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Are WE the only life in the Universe?


IrishEyes

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Okay, let's suppose there are 2 x 10^25 stars and each one has a total of 500 planets and moons. We won't worry about things like the fraction of stars that can produce Earth-like planets: we'll accept all stars and all planets and all moons as being appropriate. That would bring the total number of celestial bodies to 10^28. Huge number, isn't it. Now suppose that each of those celestial bodies gets a trillion trillion trillion trillion - that 10^48 - shots are originating life. That would come to a staggering 10^28 * 10^48 = 10^76 shots at generating life in this system of celestial bodies. Wow!

 

But now what if the probability of life arising in a "single shot" is 1 in 10^120? See how much bigger the exponent is on that number than on the number of possible shots? It is so much larger that life's arising indepdently twice on these celestial bodies should be rejected. And what empirical/scientific evidence do we have that the "single shot" probability of life arising by a prebiotically plausible mechanism can't be as small as 1 in 10^120? None. In fact, some evidence (based on the closest things to an RNA replicase yet produced by directed evolution) supports the notion that it could be that small.

 

Some people get too excited when they think about the number of celestial bodies on which life might arise that they are blinded to the fact that there being other life in the universe depends critically on how probable life's arising under prebiotic conditions is: a number they ignore.

 

The output of the Drake equation depends on what value one assigns to this most uncertain parameter.

Telemad,

 

I do math just fine. What I have problem with is the unsubstantiated claim of this

extreme probability you call a "Single Shot" being in the neighborhood of 1 in 10^120!

You don't explain it nor how you derived it -- you just claim as fact and justifies some

conclusion that we must somehow be alone in the universe...??? :) Huh?

Assume that I am butt stupid (you already have) and spell it out... Where does this

value of 1 in 10^120 come from ?

 

The Drake equation works fine. No longer using Jeans Hypothesis for forming planets

and the recent evidence for the planets discoved implies they are way more likely. The

sample so far has many different Pop II stars along the main sequence in our galaxy.

Knowing what we do so far, our galaxy is a representative galaxy among the universe.

Studying the lifetime of most Pop II stars have a nice stable lifetime with a wide range

of habitable life zone. Statisically signifigant would find a terrestrial planet there. What

is needed for "life". I agree - big question. At least H2O. For the moment assume

Carbon life only. Then atmosphere of Ammonia NH3, Methane CH3. How often do

terrestrial planets meet criteria -- need to fudge a number, don't just call it 1 in 10^120

though.

 

Now I recently have found two instances where 1 in 10^120 has come up. First is the

probability in the origin of the universe having exactly our physical parameters like the

speed of light, the fine constant, Boltzman's constant, gravitational constant, etc. The

second case I found was brought up by a physicsist João Magueijo where in his book,

"Faster than the speed of Light" (he is a VSL theorist), he mentions how flat our universe

is. Both of these factor have the value 1 in 10^120. Coincidence ? :eek: I wonder. :P

 

Maddog

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I saw nothing on the page you linked to that had to do with Woese's "community, not LUCA" ideas.

 

I reread the article and again thought it gave a pretty good explanation about how there is probably no single cell that can be considered the origin of life. There was probably a lengthy period of gradual evolution even before life actually took hold.

 

"Several other classes of membrane-bounded organelles occurring in the cytoplasm between the nucleus wall and the outer cell wall resemble bacteria in their behavior and metabolism. Examples are plastids, mitochrondria, and microtubules. Further study will reveal the ancestry of these highly modified colonies of symbionts. We are their descendants."

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I reread the article and again thought it gave a pretty good explanation about how there is probably no single cell that can be considered the origin of life.

 

Scientists don't consider a cell to have been the first life: a cell is too complex. Instead, they believe a "simple" self-sustaining, self-replicating molecule capable of evolving was. Only later did ribosomes, genetically encoded proteins, and the other things needed to make a cell arise.

