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I was reading an article by two Harvard Astrophysicists, which mentioned the following:

"We value gold for many reasons: its beauty, its usefulness as jewelry, and its rarity. Gold is rare on Earth in part because it's also rare in the universe. Unlike elements like carbon or iron, it cannot be created within a star. Instead, it must be born in a more cataclysmic event - like one that occurred last month known as a short gamma-ray burst (GRB). "

From this, it is clear that what they are saying is that gold cannot be formed on earth, let alone in stars, and further, that the only event it can be formed by is a "cataclysmic event" like a "gamma-ray burst". Moreover, why can gold only form in outer space and not on earth? How did they conclude this?

My questions are simple, and should occur to anyone who reads this and doesn't know the answer: First, how did they conclude that gold can only be formed in a cataclysmic event? No explanation or even a hint of an explanation is provided, it is just stated.

Second: Is this a special property of gold (and therefore may possibly account for the "superiority" of its properties to other metals) or does the same hold true for other metals, such as silver, copper, iron etc. Or perhaps these other metals are not like gold and are produced on earth? Or maybe it depends on their relative sophistication, so that silver can, unlike gold, can be formed both in cataclysmic-events as well as stars, while iron (say) can be formed even on earth?

(I should add that I only know basic "school" (non-calculus!) physics and so any errors in the above are due to my own lack of knowledge.)

Raghib
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    See this answer to the question that John indicated... in my opinion it is much better (complete, accurate) than the "accepted" answer! – Floris Jul 11 '17 at 15:39
  • @JohnRennie: Thank you. However, my question is more specific, and I also ask why it must be in outer space and not on earth. – Raghib Jul 11 '17 at 15:40
  • @Floris: Why does it have to be in outer space? Why can't gold form on earth; what is the reasoning behind this? – Raghib Jul 11 '17 at 15:40
  • It could form on earth with sufficiently high neutron flux. But it's pretty hard to get that kind of neutron flux... especially "naturally". – Floris Jul 11 '17 at 15:41
  • See for example this

    Nuclear experiments have successfully transmuted lead into gold, but the expense far exceeds any gain

     – Floris Jul 11 '17 at 15:43
  • @Floris: Sorry, what is neutron flux? Also, why does the "neutron flux" need to be very high, how did you conclude that this is the only way gold may be produced? (Note: Transmutation seems to require high energy according to that article, but how do we know that the formation of gold ab initio also requires high energy?) – Raghib Jul 11 '17 at 15:43
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    Hi Raghib. The linked question states Elements heavier than iron are only produced during supernovae and they happen out in space. I guess you're really asking why can gold only be produced in supernovae, and the answer is that, as Rob Jeffries' answer to the linked question states, the synthesis requires a high neutron flux and that only happens in supernovae. – John Rennie Jul 11 '17 at 15:45
  • You have to bombard a nucleus with neutrons to cause it to change its mass. The most stable nucleus is Fe-56 (Or Ni-62 depending on your definition); beyond that, adding mass makes something that is "less stable" (and that therefore risks falling apart, especially when you hit it with a neutron; that's how fission works). The chances of making gold with this process are small. "Flux" is number of neutrons per second per unit area. – Floris Jul 11 '17 at 15:47
  • Elements are produced by nuclear reactions. Such reactions involve much higher energies than chemical reactions, they generally can't be triggered by naturally occurring energy sources like sunlight or geothermal activity. So most of the elements on Earth were produced in space, mostly in stars (hydrogen was produced in the Big Bang itself); the only elements naturally produced in the Earth are the decay products of radioactive elements. OTOH, cosmic rays hitting the upper atmosphere can cause nuclear reactions (and I guess lightning can too), but the quantity of elements synthesized is tiny. – PM 2Ring Jul 11 '17 at 16:37

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