Thoughts on the early formation of life

[kolleamm]

I watched a video lately describing how life could have arisen on Earth near the hydrothermal vents, with the exact way it formed being unknown.
This made me wonder could there be a very simple configuration of DNA (or RNA?) that could give rise to life?
I'm thinking the earliest life forms may have had the simplest/bare minimum assembly of molecules for it to be considered life.
So perhaps if scientists find this simple configuration then the question of how life formed may not be so complicated to answer after all.

I'm curious to hear your thoughts on this.

 

[BillTre]

This made me wonder could there be a very simple configuration of DNA (or RNA?) that could give rise to life?

Life (as we know it on Earth) will have to involve more than just one or a group of RNA (or DNA molecules).
It would require many different kinds of molecules assembled into an entity (like a cell) that can metabolize environmental energy, produce organic molecules, contain its components, and reproduce.The hydrothermal vent origin of life scenario as I understand it is:
The vents bring sea water (the ancient ocean formulation) into contact with different fluids coming from the vent different pH and containing CO₂ and H₂.
These kinds of vents are not black smokers. They can precipitate a sponge like rock material with iron, nickle, and sulfur containing minerals embedded in the walls of the sponge cells that separate the different fluids.
These minerals are supposed to act as catalysts using energy available in chemistries of these different fluids to generate a mix of organic molecules from the CO₂.

The hydrothermal vents can be very large with billions of different "compartments" where different combinations of components could reside. They are driven by geochemical processes and can last a long time. Many possible chemical combinations could be given a chance to survive and proliferate.

Some of these molecules will eventually from lipids that in high enough concentrations will form membranes.
In some not detailed way, the the catalysts get located into a membrane. This eventually was transformed into a power source for the primitive cell. The membrane houses the primitive power source as well as containing the cells products (so they don't diffuse away) and preventing predatory molecular systems from taking advantage of the cell's production.

Other molecules generated could be peptides or nucleic acids.
RNA may form into some sequence/configuration that has enzymatic properties and possibly duplicate their sequence.
DNA is thought to have come along later. It is more stable but a step removed from the biochemical action.
Peptides assembled some what randomly and not sequence directed may have combined with RNAs to refine their catalytic properties.

RNA or DNA sequence driven production of proteins is required to produce the extremely complex proteins underlying energy production the are found in all current forms of cellular life and therefore the last common ancestor of all life. These proteins are most likely too complex to generated except in a sequence driven manner.
DNA synthesis enzymes are not conserved between the bacteria and archaea (to two branches of life derived from the last common ancestor of all living things on Earth). Thus, DNA synthetic enzymes are thought to have arisen and been encoded in sequence at a later time than the last common ancestor.

The last common ancestor is not necessarily the first live cell, by whatever definition of life you might be using. The first living unit could have arisen earlier and then been refined many times before the separation of the two lineages that became the bacteria and archaea. The separation point is the last common ancestor.

 

[DennisN]

hydrothermal vents

The hydrothermal vent origin of life scenario as I understand it is:

I learned about hydrothermal vents just a couple of years ago, and got quite fascinated by them.
After that I watched a couple of amazing videos of them on youtube, the videos were really beautiful, but I don't have any links to any at the moment.

 

[DennisN]

After that I watched a couple of amazing videos of them on youtube, the videos were really beautiful, but I don't have any links to any at the moment.

I found one of them, quite magical:

40 Years of Hydrothermal Vent Exploration (EVNautilus)

 

[BillTre]

Terminology Note:

Different people use terms related to different kinds of hydrothermal vents at the bottom of the ocean.

There are at least two classes of these vents, driven by different energy sources with outflows with different chemical properties.
These different sites have different credibilities as possible sources of living system origins (locations where origin of life seems feasible).

Vents with flows driven by contact of sea water with very hot rock or magma. I have seen these called geothermal vents (geological heat source) or hydrothermal vents.
These have:

• high temperature outflows
• usually high velocity flows
• high levels of dissolved metals (resulting in "black smokers" when the precipitate).

Possible problems for origin of life events:

• The high temperatures are considered by some to make organic chemical significantly less stable (break down rapidly).
• The high flow rates would be more likely to blow organics materials away, reducing their concentration which makes possible biochemical interactions much less likely. These would be needed to build up the biochemical complexity for life processes.

Vents driven by serpentinization of seawater reactions with the kind of rock (mafic or ultramafic) created at the seafloor, where the spreading occurs. These vents were first predicted by Michael Russell in 1993, and first found in 2000. (He also hypothesized them as a potential origin of life site.) The rock recently brought into contact with the ocean, gets oxidized and hydrated, by reacting with seawater, to form serpentinite or related kinds of rocks.
I have seen these called hydrothermal vents and alkaline hydrothermal vents (which is longer but clearly distinct from the other group).
Going forward, I will try to use "alkaline hydrothermal vent" due to clarity, but not what I've done before.

