The eight ways that all the elements in the Universe are made (2021) | Hacker News Reader

The eight ways that all the elements in the Universe are made (2021)

bigthink.com

58 pointszdw40 comments

The thing that is unintuitive to me is the timeline and scale. The age of universe is 13.8B years and age of Earth is 4.5B years. And yet Earth has many of these elements in abundance which are produced by complex chains and in trace quantities. Like the elements need first to be produced in stars, then ejected out, then accumulated into protoplanetary dust, then aggregated into planets. It feels wild to me that the process took only twice as long as what Earth has existed.

This is another thing that feeds into the Fermi paradox. Previous generations of stars and planets might be too low metallicity to give rise to very complex intelligent life. We might be part of the first crop to evolve as the metallicity of the cosmos reaches a threshold.

Life on Earth is mostly C, H, O, and N, but it makes use of many heavier elements to conduct complex chemical synthesis processes. Some are only used in trace amounts but are still necessary. Then there’s technology which could not have developed to this level without most of the periodic table. Low metallicity is likely to put a ceiling on what can evolve.

You’re not getting spacefaring aliens until you have the building blocks. Then it takes billions of years, and on top of that stable nurseries like Earth are probably rare.

So TL;DR my guess is that we are early and rare.

In a few billion years the galaxy might resemble Star Wars with aliens all over the place, albeit without FTL unless we are very wrong about core physics or there’s some huge aspect of reality we haven’t found yet.

I don’t buy this hypothesis, because we’ve had complex life on land for 250 million years. Evolution is not a steady upwards path (especially when you take into account mass extinctions). There’s no reason an intelligent species couldn’t have evolved on Earth any time in the mesozoic. Just a single million year head start would be huge for a civilization.

Seems highly unlikely that the resolution to the Fermi paradox is just that we’re the first intelligent species in the galaxy.

I agree. My own suspicion for the resolution of the fermi paradox is that there are 4 steps that we have seen occur only once (or zero times) so it is difficult to measure their probability. If some of those probabilities are significantly lower than we think it could resolve the "paradox".

Those 4 steps are: (1) Formation of life (2) Formation of multicellular life (3) Formation of "runaway intelligence", where a species evolves enough intelligence to manipulate their environment in ways that supercede evolution. Parrots and dolphins, for instance, are both quite smart, but don't look close to getting a runaway benefit from that which would allow them to invent technology like agriculture and overpower all other species. (4) Technical civilization manages to manipulate their planet or spread beyond one star system in a way that would be detectable from elsewhere in the galaxy. (Hasn't happened yet.)

I don’t think these hypotheses are mutually exclusive. Low metallicity in the past might explain how we could be first even though the galaxy is very old. The conditions did not exist until recently, on cosmic time scales. If the probabilities are also low then you’re not going to get many even when conditions are right.

Much like there is a water cycle on earth, we are discovering there are element transportation cycles in galaxies. Anton Petrov did an episode on this. https://www.youtube.com/watch?v=SjToE8XJaL4

The early star were huge and exploded extremely fast, like a few million years. It's likely they did this in rapid succession many times priming the universe with a lot of building blocks. The early universe was wildly energetic.

There is a sampling bias. Earth-like planets are too small to retain hydrogen and helium, so even if the proportion of heavier elements in the initial gas cloud were 10 times lower, the planets would still be rich in heavy elements.

I learned about all these methods (and many other things!) from PBS SpaceTime's YouTube channel.

You can buy a "Remember where you came from" periodic table here:

https://crowdmade.com/products/pbsspacetime-2030-poster

It's a mind boggling that overwhelming majority (more than 98%) of the visible universe's mass are only from the two most lightweight of chemical elements namely Hydrogen and Helium.

Blood is red due to iron content. Iron can only be produced by nuclear fusion in stars. We are all stardust.

I feel like iron in the blood gets a lot of airtime, but literally all the carbon in our bodies is star stuff too. As is the oxygen making up the water. And almost everything else.

The CNO cycle dominates fusion in stars much larger than our own.

The carbon transitions to nitrogen and oxygen repeatedly.

https://en.wikipedia.org/wiki/CNO_cycle

From your link:

> This result therefore paves the way towards a direct measurement of the solar metallicity using CNO neutrinos. Our findings quantify the relative contribution of CNO fusion in the Sun to be of the order of 1 per cent;

I find it amazing that we can analize the composition of the core of the Sun measuring the energy of the neutrinos.

(Photons are not useful, because they bounce a lot of times before escaping from the Sun, so they provide only information about the outher layers.)

