I get that gold on the molecular level is older than the earth, but how long has it been since gold in say a random gold ring for sale at a mall jewelry shop been since it was mined? Is it possible or probable part of it was once a Roman coin, having been melted down again and again, or is it more likely it was just mined last year?
Just a nitpick, but gold is actually an element, not a molecular compound. The gold in Earth’s crust is, as you note, much older than the Earth, having largely been produced by collapsar supernovae and magnetorotational supernovae (and perhaps a small amount through neutron star collisions) generating conditions for r-process nucleosynthesis). Once the planets coalesced the heavier elements tend to migrate down to the core but because of Earth’s tectonic processes many collections of heavy elements can convect up through the mantle and find themselves in the outer crust (where they can be accessed via mining or due to weathering and erosion) via volcanism.
Gold is particularly easy to identify and separate because it does not oxidize or readily combine with common elements, and is also very dense and has a low melting point allowing it to be separated from surrounding minerals by mechanical or chemical milling and gravity. Once gold is extracted it generally remains in a pure form or alloyed with other valuable metals like silver, copper, platinum, nickel, or palladium, and even when used for industrial purposes can be easily reclaimed, and historically gold artifacts that were not assessed to be of great historical or artistic value were melted down for reuse. However, most existing stocks of gold are either tied up in bullion mostly held by national treasuries as ‘specie’ or have found their way into artifacts with historical or aesthetic value. Inexpensive gold items such as wedding bands, chains, and coatings are commonly reclaimed and reused but extraction of new gold has been almost ever increasing, achieving an all time high in 2012, and while it has fallen slightly (because of lack of demand and lower prices) it has been on the rebound with an increase of about 1% per year per year over the last few years. So, if you are buying a gold ring at a mall jewelry store it is more likely to have been mined relatively recently (within the past decade or two).
There is, by the way, quite the ‘grey market’ for unethically mined gold (that which uses child or effectively slave labor, extraction methods that are extremely toxic and environmentally harmful, and gold illegally mined without compensating mineral rights holders), and because isotope tagging methods are used to identify the source of gold in large sales, a lot of gold used in jewelry tends to be unethically sourced as there is little traceability through the complex supply chain where gold is sold in small quantities.
Stranger
Actually, something like 45%-50% of all extant gold is currently in the form of jewelry. Sure, there’s a lot of bullion out there, but there are billions of people in the world who own at least a small amount of gold, and it adds up.
There’s a lot of gold in electronic components also. Less so than in the past since the components are smaller and there alternative conductive metals to use, but then there are a lot more electronic devices today. It is largely recycled, though not necessarily using ‘clean’ techniques.
Gold is not quite inert either. It doesn’t combine readily with other substances on dry land or even much in fresh water. It is soft though, and as a result the land is full of tiny bits of gold. As it’s been said and proven, you can find gold in a bag of Home Depot play sand. Not enough to make it worth extracting, just like much of it spread around the world. In the ocean it has combined with other substances to form salts. The world is full of gold that can’t be accessed in a practical manner.
Awesome terms, thanks. I reckon the blue-super-giants that go kablooey in a time frame of millions of years. I remember Carl Sagan saying those star systems wouldn’t have time for intelligent life to evolve (probably not even planets) and our Sun is just right. Billions old and billions to go.
It’s possible that your gold jewelry was once part of a Roman coin, but not probable. Consulting Our World in Data, we see that world gold production was pretty minimal until the the middle of the 19th century — the California Gold Rush — and didn’t really get going until the 20th century.
Looking at the underlying Clio Infra data set (which runs up to 2012), there had been about 150,000 tons of gold mined up to that date. Of this amount, about half was mined after 1975, and only about 10% of it was mined before 1906. So a random atom of “above-ground” gold has probably only been above ground for a century or so, and it’s not unlikely that it’s younger than I am.
Note that it really starts the steeper upwards trend in the 1890s - that’s the discovery of gold on the Witwatersrand. Note the small drop around 1900? Anglo-Boer war. Fascinating that you can see that so clearly in the data.
The Witwatersrand has been by far the largest single source of all mined gold - 22%. So quite a lot of gold can’t be any older than the 1890s.