High-power laser hints at origin of RNA

Posted 9 December 2014 by Matt Young

The Hebrew Bible says that God made humans from dust,* but maybe it was a slurry of clay and water. That is a tentative conclusion you might draw from an experiment that used a (very) high-powered laser beam to zap a suspension of clay in an aqueous solution of formamide, a very simple organic compound. The result has been reported in the press, but there is a somewhat more-precise article in Science magazine. (You may find the abstract of the original article here and the supporting information here. I did not get access to the full article.) In a nutshell, a team at the J. Heyrovský Institute of Physical Chemistry in Prague used a laser that can produce up to 1 kJ in a 300 ps pulse,** irradiated the suspension, and produced adenine, cytosine, guanine, and uracil, which are the bases of the RNA molecule. And apparently not a drop of thymine, one of the bases of DNA. The experiment is supposed to simulate the bombardment of the early Earth by comets and presumably supports the hypothesis that an RNA world came first. _____
* Actually, Job, Isaiah, Psalms, and I imagine elsewhere say clay, as in, "We are the clay, and you are our potter." (Don't get excited; I consider the fact to have no significance whatsoever.) ** I am a laser physicist and wrote my thesis on laser-produced plasmas, so you must forgive me for somewhat stressing the laser, which to this day gives me a certain amount of pulse envy.

10 Comments

gdavidson418 · 9 December 2014

Ah ha, the poof theory wins after all.

Comet goes poof. And they laughed at Behe's poofs.

Glen Davidson

TomS · 9 December 2014

You say this is in "Science", but I think it is "PNAS".

Mike Elzinga · 10 December 2014

It is not surprising that some of the chemistry of life would likely have come from an energy cascade, either from lightning, comet impacts, or deep in the oceans near thermal vents.

As a rough rule of thumb, chemistry takes place on the order of 1 electron volt. Using E = kT/2, we find that this corresponds to a temperature of about 23,000 K. Forming molecules in energy cascades requires the fairly rapid shuttling of products into lower energy environments in which they can anneal and remain stable.

Depending on the presence of catalyzing agents or deformations in molecules that pull down potential energy barriers to the formation of molecules, one could expect a rather large span of energies within the cascade in which a particular chemical reaction would find a niche.

The notion of a "warm little pond" is a bit misleading; and the early suggestions of such an environment in which the molecules of life would form came before there was a detailed understanding of chemical kinetics. The "warm little pond" is a relatively low energy "backwater" into which spilled the products produced in a much more energetic process.

Rolf · 10 December 2014

My opinion carries no weight but the most convincing argument for a possible explanation for the origins of life on this planet I've read so far is Stuart Kauffman's "At Home in the Universe."

I don't expect the debate to be over for quite some time yet.

harold · 10 December 2014

Mike Elzinga said: It is not surprising that some of the chemistry of life would likely have come from an energy cascade, either from lightning, comet impacts, or deep in the oceans near thermal vents. As a rough rule of thumb, chemistry takes place on the order of 1 electron volt. Using E = kT/2, we find that this corresponds to a temperature of about 23,000 K. Forming molecules in energy cascades requires the fairly rapid shuttling of products into lower energy environments in which they can anneal and remain stable. Depending on the presence of catalyzing agents or deformations in molecules that pull down potential energy barriers to the formation of molecules, one could expect a rather large span of energies within the cascade in which a particular chemical reaction would find a niche. The notion of a "warm little pond" is a bit misleading; and the early suggestions of such an environment in which the molecules of life would form came before there was a detailed understanding of chemical kinetics. The "warm little pond" is a relatively low energy "backwater" into which spilled the products produced in a much more energetic process.

The "warm little pond" is a category of hypothesis about where proto-cells would have originated, which is different from where molecules that later became part of life would have originated. There is, as you accurately point out, a very narrow energy range in which living cells function. Some small proportion of the biosphere lives in more extreme environments, hot springs and the like, than the rest does. These organisms are highly adapted. It seems more plausible that "ordinary" cells would have emerged first and cells adapted to extreme conditions evolved later. But of course, "seems more plausible" is just me expressing a guess. Models that show the non-biological synthesis of major biochemical compounds so far seem to slant toward applying a lot of energy to the system. So I suppose one very oversimplified way of looking at it might be "First some lightening bolts or something added a lot of energy to the system and that synthesized some molecules which then stuck around, and later became incorporated into proto-cells in a less severe environment". NOTE - RNA today is synthesized by cells, and that includes synthesis of the nucleic acids themselves. Also, a model in which a living cell or even self-replicating nucleic acid strand emerges in an environment which is too harsh for self-replicating RNA strands would seem to be a stretch, but a model suggesting that this is how such molecules first entered the terrestrial environment would not necessarily be stretch.

Matt Young · 10 December 2014

You say this is in âScienceâ, but I think it is âPNASâ.

