The Heavier Elements: A Question About Their Abundance

[Newtons Apple]

Hi,
So I've been reading and watching things recently about the origin of the Elements in the universe... And maybe it's me just over thinking..but I just feel like my simple understanding isn't really adding up...So we have 118 elements, the last few are man made, so let's remove those from this question. My main question is this, after the big bang we have the first handful created... which was enough to fuel star birth later on..Those stars may have fused up to iron and then exploded to seed more of those elements into the universe.. But how is it possible that the 100+ remaining are so well spread out through the universe...? Let's take Gold for example...The only theory I see for it's creation was big neutron star collisions...that seems so implausible that all of the gold in the universe...we have tons right here on Earth alone... was created just on the off chance that two neutron stars which are EXTREMELY small just happened to collide? With the sheer scale of space...how many times could this have even occurred? And I mean this with all of the other elements. Are we saying that this mere coincidence is the cause for the rest of the entire table? I can see if this happened and the created elements were local to the area of a neutron star collision...but the thought is that these elements are all over the unvierse?

Let's say they're not and that only our solar system is privy to these elements.. That just seems so conveinent that the entire table (minus the man mades) are all on Earth... It's hard for me to believe. And back to the neutron star theory.. Getting to a neutron star is resereved for the bigger stars, it just seems that there would be so few and that they would be randomly spread out not right next to each other that would inevitably lead them to collide.

Are there any other theories for the creation and spread of the elements?

 

[jedishrfu]

Supernova explosions can also generate heavier elements, including gold. I'm sure there are papers on the subject, including the % of elements made.

However, like so many things, our understanding is limited, and our skills in probability estimations are very weak.

We know nuclear processes are involved, and we know that nuclear fusion is insufficient to create heavier elements beyond iron, so it leaves only two choices: neutron star collisions and supernova explosions. Planet-sized chunks of material high in heavier elements are likely spewed out into space and later captured into planetary systems.

Our Earth itself is the product of one of those processes, and so the abundance of gold would be higher on Earth based on that fact.

 

[Ibix]

There are links to previous discussion in the "Similar threads" at the bottom of the page. This one seems helpful.

In particular, one of the posts in that thread notes that there's a known dwarf galaxy that's got more of the very heavy elements than others, suggesting a single really large event in that galaxy.

It's also worth noting that neutron star collisions may well be more likely than you think. It isn't just a case of a pair of tiny stars randomly colliding. A binary pair of giant stars will eventually turn into a neutron star binary which will necessarily decay via gravitational radiation into a merger unless disrupted by something.

 

[Bandersnatch]

The only theory I see for it's creation was big neutron star collisions...that seems so implausible that all of the gold in the universe...we have tons right here on Earth alone... was created just on the off chance that two neutron stars which are EXTREMELY small just happened to collide? With the sheer scale of space...how many times could this have even occurred?

It's not only the scale of space that is large here. All the numbers involved are extreme - and unintuitive. The rates of occurrence, the time scales, the amounts produced, the fraction that is present on Earth. But they do add up in the end.
Think of it as multiplying a string of coefficients, some very small, some very large. The large ones can very well compensate for the small ones, to arrive at a reasonable number in the end.

Doing a back-of-an-envelope calculation can help in seeing this.
The current expected rate of binary neutron star merger events in our Galaxy is 30 per million years. It is extremely rare.
But, when taken over the ~ 9 billion years the Milky Way had to evolve in the time before the formation of the Solar System, you end up with something on the order of ~270 thousand events.
Each explosion is estimated to eject on the order of 1% of a solar mass of heavy elements into the interstellar medium. This is thousands of Earths worth of the stuff.
(The time for the ejecta to mix with the surrounding environment is counted in tens or hundreds of thousands of years - completely negligible given the numbers we're juggling here)
This translates to the approximate total of 2.7 thousand solar masses-worth of heavy elements produced and re-seeded into the galactic gas over the time period.
The estimated present-day abundance of heavy elements in the Milky Way is on the order of 3 thousand solar masses, which is in broad agreement with the slapdash number we've come up with.
So at the very least one could say it is entirely plausible for this rare process to supply all the required heavy metals.