The color of feces is also due (partly) to the iron content of blood. Stars are fecal particles that haven't been shat out yet.

> stardust

What form does stellar iron take once the star it was formed in fails? Is it a gas? Small solids? Individual atoms?

As I understand it, much comes out as nickel-56 that undergoes radioactive decay to iron-56 in short order.

It is also somewhat ionized.

A hot, expanding, fully ionized plasma. Over weeks to years it cools, recombines into ions/neutral atoms, forms molecules in some regions, and a fraction condenses into dust grains, often as iron-bearing compounds like FeS and as inclusions in silicates.

> Over weeks to years it cools

Neat. Good source for reading up more on this?

> a fraction condenses into dust grains

Does it deposit straight into grains from gas? Or is there a period when a bunch of liquid iron is sitting around radiating its tail off?

I don't think liquid can exist in space.

If I remember from undergrad thermodynamics, the vapor dome describes states where liquid can exist, and (gas) pressure must be present.

https://www.sciencefocus.com/space/strange-reason-space-wont...

> don't think liquid can exist in space

Ordinarily, no. Whether supernova remnants count as “space” might be an alternate phrasing of my question.

Even before it exploded it would have been less dense than water. It just goes from a hot cloud of gas to a cold one.

As I understand it, a white dwarf is "electron degenerate matter," which is more dense.

https://en.wikipedia.org/wiki/Degenerate_matter

Here you go bro: https://orca.cardiff.ac.uk/id/eprint/110293/1/10.1007%252Fs1...

:D Thank you!

> liquid iron is sitting around radiating its tail off

With the energy imparted by the cataclysmic devastation of a supernova I'd assume it's a plasma that cools and sublimates into a gas. These clouds of gas typically have magnetic fields that can bring particles close together where they form dust/grains.

> We are all stardust.

Is that meant to be good? I always chuckle when people make these kind of statements. Is the association to cosmic objects meant to make you feel better about something? I personally don't find stardust particularly interesting. The fundamental forces of nature on the other hand are much more appealing to me.

I believe it’s quite common for people to marvel at the vastness of the universe. For that reason, people might like the tangible link that they feel to the rest of the universe when they think of this - it’s amazing to think of how small we are in it, but also amazing to think of where “we” came from.

Further down in might just be geometry itself generating the rest.

https://www.researchgate.net/publication/391748575_Introduct...

https://www.researchgate.net/publication/394998720_Geometric...

This article's from 2021. Does anyone know if there are elements (no pun intended) of this classification of element origins that's impacted by those JWST observations of complex early galaxies?

White dwarf explosions result in zinc? Can someone ELI5 as to how they know this if a white dwarf has never actually been monitored closely? Or are these just theories? Pluto for example was found to have a haze with newer telescopes so what if the observarions from white dwarfs which are so far away based on assumptions - are not correct?

With as hot and dense as they are, wouldn’t black hole accretion disks and jets form stuff, too?

I think black hole accretion disks and jets are something like several orders of magnitude less dense than would be required for that.

The eightfold path, the primordial truth, praise be the ruinous powers!

Lithium is early in the periodic table (3) and low in abundance. Now that’s a story. There’s even the missing lithium problem.

I think the r process and the s process should be listed separately, rather than lumped together.

The s-, i-, and r-processes do however follow the same mechanism at the most fundamental level, even if it results in wildly different production paths. I think the author was simplifying for an audience unfamiliar with the details, for whom this distinction is less important.

(And I say that despite my own work and usual eagerness to tell people all about it!)

The claim that elements beyond 94 are only human-made is speculative and probably false. Transuranic elements up to ~100 are believed to be made in, for example, natural fission reactors and extreme stellar conditions. However, it is accurate to say that none of those exist in bulk. They’re more like astatine and francium: so rare that natural occurrence is on the scale of atoms.

For the benefit of the unfamiliar, there is only one natural fission reactor that has been found on earth.

https://www.iaea.org/newscenter/news/meet-oklo-the-earths-tw...

Also, the light from https://en.wikipedia.org/wiki/Przybylski%27s_Star apparently indicates the presence of elements well past 94. One amusing explanation being https://www.sciencedirect.com/science/article/abs/pii/001910... .

Natural fission reactors are pretty slow things, I wouldn't think they would be very good at forming transuranics.

But there's another source out there that we can't see: imagine what's happening in the electron-degenerate portion of a neutron star. The same process that creates the heavy stuff that gets tossed about from mergers is also going to create higher stuff that will decay before we ever see it.

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