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beskeptical
2004-Nov-29, 07:40 AM
This started on the "mutant nuclear bacteria from another world" thread but I hate to hijack the topic. Some posts have argued life on Earth may have been originally seeded from life that had formed elsewhere.

I accept the premise such an event could have happened. But it just isn't very likely, and it isn't a theory mainstream evolutionary biologists consider as viable an option as life originating on Earth without being seeded.

While organisms can survive in space, and maybe could survive the entry into the atmosphere, in order for them to reach Earth, it would seem logical such contaminated rocks would have to be common. It's a big Universe out there. If traveling organisms weren't common, then the odds of reaching Earth are slim. And, such contaminated meteorites certainly haven't been common among the samples we have. Perhaps there are organisms on comets, but there is no evidence to support that beyond speculation and IIRC perhaps organic molecules present.

On the other hand, research is progressing right along on the hypothesis RNA molecules were the first to form and life evolved from there.

This site (http://www.postmodern.com/~jka/rnaworld/nfrna/nf-index.html#nf-rnaworlded.html) has a good one page summary of where the current research is on this matter. And, if you link to the "RNA World" at the bottom, there is a nice brief time line.

(The 'RNA World' link in the body of the text didn't work for me but the icon on the bottom did.)

A Thousand Pardons
2004-Nov-29, 08:01 AM
While organisms can survive in space, and maybe could survive the entry into the atmosphere, in order for them to reach Earth, it would seem logical such contaminated rocks would have to be common. It's a big Universe out there. If traveling organisms weren't common, then the odds of reaching Earth are slim. And, such contaminated meteorites certainly haven't been common among the samples we have.
OTOH, they could well be just common enough that only a few have reached earth, and maybe one is all it would have taken.

parallaxicality
2004-Nov-29, 12:12 PM
The main problem I have with the "Earth-genic" theory is the rapidity with which life seems to have formed on our planet. Essentially, as soon as it was possible for life to exist on Earth, it did. I do wonder about Mars as a possible location for the formation of life. It was smaller, so it cooled into a habitable environment before Earth did. Life had the time there to form and develop and then be transported to Earth via meteorite. No need for "panspermia," since it only happened once.

John Kierein
2004-Nov-29, 02:47 PM
I think life's really common out there. Not only on planets. It's in the dust clouds seen everywhere.
http://www.geocities.com/CapeCanaveral/Galaxy/7827/

A Thousand Pardons
2004-Nov-29, 03:24 PM
The main problem I have with the "Earth-genic" theory is the rapidity with which life seems to have formed on our planet. Essentially, as soon as it was possible for life to exist on Earth, it did. I do wonder about Mars as a possible location for the formation of life. It was smaller, so it cooled into a habitable environment before Earth did. Life had the time there to form and develop and then be transported to Earth via meteorite. No need for "panspermia," since it only happened once.
Aren't you just transferring the problem to a different planet? Wouldn't it then have developed on Mars just about as soon as it was possible too? In order to set up conditions that it could be transferred to Earth?

parallaxicality
2004-Nov-29, 04:35 PM
Article by Paul Davies in the New Scientist, 12 Jul 2003 > BORN LUCKY

http://www.mail-archive.com/futurework@scribe.uwaterloo.ca/msg10593.html

Russ
2004-Nov-29, 05:12 PM
Parallaxicality: I note that you are a newbie and welcome you aboard the board. :D I enjoy new points of view.

I suspect, however, that you may not have read the rules for the board. :o The Bad Astronomer (TBA), Dr. Phil Plait, is kind'o fussy about folks posting big slabs of articles or disertations. I highly reccommend that if you would like us to read articles such as you posted, you link to them rather than post them. :)

The reasoning has to do with copyright laws and how they adversely impact TBA when you post, rather than link to, copyrighted material. :)

Again, welcome aboard. I like to hear (see :roll:) your thoughts on this article. :D

parallaxicality
2004-Nov-29, 05:18 PM
Sorry; thought I wouldn't violate copyright as long as I cited the source. The article was pasted from a usegroup; I thought it would be easier to read if I cleared up the rampant ">"s and odd breaks in the sentances. There doesn't appear to be an "official" transcription of the article on the web. I'll link to the usegroup anyway. Thanks for the welcome!

Edit: Found an "official" (I think) version that is much easier to read.

As to my thoughts on it, well, my previous post to which A Thousand Pardons responded was based on my having read that article. I am not a mathematician, nor does the article go into detail about the nature of the probability arguments used by the two astrobiologists. But it does make intuitive sense to me that Mars, being smaller, cooled and became habitable before Earth did and therefore had a longer window of opportunity between the creation of a habitable environment and the earliest known examples of life on Earth for the reactions that were the biological precursors of life to take place.