People do analyse this in a more rigorous manner. The estimates for the rate of mergers, ejecta mass, and the abundance of elements I took from the following two papers:
Sgalleta et al. 2023: https://academic.oup.com/mnras/article/526/2/2210/7273849
Chen et al. 2024: https://arxiv.org/abs/2402.08214
The second one in particular calculates that binary neutron star mergers, or a combination of those with neutron star-white dwarf mergers, may be sufficient to account for nearly all the heavy element abundances - with the exception of the lower-mass heavy elements that would then be supplied by core-collapse supernovae.

 

[PeroK]

that seems so implausible that all of the gold in the universe...we have tons right here on Earth alone...

Perhaps a ton doesn't amount to very much on cosmic scales? In fact, there are estimated to be about 250,000 tonnes of gold on Earth. That's a whopping 250 million kilograms. A huge amount of gold.

Is that 1% of the Earth's mass? Probably not. The mass of the Earth is $6 \times 10^{24} \ kg$. That's $2.4 \times 10^{16}$ times the mass of the gold on Earth. That means that gold has a tiny, trace amount.

If you are studying cosmology, you have to think big!

 

[Newtons Apple]

Perhaps a ton doesn't amount to very much on cosmic scales? In fact, there are estimated to be about 250,000 tonnes of gold on Earth. That's a whopping 250 million kilograms. A huge amount of gold.

Is that 1% of the Earth's mass? Probably not. The mass of the Earth is $6 \times 10^{24} \ kg$. That's $2.4 \times 10^{16}$ times the mass of the gold on Earth. That means that gold has a tiny, trace amount.

If you are studying cosmology, you have to think big!

yea I see your point...but then is it just accepted that every element just happens to be present on Earth? Like we got literally all of them here in some form or fashion just seems like such a conincidence!

 

[PeroK]

yea I see your point...but then is it just accepted that every element just happens to be present on Earth? Like we got literally all of them here in some form or fashion just seems like such a conincidence!

That's what happens in a random distribution.

 

[Nugatory]

yea I see your point...but then is it just accepted that every element just happens to be present on Earth? Like we got literally all of them here in some form or fashion just seems like such a conincidence!

Turn it around: calculate the number of atoms of each heavy element that is implied by 3000 solar masses, make a reasonable estimate of the number of atoms per planet, then consider how many atoms per planet that is. It would be really surprising if every planet didn’t get at least a few.

 

[gmax137]

every element just happens to be present on Earth?

Except for technetium. The Te present wasn't here at earth's birth.

 

[Drakkith]

yea I see your point...but then is it just accepted that every element just happens to be present on Earth? Like we got literally all of them here in some form or fashion just seems like such a conincidence!

The violent events that create heavy elements also distributes them throughout the interstellar medium, and in a somewhat even fashion. For example, a supernova is going to throw a lot of material in all directions, and this material is a mix of many different elements. This burst of material moves outwards and over time mixes with the rest of the material in the interstellar medium. When this happens hundreds of thousands of times in a galaxy it gradually enriches the interstellar medium with heavy elements. Eventually some of this material coalesces into new stellar systems where it forms into stars, planets, etc.

 

[BillTre]

Eventually some of this material coalesces into new stellar systems where it forms into stars, planets, etc.

And is able to undergo complex chemistry, and beyond.

 

[D H]

Supernova explosions can also generate heavier elements, including gold. I'm sure there are papers on the subject, including the % of elements made.

It is now thought that the heaviest elements, including gold and uranium, are not created in supernovae. Per the diagram below, core collapse supernovae ("exploding massive stars" in the diagram) don't contribute much beyond rubidium (atomic mass = 37), with type 1A supernovae ("exploding white dwarfs") contributing most of the elements around iron (atomic mass = 26). Beyond rubidium, it's asymptotic red giant branch stars ("dying low mass stars") and merging binary neutron stars that are the biggest contributors.

