Francis Crick and the theory of Directed panspermia

I'm Francis and I dont do Panspermia...

Oh well Hi Francis, I thought you died after discovering the double helix but alas you've come back to prove the theory of reincarnation this time?

Re: Francis Crick and the theory of Directed panspermia


Crick may have stated it, but do we know if it's true?

*IF* he is correct, and it is completely impossible for DNA to have evolved within that timeframe, *THEN* panspermia *MIGHT* be the only alternative left (although the creationists could throw at least one other theory at ya).

Panspermia is not an entirely unrealistic possibility, but that completely assumes that DNA exists extraterrestrially, and so far we haven't found even a shred of extraterrestrial DNA. (meteors have amino acids, not DNA).

The probability of a god with superpowers coming into being from nothing is equally daunting and the odds extremely high, in fact astronomically higher than DNA appearing spontaneously on Earth.

Azure, you should read the first 100 pages of At Home in the Universe. The theory of autocatalytic sets presented in these pages fits perfectly with this evidence, and I believe it

As people have calculated, in order for a self replicating life form with DNA to form randomly all at once is astronomical and completely improbable.

But what the autocatalytic set theory shows is that given an arbitrary pool of high enough complexity, chemical reactions that synthesis self replicating "life forms" naturally emerges...which is capable of natural selection WITHOUT DNA, which could evolve to have DNA later on

This suggests that given any planet with sufficient conditions and time, life will form, and also suggests that are are millions of other inhabited planets in the universe.

Saying that Earth was colonized by alien bacteria on an asteroid is a cop-out, it does not solve the problem of how does life come about, it merely says "not our problem." There's no reason to take this belief other than inability to find the real answer. Life had to evolve on some planet. Our planet had good conditions for starting life, and that's the logical place to look. If you are going to keep thinking that the chance of a small organism springing into existence purely randomly, then you could expand that state space to the entire universe...and you will would be too unlikely to have an explanation. Not to mention that there are no bettter candidate planets for life in our vicinity!

Once an organism with DNA has evolved, it will be a primitive organism and small mutations would have broad changes to the organism...over time as the organism becomes more complicated natural selection has lesser and lesser effect. Organisms can easily spread out over the globe faster than a new type of "DNA" could evolve somewhere else on the planet, such that it is not surprising that all life on Earth uses the same DNA.

It's not just a cop-out. If precursors of life arrived here instead of developing here, then it allows us a wider range of conditions from which those precursors might have developed (because we don't know anything about where they came from, or how long they might have taken to develop).

Current estimations are based on assumptions about conditions on Earth (including time-frame). But if we knew that some precursor to life rode in on meteorites, then we would have fewer limits on theories which support development of the precursors of life.

What favorable conditions could Earth have lacked? From what I've heard it had ideal conditions.

When you say current estimations...what estimations are you referring to? Estimations of what?

Also for colonization to be a elevated to the status of a theory, we would need more than just hypothetical possibility -- we would need lots of good evidence.

First of all, let me say that I'm not a big fan of the Panspermia theory yet. I'm merely considering the other possibilities.

My current belief is that life pretty much formed here on Earth, possibly with a chemical boost from amino acids riding in on asteroids and such. I won't accept that life arrived from somewhere else (including Mars) until we find at least a scrap of evidence that something that can replicate exists outside of Earth (and so far, nothing like that has been found, anywhere).



Time, for one.

It may take more time for basic replicative systems to form than was available on Earth.



Estimations of how life might have developed here on Earth. This whole thread started because Crick suggested that DNA was too complex to have formed within the timeframe available to it on Earth.

I'm not convinced that he's correct with that statement, but if he is, then we would need some other mechanism for explaining the relatively rapid appearance of DNA on Earth.

Panspermia may not have much evidence for it yet, but we can't rule it out either. And when meteorites are found to have amino acids in them, and when some of them have come from Mars, and when earth bacteria are found to survive extreme conditions and long periods of time.... well then, the obstacles to Panspermia are becoming more and more surmountable.



I agree. So far all we have are amino acids in meteors, chunks of rock moving from planet to planet (or moon to moon), and very hardy bacterial species here on Earth.

But suppose we land a probe on a comet and melt the ice and find some type of simple RNA. Then the potential environment for evolution of the precursors of life (chemical replication) becomes much larger and more varied than present assumptions.

I'm pretty sure it's been shown that amino acids can cobble themselves together in test tubes on their own in experimental time, so I don't think we need wait on an asteroid for them

Also, if Earth didn't have enough time, than nothing in the universe did. The calculations are highly exponential and if something can't happen in several billion years, adding a few more tiny paramaters are quickly going to bounce it up to hundreds of billions of years past the age of the universe.

Life simply cannot be that improbable. The calculations that you have seen are based on all the right molecules just happening to collide into each other in the right way. This is, obviously, just not the way it works. There must have been other forces of statistics or probability at work that made it much more likely than all of the atoms simply falling into perfect place.