Squink
2004-Nov-29, 05:55 PM
OTOH, they could well be just common enough that only a few have reached earth, and maybe one is all it would have taken. Sure. A density such that a life bearing rock enters the earth's atmosphere on an average of once every billion years could be enough to set the evolutionary process in motion.

pghnative
2004-Nov-29, 06:48 PM
Only if you assume that 100% of lifebearing rocks entering Earth's atmosphere make it to the surface (land or water) and also land in an area in which the lifeform can remain viable.

Evan
2004-Nov-29, 07:03 PM
On the copyright issue you are allowed under the doctrine of "Fair Use" to quote small portions of a copyright work. The reason for quoting must be either related to the content of the work or for the purpose of criticising the work. Attribution must be given. Note that "Fair Use" is a USA specific doctrine and does not exist in most other countries copyright law.

The factors that determine what is considered as Fair Use are these:


# the purpose and character of the use, including whether such use is of commercial nature or is for nonprofit educational purposes;
# the nature of the copyrighted work;
# the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
# the effect of the use upon the potential market for or value of the copyrighted work.


For more information see here. (http://www.bitlaw.com/copyright/fair_use.html)

This post is an example of fair use. It is non-profit, it only uses a very small portion of the website content and a link to the site is provided. It is for educational purposes and does not negatively impact the quoted site in any significant financial way.

Sticks
2004-Nov-29, 07:37 PM
Panspermia is a red herring, and always was.

Suppose life here came here from another planet

So how did that life originate there?

It didn't, it came from yet another world :-?

All you do is keep moving the problem instead of addressing it

How did life begin in the first place.

If the work with RNA is the correct route, then proof would have to be the creation of that which is living from that which is non living in a laboratory, under of course carefully controlled conditions. So unlike in nature, an open system.

From my reading around this subject, the main problem for getting life to start here is the early atmosphere. Evidence seems to point to an oxidising atmosphere, and if oxygen is present then the only compunds formed are the simple ones with oxygen and not the complex compounds required for enzymes and proteins and the other ingredients of a living organism.

Panspermia is a way to try and shortcut this problem and does not work.

I remember the fuss a number of years ago where they thought they had found a fossil in a rock from Mars. It turned out to be a relic from the coating process they used to get it ready for the SEM #-o

Russ
2004-Nov-29, 08:18 PM
parallaxicality: Thank you for taking my suggestion in the friendly manner it was given. Finally, my attempt at writing in a congienial, friendly voice worked.

Regarding the article. I disagree with the contention that life is hard to create and, therefore, is rare. Radiotelescopic data dating from the 1960's through today, has indicated the presents of amino acids and other complex organic molicules in interstellar nebulae. If the building blocks for life are out there just floating about, it's got to be an integral part of just about any stellar system.

Given that there is life occupying every conceivable niche (and a few inconceivable ones) here on Earth, it has to be flourishing "out there". Given that the Solar system is unremarkable as stellar systems go, it seems reasonable that the presents of life would be unremarkable as well.

Anyone have thoughts contrary to mine?

Sticks
2004-Nov-29, 08:23 PM
If this is the case, why have we not been able to get that which is non living to give rise to that which is living in a laboratory?

Amino acids and even proteins are a long way from anything classed as living.

ZaphodBeeblebrox
2004-Nov-29, 08:52 PM
If this is the case, why have we not been able to get that which is non living to give rise to that which is living in a laboratory?

Amino acids and even proteins are a long way from anything classed as living.

Oy ...

Are we going to start in on Abiogenesis, now?

If it Replicates by Itself, it's Alive!

Viruses, are an Excellent Example, of this Shadow Space, between Living and Non-Living, Technically, they CAN'T, Self-Replicate!

A Thousand Pardons
2004-Nov-29, 09:08 PM
Oy ...

Are we going to start in on Abiogenesis, now?
Start? I thought that's what we were talking about. :)


If it Replicates by Itself, it's Alive!

Wait. You gotta have some energy and additional matter, perhaps? And that doesn't exclude a partner, right?

Evan
2004-Nov-29, 09:30 PM
I agree with Russ. I also think that given the right raw materials that devlopment of life is probably inevitable. As for reproducing it in the lab that is simply a matter of time and correct conditions. We don't know what those conditions are and we most certainly don't have the time.

