I have had a related thought about uranium, though. The fissile isotope that's useful for power generation and bombs, uranium 235, is only about 0.7% of uranium that's found on Earth. When uranium is formed in a supernova, there's actually more uranium 235 produced than uranium 238; this freshly produced uranium is about 62% U-235 [1]. The reason that U-235 is so rare on Earth is that U-235 decays faster than U-238 and our uranium is billions of years old. But if it's possible for a technological civilization to develop on a planet with much fresher uranium content, natural uranium there could contain a double-digit percentage of U-235. Under those conditions it would be easy to accidentally discover nuclear fission and naturally occurring reactors like Oklo [2] would be common.
[1] https://world-nuclear.org/information-library/nuclear-fuel-c...
[2] https://www.iaea.org/newscenter/news/meet-oklo-the-earths-tw...
Does the article really mean that? " r-process can produce atoms with an atomic mass of at LEAST 260 before they fission."
https://en.wikipedia.org/wiki/Island_of_stability
and
https://www.researchgate.net/publication/279166139_Charge_sp...
Moreover, the nuclides with atomic mass close to 260, i.e. isotopes of einsteinium and fermium, would be produced in relatively small quantities in comparison with lighter elements.
Exceeding 260 is highly improbable because such nuclei fission spontaneously extremely quickly, in milliseconds or microseconds, so the neutron flux would need to be much more intense than in nuclear explosions in order to produce a non-negligible equilibrium concentration.
Most elements that are heavier than plutonium would decay before the materials containing them could aggregate into a planet (which may take at least a few million years). When the planets of the Solar System have formed, they probably still contained significant quantities of plutonium and neptunium, but then they have decayed quickly, leaving uranium as the heaviest surviving primordial element.
While there might exist an island of stability for super-heavy nuclei of elements beyond any of those that have been synthesized artificially by ion collisions, for now there is no known natural process that could produce them in measurable quantities. By "stability" it is meant that the super-heavy elements might have lifetimes measured in years instead of milliseconds, not that they could be as stable as the already not very stable uranium or plutonium.
I find it interesting that the .003% difference in U-235 was a large enough deviation to attract attention to Oklo. Thanks for the link
Look what effort we went into the last two decades trying to stop Iran from developing their uranium enrichment infrastructure.
Then back in WW2 we did a complete covert op to sabotage the heavy water (used in enrichment) generators in the mountains of Norway just to stop the Germans or Stalin from getting access to weapons grade material.
Hell, they only even had some tons set aside by accident to enrich in the first place.
Anyways, finding already fissled uranium material probably set off many alarm bells at the Pentagon and the Atomic Energy Commission in 1972.
Isn't it the case it is currently not possible to create any neutron heavy isotopes and that causes the half-lives to be on the low end?
All of these isotopes are neutron-heavy. Lawrencium 261 has 103 protons and 158 neutrons, for example.
In fact, the only stable isotopes with fewer neutrons than protons are helium 3 and ordinary hydrogen (protium).
It isn't crazy to postulate, as a layman, that if we synthesized Lr-276, say, it might have a longer half-life.
(Not that we expect that pattern to continue indefinitely, but still, have we discovered the most stable isotope of lawrencium yet?)
Outside of carbon chemistry your ability to create replicable life plummets. Biologists may speculate if non carbon life is possible, but there's no doubt it would be limited. Arsenic or silicon just don't have the chemical complexity carbon does.
As for super heavy elements - the elements alien races would have access to wouldn't be that different from ours. Heavy nuclei are terribly radioactive and thus short lived. The article points our elements heavier than 260 are too short lived, but on astronomical (and biological) scales anything past 238 (ie Uranium) is short lived.
Past Uranium (which we have on Earth naturally), only Pu-244 is relatively long lived. Its half life is 81 million years vs. U-238 at 2 billion years. 81 million sounds like a long time, but the alien race has to evolve intelligence. We've been evolving for about 4 billion years, or 40 halvings of Pu-244 initial (anyway low) concentration. 2^-40 is a small number. By comparison U-238 has halved only twice on Earth since evolution started.
To illustrate, if the entire Sun were made of Pu-244 and the entirety of the remaining Pu-244 were put on Earth after 4 billion years, the concentration would be less than 1 part per million per mass.
