Editing Gold (section)

== Origin ==
=== Gold production in the universe ===
[[File:Vredefort crater cross section 2.png|thumb|upright=1.8|Schematic of a NE (left) to SW (right) cross-section through the 2.020-billion-year-old [[Vredefort impact structure]] in [[South Africa]] and how it distorted the contemporary geological structures. The present erosion level is shown. [[Johannesburg]] is located where the [[Witwatersrand Basin]] (the yellow layer) is exposed at the "present surface" line, just inside the crater rim, on the left. Not to scale.]]

Gold in the universe is produced through several cosmic processes and was present in the [[solar nebula|dust]] from which the [[Solar System]] formed.<ref>{{Cite journal |doi=10.1086/190111 |title=Nucleosynthesis of Heavy Elements by Neutron Capture |date=1965 |last1=Seeger |first1=Philip A. |last2=Fowler |first2=William A. |last3=Clayton |first3=Donald D. |journal=The Astrophysical Journal Supplement Series |volume=11 |page=121 |bibcode=1965ApJS...11..121S |url=http://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1307&context=physastro_pubs}}</ref> Scientists have identified three main cosmic sources for gold formation: [[supernova nucleosynthesis]], [[Neutron star merger|neutron star collisions]],<ref>{{cite news |url=https://pweb.cfa.harvard.edu/news/earths-gold-came-colliding-dead-stars |title=Earth's Gold Came from Colliding Dead Stars |work=David A. Aguilar & Christine Pulliam |publisher=cfa.harvard.edu |date=17 July 2013 |access-date=16 May 2025}}</ref> and magnetar flares.

All three sources involve a process called the [[r-process]] (rapid neutron capture), which forms elements heavier than [[iron]].<ref>{{cite web |url=http://chandra.harvard.edu/xray_sources/supernovas.html |title=Supernovas & Supernova Remnants |publisher=[[Chandra X-ray Observatory]] |access-date=28 February 2014}}</ref> For decades, scientists believed [[supernova nucleosynthesis]] was the primary mechanism for gold formation. More recently, research has shown that [[neutron star merger|neutron star collisions]] produce significant quantities of gold through the r-process.<ref>{{cite journal |last1=Berger |first1=E. |first2=W. |last2=Fong |first3=R. |last3=Chornock |date=2013 |title=An r-process Kilonova Associated with the Short-hard GRB 130603B |journal=The Astrophysical Journal Letters |volume=774 |issue=2 |page=4 |doi=10.1088/2041-8205/774/2/L23 |arxiv=1306.3960 |bibcode=2013ApJ...774L..23B|s2cid=669927 }}</ref>

In August 2017, the spectroscopic signatures of heavy elements, including gold, were directly observed by electromagnetic observatories during the [[GW170817]] neutron star merger event.<ref>{{cite news |title=LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars |url=https://www.ligo.org/detections/GW170817/press-release/pr-english.pdf |archive-url=https://web.archive.org/web/20171031030151/http://www.ligo.org/detections/GW170817/press-release/pr-english.pdf |archive-date=31 October 2017 |url-status=live |publisher=[[LIGO]] & [[Virgo interferometer|Virgo]] collaborations |date=16 October 2017 |access-date=15 February 2018}}</ref> This confirmed neutron star mergers as a source of gold, after years of only indirect detection.<ref>"we have no spectroscopic evidence that [such] elements have truly been produced," wrote author Stephan Rosswog.{{cite journal |last=Rosswog |first=Stephan |date=29 August 2013 |title=Astrophysics: Radioactive glow as a smoking gun |journal=[[Nature (journal)|Nature]] |volume=500 |issue=7464 |pages=535–536 |doi=10.1038/500535a |bibcode=2013Natur.500..535R |pmid=23985867|s2cid=4401544 }}</ref> This single event generated between 3 and 13 [[Earth mass]]es of gold, suggesting that neutron star mergers might produce enough gold to account for most of this element in the universe.<ref>{{cite news |title=Neutron star mergers may create much of the universe's gold |work=Sid Perkins |publisher=Science AAAS |url=https://www.science.org/content/article/neutron-star-mergers-may-create-much-universe-s-gold |date=20 March 2018 |access-date=24 March 2018}}</ref>

