Mimicking an impact on Earth’s early atmosphere yields all 4 RNA bases
arstechnica.com
arstechnica.com
RNA bases -> RNA -> proteins -> life
seems to sidestep the issue of metabolism, i.e. what did the first organism eat? What was its energy source?
When I picture life arising from nothing, the most plausible scenario seems to involve increasingly intricate chemical reactions that initially do absolutely nothing other than create longer and longer staircases for energy to step through through before dissipating and becoming useless. In other words, you start with metabolism first, and then get structure later.
It seems plausible that the earliest proto-metabolisms didn't use RNA or resemble modern life in any way. There might have been a succession of proto-metabolisms before getting to anything we would recognize as life. They would likely not have left any fossil record.
Does this make any sense to anybody?
(disclaimer: the article is quite handwavy, but could be a good jumping-off point if you so choose. Sounds dubious to me but interesting to consider)
The most efficient way of dissipating energy seems like it would be something like
Photon comes in -> photon reflects off water -> photon goes back out to space
Perhaps that's our reason for being.
It seems like a good way to dissipate complex energies. Chemicals pouring out of deep sea vents contain lots of chemical potential energy, but it's difficult to unlock without a complex mechanism. Life unlocks those mechanisms. Taking it several steps further, a uranium-powered particle accelerator produces massive amounts of complex entropy.
> When I picture life arising from nothing
Please don't. Life didn't arise from nothing. That would be like saying "When I picture a supernatural entity creating life".
The rest of your post sounds interesting though. Can't comment on that, not my field.
Or in othet words, there was "stuff" that wasn't alive and then something happened and life was formed. Instead of "there was this absolute void thennlife was formed".
http://bytesizebio.net/2009/10/11/weekly-poll-replicators-fi...
"Replicators First
Aka RNA World: RNA emerges as the first molecule that can replicate and perform enzymatic processes. It stores information and it is biochemically active. Thus it can both replicate and control a primitive meabolism. Later came the transition to DNA as an information storage, and the enzymatic role was mostly relegated to proteins.The first replicators might not even have been RNA molecules, but some pre-RNA nucleic acid such as PNA or TNA..."
"Metabolism First
Metabolism First holds that metabolic processes assembled prior to the existence of replicators. Günter Wächtershäuser proposed that the pioneer organism originated in high (>100C) temperatures in hydrothermal vents. This organism resembled the catalytic converter in a car, more than a primitive cell: it had a composite structure of a mineral base with catalytic transition metal centers, such as iron-sulfide and nickel-sulfide... "
Most intriguingly the book presents an extremely specific and extremely plausible theory for the very beginnings of life. i.e., resolving the questions: Was there a cell before there was metabolism? Or conversely, what is metabolism before there is a cell?
The fact that a self-replicating RNA could have arisen given what we know of primordial earth is extremely convenient. Something different and unknown could have come first, but it would have to fit the bill of "can arise spontaneously" and "can self-replicate and pass down incremental modifications", which is very difficult to pull off. We also have good certainty that LUCA (last universal common ancestor) featured RNA.
I will also try to answer: what did the first organism eat? The concept of food/energy source doesn't apply so well to the first self-replicating RNA. The environment features constantly interacting bases, and the competition between self-replicating RNAs stems from this. The distinction between individual organisms and the environment isn't as clear-cut as what we know now. Through this competition, one of the first things to be acquired was probably a membrane. Eating can become possible and/or useful after you have a membrane, which also allows you to extend the environment in which you can thrive.
Self-replication can itself be viewed as a metabolic process. You really can't have replication before metabolism, because replication is metabolism. The question is which metabolic process came first.
Since replication is anabolic and requires an energy source, it seems like it makes sense to deal with energy first.
You can have reactions that harness energy to do nothing useful -> reactions that harness energy to cause self-replication -> life.
I also edited it quite a bit (but now I'm done, promise...) One of my points is that replication does not require a separate energy source, in the right environment. RNA is highly reactive given the right temperature and conditions, this is why all modern life does not use it as permanent storage medium (this also makes it very difficult to work with in the lab). Only replication of a DNA-based life form strictly requires a control mechanism and energy source.
I actually don't know what a flask full of RNA will do when left to its own devices. My science education has gaps. However, really basic chemistry says that you can't create big molecules from small molecules without some sort of energy gradient, because the big molecules have less entropy than the small ones.
When you have a flask full of stuff, what it does spontaneously is go to thermodynamic equilibrium. If you want a self-sustaining reaction that creates specific big molecules over and over, you need to keep adding energy.
Chemical compound soup, natural reactions -> natural reaction produces the first reaction which is self replicating (I'd assume RNA here) -> self replication reaction dominates natural reactions (to what order, who knows) -> self replicating reaction mutates into a form that better harnesses energy from environment (your metabolism) -> metabolic empowered reaction dominates -> etc
From a primatives perspective, it seems reasonable that the first "evolutionary" advances would have all been incredibly preferential. In the sense that they had no competition with similar capabilities.
Imagine the first organism able to metabolise something (sunlight?) for its own purposes. Against "organisms" that were still waiting for chance to bash them against the right compound.
My idea of how Metabolism First would work is something like this:
1. You get a lot of weird chemistry happening, say, in pools of water. This chemistry starts creating large organic molecules that are like sludge building up in the pools. These molecules are dead, but they are rich in energy and perhaps interesting building blocks. Maybe they are made of amino acids.
2. Now you have this unbelievably rich energy source, and at some point there start appearing chemical chain reactions that start "eating" the sludge.
3. Life originates from these chemical chain reactions.
I suppose it kind of flips the prevailing hypothesis around. Rather than have lightning and such build our proto-organism directly, instead it builds up a sludge that the proto-organism eats.
