60 years of silence - so far

[bilby]

Sounds like a which came first the chicken or he egg problem.

No. It’s not really that. It‘s an issue of coevolution. Prior to eyes, organisms still needed to eat. They may have filter fed, like corals do. They may have simply gotten lucky, but then developed the ability to detect light and dark. That helped catch things better, but prey would do better with that too. Suddenly it’s an evolutionary arms race to see better. Hard shells then develop to protect. And suddenly, these shells fossilize a lot better. Hence the Cambrian “explosion.”

The development of hard shells also depended on oceanic pH. In an acidic ocean, a calcium carbonate shell simply dissolves as fast as the animal can excrete it.

It doesn't matter how much protection you need from predators, if you're prevented by chemistry from building a shell, you won't evolve one.

Ok. But what do we know about the acidity of the Ediacaran oceans?

It's not something I know a huge amount about, but simple chemistry and physics says that the ocean cannot sustain calcium carbonate shells if atmospheric carbon dioxide levels are too high - and it seems that was the case for much of the Edicarian, with high carbon dioxide levels in the atmosphere being a prerequisite for the oxygenation events in that era (basically all of the oxygen starts out as carbon dioxide, with the carbon being sequestered by photosynthesis and then buried by sedimentation).

There's a big lag between increasing carbon dioxide in the atmosphere and falling pH in the oceans, but we are taking about eras of hundreds of millions of years duration, so that isn't really significant.

As a very crude rule of thumb I would expect a strong correlation between atmospheric oxygen levels and oceanic pH, so in low oxygen eras, I wouldn't expect to find much or even any tendency for calcium carbonate seashells to arise, simply as a consequence of low pH in the oceans.

 

[Bomb#20]

So in a couple billion years, our planet will be much like Venus.

Except we can’t predict our orbit that far out, right?

what would happen if a star would come swinging by our solar system enough to cause us to be thrown out of whack such that we would find ourselves in an orbit near the Kuiper belt? Could we technologically develop an underground civilization such that we could survive? We’d have 10,000 years warning.

Doubtful. A star passing through our solar system couldn't actually disrupt our orbit very much unless it came so close to the earth it would burn us to a crisp. Also, any interaction that kicked us out to the Kuiper belt would by definition put us in an orbit that takes us from where we are to the Kuiper belt -- i.e., a highly elliptical orbit that would also bring us back here periodically. Circularizing an orbit takes millions of small random perturbations over millions of years, not one giant pull. If we want Earth not to turn into Venus, we'll need to do it ourselves.

 

[lpetrich]

...
So in a couple billion years, our planet will be much like Venus.

Except we can’t predict our orbit that far out, right?

We have some indirect evidence that the orbits of the planets have been very stable for a long time:  Cyclostratigraphy and  Milankovitch cycles

The other planets make the Earth's orbit precess, and that precession combines with the Earth's spin precession to change how much sunlight each part of the Earth receives over each year. There are three kinds of cycle:

• Precession of the perihelion direction relative to the seasons - 19 kyr, 23 kyr - "pure" spin precession has a period of 26 kyr
• Obliquity (axial tilt) because of Earth-orbit precession - 41 kyr, 1.2 Myr
• Eccentricity (controls the strength of precession effects) - 100 kyr, 405 kyr, 2.4 Myr

This is well-verified for the comings and goings of the continental glaciers over the last 2.5 million years, and this has been used to extend dating over the Cenozoic Era. The precession and/or obliquity cycles go into the mid-Cenozoic, and the 405-kyr eccentricity cycle to the beginning, the K-Pg mass extinction, at 66 million years ago.

There is an abundance of evidence of astronomical cycles before that mass extinction, but it has been harder to piece that evidence into a continuous record. But there is evidence of such cycles over the entire Phanerozoic Eon and just before, in the Ediacaran Period, over 600 million years ago. Before that, evidence is more scanty, but there is some evidence at 1.4 billion and even 2.45 billion years ago.