 

quote from page: "Several other classes of membrane-bounded organelles occurring in the cytoplasm between the nucleus wall and the outer cell wall resemble bacteria in their behavior and metabolism. Examples are plastids, mitochrondria, and microtubules. Further study will reveal the ancestry of these highly modified colonies of symbionts. We are their descendants." [/size]

 

That quote is talking about eukaryotes, with mitochondria and chloroplasts that were once free-living prokaryotes. Eukaryotes weren't around for about the first billion years of cellular life's existence on Earth. That quote is talking about a very late period of time, nowhere near the beginning of life or the LUCA.

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Telemad,

 

I do math just fine. What I have problem with is the unsubstantiated claim of this

extreme probability you call a "Single Shot" being in the neighborhood of 1 in 10^120!

You don't explain it nor how you derived it -- you just claim as fact and justifies some conclusion that we must somehow be alone in the universe...??? :eek: Huh?

 

No no no! I don't know why everyone misinterprets my statements on these matters.

 

1) First, I have said multiple times that I do not assert that there is no other life out there, but rather that neither side can claim that they are right and the other side is wrong.

 

2) Look at what I actually said ... I do not claim it is a fact that the probability of life arising in a single shot is 10^-120.

 

Telemad: But now what if the probability of life arising in a "single shot" is 1 in 10^120? See how much bigger the exponent is on that number than on the number of possible shots? It is so much larger that life's arising indepdently twice on these celestial bodies should be rejected. And what empirical/scientific evidence do we have that the "single shot" probability of life arising by a prebiotically plausible mechanism can't be as small as 1 in 10^120? None. In fact, some evidence (based on the closest things to an RNA replicase yet produced by directed evolution) supports the notion that it could be that small.
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What I have problem with is the unsubstantiated claim of this

extreme probability you call a "Single Shot" being in the neighborhood of 1 in 10^120!

You don't explain it nor how you derived it -- ... Where does this value of 1 in 10^120 come from ?

 

A back of the envelope style calculation. The reasoning behind has been discussed in some thread here, between Mortens and myself in relation to the closest thing to an RNA replicase produced by directed evolution to date.

 

I wrote a letter to the editor of Discover magazine on the origin of life that got printed, and the scientist's response did not show any flaws in my reasoning (he did say he felt I was being too pessimistic, but he could offer no experimental support for his optimism). Here is the original letter before the editors modified it for printing.

 

 

The front-cover article “What Came Before DNA?” painted a far-too-rosy picture of life arising as proposed by the RNA World theory…for balance, I’ll point out some of the thorns. For example, it is stated in the article that “Under the appropriate conditions, phosphate reacts with ribose and nucleobases to form a large organic molecule called a nucleotide”. That statement is misleading because the only "appropriate conditions" known to do such occur in actual living cells, and, they use protein enzymes - which are not applicable to the origin of life - to do so. In fact, no experiment carried out under prebiotically plausible conditions has yet to produce a single RNA nucleotide. What about polymerization of nucleotides? Twice the article states that nucleotides spontaneously link up into chains in the presence of montmorillonite. This is not correct: formation of an RNA polymer from free nucleotide monomers is a non spontaneous (endergonic) process and no catalyst can change that. The type of experiments being referenced use preactivated nucleotides, and, the prebiotic plausibility of the main preactivating substances – phosphorimidazolides - is questionable at best. We should also not lose site of the fact that any attempts to create an RNA replicase using in vitro evolution, as mentioned in the article, invalidate their own prebiotic applicability. If nature has biologically relevant genetic/catalytic molecules evolving by mutation and selection then it already has life; and one simply can’t use preexisting life to explain how life could have first originated...that would be nonsensical. Another very important point glossed over in the article is the low probability of hitting upon an RNA sequence capable of serving the RNA replicase role. The closest thing to an RNA replicase produced by directed evolution to date – which was mentioned in the article - is about 180 nucleotides long (and even it can copy only 14 nucleotides). Even if we assume that a trillion trillion trillion trillion unique sequences 180 nucleotides long could function as RNA replicases, the probability of hitting any one of them in a single shot is still only about 1 in 10^60. What about in multiple shots? Roughly speaking, to have an even chance of success we’d need to have a trillion trillion trillion “shots” on each and every of the approximately 10^20 planets thought to exist in the known Universe. Worse yet, a single RNA replicase arising by the chance (i.e., undirected) ordering of nucleotides would not suffice since the ribozyme would make copies only of other RNA molecules it encountered, not itself. What is needed is for a pair of RNA replicases to arise at virtually the same instant and in the same microscopic, bacterial-sized volume. Now, how likely is that to occur prebiotically? Something like 1 in 10^120?
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From his Discover letter article:

... The closest thing to an RNA replicase produced by directed evolution to date – which was mentioned in the article - is about 180 nucleotides long (and even it can copy only 14 nucleotides). Even if we assume that a trillion trillion trillion trillion unique sequences 180 nucleotides long could function as RNA replicases, the probability of hitting any one of them in a single shot is still only about 1 in 10^60. What about in multiple shots? Roughly speaking, to have an even chance of success we’d need to have a trillion trillion trillion “shots” on each and every of the approximately 10^20 planets thought to exist in the known Universe. Worse yet, a single RNA replicase arising by the chance (i.e., undirected) ordering of nucleotides would not suffice since the ribozyme would make copies only of other RNA molecules it encountered, not itself. What is needed is for a pair of RNA replicases to arise at virtually the same instant and in the same microscopic, bacterial-sized volume. Now, how likely is that to occur prebiotically? Something like 1 in 10^120?

So how does this "shot" get to 1 in 10^60 and how does the over all get 1 in 10^120 ?

Where is your math ? Sounds just like a claim to me! :eek:

 

Maddog

 

ps: You may understand the genetics and biology better than me. I do see faulty use of

probability here... :)

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Telemad,

 

I missed this one.

 

... 1 in 10^120? None. In fact, some evidence (based on the closest things to an RNA replicase yet produced by directed evolution) supports the notion that it could be that small.

I assumed you are concluding we are only ones (maybe my error) by having such small

probabilities. Give me a link to this evidence and I will investigate. Basically regarding

the origin of RNA. This is all new information to me. Have I been winking as in Rip Van

Winkle ? No, I have more knowledge in Physics/Astrophysics/Mathematics than Biology

& Genetics. Basically a learning curve for me. So if you instruct what we (I am inlcuding

others) might be less atagonistic and not get you conclusions wrong. :eek:

 

Maddog

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This topic is also getting a bit long in the tooth now. I think we are a bit far from the original topic, "Are WE the only life in the Universe?" and leaning more towards another "How did life on Earth develop" thread.

 

So I suggest we close down this thread in a day or so and pick up the loose ends in new threads.

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So how does this "shot" get to 1 in 10^60 and how does the over all get 1 in 10^120 ? Where is your math ? Sounds just like a claim to me! :eek:

 

Maddog

 

ps: You may understand the genetics and biology better than me. I do see faulty use of

probability here... :)

 

My "model" is based off of the one Leslie Orgel used in "The RNA World: Second Edition". Except he based his calculation on a hypothetical 40-mer replicase. I changed it to a 180-mer based on the closest thing to an RNA replicase yet produced by directed evolution.

 

Here is Orgel's original.

 

“It is difficult to state with certainty the minimum possible size of an RNA replicase ribozyme. An RNA consisting of a single secondary structural element, that is, a small stem-loop containing 12-17 nucleotides, would not be expected to have replicase activity. A triple stem-loop structure, containing 40-60 nucleotides, offers a reasonable hope of functioning as a replicase ribozyme. One could, for example, imagine a molecule consisting of a pseudoknot and a pendant stem-loop that forms a cleft for template-dependent replication.