The outflow from these vents is different chemically:

• less hot, high pH (alkaline)
• dissolved CO₂ (could be used to make organic molecules) and H₂
• lesser amounts of dissolved metals (Fe, Ni, ...)
• Contact of the vent water with seawater creates "white smokers" due to carbonate precipitation, but can be greyish depending on metal content.

The slow flows that get divided up into smaller and smaller passages, allow many small outflow passages with gradual mixing of vent and sea water. Ultimately it can become a very slow flow through a lot of small passages (somewhat like a sponge filter if you know aquarium technology).
Potentially many different little crevices making many little opportunistic laboratories for different combinations of undirected organic syntheses.

Differences between seawater and the ocean have a difference in proton concentration (H⁺ or pH) are what the some consider to be the driving force for chemistry at the origin of life. A proton gradient parallels the cell's use of a proton gradient across a membrane by its energy generation mechanisms. By this, I mean all eukaryotic, bacterial and archeal cells.
This is a feature conserved in all life. Viruses are not cells, don't make their own energy, and don't have these features. However, they require cells that do, in order to reproduce.

The hot water vents are usually located where ocean spreading is occurring and the hottest rock/lava material is exposed. They dissolve minerals in the hot water, which when it contacts the cooler ocean water will start to precipitate, creating the outflow towers. As the ocean floor spreads and local areas move away from the heat source, old vents will stop and new ones will form where the sea floor is now opening up.

The alkaline hydrothermal vents are located further from the actual site of ocean floor spreading.
They are found in older rocks that are not so hot, but have had time to react with the seawater. The reaction releases some heat but they don't get nearly as hot as the geothermal vents. Perhaps because of this they have (generally) slower outflow speeds.
Alkaline hydrothermal vents can be very large and last for thousands of years, providing the opportunity for many different random experiments in biochemistry.

In both cases (vent types), the dissolved metals can precipitate out, in small crystals that are related to enzymatic reaction centers in biological enzymes today. The reaction promoting properties of these kinds of Fe/Ni containing molecules are important components of many different origin of life scenarios. Scenarios that have been proposed to have occurred at several different sites.

 

[David_777]

The decades long search to discover how life might have arisen on Earth has been looking increasingly less probable in recent decades as the once derided various ideas of panspermia rise. That is because the time between heavy bombardment when the Earth was likely a hot molten surface and the first fossil signs of life in oldest rocks has been reduced to a ridiculously short period. That is why many now are expecting as we explore out beyond our planet, we may soon find signs of DNA life elsewhere. Also pointing in that direction are the large numbers of planets apparently around star systems. To think our system with billions, trillions of other stars out there, is special does not follow logically.

 

[BillTre]

The decades long search to discover how life might have arisen on Earth has been looking increasingly less probable in recent decades as the once derided various ideas of panspermia rise.

On the contrary, I think that the idea of panspermia is getting less consideration because the newer ideas concerning the origin of life are much more promising than previous approaches. They hypothesize more well thought out and reasonable mechanisms in more realistic settings.

That is because the time between heavy bombardment when the Earth was likely a hot molten surface and the first fossil signs of life in oldest rocks has been reduced to a ridiculously short period.

Many take this as an indication that it is not really that difficult for life to arise. If it happened quickly, it was not such an unlikely and difficult to generate occurrence.

we may soon find signs of DNA life elsewhere

Of course, this only puts the problems of the origin of life off to another explanation at another site.

Also pointing in that direction are the large numbers of planets apparently around star systems. To think our system with billions, trillions of other stars out there, is special does not follow logically.

If you want to put the origin of life off on some unknown and unstudied planet in unknown conditions, it seems contradictory to make the argument that the Earth is not different and yet that it is not the where life on Earth originated.

 

[David_777]

Good questions making me think haha while this shelter in place reality is going on. Indeed, it is true there are different perspectives on how life started and none are convincing enough to eliminate alternate ideas even if others bothered to try.

Well if it was that easy to start life in such a short time, it would also be more likely throughout the galaxy and universe and maybe into an eternity of Big Bangs whatever. And by so, it is likely individual planets when life did blossom would all be the same at some lower primary chemical level where the big jump was made, because of contamination from other bodies in the universe over its age and that includes much dust, rocks, and assorted nebula debris, especially frozen gas elements. Of course here we are ony discussing the most primitive life to jump to rna/dna replications, a long long ways from cells etc.

Dominantly, most think in terms of a one time 16 to 70(?) billion year old universe. However IMO it is more likely what the universe is now, has already permeated eternity dimensionally even though that may not always be continuously. So as one accepts eternity versus even a 100 billion years, it is a lot more sobering. And once life bloomed, over eternity it has permeated the universe and evolved to a highly positive selection of phenomenal parameters that may be why so much looks more fine tuned, the more knowledge we discover.