Proterozoic Milankovitch cycles and the history of the solar system | PNAS and Bayesian estimation of past astronomical frequencies, lunar distance, and length of day from sediment cycles

Milankovitch cycles in banded iron formations constrain the Earth–Moon system 2.46 billion years ago | PNAS and Climate control on banded iron formations linked to orbital eccentricity - PMC

If the planets moved around by sizable fractions of their orbit sizes, their resulting orbit-precession frequences would change a lot. This observed period stability means that the Solar System has had planetary-orbit stability for at least half of its existence, and one may plausibly extrapolate that stability into the future.

what would happen if a star would come swinging by our solar system enough to cause us to be thrown out of whack such that we would find ourselves in an orbit near the Kuiper belt? Could we technologically develop an underground civilization such that we could survive? We’d have 10,000 years warning.

That's a very improbable event. I estimate that it is likely to happen in around 10¹⁵ years.

 

[Loren Pechtel]

So in a couple billion years, our planet will be much like Venus.

Except we can’t predict our orbit that far out, right?

what would happen if a star would come swinging by our solar system enough to cause us to be thrown out of whack such that we would find ourselves in an orbit near the Kuiper belt? Could we technologically develop an underground civilization such that we could survive? We’d have 10,000 years warning.

Doubtful. A star passing through our solar system couldn't actually disrupt our orbit very much unless it came so close to the earth it would burn us to a crisp. Also, any interaction that kicked us out to the Kuiper belt would by definition put us in an orbit that takes us from where we are to the Kuiper belt -- i.e., a highly elliptical orbit that would also bring us back here periodically. Circularizing an orbit takes millions of small random perturbations over millions of years, not one giant pull. If we want Earth not to turn into Venus, we'll need to do it ourselves.

This. A while back I did some simulations trying to answer a Stack Overflow question--throwing a black hole through the solar system and seeing what happened. Anything farther out that it was generally stripped, the planet inward might be stripped depending on where in it's orbit it was, the planets farther in were never stripped. I did get one (using a larger black hole) that I do not believe would be inhabitable and one more where Jupiter was put on an orbit that would almost certainly doom Earth in the long run.

Anything that would have substantially altered Earth's orbit would have cooked us had it been a star. (Although I didn't try throwing something through the inner solar system. I would think anything that came through the inner system would cook us.)

 

[SLD]

So in a couple billion years, our planet will be much like Venus.

Except we can’t predict our orbit that far out, right?

what would happen if a star would come swinging by our solar system enough to cause us to be thrown out of whack such that we would find ourselves in an orbit near the Kuiper belt? Could we technologically develop an underground civilization such that we could survive? We’d have 10,000 years warning.

Doubtful. A star passing through our solar system couldn't actually disrupt our orbit very much unless it came so close to the earth it would burn us to a crisp. Also, any interaction that kicked us out to the Kuiper belt would by definition put us in an orbit that takes us from where we are to the Kuiper belt -- i.e., a highly elliptical orbit that would also bring us back here periodically. Circularizing an orbit takes millions of small random perturbations over millions of years, not one giant pull. If we want Earth not to turn into Venus, we'll need to do it ourselves.

This. A while back I did some simulations trying to answer a Stack Overflow question--throwing a black hole through the solar system and seeing what happened. Anything farther out that it was generally stripped, the planet inward might be stripped depending on where in it's orbit it was, the planets farther in were never stripped. I did get one (using a larger black hole) that I do not believe would be inhabitable and one more where Jupiter was put on an orbit that would almost certainly doom Earth in the long run.

Anything that would have substantially altered Earth's orbit would have cooked us had it been a star. (Although I didn't try throwing something through the inner solar system. I would think anything that came through the inner system would cook us.)

I realize that. My question is a technological one. Could we build an underground civilization that could survive the loss of the sun? However that could happen and Given that we would have 10,000 years to do it?

The long term survival of civilization is the key to whether we will ever find extraterrestrial civilization.

Maybe the ultimate interstellar spaceship is the earth.

 

[Bomb#20]

I realize that. My question is a technological one. Could we build an underground civilization that could survive the loss of the sun? However that could happen and Given that we would have 10,000 years to do it?

 

[bilby]

Could we build an underground civilization that could survive the loss of the sun? However that could happen and Given that we would have 10,000 years to do it?

Have you read Liu Cixin's short story The Wandering Earth?

