Comment by echelon
6 days ago
Imagine if life had evolved on Earth or Theia prior to impact. Imagine if it was intelligent and played witness to the giant cataclysm.
Given that intelligence took an awfully long time to emerge from LUCA, that seems implausible. But it's fun to imagine pre-Theia "Silurians". That sort of impact would have scorched earth of any trace or remnant of their existence. It feels as though there must be sufficiently advanced civilizations out there witnessing this exact scenario play out without the necessary technology to stop it. Though that fate would be horrifying.
Another thing to think about is that shortly after the Big Bang (if there was one, Lamda-CDM or similar models holding up), was that shortly after the Big Bang the temperature of the early universe was uniformly 0-100 degrees Celsius. It may have been possible for life to originated in this primordial interstellar medium without even so much as needing a host planet or star! Just life coalescing in space itself.
That early primordial soup, if it existed, could have seeded the whole universe. Most aliens might have matching molecules and chirality if those decisions predate our galaxy.
That early warm interval would have been a soup of 75% H, 25% He, and 0.0000000% or so Li, with nothing heavier.
Not much to start life with.
Also more importantly: it was uniformly warm. No gradients.
Life on earth doesn't work because we get energy from the sun. It works because we get low entropy energy from the sun and can radiate high entropy energy into cold space.
(There's approximately no net energy inflow.)
You are right about gradients, but while the energy from the Sun is what sustains most of the life today, it played no role in the appearance of life (because capturing solar energy requires exceedingly complex structures).
For the appearance of life it is necessary for the planet to have a much warmer interior than its surface (i.e. a radial gradient of temperature). In that case, volcanism and related phenomena bring to the surface chemical substances that have formed at higher temperatures and which are no longer in chemical equilibrium at the cooler planet surface, providing the chemical energy for the synthesis of the complex organic substances.
Some bacteria and archaea (belonging to the so-called acetogens and methanogens) still exploit the inner heat source of the Earth, living completely independently of the solar energy, in the same way like the first living beings. (However, in many popular science publications one can see frequently wrong claims about various organisms, including some animals, that they do not depend on solar energy, but those claims are false, because those living beings depend on using free oxygen for the oxidation of various substances, like hydrogen sulfide from oceanic vents, and the free oxygen comes from algae and plants that have used solar energy to separate it from water.)
1 reply →
No metals whatsoever. That's unfortunate.
Metal and hard rock are essential for life.
6 replies →
> It feels as though there must be sufficiently advanced civilizations out there witnessing this exact scenario play out without the necessary technology to stop it. Though that fate would be horrifying.
I suspect this is not actually that common. Giant impacts are more common in early solar systems; things eventually settle into nice circular orbits like we have now. Whereas intelligent life does seem to take a while to evolve, so probably more common later in a solar system's life cycle.
Uncommon for sure.
Our sun and earth won't last long enough, but Mercury's orbit is potentially unstable.
A red dwarf might harbor live bearing planets long enough to see its long-lived orbits eventually destabilize. Or perhaps witness the even rarer interstellar collision or destabilization from rogue planets, etc.
> Whereas intelligent life does seem to take a while to evolve
basing that theory on an anecdotal story of 1.
Depends how you count it. One planet, but a solid handful of mass extinctions with big adaptive radiations, most with several million years of development, and tons of reasonably intelligent social animals, only one of which produced industrial civilization. But yes, working with the best evidence we have...
While true, the opposite is true that we have zero evidence of any life whatsoever, anywhere, ever, except with us.
You got better evidence?
This animation makes it appear that proto-Earth was very comprehensibly torn apart, stunningly so
https://en.wikipedia.org/wiki/Theia_(hypothetical_planet)#Co...
I remember there being some modeling done to determine whether the Theia impact blew a chunk off Earth or basically re-liquified the planet. If I recall correctly, the resulting hypothesis was that the thermal load would have re-melted at least the crust (evidence for this was stacking of density in the moon, suggesting it formed out of a basically completely-liquified ball, which would have implied the crust was also liquified).
There is some interesting evidence suggesting the deeper layers remained intact, in the form of a region under the Pacific that might be the impact scar. It's an inexplicably-dense zone that causes hot-spots at its corners resulting in increased surface volcanism, like how the edges of a leaf burn before the middle in a fire.