As for discussing the discoveries of many galaxy planets, that is also an argument that galaxies have the ripe ingredients to create occasional planets and because their are billions of stars in galaxies like the Milky Way, opportunity is great even if uncommon and the churning changes and variations, especially in star nebula is so vast that life would arise even a single Big Bang evolutionary cycle and then disperse widely. Personally I'm expecting we will find primitive life per the hypothesis, that is life on Jupiter and Saturn moons, and it will be DNA based wallah!, Maybe even on Mars at thermal sites near the pole where water annually may have flow if there is heat below. Of course I've long read reasons why that may not be. But it is one reasonable possibility worth considering. And the one I personally am leaning towards and hope is the case. Part of that is because for so long it has been a long shot theory that shows how experts once again are not always correct within consensus.

Note I'm one that has been long leaning towards a reality from the educational astrobiology 2k book Rare Earth: Why Complex Life Is Uncommon in the Universe.

 

[jim mcnamara]

Before we get a 'little green men' post, please do not speculate further. That way we do not have to lock an interesting thread. Thanks

For those interested - Brownlee & Ward Rare Earth: Why Complex Life Is Uncommon in the Universe 2000
is a popular science book by two professional scientists - astronomer and a geologist/astrobiologist.
They do speculate somewhat.

There are problems with panspermia - it implies that DNA/RNA had to be originate naturally somewhere other than earth, then survive the UV in interstellar space or/and maybe also survive the early solar system accretion disk.

So, the logical shortcoming of panspermia is that we have not answered the question 'where does life originate'? We are simply putting it off to some other place. And time.

In other words - Not that it cannot be true or false. Panspermia is merely not very helpful or instructive about life's origins. Why? It defers life's origins to another earlier time. So do we invoke panspermia again and again on back to the start of the universe, or do we actually determine precisely how abiogenesis occurred?
And when and where.

Another issue. We find DNA or some kind of life on Europa, then what?

Finding extraterrestrial DNA-like or RNA-like molecules can then be construed either way - abiogenesis or panspermia - thinking in terms of Europa's under ice sea. Or more likely, Mars. It will not resolve the question of panspermia or abiogenesis easily.

I'm not going to speculate any further. But simply finding life or DNA on a meteor without a lot of detailed data about it, largely abiochemical synthesis, won't clarify much. Except to grant an 'I told you so' to somebody.

 

[BillTre]

Have not heard of this book before: Rare Earth: Why Complex Life Is Uncommon in the Universe,but here is a wikipedia link on it.
It would seem that the basic premise of the book is that complex life is uncommon in the universe. Well, there is no data backing that claim up.
Observations from telescopes of various kinds and from the few visits space probes have made to our closest planetary neighbors are insufficient to rule out either simple (bacteria-like) or more complex life (like eukaryotes). Small simple animals 1 mm or smaller in length) would also be easily missed.

Some say that it took maybe morer than a billion years for eukaryotes to evolve and it was therefore a very unlikely fortuitous accident. On the other hand, some say that it occurred around the time when O₂ levels started to raise, altering the world's overall environment and creating new environments where such new life forms could live long and prosper.

 

[Phil Core]

A very good book that all should read about the Origins of Life is - "In Search of Cell History - The Evolution of Life's Building Blocks" - Franklin M. Harold. It will give all who have not read it something to dwell on.

The classic Origin book is - "Life : Its Nature, Origin, and Development." - A. I. Oparin

Both are highly recommended.

 

[Drakkith]

Part one of an excellent presentation on the possible origin of life on Earth:

 

[BillTre]

For a book that presents a overview of the alkaline hydrothermal vent scenario of the origin of life, I would suggest Nick Lane's "The Vital Question: Energy, Evolution, and the Origins of Complex Life" (2015). He presents ideas concerning the alkaline hydrothermal vents clearly. This book is now about 5 years old and therefore not really upto date with recent findings. They would have to be found in papers. It also covers several related issues including mitochondria and their advantages in eukaryotes.

I am now reading David Deamer's book "Assembling Life: How Can Life Begin on Earth and Other Habitable Planets" (2019). This book presents the main competitor to the alkaline hydrothermal vent scenario, the terrestrial hydrothermal field scenario. The terrestrial hydrothermal field scenario shares many aspects with the alkaline hydrothermal vent scenario, but proposes the main activity occurred in hydrothermal fields on volcanos that projected above the surface of the oceans (no continents at that time) where mineral rich waters accumulated in pools which would periodically dry up. This is thought to have concentrated chemicals and driven polymerization reactions.

Each approach claims a different set of observations and experimental findings to support their ideas.