 

[SLD]

Could we build an underground civilization that could survive the loss of the sun? However that could happen and Given that we would have 10,000 years to do it?

Have you read Liu Cixin's short story The Wandering Earth?

No. Will look it up.

 

[steve_bank]

So in a couple billion years, our planet will be much like Venus.

Except we can’t predict our orbit that far out, right?

what would happen if a star would come swinging by our solar system enough to cause us to be thrown out of whack such that we would find ourselves in an orbit near the Kuiper belt? Could we technologically develop an underground civilization such that we could survive? We’d have 10,000 years warning.

Doubtful. A star passing through our solar system couldn't actually disrupt our orbit very much unless it came so close to the earth it would burn us to a crisp. Also, any interaction that kicked us out to the Kuiper belt would by definition put us in an orbit that takes us from where we are to the Kuiper belt -- i.e., a highly elliptical orbit that would also bring us back here periodically. Circularizing an orbit takes millions of small random perturbations over millions of years, not one giant pull. If we want Earth not to turn into Venus, we'll need to do it ourselves.

This. A while back I did some simulations trying to answer a Stack Overflow question--throwing a black hole through the solar system and seeing what happened. Anything farther out that it was generally stripped, the planet inward might be stripped depending on where in it's orbit it was, the planets farther in were never stripped. I did get one (using a larger black hole) that I do not believe would be inhabitable and one more where Jupiter was put on an orbit that would almost certainly doom Earth in the long run.

Anything that would have substantially altered Earth's orbit would have cooked us had it been a star. (Although I didn't try throwing something through the inner solar system. I would think anything that came through the inner system would cook us.)

I realize that. My question is a technological one. Could we build an underground civilization that could survive the loss of the sun? However that could happen and Given that we would have 10,000 years to do it?

The long term survival of civilization is the key to whether we will ever find extraterrestrial civilization.

Maybe the ultimate interstellar spaceship is the earth.

I'd say maybe. It always comes down to energy and the size of the population. If there is a water supply O2 can be produced.

If the surface is uninhabitable everything has to be manufactured underground. Electronics needs to be replaced and making solid state devices require poisonous gasses and materials.

IMO as on Mars a major problem would be social. Population control and civil order.

There is the goofy old British series Space 1999 where the moon is knocked out of orbit and heads into space with a coolny. Cities in Flight by Blish.

 

[Loren Pechtel]

I realize that. My question is a technological one. Could we build an underground civilization that could survive the loss of the sun? However that could happen and Given that we would have 10,000 years to do it?

The long term survival of civilization is the key to whether we will ever find extraterrestrial civilization.

Maybe the ultimate interstellar spaceship is the earth.

Given enough prep time, certainly. Dig in to the right depth, your power source is a heat engine between the heat of the depths vs the extreme cold of the surface.

 

[SLD]

I realize that. My question is a technological one. Could we build an underground civilization that could survive the loss of the sun? However that could happen and Given that we would have 10,000 years to do it?

The long term survival of civilization is the key to whether we will ever find extraterrestrial civilization.

Maybe the ultimate interstellar spaceship is the earth.

Given enough prep time, certainly. Dig in to the right depth, your power source is a heat engine between the heat of the depths vs the extreme cold of the surface.

You could have elevators to the surface to see the stars and where you’re going.

 

[lpetrich]

Drake-equation parameters:

• R(star) - reasonably well-known when the equation was proposed in 1961
• f(planets) - likely close to 1
• n(Earth) - though numerous exoplanets are now known, and some are almost Earthlike in some ways, no almost exactly Earthlike one is known, likely from the difficulty of discovering such a planet
• f(life), f(intelligence), f(communicative) - one known example each
• L: lifetime - only a lower limit of possible values

As I'd posted earlier, there are two routes to researching the origin of life, prebiotic synthesis and extrapolating early evolution backward.

About the first one, I look at news reports of prebiotic synthesis of RNA, and it's all assembly from building blocks: ribose, nucleobases, and phosphate ions. Of these, phosphate ions are leached out of minerals, and nucleobases can be made by prebiotic synthesis without much trouble, while ribose is *very* difficult to make prebiotically. One can do it with the Butlerov formose reaction, but it produces a whole lot of other sugars, like a lot of stereoisomers of ribose, sugars that differ from ribose only in mirror-image asymmetries of some or all of their asymmetric carbon atoms. A carbon atom is asymmetric if it has bonds to four different molecule parts. Furthermore, the formose reaction is easily poisoned by nitrogen compounds.