The original article was in PNAS, but the article I cited was in Science. I did not read the original article.

Mike Elzinga · 10 December 2014

harold said: The "warm little pond" is a category of hypothesis about where proto-cells would have originated, which is different from where molecules that later became part of life would have originated. There is, as you accurately point out, a very narrow energy range in which living cells function. Some small proportion of the biosphere lives in more extreme environments, hot springs and the like, than the rest does. These organisms are highly adapted. It seems more plausible that "ordinary" cells would have emerged first and cells adapted to extreme conditions evolved later. But of course, "seems more plausible" is just me expressing a guess. Models that show the non-biological synthesis of major biochemical compounds so far seem to slant toward applying a lot of energy to the system. So I suppose one very oversimplified way of looking at it might be "First some lightening bolts or something added a lot of energy to the system and that synthesized some molecules which then stuck around, and later became incorporated into proto-cells in a less severe environment". NOTE - RNA today is synthesized by cells, and that includes synthesis of the nucleic acids themselves. Also, a model in which a living cell or even self-replicating nucleic acid strand emerges in an environment which is too harsh for self-replicating RNA strands would seem to be a stretch, but a model suggesting that this is how such molecules first entered the terrestrial environment would not necessarily be stretch.

I think that the currently most attractive hypothesis is the formation of molecules that make such things as RNA. Highly bipolar molecules that can form lipids are also needed in order to form closed structures within a water bath. So most people working in this area think metabolism came first. Going back to the rough rule of thumb, solids such as iron have binding energies on the order of 0.1 eV corresponding to temperatures of about 2000 K. Liquid water at atmospheric pressure and 100 Celsius corresponds to about 0.02 eV. Extremophiles forming in the vicinity of thermal vents at great depths in the ocean and in superheated water might push that energy up to about 0.04 eV. Highly bipolar molecules such as lipids would also have to survive in a liquid environment in order for them to remain flexible and form chains and sheets that then fold into stable, closed structures. RNA, as we know it, exists in liquid water within this temperature and pressure range. That would suggest that the molecules that originally "manufactured" things like RNA are somewhat more robust and were formed in more energetic environments. If I am not mistaken, I think extremophiles are indeed more robust - in terms of their binding energies - than life that exists on the surface of the Earth; they just have different temperature ranges for what constitutes hypothermia and hyperthermia for them. We tend to think of hyperthermia and hypothermia as being associated more with the nervous systems of living organisms, but other coordinating processes across distances within a cell could just as likely exist only within a narrower temperature range than what is required for the stability of these molecular structures. The main requirement in every case is that these structures are what condensed matter physicists refer to as "soft matter." These structures exist at temperatures that produce internal kinetic energies that are slightly less than the binding energies among constituents comprising the structure. Any colder, they freeze; any hotter, they come apart. They also need an environment of liquid water - or perhaps some other liquid chemical - in order for them to explore millions of additional configurations.

Henry J · 11 December 2014

It seems more plausible that âordinaryâ cells would have emerged first and cells adapted to extreme conditions evolved later.

But the conditions that were prevalent 3 or 4 billion years ago might be something we'd call extreme today.

harold · 12 December 2014

Henry J said:
It seems more plausible that âordinaryâ cells would have emerged first and cells adapted to extreme conditions evolved later.
But the conditions that were prevalent 3 or 4 billion years ago might be something we'd call extreme today.

I suppose it depends on what you call extreme, as they were different. We don't know what microenvironment gave rise to whatever could be called the first cells. My main point is that models in involving lightening blasts or high power laser beams model the possible terrestrial origin of molecules rather than cells. That's simply a fact. this article is about producing nucleotides, not cells. So was the Urey-Miller experiment. This is a point that creationists often distort, by the way.

Palaeonictis · 15 December 2014

harold said:
Henry J said:
It seems more plausible that âordinaryâ cells would have emerged first and cells adapted to extreme conditions evolved later.
But the conditions that were prevalent 3 or 4 billion years ago might be something we'd call extreme today.
I suppose it depends on what you call extreme, as they were different. We don't know what microenvironment gave rise to whatever could be called the first cells. My main point is that models in involving lightening blasts or high power laser beams model the possible terrestrial origin of molecules rather than cells. That's simply a fact. this article is about producing nucleotides, not cells. So was the Urey-Miller experiment. This is a point that creationists often distort, by the way.

Another thing creationists fail to mention is that we have produced "proto-cells" or proto-bionts in the laboratory. They also conflate evolution with pre-biotic chemistry, which anyone with even only a high-school level of understanding modern biology knows. Anyways, we may never know how life truly originated, although as Scientific American put it, "Rosetta pours cold water on cometary origin of Earth's water" hypothesis. And this experiment tends to lend credence to the RNA world hypothesis.