Life as an aspect of the universe

[Ann]

I sacrificed several hours' sleep (well, I often go to bed around seven because I get up so awfully early when I work) to listen to a lecture about the emergence and evolution of life in the universe. The lecturer was pretty lousy. He fired off pictures of molecules and DNA strands and cells at us like a machine-gun, but he offered few descriptions and fewer clarifications and explanations. For example, he used a term like "Kepler" for the planet-searching Kepler mission without the slightest explanation, even though he was talking to an audience mostly made up of interested members of the general public.

He repeated things too, without making them any clearer. One thing he said three times - and I'm not sure I remember it really well in spite of the repetitions - was something like this: Life is an aspect (or a consequence) of the thermodynamical nature of the universe and the molecular evolution. Thank you, professor, now I understand!

So I'll try to ask here instead. Was the professor trying to say that the physical laws of this universe are such that, given enough time and sufficiently sheltered and generally favorable conditions, molecules will naturally grow so large and complex that they are sort of destined to start self-replicating? Was he saying that molecules containing carbon will so readily form fascinating complexes, that, given the presence of sufficient quantities of the ideal solvent, liquid water, they will eventually start making copies of themselves, making use of external energy and excreting waste products as they do so?

Ann

[rstevenson]

.... Was the professor trying to say that the physical laws of this universe are such that, given enough time and sufficiently sheltered and generally favorable conditions, molecules will naturally grow so large and complex that they are sort of destined to start self-replicating? Was he saying that molecules containing carbon will so readily form fascinating complexes, that, given the presence of sufficient quantities of the ideal solvent, liquid water, they will eventually start making copies of themselves, making use of external energy and excreting waste products as they do so?

Well, I can't speak for what he was trying to say, but I certainly would agree that the universe is making it easy for life to start. We've found all sorts of organic compounds and molecules in space, from carbon to sugar, several of which are precursors of things like proteins and even RNA. Whether or not life itself is as ubiquitous as its building blocks would imply depends on one's answer to what is an essentially religious question: Are we unique? In other words, if a "spark" is required to form life, does that imply a "sparker"? I think not, but lots of others, as you know, would argue otherwise (in other forums.)

I think it is only reasonable to take ubiquity of building blocks and add energy, with the result being life -- of some sort. But we need lots more data before that can be an accepted foundational point of view.

Rob

[Chris Peterson]

So I'll try to ask here instead. Was the professor trying to say that the physical laws of this universe are such that, given enough time and sufficiently sheltered and generally favorable conditions, molecules will naturally grow so large and complex that they are sort of destined to start self-replicating?

I would say that's probably what he meant, more or less.

It's a reasonable view, that life is an inevitable consequence of how the Universe works. All the ingredients are there, and wherever you have energy, systems tend to increase in complexity. I doubt you even need much time, or particularly "sheltered" conditions (as we think for our sort of life) to produce complex, self-replicating systems that might reasonably be called alive.

[neufer]

It's a reasonable view, that life is an inevitable consequence of how the Universe works. All the ingredients are there, and wherever you have energy, systems tend to increase in complexity. I doubt you even need much time, or particularly "sheltered" conditions (as we think for our sort of life) to produce complex, self-replicating systems that might reasonably be called alive.

• . http://asterisk.apod.com/viewtopic.php? ... 49#p166847

[neufer]

<<The Miller–Urey experiment in 1952, and others since, demonstrated the synthesis of organic compounds, such as nucleobases, amino acids, formaldehyde and sugars, from the original inorganic precursors presumed to have been present in the primordial soup. The RNA world hypothesis shows how RNA can become its own catalyst (a ribozyme), and so become the basis for evolution of life. In between there are some missing steps such as how the first RNA molecules could be formed. The PAH world hypothesis was proposed by Simon Nicholas Platts in May 2004 to try to fill in this missing step.