So I'll look at the second one, and it has gone remarkably far. We now have a family tree of every well-studied cellular organism, even if many of its details are not well-resolved. The oldest known branching, between domains of prokaryotes (Eu)bacteria and Archae(bacteri)a, was discovered in the mid-1970's, and no older one has been discovered in the half-century since then, despite the sequencing of genes and genomes of numerous organisms.

The remaining domain, Eukarya, of eukaryotic cells, was the result of a symbiosis of at least two different prokaryotes.

Viruses are replication-system parasites, and there are three theories of their origins. These are not mutually exclusive, and each possibility can have multiple instances.

• Some very early organism
• Some cellular organism that degenerated
• Some transposable element ("jumping gene") that goes from organism to organism

Viruses often have very small genomes, and they are sometimes very fast-evolving, and it is thus difficult to track down their origins.

In any case, they don't tell us much about the origin of life.

 

[lpetrich]

Some time between 4.5 and 3.5 billion years ago, a very early prokaryote multiplied by dividing, with one child becoming the ancestor of the domain Bacteria and the other child becoming the ancestor of the domain Archaea.

That organism was the Last Universal Common Ancestor, the LUCA.

What was it like?

• The physiology and habitat of the last universal common ancestor | Nature Microbiology - reprinted here
• Evolution: A four billion year old metabolism | Nature Microbiology
• Frontiers | Energy at Origins: Favorable Thermodynamics of Biosynthetic Reactions in the Last Universal Common Ancestor (LUCA)
• Protein Superfamily Evolution and the Last Universal Common Ancestor (LUCA) | Journal of Molecular Evolution
• Electron transport chains as a window into the earliest stages of evolution | PNAS

The LUCA was a full-scale cellular organism, much like present-day methanogens, though it likely made acetic acid, the vinegar acid, instead of methane. Like present-day methanogens, the LUCA was autotrophic, making all its biomolecules from simple precursors, as plants do. Also like present-day methanogens, it did not use oxygen, and it was likely poisoned by that gas.

It had a DNA genome, and also DNA replication, DNA-to-RNA transcription, and RNA-to-protein translation, though some of the details differ between Bacteria and Archaea.

DNA has only one function: carrying primary copies of genetic information. RNA carries only secondary copies, except in some kinds of viruses. In fact, RNA has a variety of functions, including being enzymes: ribozymes.

The LUCA had a variety of cofactors and prosthetic groups:

• Riboflavin (vitamin B2) - in flavins (with a bit of RNA)
• Niacin (nicotinic acid, nicotinamide) (vitamin B3) - in NAD(P) (with a bit of RNA)
• Pantothenic acid (vitamin B5) - in Coenzyme A (with a bit of RNA)
• Folic acid (vitamin B9)
• Porphyrins, corrins, etc. (vitamin B12, heme, part of chlorophyll)

Involved in energy metabolism was ATP, a RNA building block with extra phosphates - the energy resides in the bonds between the phosphates.

The RNA-to-protein translation process is rather complicated. The protein building blocks, amino acids, are attached to little bits of RNA, transfer RNA's. This combination is then paired with the strand of RNA with the sequence to be translated, the messenger RNA, and the amino acid joined to the chain of amino acids that is being assembled. These operations are done on a sort of workbench molecule called a ribosome. The main working parts of these are RNA molecules.

RNA also has various other functions, like gene regulation and messenger-RNA manipulation.

So we see lots of RNA, RNA, RNA, RNA, RNA, and only one function for DNA. So how is DNA related to RNA? Its building blocks are all made from RNA ones, and one conclude that DNA is a specialization of RNA.

Likewise, the main molecules in protein assembly are RNA molecules.

So from these lines of evidence, one concludes the existence of a "RNA world", where RNA served as information carrier and as enzyme.