With the planet being sterile, this organic sludge could build up forever until something figures out how to eat it.
Do you have a source? If by small you mean 100+ bases it has little chance of arising spontaneously. The article speaks only to the possible spontaneous formation of building blocks, not of them assembling into complex forms.
Here's a nice recent review of the field:
The idea of how MF would work presented in the article sounds really implausible.
My idea of how MF would work is something like this:
1. You get a lot of weird chemistry happening, say, in pools of water. This chemistry starts creating large organic molecules that are like sludge building up in the pools. These molecules are dead, but they are rich in energy and perhaps interesting building blocks. Maybe they are made of amino acids.
2. Now you have this unbelievably rich energy source, and at some point there start appearing chemical chain reactions that start "eating" the sludge.
3. Life originates from these chemical chain reactions.
In that article, their version of MF seems to require high energy. Mine happens under gentle conditions.
I think that's the whole of my idea.
It seems like having big molecules of junk lying around would set the stage for self-replicating processes to be able to "eat" the junk molecules and put the energy into synthesizing its own molecules.
Imagine a simple chemical chain reaction, where RNA is floating around in the "primordial soup", and self-replicates simply when it encounters the molecules needed to do so.
RNA is just a chemical, you don't need a whole organism for it to float around and react with other chemicals.
Of course, maybe these two things happened at the same time. Maybe mitochondria developed as the dumb metabolic engine, while RNA developed into the structure. Eventually the structure captures metabolic engines to fuel it directly, rather than harvesting free chemical energy from the environment.
Define "eating".
"and self-replicates simply when it encounters the molecules needed to do so."
It self-replicates, destroying those molecules. One could call that "eating", and probably should, as, if one calls this self-replication, there's an underlying assumption that there is life.
I enjoy works which look for scenarios where both could have emerged simultaneously. Reading the introduction of this paper/article provides an accessible exposition to the topic: http://www.mdpi.com/1422-0067/10/4/1838/htm
If you are curious about under what conditions self-organization might more effectively dissipate entropy I suggest reading anything by Ilya Prigorine. But this short minute physics video narrated by Sean Carroll is good for a start: https://youtu.be/HxTnqKuNygE?t=2m07s
The hard part seems to be getting to the point where the chemistry is so complex that self-replicating things are even possible.
----
Going from a string of RNA to another string of RNA is no easy task. Additionally, going from RNA to a protein requires more than just energy. It requires a molecular factory which can commence protein synthesis.
This requirement is somewhat mitigated by the fact that RNA itself can fold in on itself to form useful structural elements, albeit far simpler than protein-based chains.
If you're starting from something simple that already works, you can imagine how it might evolve into something more complex in small increments, with the new stuff gradually replacing the old stuff until the old stuff is completely gone.
The important thing is that you start with something that already works.
That's why I'm proposing that you start with some kind of self-sustaining chemical reaction, i.e. a metabolism. If you start with a dead strand of RNA, it's hard to imagine how a metabolism springs up spontaneously around it and suddenly starts doing anything at all, much less anything useful like making proteins.
RNA can do the same thing. Transcriptase and polymerases are catalysts but they are not strictly necessary. Simple RNA can have a lifespan of hundreds of years and it just needs to replicate more than once to propagate. Over time a primitive polymerase would eventually be made by freak chance and mutation, and then everything would kick off.
Once you have polymerase natural selection would speed up massively and become resource-limited rather than reaction-limited. Thats when a metabolism would evolve, and enzymes that were successful at catalyzing the conversion of material into resources would stimulate local growth. You'd still only have a frothy mess of chemicals, but it would be a frothier mess than the surrounding mess. The first organism to make some kind of container wins- most likely they'd evolve mucus-y proteins that would help keep their resources concentrated. Over time that mucus would give way to a hollow bubble, which would then become a lipid layer, which would then become the first cell.
As the RNA/pre-RNA chain grows, there will be natural selection for any sequences that catalyze polymerization. This will eventually either lead to self-catalyzing replication or a mutual replication. AFAIK the second one is considered more likely because although RNA can self-catalyze it's not very good at it (of course, it doesn't really need to be). Mutual replication would require a primitive polymerase being spontaneously generated, which would allow an RNA-like molecule to -self-replicate. Eventually an chain would be created that could replicate via copies of itself, and that molecule would be able to spread beyond the original catalyzing molecule and outcompete anything else (since it would be able to replicate with any copies it made, it would grow exponentially rather than linearly).
As I've aged, I've been consistently disappointed. I now believe differences in how people behave, according to age, are really a product of generational differences, and that people really don't change very much after they pass 30.
Comets may have brought much of Earth's water.
Ice, dust & tholins.
Tholins are a sort of like a simple crude oil, thick tarry and orangy brown - very rich in primitive organics and amino acid precursors.
Pluto is red with tholins.
http://www.planetary.org/blogs/guest-blogs/2015/0722-what-in...
The mystery revolves around how these building blocks turn into life through abiotic processes. We really haven't got a clue. As a chemist, I view this as the most important unsolved problem the discipline has to offer.
Solving this mystery would likely be the most significant turning point in human history.
This reminds me of something Paul Graham once said. Knowing a problem exists isn't sufficient justification to solve it. You also need an approach. The approach to solving the origin of life problem does not exist (yet).
Of course you need an attack to solve a problem. Just formulating the problem doesn't guarantee a solution. There must be more to what Graham said than what you are reporting.
I can't imagine how; most people will simply dismiss it and continue praying to their Gods and scientists already believe what it would prove so few minds would change and unless it directly leads to some practical output it simply won't matter to most of the world.