Elements may have been forged on Earth, as well as in space | Hacker News Reader

Elements may have been forged on Earth, as well as in space

physicsworld.com

90 pointssohkamyung32 comments

> The resulting supernovae, however, yield high-speed neutrons that are captured by nuclei to create elements heavier than iron.

Current theoretical physics indicates that actually half of the elements heavier than iron are created not by supernovae but instead by binary neutron start collisions. These are R-Process elements. [1]

Thus, the article is incorrectly attributing elements heavier than iron to generally be from supernovae when most the elements by mass heavier than iron are from neutron stars ripping each other apart and causing a rapid decay of these hadrons into the stable heavy elements.

[1] https://en.wikipedia.org/wiki/R-process

What about fusion with hydrogen? Iron + hydrogen.

Not impossible, just very uncommon as it is not energetically favourable.

https://en.wikipedia.org/wiki/Nuclear_fusion#/media/File:Bin...

And a related PBS Space Time:

https://youtu.be/MmgMboWunkI

The theory was mentioned in passing towards the end of a video before LIGO's neutron merger observation:

https://youtu.be/6yLGeviU8FM

1. The article is about low atomic numbers 2. The r process creates the super heavy elements in greater importance as the atomic number increases. 3. Fusion confinement is hard to achieve even with small nuclei, so if true the earth fusion reactor would be extraordinary. I would be interested to see experiments and more data (as the article calls for)

TLDR: article is not principally about high atomic number elements and you might be splitting hairs over the areas it is not principally about. The article proposes new physics, which needs more evidence.

I’m still not fully able to understand how if these processes create elements one atom at a time, that kilograms of the same element can then clump together and settle between rocks.

I asked a geologist this, once, although specifically only about precious metals like gold and silver. He said the natural churn of everything moving around the Earth tends to concentrate similar things together over time. For example a river bend separates more dense silt on one side and less sense silt on the other. This, but also on a grand scale throughout the whole Earth.

It's a start, but I still have questions.

It's a stochastic merge sort over millennia. The sort objective is "by atomic weight".

~millenia~ billions of years

We are a failed Universe Developer interview assignment.

similar chemistry precipitates the same element in the same conditions.

Crystals tend to push out dissimilar atoms, certain chemicals are more soluble that others in water, bacteria may be responsible for certain types of gold particles found in nature. There's always another layer of processes at work that we don't know about yet, or so it seems.

Wouldn't substances with different molecular weights tend to separate out from each other simply due to gravity while still in liquid form?

In a solution or even a colloidal solution, no. That’s the basic definition of a solution anyways.

Solutions act like that at lab scales but it’s not true at every scale. For example you get differences in ocean salinity with depth.

No. What separates out are immiscible phases of different density. A heavy element in a light phase will go up (example: uranium, which is enriched by a factor of 1000 in the Earth's crust).

You can get density gradients in fluids under gravity, but it requires extreme conditions and no mixing (example: cesium chloride in an ultracentrifuge.)

Interesting, thanks!

Processes involving water often collect similar chemicals from a wide area and drop them in one spot. Also (and this was a big one for my understanding) fractional crystallization can help organize things: https://en.wikipedia.org/wiki/Fractional_crystallization_(ge... I'm not sure how chunks of solid metallic elements form, but from what I remember it's probably water-based geochemistry. Don't forget, though, that "kilograms of the same element" is pretty rare, and the Earth's crust is almost entirely silicates and a smattering of other molecules, with pure elements being hardly a rounding error.

Ed: here's a lecture from a geologist about the geology behind a particular gold mine. I saw it a while back and don't remember the details, but I'm posting now before noprocrast kicks me out: https://youtu.be/QsBZfRJihdw

Thanks, will binge through this!

Cool, yeah, Zentner has a lot of cool content. He has his own channel too, if the CWU lectures aren't enough.

I've wondered this myself, and haven't found much by way of clear answers in the literature. In part I suspect this is because a fair bit of the transmutation process has only been worked out relatively recently.