The argument that is often given that the right arrangement of conditions and material is vanishingly unlikely simply ignores the fact that even unlikey events have a high probability of happening given enough time. If an event only has one chance in a million of occuring and the attempt at the event happens every day then it is virtually certain to happen in a million years.

I am of the opinion that the chance occurrence of life from basic materials known to be easily produced naturally probably isn't unlikely at all. All it takes is time.

As for intelligent sentient life that is a different matter. The universe is a very violent place. It may be very unlikely for sentient life to get a chance before something wipes it out. It also may be unlikely for sentient life to develop in the first place. If the asteroid hadn't wiped out the dinosaurs they might still be the dominant life form on Earth.

AGN Fuel
2004-Nov-29, 11:25 PM
Panspermia is a red herring, and always was.

Suppose life here came here from another planet

So how did that life originate there?

It didn't, it came from yet another world :-?

All you do is keep moving the problem instead of addressing it

How did life begin in the first place.




Don't throw the baby out with the bath water. By moving the origin of life from off the Earth, you are hugely increasing the possible time spans and locations for life to arise. Nebulae are chokkas with hydrocarbons, amino acids have been found in meteorites, water is ubiquitous, etc, so it is evident that reasonably complex chemistry can take place in interstellar space.

Complex enough for life to arise? I don't know. But surely your odds increase dramatically if you have eons of time and a reactive volume compared to which our entire solar system is but a flyspeck, no?

Squink
2004-Nov-29, 11:39 PM
So how long did it take for a major biochemical pathway to appear on earth?

Scientists claim to have found the oldest evidence of photosynthesis - the most important chemical reaction on Earth - in 3.7-billion-year-old rocks. Oldest evidence of photosynthesis (http://news.bbc.co.uk/2/hi/science/nature/3321819.stm)
Unless the process evolved more than once, that implies DNA based protein synthesis within 100 million years of the end of earth's early bombardment with asteroids.
After that quick start, it took 3 billion years for life to go multicellular? That's difficult to believe. Building a reliable self replicating DNA->RNA->protein automata seems to me much more difficult than figuring out how to glue copies of preexisting automata together into a larger whole.
Panspermia permits the initial low probability assembly of the coding system and chemistry to be spread about between any number of planets.

SkepticJ
2004-Nov-30, 12:04 AM
intelligent sentient life that is a different matter. The universe is a very violent place. It may be very unlikely for sentient life to get a chance before something wipes it out. It also may be unlikely for sentient life to develop in the first place. If the asteroid hadn't wiped out the dinosaurs they might still be the dominant life form on Earth.

And why couldn't a dinosaur evolve smarts? Beware the vice of xenocentric thinking.

Evan
2004-Nov-30, 04:27 AM
We have pretty good evidence that they didn't evolve smarts even given many millions of years. Why they didn't is probably the same reason that sharks have not. They evolved to fill the niche they were adapted to and sentience offered no needed advantage. The real question is why did we begin to think upon our own existence?

Evan
2004-Nov-30, 04:34 AM
Squink,

Mass extinctions were probably a very common event in the early part of Earth's history. I suspect life evolved numerous times until things settled down enough. The Burgess Shales life forms (http://www.burgess-shale.bc.ca/history/history.htm) are the earliest known multicellular forms and they did not survive.

Squink
2004-Nov-30, 05:31 AM
Squink,

Mass extinctions were probably a very common event in the early part of Earth's history. I suspect life evolved numerous times until things settled down enough. Then someone should be able to find fossil evidence of earlier "cambrian explosions" where multicellular organisms evolved, only to be lost to extinction. Such fossil evidence is not known to exist. All the evidence we have points to a single explosion from unicellular to multicellular organisms about 570 MYBP.
The theory of earthly abiogenesis thus allots 100 million years to evolve the standard transcription, translation and even photosynthetic machinery, vs 3 billion years to upgrade the hardware to handle multicellular lifestyles. That apparent difference in the rate of evolution over time suggests to me that the complex early steps of the process may have received a kickstart from another source, panspermia.
I won't be too surprised if we find bacteria on Mars that use the same codon table as those on earth. However, if those organisms use a different table, or even a completely different chemistry, I'll have to rethink the amount of trial and error I suspect goes into the random assembly of "simple" self reproducing systems.

Evan
2004-Nov-30, 07:00 AM
The problem, as I pointed out elsewhere, is that no matter what we find it doesn't confirm or deny the validity of the panspermia hypothesis. It is essentially unprovable since there are equal or better explanations for whatever we find. Even if we find nothing at all it won't disprove it. You can't prove or disprove something with an absence of evidence. Panspermia is an idea that really serves no purpose. Even if true it explains nothing.