 

Suppose there is some 40-mer that enjoys a superiority … of 10^3 and replicates with about 90%fidelity. This should be regarded as a highly optimistic but not outrageous view of what is possible for a minimum replicase ribozyme. Would such a molecule be expected to occur within a population of random RNAs? A complete library consisting of one copy each of all 10^24 possible 40-mers would weigh about one kilogram. Furthermore, there may be many such 40-mers, encompassing both distinct structural motifs, and more importantly, a large number of equivalent representations of each motif. As a result, even a small fraction of the total library, consisting of perhaps 10^20 sequences and weighing about one gram, might be expected to contain at least one

self-replicating RNA with the requisite properties. The above calculations assume that a self-replicating RNA can copy itself (or that a fully complementary sequence is automatically available; see below). If two or more copies of the same 40-mer RNA are needed, then a much larger library, consisting of 10^48 RNAs and weighing 10^28 grams, would be required. This amount is comparable to the mass of the Earth.” (Prospects for Understanding the Origin of the RNA World, Gerald R Joyce and Leslie E Orgel, Chapter 2 of The RNA World: Second Edition, Cold Spring Harbor Laboratory Press, 1999, p60-61)

 

Orgel's general math worked like this.

 

1) Determine how many unique RNA sequences there are for an X-mer.

 

2) Assume a good number of the possible sequences could function as an RNA replicase.

 

3) Then consider needing 2 RNA replicases (one needed to copy the other to get things going)

 

Now, using a 180-mer.

 

1) There are 4^180, that is about 10^108, possible unique RNA sequences 180 monomers long.

4^180 = (2^2)^180 = 2^360

2^360 = (2^10)^36

2^10 ~ 10^3.0103

(2^10)^36 ~ (10^3.0103)^36 ~ 10^108

 

2) Assume that a trillion trillion trillion trillion (10^48) of those sequences could function as RNA replicases. The single-shot probability of hitting one of those sequences by chance ordering is the fraction of successsful sequences to total sequences.

P(replicase) = 10^48 / 10^108

P(replicase) = 10^-60

 

There's the first probability.

 

3) If you need two replicases to arise at vitually the same instant in the same bacterial-sized volume, then you need the 10^-60 event to occur twice. The probability of that occurring is roughly the square of the one event occuring.

 

(10^-60)^2 = 10^-120

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Telemad,

 

OK. I think I get this. So how many "single shots" per sec do you get ? When you say

this "Single shot" these reaction just happen once and self destruct ? No, I don't think

so. So you are saying there are other competing reaction going (some this I didn't get).

on. So what is the reaction time of this assimilation "180-mer" process ? Would even

a 100 or a 1000 "single shot" chance per sec occur ? So, summing over a billion years

on this 10^28 of your potential planets. And you would have more than a gram of this

soup material per planet. If we were to make it simple that all of our sample planets

had water present with all the right ingredients. How many grams of this material would

likely be in the oceans of each planet... Could 10^10 grams be possible per planet.

I will concede that my concoction will to liberal to match reality. Yet in the spirit of back

of the envelope calculations, wouldn't I be approaching the 1 in 10^60 figure for the

40-mer sample mention this article. Couldn't a combinatorical assimilation of multiple

40-mer samples conjoin together (especially if concentration were high enough). See

I agree, I am not saying this is what happened. I just following the reasoning (I think)

of how to build bigger RNA chains into replicating from smaller. I admit if there are

destructive process going on (like tearing down chains) then that would have to be

taken into account too. I do appreciate you giving me the benefit of your more in depth

analysis. I don't think it was impossible in that we exist. I do wonder as you how it

would come about. :eek:

 

Maddog

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The back-of-the-envelope probability of 10^-120 is based on acquiring two 180-mer RNA sequences, at virtually the same time at virtually the same microscopic locale, capable of RNA replicase function.

 

How many shots the observable universe gets is a different matter. When I came up with something like 10^80 (I didn't both to look back) shots based on the number of stars and each star having 500 satellites etc., it did not take into account other reactions, such as those that would be forming the nucleotides themselves, those that would be forming amino acids, those that would be forming various other organic and even inorganic compounds: they were all assumed to be being used to form 180-monomer sequences of RNA.