Source: Origin of the Elements in the Solar System, Jennifer Johnson

 

[Newtons Apple]

It is now thought that the heaviest elements, including gold and uranium, are not created in supernovae. Per the diagram below, core collapse supernovae ("exploding massive stars" in the diagram) don't contribute much beyond rubidium (atomic mass = 37), with type 1A supernovae ("exploding white dwarfs") contributing most of the elements around iron (atomic mass = 26). Beyond rubidium, it's asymptotic red giant branch stars ("dying low mass stars") and merging binary neutron stars that are the biggest contributors.

View attachment 355378
Source: Origin of the Elements in the Solar System, Jennifer Johnson

It just boggles my albeit simple mind... that these solitary events... a few each million years is enough to sow these elements throughout the entire universe... Maybe we live on a Planet that is so insanely lucky to get mostly all of the elements naturally in large amounts. However, would it be fesible then, if we move to another system far out, that there's some elements on our table that simply do not exist there? That they were not fortunate enough to have just happened to be in the vicinity of neutron star collisions?

 

[DaveC426913]

... a few each million years is enough to sow these elements throughout the entire universe...

Well, it was a lot smaller, then...


"The first supernovae formed when the first stars exploded, which was a few hundred million years after the Big Bang..."

 

[Hornbein]

The further down into the crust of a neutron star, the greater the pressure and heavier the elements. It's gradual so I'd expect to find all of the heavier elements

 

[D H]

It just boggles my albeit simple mind... that these solitary events... a few each million years is enough to sow these elements throughout the entire universe... Maybe we live on a Planet that is so insanely lucky to get mostly all of the elements naturally in large amounts. However, would it be fesible then, if we move to another system far out, that there's some elements on our table that simply do not exist there? That they were not fortunate enough to have just happened to be in the vicinity of neutron star collisions?

Our Sun is a typical third generation star. "Third generation" does not mean that only two events (e.g., supernovae) separate our solar system from the Big Bang. Our solar system most likely contains remnants of several thousands of stars, plus a lot of primordial hydrogen and helium. There was a lot of time (think billions of years rather than just a few million) for those remnants to mix with the primordial hydrogen and helium in the interstellar gas cloud that eventually formed the Sun and the planets.

We live on a terrestrial planet. All four of the solar system's terrestrial planets (Mercury, Venus, Earth, and Mars) have a very different makeup than the solar system as a whole. As a whole, our solar system is mostly hydrogen and helium, plus a little bit of everything else. The Earth contains practically no helium, and most of what is there is a result of radioactive decay. The Earth does contain some hydrogen because hydrogen is chemically active. Terrestrial planets are accumulators of elements heavier than helium. Astronomers denote everything heavier than helium to be a metal. As accumulators of metals, it only stands to reason that the terrestrial planets are very metal-rich, by the astronomical definition of metals.

The very first generation of stars had no terrestrial planets. The second generation of stars had very, very few terrestrial planets. When we see a star with terrestrial exoplanets we are almost certainly looking at a third generation star. As mentioned above, "third generation" does not mean two explosions between the Big Bang and the formation of the star system. It merely means that the star is not metal-poor. There are many stars in our galaxy that are even more metal-rich than is the Sun, including several in our own astronomical backyard. Our Sun is quite average with regard to third generation metallicity.

I mentioned chemistry a bit earlier. Chemistry is very important! As an example, the solar system (and the Earth as a whole) contains a lot more gold than it does uranium. In the Earth's crust, it's the other way around: The Earth's crust contains a lot more uranium than gold. This is because of chemistry. The Earth's core contains the vast majority of the Earth's gold, and also the vast majority of the Earth's iron. Gold is a siderophile, which means it is an "iron loving" element. Uranium is a lithophile, which means it is a "rock loving" element. Moreover, uranium is an "incompatible element", which means it doesn't crystalize with other elements when igneous rock forms. It instead stays with the partial melt, thereby making it more concentrated the Earth's crust than in the mantle.

 

[gmax137]

This thread led me to pull this for a re-re-read:

 

[Drakkith]

Maybe we live on a Planet that is so insanely lucky to get mostly all of the elements naturally in large amounts.

No, our planet is probably pretty average in terms of abundance of different elements given its size and formation history. There's no reason to expect Earth to be special in this regard.