Lam
2004-Nov-30, 07:17 AM
If this is the case, why have we not been able to get that which is non living to give rise to that which is living in a laboratory?

Amino acids and even proteins are a long way from anything classed as living.

Actually, scientists have been able to produce pre-cells in laboratory conditions. A pre-cell is a metabolising self-reproducing entity that exhibits most of the basic properties of a cell but unable to limit the frequent mutual exchange of genetic information (Wachtershauser, "From Pre-cells to Eukarya" , 1).

Although scientists haven't been able to make cells out of pre-cells, there are various theories out there that are still being investigated.

Sorry, the entire article is in PDF format and only university people can access it.

Evan
2004-Nov-30, 07:30 AM
Squink,

It may well be that the jump from single cell to multicellular is not an easy one. If the life forms were wiped out multiple times before that happened then it would be consistent with what we observe in the fossil record. The Burgess shale life forms are the oldest multicellular forms that we have found. It doesn't by any means mean they were the first. They certainly weren't the last although they didn't last. It seems extinction events are the rule, not the exception.

Lam
2004-Nov-30, 07:35 AM
Here (http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=165426&action=stream&blobtype =pdf) is the full text of a peer reviewed article that models how UV radiation can act as a driving force for RNA evolution.

Squink
2004-Nov-30, 07:49 AM
The problem, as I pointed out elsewhere, is that no matter what we find it doesn't confirm or deny the validity of the panspermia hypothesis. I'd be mighty interested in panspermia if samples of bacteria from the Oort cloud could be shown to have the same biochemistry, and codon usage as that of earthly bugs. The fact that we won't be getting that sort of evidence for quite a few years, if ever, doesn't invalidate the panspermia hypothesis.
If you're going to be a stickler for positive evidence that's available now, the competing hypothesis that abiogenesis occurred on earth rests on little more than a few experiments with test tubes and electricity, and the the finding that certain RNA sequences can cut themselves into pieces, catalyze reactions, or make copies of themselves . The rest is handwaving.
Until we find evidence that alien life is biochemically similar, or different, from earth life, or on the other hand, find a mechanism whereby a primitive RNA World (http://nobelprize.org/chemistry/articles/altman/) could have rapidly evolved into the DNA->RNA->protein world we live in today, it's really impossible to rationally choose one hypothesis over the other. Both hypotheses have troubling aspects, and without evidence, which we lack, there's little point in running down one versus the other.

Lam
2004-Nov-30, 07:57 AM
This is why abiogenesis is still a very young discipline in biochemistry. There's really not much scientists can go on with. However, I must disagree with what you said:


...little more than a few experiments with test tubes and electricity, and the the finding that certain RNA sequences can cut themselves into pieces, catalyze reactions, or make copies of themselves . The rest is handwaving.
I'd say that 50 years worth of experiments are more than "little more than a few," given that they haven't directly created a fully functional living cell in a lab.

Evan
2004-Nov-30, 08:28 AM
As I said and it is true, we don't know the conditions required for life to form. That includes all possible scenarios, including creation scenarios. Fifty years is not even an eyeblink. Try fifty million. The time scale is mainly incomprehensible.


it's really impossible to rationally choose one hypothesis over the other.

No, it's not. We have obvious evidence that life appeared on Earth. We have no evidence at all for panspermia.

Squink
2004-Nov-30, 05:02 PM
We have obvious evidence that life appeared on Earth. Sure, we just have no proof that abiogenesis took place on earth. We've all sorts of experiments which detail how abiogenesis might have occured:

I'd say that 50 years worth of experiments are more than "little more than a few," It's fascinating stuff, but all that evidence says very little about the time spans required for the various steps. If the initial steps of evolving a DNA->RNA->Protein based self-replicating system take longer than the 100 million years or indicated by the fossil record, then life must have originally come from someplace else.
The panspermia/earthly origin debate is rather like the arguments over the Steady State vs Big Bang hypotheses. The absence of evidence on both sides of that issue did not prevent proponents of either side from prematurely declaring themselves to have the correct interpretation, but in the end, it was new data that won the day.

Evan
2004-Nov-30, 05:10 PM
If the initial steps of evolving a DNA->RNA-Protein based self-replicating system take longer than the 100 million years or indicated by the fossil record, then life must have originally come from someplace else.

Why?

Squink
2004-Nov-30, 05:26 PM
Why???? Because that would mean that there wasn't enough time for life to have evolved here. I'm not sure what you're trying to get at there. I'm certainly not claiming that panspermia is the correct description of how life came about on earth, but if earthly abiogenesis can be ruled out due to time constraints, there are no other likely hypotheses available.