... but on the surface? Yeah, no hiding place.
Would oceans have remained at all?
2 replies →
If life had appeared before the Earth-Theia collision, it could have been terminated by any of the earlier impacts.
The Earth-Theia collision has been only the last of a great number of collisions.
The original Earth had been much smaller and it had grown by colliding with many similar bodies.
The reason why the last collision is likely to have been also the greatest is that both Earth and Theia had grown previously through many collisions.
This has been similar to the "Highlander" movies, where each victorious immortal took the force of the decapitated one, until only 2 remained for the final confrontation, which were stronger than any of the previous immortals, because these 2 had gathered the forces of all the others.
In the same way the planets close to Earth have grown after each collision, at the expense of the smaller impactor, so the impacts have been between bigger and bigger planets, until the final collision between Earth and Theia, which both were bigger than the participants to earlier impacts from their history.
Before this final impact, the time intervals between 2 successive big impacts might have been too short for life to appear.
The pre-Theia "Silurians" as you call them, depending on technological level could have left traces in the solar system like our Parker Solar Probe or something in the Lagrange points.
Then again, how well do we know of stuff in these spaces today? It seems to me we barely have a clue of the space junk we ourselves sent up orbiting in our backyard.
Temperature on its own wouldn't be enough for life would it? Isn't everything moving around way too fast after the Big bang and therefore too far apart for whatever life there would be to find food (or whatever equivalent source of energy)
Temperature isn’t even close to being enough. If we didn’t have a moon, despite everything else being so good for life, we may have been stuck at the bacterial phase if we didn’t have tides, or life may have never formed at all due to minerals not being recycled, tide pools not concentrating amino acids, and constant wet-dry phases driving evolutionary pushes.
Edit: beyond that, there’s the need for a stable orbit, a stable axial tilt, a stable star (few mega flares), some kind of galactic shield a la Jupiter, and more.
"Need" may be overstating it. Those things certainly all seem to have helped, though.
1 reply →
We certainly cannot know if a previous intelligent civilization was present on earth before the impact.
And is not even that the impact erased their trace from earth, is that if they got extinct long enough (more than 100 million years ago), with today's technology, we cannot infer their presence, given the fossil (and other types of) record.
A great write up about this is: https://archive.is/https://pacificklaus.com/the-silurian-hyp...
Gurdjieff takes a different view on the cause and formation of the moon, which in some sense lines up with this - https://www.gurdjieff.org/beelzebub9.htm
He makes no claim to what life was before the formation of the moon, but rather than the cataclysm of formation of the moon is what changed life on Earth - of course he wraps the whole idea up in his mysticism - but his 1950s writing on this was not far off what happened.
Damn I'd like to know in a -lot- more detail what other cultures GG might have bumped into in his travels. Meetings falls way short there. Else: what an imagination.
That second idea (cosmic primordial soup causing universal similarity / compatibility of life) could be a great component of a sci-fi story.
The early universe was actually billions of degrees immediately post-Big Bang and remained far too hot for liquid water for hundreds of thousands of years, only reaching "habitable" temperatures long after matter had already begun forming into structures.
> Imagine if life had evolved on Earth or Theia prior to impact.
There's good reason why this first era of Earth's history is called the "Hadean eon" - as in the fires of hell.
> Throughout part of the eon, impacts from extraterrestrial bodies released enormous amounts of heat that likely prevented much of the rock from solidifying at the surface. As such, the name of the interval is a reference to Hades, a Greek translation of the Hebrew word for hell.
https://en.wikipedia.org/wiki/Hadean
https://www.britannica.com/science/Hadean-Eon
>Imagine if it was intelligent and played witness to the giant cataclysm.
They'd have had to be watching from one very high orbit, and even then I wouldn't bet favorably on their chances considering the sheer gargantuan volume of debris Theia tossed into the space above earth.
Anywhere terrestrial and they'd be dead far too quickly to watch much of anything. I've seen some fairly detailed models on the presumed effects of this collision and it would have rapidly super-heated the whole Earth's atmosphere while vaporizing or melting the crust of the entire world down to a depth of at least several hundred meters. Good luck finding a bunker that can handle that.