However, would it be fesible then, if we move to another system far out, that there's some elements on our table that simply do not exist there? That they were not fortunate enough to have just happened to be in the vicinity of neutron star collisions?

The abundance might be different for different planets, but it is unreasonable to expect there to be absolutely zero of some element in a planet unless our understanding of nucleosynthesis and the distribution of the elements is very wrong.

 

[snorkack]

Perhaps a ton doesn't amount to very much on cosmic scales? In fact, there are estimated to be about 250,000 tonnes of gold on Earth. That's a whopping 250 million kilograms. A huge amount of gold.

Is that 1% of the Earth's mass? Probably not. The mass of the Earth is $6 \times 10^{24} \ kg$. That's $2.4 \times 10^{16}$ times the mass of the gold on Earth. That means that gold has a tiny, trace amount.

If you are studying cosmology, you have to think big!

Interestingly, I get another estimate for amount of gold on Earth.
The gold concentration in chondrites is quoted as 0,17 ppm, and that on Earth should be similar.
But that is $1 \times 10^{18} \ kg$, not $2.5 \times 10^{8} \ kg$.

 

[PeroK]

Interestingly, I get another estimate for amount of gold on Earth.
The gold concentration in chondrites is quoted as 0,17 ppm, and that on Earth should be similar.
But that is $1 \times 10^{18} \ kg$, not $2.5 \times 10^{8} \ kg$.

The estimate I quoted was total mine-able gold. There must be many times that buried deeper!

 

[D H]

The estimate I quoted was total mine-able gold. There must be many times that buried deeper!

Gold, as I mentioned earlier, is a siderophile. It "loves" iron (that's what "siderophile" means). In fact, gold is more siderophilic than is iron itself; see the wikipedia article (which is fairly good) on the Goldschmidt classification. The vast majority of the Earth's gold is buried very deep inside the Earth; it migrated as a trace element with iron to the Earth's core during the iron catastrophe.

 

[snorkack]

The vast majority of the Earth's gold is buried very deep inside the Earth; it migrated as a trace element with iron to the Earth's core during the iron catastrophe.

What evidence exists that there was any "iron catastrophe"?
Also, how many different nickel concentrations do iron meteorites have?

 

[D H]

What evidence exists that there was any "iron catastrophe"?

The Earth's core is the evidence. The core is mostly iron and is where most of the Earth's iron resides. Another name for this process is planetary differentiation. The differentiation process releases quite a bit of heat, thereby further enabling continued differentiation.

Also, how many different nickel concentrations do iron meteorites have?

According to Iron Meteorites: Composition, Age, and Origin (DOI: 10.1093/acrefore/9780190647926.013.206; published in the online Oxford research encyclopedia of planetary science) by Edward R. D. Scott,

A typical iron meteorite contains 5–10% nickel, ~0.5% cobalt, 0.1–0.5% phosphorus, 0.1–1% sulfur and over 20 other elements in trace amounts. ... Chemical analysis show that most iron meteorites can be divided into 14 groups: about 15% appear to come from another 50 or more poorly sampled parent bodies. Chemical variations within all but three groups are consistent with fractional crystallization of molten cores of planetesimals. The other three groups are richer in silicates and probably come from pools of molten metal in chondritic bodies.

This is a rather interesting and fairly recent (2020) article.

 

[snorkack]

The Earth's core is the evidence. The core is mostly iron and is where most of the Earth's iron resides. Another name for this process is planetary differentiation. The differentiation process releases quite a bit of heat, thereby further enabling continued differentiation.

But is the energy of differentiation important to enable differentiation?
How could Earth ever have been a sizable undifferentiated body?
By accreting exclusively fine dust containing no separately accreted asteroids, and doing that exactly slowly enough to promptly radiate away all the heat of impacts?
Even so, once the dust was of some depth to be heat insulating, whatever happened to the heat of radioactive decay?

According to Iron Meteorites: Composition, Age, and Origin (DOI: 10.1093/acrefore/9780190647926.013.206; published in the online Oxford research encyclopedia of planetary science) by Edward R. D. Scott,
This is a rather interesting and fairly recent (2020) article.