A Thousand Pardons
2004-Nov-30, 05:28 PM
if earthly abiogenesis can be ruled out due to time constraints, there are no other likely hypotheses available.
Somehow, 100 million years doesn't seem like much of a constraint. :)

Squink
2004-Nov-30, 05:33 PM
Somehow, 100 million years doesn't seem like much of a constraint. :) It took all the matter in the universe 200 million years to condense under gravity and form the first stars. (http://www.space.com/scienceastronomy/hubble_first_stars_030430.html) Life is a little more complex than a condensed blob of gas, and the earth is a little smaller than the universe.

A Thousand Pardons
2004-Nov-30, 05:38 PM
Life is a little more complex than a condensed blob of gas
You're saying that the Sun is less complex than an amoeba? I think there would be some argument there.

Entire life forms evolved and disappeared during the Cretaceous--only 79 million years. And look what we've done in the past 65 million. :)

Squink
2004-Nov-30, 06:03 PM
You're saying that the Sun is less complex than an amoeba? I think there would be some argument there. Yeah, can you tell I'm a biochemist, and not an astronomer? :P I bought a copy of "Stellar Atmospheres" back in 72, and was very impressed with all the differential equations. Still, the minimum number of proteins required for a living, self replicating cell is probably in the low hundreds (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=153535 68&dopt=Abstract&holding=f1000). That's a lot of genes to come together in one place through the mechanism of happenstance.

A Thousand Pardons
2004-Nov-30, 06:06 PM
That's a lot of genes to come together in one place through the mechanism of happenstance.
One hundred million is a lot of years! :)

Just think of the stack of papers that Euler could have written in that time...

Evan
2004-Nov-30, 06:12 PM
That's a lot of genes to come together in one place through the mechanism of happenstance.

Who says it is happenstance? There are many examples of self organizing systems in the natural world that given energy input self organize in ways that do not reflect least energy configurations. The chance argument ignores the strong possibility that it is not entirely by chance but that the various components that make a living organism may automatically assume the right configuration given the right conditions. That is in fact how DNA replicates.

Russ
2004-Nov-30, 06:48 PM
If this is the case, why have we not been able to get that which is non living to give rise to that which is living in a laboratory?

Amino acids and even proteins are a long way from anything classed as living.

The universe is under no obligation operate within the limits imposed by our ignorance. :lol:

Russ
2004-Nov-30, 07:31 PM
I agree with Russ.
AT LAST! SOMEONE FINALLY AGREES WITH ME!!!! :D:D
I know, I know. It has happened before but...it just feels sooooo good when it happens. :lol: ;)


I also think that given the right raw materials that devlopment of life is probably inevitable. As for reproducing it in the lab that is simply a matter of time and correct conditions. We don't know what those conditions are and we most certainly don't have the time.
I'll disagree with you just a little bit here. I think it is more a matter of our ignorance than a lack of time, that we can't develop life in the Lab.


The argument that is often given that the right arrangement of conditions and material is vanishingly unlikely simply ignores the fact that even unlikey events have a high probability of happening given enough time. If an event only has one chance in a million of occuring and the attempt at the event happens every day then it is virtually certain to happen in a million years.
It would be 200,000 times in a million years, in our galixy alone, if my arithmatic is correct.


I am of the opinion that the chance occurrence of life from basic materials known to be easily produced naturally probably isn't unlikely at all. All it takes is time.

As for intelligent sentient life that is a different matter. The universe is a very violent place. It may be very unlikely for sentient life to get a chance before something wipes it out. It also may be unlikely for sentient life to develop in the first place. If the asteroid hadn't wiped out the dinosaurs they might still be the dominant life form on Earth.

I fully agree that life "...isn't unlikely at all." If we're here, your contention is true.

I disagree about sentience. Based on our one planet here, it is obvious that life will employ every conceivable strategy for survival. Beings that rely on their brains for survival are manditory not exceptional. The only issue in question is when it develops relative to other strategies.

Evan
2004-Nov-30, 08:05 PM
I disagree Russ :)

Brains are not essential for survival. The most successful living things on this planet are the insects and none have brains.

Russ
2004-Nov-30, 10:24 PM
I disagree Russ :)

Brains are not essential for survival. The most successful living things on this planet are the insects and none have brains.

Ahem. :-s That is not what I said. [-X I said that a species that relied on brains to survive was mandatory (a niche to be filled). Not that said species was the most successful. I'm not sure whether this clarification will change whether you feel you agree with me or not, but hope it clears up what you think I said.