The main criticism I've seen of the RNA world is the difficulty of making RNA prebiotically. I've seen proposals of predecessors of the ribose-phosphate backbone, like proteins (peptide nucleic acids) and polycyclic aromatic hydrocarbons (PAH nucleic acids).

So we are not quite at the origin of life.

 

[lpetrich]

I'll now consider energy metabolism, since organisms must be powered in some way.

How did LUCA make a living? Chemiosmosis in the origin of life — Nick Lane

A lot of discussions feature fermentation as an early sort of energy metabolism, but biochemist Nick Lane considers that conception flawed. Fermentation does not have a very good energy yield, it is rather complicated, and it arose more than once. Instead, he proposes  Chemiosmosis as an ancestral form of energy metabolism.

In it, a cell pumps protons (hydrogen ions) out of its interior across its membrane, and then allows those protons to return. As they do so, they power ATP-synthase complex, which adds phosphate ions to a RNA building block, building ATP:

Adenosine monophosphate (RNA building block) + Pi (inorganic phosphate) -> Ad diphosphate
Ad diphosphate + Pi -> Ad triphosphate (ATP)

AMP: A-P
ADP: A-P-P
ATP: A-P-P-P

The energy resides in these phosphate bonds, and it is tapped by various metabolic processes.

NL proposes that places like alkaline hydrothermal vents have proton gradients in them, and that these gradients were used by early organisms before they created their own gradients. That seems like a good path from the prebiotic world to early organisms.

It also means that the origin of life may be a common event on celestial bodies with suitable conditions.

 

[bilby]

It also means that the origin of life may be a common event on celestial bodies with suitable conditions.

...such as talking snakes, right?

 

[lpetrich]

So we go from an organism that exploited a proton gradient in its environment to one that created its own proton gradient by pumping protons out of its interior.

That is done with an  Electron transport chain - transferring electrons from materials with high reduction-oxidation (redox) potential to those with low redox potential, and extracting their energy by pumping protons across the cell membrane. This mechanism goes back to the LUCA, and likely earlier. Some components of it, with their bits of RNA, likely go all the way back to the RNA world.

Redox reactions are simple and prebiotic. A common one is rusting:
2 Fe -> 2 Fe+++ and 6 e- (oxidation)
3 O2 and 6 e- -> 3 O-- (reduction)
Combined:
2 Fe + 3 O2 -> 2 Fe2O3

Returning to electron-transfer energy metabolism, two common types in the present-day biosphere are:

• Heterotrophic: electron donor: biomolecules, electron acceptor: O2
• Phototrophic: electron donor: H2O, electron acceptor: CO2

Many prokaryotes use various other donors and/or acceptors:

• Donors: organic molecules, H2, CO, NH3, S, sulfide, Fe++, ...
• Acceptors: some organic molecules, CO2, NOx, SO4--, Fe+++, ...

 

[lpetrich]

 Biological carbon fixation and The Emergence and Early Evolution of Biological Carbon-Fixation | PLOS Computational Biology and Carbon fixation pathways across the bacterial and archaeal tree of life | PNAS Nexus | Oxford Academic -- several pathways, and some of them go back to the LUCA, supplying organic carbon to different biosynthesis pathways.

 Nitrogen fixation is another ability that goes back to the LUCA.

With those abilities and autotrophy, the LUCA was independent of the primordial soup, independent of prebiotic organic synthesis.

Which fits in with being a full-scale cellular organism much like some present-day ones, like methanogens.

 

[Jarhyn]

In structural engineer, the shear, moment, angular rotation, and deflection are all intimately related, with the later being equal to the integration of the prior related equation. Calculus is very very real and very very physical. While numerical systems can vary, can Calculus? Two people invented generally the same thing, somewhat independently on this planet. Can science exist with an alternative to calculus? What would it look like?

The trouble with alien signals is that we need to be intersecting the signal in a sense of space and time. A civilization from 50,000 years ago and 40,000 light years away, could have been broadcasting for 1000 years, up until the 1850s, and then stopped. One possible problem is intelligent races aren't communicating out there with others, because the limits on travel are quite real, and the inability of travel faster than light (for anything), makes the entire thing pointless. Even when signals reach another, it isn't actually possible to respond due to the distance involved. Sure, we could reply, but if they are thousands of light years away, we are less responding and more just saying "hi" to even more random strangers if they are still there. The reality is that intelligent life could be all over the universe, but spaced apart at such distances that tens of thousands, hundreds of thousands, millions of light years separate us.