That´s my evidence against "iron catastrophe".
Meteorites sample the cores of at least 61 asteroids that had molten metal cores. Suggesting fairly small asteroids melted and formed molten cores.
If such small asteroids could and would heat up and get molten cores, how could Earth ever have had an "iron catastrophe"? Should Earth rather not have formed a molten interior back when Earth was an asteroid, not even yet a dwarf planet?
About the heat of radioactive decay, I find a bunch of isotopes with half-life between 100 ky and 100 My. Ordered by element and mass:

1. Be-10 lithophile > 1,4My, β^- to B-10 also lithophile
2. Al-26 lithophile > 720 ky, β⁺ to Mg-26 also lithophile
3. Cl-36 "lithophile" (?) > 300 ky, β^- to Ar-36 lithophile and β⁺ to S-36 chalcophile
4. Ca-41 lithophile > 102 ky, β^- to K-41 "lithophile"
5. Mn-53 siderophile (? or lithophile?) > 3,7 My, β⁺ to Cr-53 lithophile
6. Fe-60 siderophile > 2,6 My, β^-+5 y β^- to Ni-60 lithophile
7. Se-79 chalcophile > 300 ky, β^- to Br-79 "lithophile"
8. Kr-81 atmophile > 230 ky, β⁺ to Br-81 "lithophile"
9. Zr-93 lithophile > 1,5 My, β^- to Nb-93 lithophile
10. Nb-92 lithophile > 35 My, β^- to Mo-92 siderophile? and β⁺ to Zr-92 lithophile
11. Tc-97 ?(lithophile? chalcophile? siderophile?) > 4,2 My, β⁺ to Mo-97 siderophile?
12. Tc-98 ?(lithophile? chalcophile? siderophile?) > 4,2 My, β^- to Ru-98 siderophile (β⁺?)
13. Tc-99 ?(lithophile? chalcophile? siderophile?) > 210 ky, β^- to Ru-99 siderophile
14. Pd-107 siderophile > 6,5 My, β^- to Ag-107 chalcophile
15. Sn-126 chalcophile? > 220 ky, β^-+12 d β^- to Te-126 chalcophile
16. I-129 "lithophile" > 16 My, β^- to Xe-129 atmophile
17. Cs-135 "lithophile" > 1,3 My, β^- to Ba-135 lithophile
18. Sm-146 lithophile > 92 My, α to Nd-142 lithophile
19. Gd-150 lithophile > 1,8 My, α to Sm-146 > as above
20. Dy-154 lithophile > 1,4 My, α to Gd-150 > as above
21. Hf-182 lithophile > 8,9 My, β^-+114 d β^- to W-182 siderophile
22. Re-186 siderophile > 200 Ky, γ+3,7d β^- to Os-186 siderophile or EC to W-186 siderophile
23. Pb-205 chalcophile > 17 My, β⁺ to Tl-205 chalcophile
24. Bi-208 chalcophile > 370 ky, β⁺ to Pb-208 chalcophile
25. Bi-210 chalcophile > 3 My, α+4 min β^- to Pb-206 chalcophile
26. U-233 lithophile > 160 ky, α+Np series to Bi-209 chalcophile
27. U-234 lithophile > 245 ky, α, > in U series
28. U-236 lithophile > 23 My, α to Th-232, lithophile > Th series
29. Np-236 lithophile > 160 ky, EC to U-236 as above, or β^-+2,8 y α+69 y α to Th-228 in Th series
30. Np-237 lithophile > 2,2 My, α to Np series as above
31. Pu-242 lithophile > 370 ky, α to U series
32. Pu-244 lithophile > 81 My, α+14 h β^-+ 62 min β^-+6500 y α to U-236 as above
33. Cm-247 lithophile > 16 My, α+5 h β^-+ 7350 y α+2,3 d β^- + 24 ky α to U-235, lithophile > Ac series
34. Cm-248 lithophile > 350 ky, α to Pu-244 as above, or spontaneous fission

Looks like these isotopes contain some which may have heated up asteroids or Earth a bit. What were their primordial abundances like?