1: https://en.wikipedia.org/wiki/Island_of_stability#Possible_n...
1. the kinetic barrier is impossibly large that even novas cant cross it, or
2. the "stable" elements are not very long lived in astronomical time scales.
Probably both are true, either way, it's a wash - no super heavy elements for alien races to play with.
Best argument for carbon I've seen so far is that despite carbon being just 0.02% of all elements on earth it became preferred engine of life. Although I can't rule out that under different temperature, pressures and radiation some other element might be preferred if it's reasonably abundant somewhere. In my opinion if there's mostly stable, reasonable energy gradient somewhere life will find a way if possible.
Although carbon is relatively scarce on Earth, it is the fourth most common element by mass in the universe (and in Earth's solar system) [1].
The four most common elements in the human body are the same as the four most common elements in the universe, albeit in different proportions [2].
[1] https://en.wikipedia.org/wiki/Abundance_of_the_elements#Univ...
[2] https://en.wikipedia.org/wiki/Abundance_of_the_elements#Huma...
The authors of the paper suggest that the material that formed the Earth was depleted of carbon early in the solar system's history due to solar activity, and that most of the carbon now on Earth was delivered to the planet later on directly from the interstellar medium.
I should note a couple of clarifications to my first comment: the elemental abundance I mentioned for the universe and Earth's solar system does not include helium and neon, which are abundant, but are usually ignored in this context as they're noble gases.
There is also estimated to be slightly more mass in the present-day universe in the form of iron than nitrogen due to the high mass of iron atoms (nitrogen is the fourth most abundant element by mass in the human body, but the body contains relatively little iron). The number of nitrogen atoms in the universe, however, is substantially higher than the number of iron atoms. The amount of iron in the early universe should also have been lower; the element is formed late in the stellar life cycle [3], whereas the other cosmologically abundant elements that are relevant to biology (carbon, nitrogen and oxygen) are formed earlier [4].
[1] https://arxiv.org/abs/2104.02702
[2] https://phys.org/news/2021-04-stardust-pale-blue-dot-carbon....
Once you study the various elements and realize that carbons' chemistry is uniquely rich with a set of capabilities other elements lack non carbon replication becomes meh.
Silicon comes close, but the energies suck, elemental Si is too stable, and its oxide a solid.
At room temperature and pressure of rooms built by beings made of carbon.
SiO2 is quartz. At a T high enough to melt it (never mind a vaporize it to have a cycle analogous to the C-CO2 cycle), Si chemistry breaks down.
Carbon chemistry is unique because it occupies a unique chemical niche. It makes interesting and stable compounds at T high enough to have appreciable rates, but low enough that things don't just rip themselves apart.
Not to mention at T high enough to vaporize SiO2 you won't have water, which is a pretty nifty solvent for life to have.
Think of it this way. We know the bond strength of the various chemical bondings. We cant get around that and each type of bonding is responsible for several unique and fundamental moiety in biological replication.
Yeah, not even iron could work as a solvent at that temperature.
Since, as stated, non-carbon chemistry is limited, non-carbon life (very broadly defined as replication of information) is either impossible or incredibly boring.
If there were stable transuranic nucleii, we'd need to work very hard to explain why we can't find any in the universe.
But how do you develop the technology for an escape velocity civilization in a medium so corrosive and viscous?
Super Earths are a likely source of water worlds, since the same percentage of water volume (~ to radius^3) results in much deeper oceans at the surface (~ to radius^2). The greater gravity would create even more hurdles. How do you hit escape velocity if your fuel to orbit is to heavy to lift itself? First orbital vehicle might have to be nuclear.
Problem 1: Develop a civilization with a sustained technology runway in a medium that corrodes, relentlessly saps temperature gradients, creates immense pressure at its solid floor, etc.
Problem 2: Create floating platforms and colonize their ocean surface.
Problem 3: Develop atmospheric flight, from their bobbing surface colonies, with heavy water filled planes.
Problem 4: Develop orbital flight with water filled space craft.
Problem 5: Develop sustainable water filled living environments off planet, as first step to going beyond.
And do this before their star or other cause finishes them off!