As quoted in the sci-fi classic film Spaceballs, "Lightspeed is too slow."

Well, if we look at the time frame in which our universe can support life chemically, our universe is vanishingly young.

As things go, we are at this weird point in spacetime where we are more likely to have very wide margins and a fairly long lead.

In the 4 billion years that chemical systems have been applying mathematically representative models to preserve said models, radio communication, as others point out, is only 100 years old. 100 out of 4 billion is nothing. Neither is a thousand or ten thousand.

There is a time for everything to be relatively new, and that time seems to be now.

IT would be nice to make a friend, and hopefully they will, actually be friends... But if we are to use a metaphor of a story, there's always the possibility WE are the ancient progenitor of intelligent life across the universe. We may look out on the universe, assuming we survive this time period, and discover it is very lonely and feel that loneliness for a very long time.

I'm really hoping for contact when Andromeda collides with us.

Sneakernet is a reliable mechanism especially for interstellar communications. I think the sorts orbital slingshot maneuvers that will get something out of a solar system or galaxy will probably be easier when there are things moving at odd angles with respect to each other.

 

[lpetrich]

One ability the LUCA didn't have was photosynthesis. That evolved twice on our planet, what I like to call retinal and chlorophyll photosynthesis, after their main pigments.

 Retinal photosynthesis first. Some prokaryotes, notably the halobacteria, use it in a protein -  Bacteriorhodopsin - as part of their photosynthesis. But it's very limited photosynthesis, because that molecule only pumps protons across the cell membrane out of the cell, thus supplying energy.

Though at present they are not very common, mainly living in very salty water, organisms that use retinal photosynthesis may have been common some 3 billion years ago, in the  Purple Earth hypothesis

 Chlorophyll photosynthesis is the best-known kind, much better-known than retinal photosynthesis.

It works by chlorophyll-protein antenna complexes capturing light and energizing electrons, much like a photovoltaic cell. These antenna complexes are parts of those organisms' electron-transport chains, rather evidently add-ons. There are two types of them, Photosystems I and II, with electrons energized first by II and then by I. The electrons' source is water molecules, split into protons, electrons, and oxygen molecules. Their destination is biosynthesis processes, including carbon fixation and sometimes nitrogen fixation. As electrons go from II to I, energy is extracted from them, and I can feed into the top of II to make electrons go in a loop to extract energy.

 Photosynthesis and  Anoxygenic photosynthesis and Early Evolution of Photosynthesis - PMC

Organism	Superphylum	PS I	PS II	C fixation
Cyanobacteria	Terra	X	X	Calvin
Purple bacteria	Hydro		X	Calvin
Green sulfur bacteria	Hydro	X		Reverse TCA
Green nonsulfur filamentous bacteria	Terra		X	3-hydroxypropionate
Heliobacteria	Terra	X		(none?)

Taxonomy:

• Terrabacteria
  • Cyanobacteria
  • Chloroflexota - Chloroflexia - Green nonsulfur filamentous bacteria
  • Firmicutes - Clostridia - Eubacteriales - Heliobacteria
• Hydrobacteria
  • Proteobacteria - Purple bacteria (scattered in alpha, beta subtaxa)
  • FCB Group - Chlorobiota - Green sulfur bacteria

So chlorophyll photosynthesis is very scattered across Bacteria. That suggests that photosynthesis was likely transmitted by lateral gene transfer, though it is difficult to go any further in untangling its evolution.

BTW, the chloroplasts / plastids of photosynthetic eukaryotes are descendants of cyanobacteria, photosynthetic apparatus and all.

 

[steve_bank]

Seriously, would we want to travel all across the galaxy hoping to find a planet populated with creatures like us?

If evolution is a constant with predator and prey then what would we expect to find?

Benevolent warm and fuzzy creatures? Supreme wisdom and kn wedge?

A flying saucer lands on the WH lawn. A hatch opens and ET pisses on the lawn, throws out trash, and flies off.