simple sugars present in the comet? Have we established the fact that comets are isolated since formation and had not been contaminated by picking up planetary compounds during their passage to the inner solar system?

2. They noted the sugars are a precursor to forming ribose (observation)
What are the conditions necessary for the formation of ribose? Where in the solar system does the same conditions exist except for earth? Did we detect the same ribose in these extra-terrestrial locations? Have other mechanisms for the formation of ribose from sugars excluded?

3. Since the comets are out in space, they hypothesize simple sugars, and possibly nucleotides, can form naturally in space (hypothesis)
Not exactly null hypothesis, but I'll go along with it. Note that this hypothesis will only lead to one conclusion if proven, i.e., it is possible to produce a specific nucleotide(s) from specific sugars and other compounds and under specific conditions. It does not prove that it indeed happened on Earth.

4. Scientists noted that vesicles form naturally in solution, and their structure is similar to the bilipid membrane in cells (observation)
True. However, note that the cell membrane is not just a simple bilipid membrane. Transmembrane proteins are *essential* for the proper functioning of the cell membrane. Creating such a membrane without affecting the integrity of the bilayer member (and remaining stable) is a challenge.

5. Scientist hypothesize simple cells could be formed in a similar fashion (hypothesis)
You are building one hypothesis upon another one. First, you have to prove the first one. The reason is that if you managed to have positive results, you would not know which hypothesis is driving the results. But let's just go ahead anyway.

6. From 3, scientists experiment on how nucleotides form (experiment+conclusions) In the comet? Or in the lab? If in the lab, then they have to further prove that it can be done in the comet, and remain stable in the face of solar radiation. In other words, the experiment would have to be done in the comet itself.

7. From 6, they observe nucleotides forming under a variety of conditions (observation)
I assume you mean under different physical conditions? That would satisfy my 'range of values' condition in the previous post. In fact, I would view this as a very powerful argument if it is successful - that regardless of variation in temperature, pressure, radiation levels or presence/absence of other compounds, nucleotides can form, then the possibility of it forming in any given location would greatly increase. First, it has to be done!

8. From 5 and using results from 7, scientists create a very simple artificial “cell” in a lab, like what we are seeing (experiment+conclusions)
First, what is the definition of 'cell'? Ask 10 scientists and you will get slightly different answers. For me, a cell should metabolize, reproduce, and interact with the surroundings. Many groups are racing to do this now. Venter's group is trying to access the minimum components needed for a functioning cell. It would be interesting to see their results.

9. From 8, we say it is possible life on Earth was created in a similar way to the experiments (hypothesis)
I assume there is concrete proof from geological data. Air pockets trapped in lava in early years of earth formation may provide the answer, but first we have to find these 'gems'.

10. Future work……
And more work! That's why a scientist's life is never boring!

One more thing (aka doing a Steve Jobs here...), yes, my requirements are strict. But if one has to be selective about one believes in - in the face of so many theories, experiments, and pseudo-science, I want to make sure I bet on the right horse. But that's what science is - explore every theory but never believe in any. Because the true joy of any scientist is not being right, but being proven wrong so that we can move closer to the truth!

[ChaosKnight]

Precisely! There's no such thing as 'spontaneous' at the macro level. There is always 'cause and effect' - unless you are talking about quantum level, in which case I do not know enough to comment.

Interesting. I have to say your idea of “spontaneous” is rather out of the ordinary. In that case, I suppose the word “natural” will be better for this discussion.

Which is why those threads exist - for pure speculation. Unless you want to turn this thread into speculation also. In which case, I will be happy to share with you my many theories of our existence - all without proof, of course!

If it pleases you, why not? Especially if they are worth discussing. Probably beats looking at those threads in Equipment Discussions.

Research always have a scope. Nobody can do everything. Basically all your questions are questioning the scope of findings announced. So I’ll give you some references where possible for you to see yourself.

1. Scientist noted the spectra of simple sugars in a comet (observation)
Are these multiple overlapping spectra or just one? How many simple sugars are detected in a single comet - all, or just a selected few? What percentage of comets have the exact same compositions? What about other compounds which are not simple sugars present in the comet? Have we established the fact that comets are isolated since formation and had not been contaminated by picking up planetary compounds during their passage to the inner solar system?

2. They noted the sugars are a precursor to forming ribose (observation)
What are the conditions necessary for the formation of ribose? Where in the solar system does the same conditions exist except for earth? Did we detect the same ribose in these extra-terrestrial locations? Have other mechanisms for the formation of ribose from sugars excluded?

3. Since the comets are out in space, they hypothesize simple sugars, and possibly nucleotides, can form naturally in space (hypothesis)
Not exactly null hypothesis, but I'll go along with it. Note that this hypothesis will only lead to one conclusion if proven, i.e., it is possible to produce a specific nucleotide(s) from specific sugars and other compounds and under specific conditions. It does not prove that it indeed happened on Earth.

Apologies, I remembered wrongly. The spectra of sugars were not found in a comet, but in interstellar space. Ethylene glycol was the one found on a comet.

Hollis J. M. et al, “Green Bank Telescope Observations of Interstellar Glycolaldehyde: Low-Temperature Sugar (2004)”, The Astrophysical Journal, vol 613, pp 45-48

5. Scientist hypothesize simple cells could be formed in a similar fashion (hypothesis)
You are building one hypothesis upon another one. First, you have to prove the first one. The reason is that if you managed to have positive results, you would not know which hypothesis is driving the results. But let's just go ahead anyway.

Does building one hypothesis on another, then going on to get positive results, equate bad science?