[b][color=#0000FF]In the self ordering PAH stack, the separation between adjacent rings is 0.34 nm. This is the same separation found between adjacent nucleotides of RNA and DNA.[/color][/b]

---

Polycyclic aromatic hydrocarbons are the most common and abundant of the known polyatomic molecules in the visible Universe, and are considered a likely constituent of the primordial sea. PAHs, along with fullerenes (or "buckyballs"), have been recently detected in nebulae. (Fullerenes are also implicated in the origin of life; according to astronomer Letizia Stanghellini.)

http://apod.nasa.gov/apod/ap091230.html
http://apod.nasa.gov/apod/ap080605.html
http://apod.nasa.gov/apod/ap080428.html
http://apod.nasa.gov/apod/ap080111.html
http://apod.nasa.gov/apod/ap060414.html
http://apod.nasa.gov/apod/ap050409.html

PAH's are not normally very soluble in sea water, but when subject to ionizing radiation such as solar UV light, the outer hydrogen atoms can be stripped off and replaced with a hydroxyl group, rendering the PAHs far more soluble in water. These modified PAHs are amphiphilic, which means that they have parts that are both hydrophilic and hydrophobic. When in solution, they assemble in discotic mesogenic stacks which, like lipids, tend to organize with their hydrophobic parts protected.

In the self ordering PAH stack, the separation between adjacent rings is 0.34 nm. This is the same separation found between adjacent nucleotides of RNA and DNA. Smaller molecules will naturally attach themselves to the PAH rings. However PAH rings, while forming, tend to swivel around on one another, which will tend to dislodge attached compounds that would collide with those attached to those above and below. Therefore it encourages preferential attachment of flat molecules such as pyrimidine and purine nucleobases, the key constituents (and information carriers) of RNA and DNA. These bases are similarly amphiphilic and so also tend to line up in similar stacks.

According to the hypothesis, once the nucleobases are attached (via hydrogen bonds) to the PAH scaffolding, the inter-base distance would select for "linker" molecules of a specific size, such as small formaldehyde (methanal) oligomers, also taken from the prebiotic "soup", which will bind (via covalent bonds) to the nucleobases as well as each other to add a flexible structural backbone.

A subsequent transient drop in the ambient pH (increase in acidity), for example as a result of a volcanic discharge of acidic gases such as sulfur dioxide or carbon dioxide, would allow the bases to break off from their PAH scaffolding, forming RNA-like molecules (with the formaldehyde backbone instead of the ribose-phosphate backbone used by "modern" RNA, but the same 0.34 nm pitch).

The hypothesis further speculates that once long RNA-like single strands are detached from the PAH stacks, and after ambient pH levels became less acidic, they would tend to fold back on themselves, with complementary sequences of nucleobases preferentially seeking out each other and forming hydrogen bonds, creating stable, at least partially double-stranded RNA-like structures, similar to ribozymes. The formaldehyde oligomers would eventually be replaced with more stable ribose-phosphate molecules for the backbone material, resulting in a starting milestone for the RNA world hypothesis, which speculates about further evolutionary developments from that point.>>

[owlice]

A few years ago while taking a graduate class, a question came up about something in one of the books we'd read. Some of my fellow students thought the author meant one thing, others something else. Well, heck, I thought, let's just ask the author! So I found his email address on line and fired off an email to him -- and he's a well-known author/business guru -- and got back an answer in an hour or two. Had a follow-up question, too, which he answered very quickly.

Ann, maybe you could ask the professor what he meant?

[Ann]

A few years ago while taking a graduate class, a question came up about something in one of the books we'd read. Some of my fellow students thought the author meant one thing, others something else. Well, heck, I thought, let's just ask the author! So I found his email address on line and fired off an email to him -- and he's a well-known author/business guru -- and got back an answer in an hour or two. Had a follow-up question, too, which he answered very quickly.

Ann, maybe you could ask the professor what he meant?

That's a good idea, owlice. I have, in fact, written to astronomers and astrophotographers before to ask questions. Once I wrote to Adam Riess to ask a question about dark energy, and I actually understood a bit better thanks to the answer he gave me.

However, in this case I'm not going to ask. I have completely forgotten the professor's name - not that I couldn't find out about it if I wanted to - but his lecturing style did not inspire any confidence in me. And unlike Adam Riess, who is one of the discoverers of dark energy, I don't think that the professor I listened to is such an expert and pioneer in his field that he is necessarily more knowledgeable about the emergence of life in the universe than a lot of other people are.

So instead I want to thank Art for his very interesting post about the possible stages in the emergence of self-replicating proteins and RNA.

Ann