I have a few hunches though. Mind this is all conjecture.

Different elements form at different stages of stellar evolution. For the lighter elements (helium, carbon, neon, oxygen, silicon, iron), these are thought to actually form in distinct shells within the star. Note that only iron and silicon are solids at most temperatures we'd encounter.

https://en.wikipedia.org/wiki/File:Evolved_star_fusion_shell...

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

Iron in particular forms in high abundance as the final fusion product. I don't have a good sense of what happens with it, but I suspect there's a distinct iron-emission that occurs from a sufficiently large nova or supernova.

Once in open space, you've got a rapidly-cooling plasma that eventually cools to gaseous and liquid phases of these materials. To an extent there's probably some effective distillation going on, where lighter (and more volatile) elements boil out of the cooling iron, possibly reacting with it (in the case of oxygen). Given that we're talking a star-sized mass, even if only some of the ejecta consolidates, those will tend to form large clumps. Eventually, some of these start interacting under their local gravitational potential.

For heavier elements, I'm assuming that there is similarly preferential formation based on conditions such that given a certain set of temperatures and pressures, lead or gold or copper or other elements are more likely to be formed. (Lead is also a daughter product of many fissionalbe elements.) Again, there may be some clustering of such elements.

And where large quantities conglomerate --- dwarf-planet through planetary masses --- then you'll see density stratification within a molten or semi-molten mass (the heat coming from both residual temperature and residual thermal energy of gravitational potential, probably also heavy elements fissioning at object cores). This again gives at least a rough stratification. So you get planetoids / protoplanets with material segregating by mass. If those survive long enough, convention starts occurring, which probably mixes up materials to an extent. And if there are enough such bodies, they collide such that what was an interior iron-nickle-rich core is now floating through space on its own as what we'd call a meteor or asteroid.

I'm not sure which of these segregation/aggregation mechansims dominates. Thinking it through, I suspect that the principle result of the initial explosion is mostly dust and smaller-particle dispersion, and that more effective seggregation occurs as more substantial bodies form, and more robust differentiation processes can emerge.

I commented on a similar question a few months ago here: https://news.ycombinator.com/item?id=27924151

I'd turned up one of the few substantive articles I could find on the question at the time, which largely discusses chondritic meteorites:

"Dating the Earliest Solids in our Solar System"

http://www.psrd.hawaii.edu/Sept02/isotopicAges.html

> For the lighter elements (helium, carbon, neon, oxygen, silicon, iron), these are thought to actually form in distinct shells within the star. Note that only iron and silicon are solids at most temperatures we'd encounter.

Not carbon? (I’m not sure if I’m missing something that could be incredibly enlightening or if you made a simple editing mistake.)

Doh!

Yes, of course, carbon would also be a solid.

Note also that common simple compounds such as methane (CH4), water (H20), and carbon dioxide (CO2) are also likely created in abundance.

Weathering of silicates and iron seems to have occurred on Earth mostly due to atmospheric action, rather than in deep space, as I understand.

Google «test for clay in soil» and then perform the same experiment in your garden. You will see with your own eyes how easy it is for molted elements to separate into layers.

Like natural nuclear reactions producing things like

142 Nd & 99 Ru

https://en.m.wikipedia.org/wiki/Natural_nuclear_fission_reac...

Interesting but seemingly quite speculative, evidence or experimental verification of this happening would seem to be a huge discovery.

Most of the more interesting physics stories seem to be near-fanciful these days.

For some solid physics news:

https://news.uchicago.edu/story/what-muon-g-2-results-mean-h...

I wouldn't exactly consider muons to be solid ;)

But yeah more like this would be better than sites like Physics World.

This article seems to suggest this idea is a little more than a thing a physicist thought up in the bath, and hasn't yet done the sums to verify that these reactions might even happen, let alone tested it experimentally.

The idea has been peer reviewed it seems and is worthy of further validation...as mentioned in the article.

Reply on news.ycombinator.com