The panspermia idea (exogenesis to most of us) has a lot against it, Namely the vaccum and cold of space wouldnt be condusive to transporting cell precursors for the time it takes to escape one environment (where presumably the life began) and going to another. Its like the old pilots mantra
"Flying (in space) Is thousands of years of icy cold vaccuum, punctuated by events of incineration"

The evidence for a geogenesis is , of course , only a collection of time related events
1Shortly (about 10 to 50 million years) after the earth and its moon forming collision with a smaller planetoid occured, the energy budget allowed for a proto atmosphere that was enriched in hydrogen. (Two necessary elements for the Tropsch process to work are H and C in abondanza) The earth gets cool enough and begins acquiring water (degassing and/ or cometary showers containing water). At about almost 4 BY some proto crusts form and these have preserved a sense of a oxygen free, reducing environmnet.
At about 3.9 (+/-) Billion years The Isua formation shows the enrichment of C12 (life preferring isotope). Later (shortly later) the same formation , up section, shows the initiation of banded iron formations (which show that some free oxygen is available from some cause)
Almost 0.5 Billion years after the Isua , are a number of locations where Archean bacteria fossils are deposited(these are prokaryotic cells) , then another .3 Billion years and we begin to see cyano bacters in stromatolite deposits in larger groupings (we cant say anything about the location of crustal elements this early because we dont have any idea as to how the crustal sections were arranged from earliest plate movements. Then , at the VEndean lower boundary we see the beginnings of the first plate movements in the Rhodinia (This is all waay pre Iapetus, and Pangea, Gondwana and LAurasia times), in this time we begin to see more complex life forms that terminate in "hard shell" examples during whats been popularly called the Cambrian Explosion

The whole point is that the appearnce of life on this planet was a gradual ascendancy from mere chemical traces, through simplest non oxygen emitters , to oxygen emmitting bacteria, to plants and animals living together in preVendean time.
If life came in on a train or a comet. Wed see (Id think) an abrupt starting point of existence, maybe a cellular form that , like the reawakened Permian bacteria, could be able to colonize the planet very rapidly. Instead it appears to beslow mincing steps. IMHO, probably autocatalytic reactions meet proper conditions , meet opportunity.

Cricks argument never resonated with most science . CAuse Crick didnt have any understanding of all the available evidence when he died (hed been sick since the early 2002 and died in 2004). Lots of real work on the Isua has been done only in the last 5 years. Its like the Burgess shale, it sat out there for 100 years from first discovery to a time when some curious geochemists started to take a real look at it and its evidence.
Wish we had another Isua area , like maybe the Grampians of Scotland or the peri Deccan area of India or the sub pC shales of Australia. Even the Canadian shield has thousands of square miles of untouched pC sedimentary rocks

stuh-exactly. Theres almost an implied Uniformitarianism. "If it happened somewhere else, it probably happened here too"
We can see spectra of nucleotides and one of the necessary amino acids in spectra from specific stars.
The nuclei of life (in order to get the mathematical improbabilities down to scale) have never considered each atomic radius as a potential reaction site .
When you consider it, 88% of our planets time was in the non-life to simple life phase. All the major development, experimentation, and appearance of new orders occured in the last 12%. After all, how improbable is the appearance of a dinosaur or a monkey from a little Cambrian "notochord" called Pikaia

Again, I'm playing devils advocate here because I actually prefer an earth based development cycle. But just to make a couple of logical points...



We don't *need* them to come from asteroids, but abundance of amino acids (or other stuff) raining down might have changed probabilities.



The Isua formations indicate that replicative life was ticking away on Earth only about a half billion years after the first solid crusts formed on Earth (and proably less time since the first water accumulated).

Purely from a time consideration point of view, since the Universe is around 13.5by old, then there would have been a lot more time for things to form elsewhere in the Universe if life is not limited to the .5 billion year slice available to it on Earth.

Unless what might have arrived here was not some form of cell, but some replicative molecule.

I completely agree that we see a gradual ascendancy from chemical to cellular forms, so I don't think anything extraterrestrial could have been inserted into the sequence at that point.

But the jury is still out on whether some precursor to life may have been introduced into the environment during planetary formation and boosted things along during that initial period before Isua formation.

Correct. In all liklihood the chemical conditions required to promote replication were probably very common on the Early Earth.

Also, chemical reactions can occur very quickly, especially when they are still simple. So a lot more replication and selection was probably happening in a shorter time frame earlier in the system.

farmerman, right -- but as rosborne has pointed out the fossil record doesn't do much to show us how exactly the first reproductive cells were formed. natural selection and evolution cannot begin to occur until there is a cell that can reproduce and has the capacity to evolve. this is why I am so attracted to the autocatalytic sets hypothesis

ros says

The discussion then follows an Occams Razor direction. If it happened out there, why couldnt it have happened here without the extraneous step of riding pre-life in on a comet? Simpler the better.

Of course we dont know, but if we work backwards with our existing evidence, a "test tube earth" concept is rather compelling to me.

What is an autocatalytic sets hypothesis? I'm not familiar with that.

Thanks,

It's a network of molecules that, given a constant supply of certain molecules, can quickly and repeatedly reproduce itself because the set contains molecules which are catalysts to all the reactions that would produce the set. Given a high variation of molecules in high concentration these sets form with nearly guaranteed statistical probability. They can evolve by assimilating new molecules into the set. There's a lot more evidence than this but that's the basic idea.