Doubting Didymus

A cell is composed of complicated proteins, long strands of information-encoding DNA, enzymes, special energy-storing molecules, and organelles, some of which which are almost as complicated on their own as the rest of the cell and all held in place by membranes. All of these components work in a near-perfect balance with every other component.

For this set up to form by chance alone (that is, by having all the right molecules fall into the right places) is far too improbable for anyone to sensibly say that it ever happened, on any planet, at anytime in the past nor does anyone expect it to ever happen in the future. Technically, it is possible, but the probability is quite a bit greater than the probability that all the molecular vibrations in the atoms of mount rushmore should happen to line up in a certain way, and have the dead presidents heads scream "PLEASE TAKE 'UNDER GOD' OUT OF THE PLEDGE AND THROW ALL YOUR HANDGUNS AWAY, JESUS IS UPSET."

To call these kind of things 'technically possible' is almost perverse.

Just in case anyone thinks I am making the creationist argument, think again. All I am saying is that the abiogenesis thing would have to have been significantly less improbable than a whole cell. RNA is currently the best contender, I think.

John M3

A key word that I have learned which corresponds to the "RNA world" hypothesis is "autocatalysis."

It suggests that the "goo" referred to above formed out of an autocatalytic chemical reaction. Some naturally occurring ribosome are "reactive", meaning that when one interacts with another a third product emerges--a newly configured ribosome.

One could conceive a situation whereby r1 with r2 catalyzes r3--r2 and r3 catalyzes r1--and r1 and r3 catalyzes r2. In a closed system this would result in a continuous reaction.

Similarly, one could imagine r3 and r1 catalyzing r4,r5, and r6. If there is some process by which the reactive loop keeps the process going, but it also happens that new sequences always give rise to even newer and novel sequences, then highly complex RNA sequences are very likely to come about.

That’s my rudimentary understanding of it that I read a while ago in Kaufman's "investigations."

They're doing simulations of such autocatalytic reactions, but at the time that Kaufman’s book was published the simulations were hitting a brick wall, so to speak, and new novelty stopped emerging. Presumably, there would be some simple molecular set and environment, though, that would allow complex life to autocatalytically emerge (like Wolframs rule 30 (Wolfram and Kaufman are friends by the way)).

[ November 05, 2002: Message edited by: John M3 ]</p>

John M3

But this would all happen much easier in space clouds the size of a galaxy, in my oppinion. I am pretty sure they can harbo amino-acids.

Are not amino-acids just carbohydrates or hydrocarbons? Some of these clouds are dense and light is absorbed into heat rather than passing through them. When a cloud is the size of a galaxy, who knows what processes could come about in its depths.

Oolon Colluphid

No, not 'just'. There's a good dose of nitrogen in there too, which is why ammonia is (was? I haven't been keeping up with abiogenesis stuff ) thought to be an important thing to have around back then.

Oolon

lpetrich

I wonder what might be a good "introduction to biochemistry" site for someone like "John M3". <a href="http://www.bioscience.org/urllists/aminacid.htm" target="_blank">This site</a> lists the 20 biological amino acids, which are the building blocks of proteins, and gives their molecular structures.

And as to prebiotic synthesis in interstellar dust clouds, there is indeed evidence that it happens -- several organic compounds have been discovered in such clouds. However, it's a bit difficult to imagine an organism emerging from interstellar clouds, because they lack liquid water, which is a convenient medium for biochemistry to take place in. Without a liquid like water, molecules would be stuck in place and not have an easy way to move and interact with other molecules.

Oolon Colluphid

Doesn’t that make it sound like gases can’t inter-react though? My initial reaction to what you wrote was ‘of course’, but thinking further, I’m not sure what the molecules would be “stuck in place” to...? Gases, by definition, have their molecules moving around more than liquids. Is not the only (admittedly substantial) advantage of being dissolved in a liquid that the molecules would have a better chance of coming together because all the molecules are closer? And isn’t that the point of things like Cairns Smith’s clays, that what they really need is a surface to get together on? In other words, why is water so important, and why might such molecules come about in a gas?

(Time to get going on Wills & Bada’s The Spark of Life I picked up off Amazon, methinks... )

Oolon

lpetrich

Except that gas-phase biochemistry has a certain problem: all but the smallest organic molecules tend to condense very readily, and the more hydrophilic ones tend to condense more readily.

Methanol has a molecular weight of 32 and a boiling point of 338 K

Ethane has a molecular weight of 30 and a boiling point of 185 K

Glycerol has a molecular weight of 92 and a boiling point of 560 K

Heptane has a molecular weight of 100 and a boiling point of 372 K

And these molecules are tiny by biochemical standards.

Source: <a href="http://webbook.nist.gov" target="_blank">NIST Chemistry Data</a>; boiling points are for 1 atm pressure.

Although boiling points will be significantly reduced at interstellar pressures, that may not be enough to compensate for the great masses of typical biomolecules. This is because the vapor pressure goes approximately as

P = P0*exp(-H/(kT))

where P0 is some constant pressure, H is the heat of vaporization, and T is the temperature. H increases with increasing molecular weight, and for constant temperature, this turns into a fast decline in P.

Boiling will occur when vapor pressure &gt;= local pressure, and solving for T yields

T = (H/k)*(1/log(P0/P))

[ November 06, 2002: Message edited by: lpetrich ]</p>

luvluv

Well, waves are not part of some system of translation as RNA and DNA are (aren't they?). It isn't that RNA and DNA carry what could be construed as information, it's that other independant molecules "read" and "build" based on that information.

Very true it falls prey to the same objections the teleological explanation does, but to me it makes it very hard to be an absolute naturalist.

luvluv

Here's a bit of an article on panspermia, (as well as some other stuff you probably want to trash ), over on Hugh Ross's website:

<a href="http://www.reasons.org/resources/fff/2001issue6/index.shtml?main#search_for_planets" target="_blank">http://www.reasons.org/resources/fff/2001issue6/index.shtml?main#search_for_planets</a>

luvluv

Man I would have expected you guys to have attempted to rip that page to shreds by now.