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what i say is that if the idea that the universe is infinite is true, then somewhere there absolutey has to be another living being. true we did find one celled beings on mars, there is proof perfect that life does exist outside our earth. if you look at us we are humans, we have a complex makeup of our body and mind. dna,our brain cells,our backbone all are very detailed in their own way. it would take a EXTREAMLY long time to acheive this perfect buildup by evolution. just for the sake of conversation, say they do achieve this, that doesn't mean that they will be any smarter if at all. then there is the idea of a "god" or some sort of control. well has anyone considered how s/he came to be? what is gods orgins? where is s/he from? again, for the sake of conversation we say there is a god, it would be something amazing to realize its whole power and knowledge, to make a whole universe out of nothing, then to make a race maybe another. then that force had to of came from somewhere, it just doesn't appear out of anywhere nowhere. plus there is also the idea that nothing lasts forever but can also last very long, can there be some kind of proof that it went by or some sort of matter-composed being? if so where is it? maybe were just a mental makeup?!?! we will never know the truth because there are too many what if's or can there be's

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true we did find one celled beings on mars, there is proof perfect that life does exist outside our earth.

We did ? I haven't seen anything to that effect. We have found rigorous evidence that standing water

once existed on mars. There was a rock discovered in Anarctica that originally came from Mars that was

thought to have the origins of life within it. I believe this was recently shown to be false.

if you look at us we are humans, we have a complex makeup of our body and mind. dna,our brain cells,our backbone all are very detailed in their own way. it would take a EXTREAMLY long time to acheive this perfect buildup by evolution. just for the sake of conversation, say they do achieve this, that doesn't mean that they will be any smarter if at all. then there is the idea of a "god" or some sort of control. well has anyone considered how s/he came to be? what is gods orgins? where is s/he from? again, for the sake of conversation we say there is a god, it would be something amazing to realize its whole power and knowledge, to make a whole universe out of nothing, then to make a race maybe another. then that force had to of came from somewhere, it just doesn't appear out of anywhere nowhere. plus there is also the idea that nothing lasts forever but can also last very long, can there be some kind of proof that it went by or some sort of matter-composed being? if so where is it? maybe were just a mental makeup?!?! we will never know the truth because there are too many what if's or can there be's

Ugh... Actually were we to encounter life elsewhere (were it intelligent) the average lifetime of their

culture would likely be in advance of 10,000 year beyond ours (these are Arthur C. Clarkes estimates).

This is based on populations of stars and the age of our galaxy. He (AC Clarke) said that any advanced

civilization that we might meet would likely be taken for "Gods" (paraphrasing) and that what they would

do would be seen as "magic". David Brin as a SF author had a series based on searching for the "first

ones". Who is to say... :naughty:

 

Maddog

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There are two answers obviously. The first one is yes and the other no.this is not as simplistic as we see it.There was a man called Sir Karl Popper whose theory of falsifiability (crudely) says that if you disprove one the other is correct in a particular frame of reference.For this particular question What one can do to understand about the answer is to increase the boundaries of our frame of reference and limits.

regards

tarak dhurjati

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true we did find one celled beings on mars, there is proof perfect that life does exist outside our earth.

 

No we did not find any such thing. You are confused, maybe about the meteorite ALH84001 (I believe it was) in which some NASA scientists suggested there were signs of life, but that claim has been hotly debated and in general dismissed.

 

***********************

Edit: I see now that Maddog already brought this up.

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what i say is that if the idea that the universe is infinite is true, then somewhere there absolutey has to be another living being.

 

Granted. Even if the single shot probability of life arising naturally were 1 in 10^120, in an infinite universe, life would have arisen not once, not twice, but an infinite number of times.

 

Two things to consider though. Is the universe infinite? This hasn't been shown to be the case, so we can't use an infinite number of trials. Also, suppose the universe is finite but so large that even with a probability of 1 in 10^120 life arose 2 times. How could we ever know? We are limited to our Hubble sphere: anything outside of it might as well not exist since we can never detect it, verify it, measure it, confirm it.

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