6. From 3, scientists experiment on how nucleotides form (experiment+conclusions) In the comet? Or in the lab? If in the lab, then they have to further prove that it can be done in the comet, and remain stable in the face of solar radiation. In other words, the experiment would have to be done in the comet itself.

7. From 6, they observe nucleotides forming under a variety of conditions (observation)
I assume you mean under different physical conditions? That would satisfy my 'range of values' condition in the previous post. In fact, I would view this as a very powerful argument if it is successful - that regardless of variation in temperature, pressure, radiation levels or presence/absence of other compounds, nucleotides can form, then the possibility of it forming in any given location would greatly increase. First, it has to be done!

Roy D., Najafian K., Schleyer P. v. R. “ Chemical evolution: The mechanism of the formation of adenine under prebiotic conditions (2007)”, PNAS, vol 104, no.44, pp 17272-17277

8. From 5 and using results from 7, scientists create a very simple artificial “cell” in a lab, like what we are seeing (experiment+conclusions)
First, what is the definition of 'cell'? Ask 10 scientists and you will get slightly different answers. For me, a cell should metabolize, reproduce, and interact with the surroundings. Many groups are racing to do this now. Venter's group is trying to access the minimum components needed for a functioning cell. It would be interesting to see their results.

Szostak J, Bartel D., Luisi P. L., “Synthesizing life (2001)”, Nature, Vol 409, pp.387-390

Irene A. Chen, et al. “The Emergence of Competition Between Model Protocells (2004)”, Science, Vol 305, pp. 1474-1476

But to certain scientists what passes for a cell could be even simpler.
Abkarian M., Lartigue C., Viallat A., “Tank treading and unbinding of deformable vesicles in shear flow: determinition of the lift force (2002)”, Physical Review Letters, Vol 88, No. 6, 068103

And more links for anyone interested:
http://www.astrobio.net/news/article122.html
http://astrobiology.arc.nasa.gov/news/e ... fm?id=9386
http://en.wikipedia.org/wiki/Origin_of_ ... her_models See section under Bubble Theory

[Tachyon]

Interesting. I have to say your idea of “spontaneous” is rather out of the ordinary. In that case, I suppose the word “natural” will be better for this discussion.

If it pleases you, why not? Especially if they are worth discussing. Probably beats looking at those threads in Equipment Discussions.

Actually, one of my pet theories is that we are created by superior beings, that have far superior technology and know-how to create living cells. My personal view is that the cellular mechanisms are too intricate and interwoven to allow a sequential creation of cells - multiple pathways have to be created simultaneously in a single cell in order to generate a functioning organisms. Aliens I buy, spontaneous creation based on probability I don't. There you have it - it's 100% speculation...

Research always have a scope. Nobody can do everything. Basically all your questions are questioning the scope of findings announced.

Sure, which is why we have to break down the problem into multiple simple ones. The problem is - many of the answers do not complement each other, as they should. So we have stories that do not match. Most government scientific agencies were formed to coordinate these studies, but because of many reasons (one of them is the need to generate papers to stay employed in the academia), most chose the simple problems to solve - so that they can obtain quick results for publication. That is why I admire people like Craig Venter who are willing to risk investigating what others feel have low probability of success.

Apologies, I remembered wrongly. The spectra of sugars were not found in a comet, but in interstellar space. Ethylene glycol was the one found on a comet.

Hollis J. M. et al, “Green Bank Telescope Observations of Interstellar Glycolaldehyde: Low-Temperature Sugar (2004)”, The Astrophysical Journal, vol 613, pp 45-48

Glycoaldehyde was proposed as a substrate of an alternate pathway for fatty acid synthesis that do away with ATP, which was creating some trouble for the 'spontaneous' camp. (Weber A.L., "Origin of fatty acid synthesis: Thermodynamics and kinetics of reaction pathways (1991)", J Mol Evol, 32(2), pp 93-100). The structure is still very simple. To get from this to more complex compounds needs a lot of convincing data:



Source: Wikipedia

Does building one hypothesis on another, then going on to get positive results, equate bad science?

Bad? I would not generalize, but confused? Definitely, if each step has not been proven conclusively. Adding too many variables produce confounding factors that may cause the results to be difficult to interpret later on.

Roy D., Najafian K., Schleyer P. v. R. “ Chemical evolution: The mechanism of the formation of adenine under prebiotic conditions (2007)”, PNAS, vol 104, no.44, pp 17272-17277

This is a hypothesis-generating paper, not a 'proof' paper. I do not see any experimental wet lab results here - back again to the 'mental hypothesis' issue.

Szostak J, Bartel D., Luisi P. L., “Synthesizing life (2001)”, Nature, Vol 409, pp.387-390

Again, not proof, but a concept paper.

Irene A. Chen, et al. “The Emergence of Competition Between Model Protocells (2004)”, Science, Vol 305, pp. 1474-1476

Finally! An experiment - however, Chen works under Szostak's group. I would like to see independent verification.

But to certain scientists what passes for a cell could be even simpler.
Abkarian M., Lartigue C., Viallat A., “Tank treading and unbinding of deformable vesicles in shear flow: determinition of the lift force (2002)”, Physical Review Letters, Vol 88, No. 6, 068103

And more links for anyone interested:
http://www.astrobio.net/news/article122.html
http://astrobiology.arc.nasa.gov/news/e ... fm?id=9386
http://en.wikipedia.org/wiki/Origin_of_ ... her_models See section under Bubble Theory

Well, I would say they are reading materials to stimulate the imagination, but I find no scientific proof yet. Read these as you would for supersymmetry - fun, provocative, but please do not believe everything that is being said.

Cheers!