However, neutron star mergers alone cannot explain all cosmic gold, particularly in older stars, because these mergers occur relatively late in galactic history and are infrequent (approximately once every 100,000 years).<ref>{{cite journal |last1=Patel |first1=Anirudh |last2=Metzger |first2=Brian D. |last3=Cehula |first3=Jakub |last4=Burns |first4=Eric |last5=Goldberg |first5=Jared A. |last6=Thompson |first6=Todd A. |title=Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806–20 Magnetar Giant Flare |journal=The Astrophysical Journal Letters |volume=984 |issue=1 |pages=L29 |date=April 29, 2025 |doi=10.3847/2041-8213/adc9b0 |doi-access=free |bibcode=2025ApJ...984L..29P }}</ref> This created a timing paradox in explaining the presence of gold in stars formed early in the universe.

In 2025, researchers resolved this paradox by confirming that giant flares from [[magnetar]]s (highly magnetic neutron stars) are also a significant source of gold formation.<ref>{{cite journal |last1=Patel |first1=Anirudh |last2=Metzger |first2=Brian D. |last3=Cehula |first3=Jakub |last4=Burns |first4=Eric |last5=Goldberg |first5=Jared A. |last6=Thompson |first6=Todd A. |title=Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806–20 Magnetar Giant Flare |journal=The Astrophysical Journal Letters |volume=984 |issue=1 |pages=L29 |date=April 29, 2025 |doi=10.3847/2041-8213/adc9b0 |doi-access=free |bibcode=2025ApJ...984L..29P }}</ref> Analysis of a 2004 magnetar flare showed these events produce heavy elements through the same r-process as neutron star mergers. The amount of heavy elements created in a single magnetar flare can exceed the mass of Mars.<ref>{{cite news |last=Patel |first=Kasha |title=We figured out where gold comes from. The answer is explosive. |newspaper=The Washington Post |date=May 4, 2025 |url=https://www.washingtonpost.com/science/2025/05/04/first-gold-universe-heavy-metals-magnetar/ |access-date=May 5, 2025}}</ref> Since magnetars existed earlier in cosmic history and flare more frequently than neutron star mergers occur, they help explain gold's presence in older stars. Scientists estimate magnetar flares may contribute approximately 1-10% of all elements heavier than iron in our galaxy, including gold.<ref>{{cite news |title=Astronomers spot a gold mine in massive cosmic flares |work=Science.org |date=May 2025 |url=https://www.science.org/content/article/astronomers-spot-gold-mine-massive-cosmic-flares |access-date=May 5, 2025}}</ref>

=== Asteroid origin theories ===
Because the Earth was molten [[History of Earth|when it was formed]], almost all of the gold present in the [[early Earth]] probably sank into the [[core (geology)|planetary core]]. Therefore, as hypothesized in one model, most of the gold in the Earth's [[crust (geology)|crust]] and [[mantle (geology)|mantle]] is thought to have been delivered to Earth by [[asteroid impact]]s during the [[Late Heavy Bombardment]], about 4 billion years ago.<ref name="Willbold-2011">{{cite journal |last2=Elliott |first2=Tim |last3=Moorbath |first3=Stephen |date=2011 |title=The tungsten isotopic composition of the Earth's mantle before the terminal bombardment |journal=Nature |volume=477 |issue=7363 |pages=195–8 |bibcode=2011Natur.477..195W |doi=10.1038/nature10399 |pmid=21901010 |last1=Willbold |first1=Matthias|s2cid=4419046 }}</ref><ref name="Battison-2011">{{cite news |url=https://www.bbc.co.uk/news/science-environment-14827624 |title=Meteorites delivered gold to Earth |last=Battison |first=Leila |date=8 September 2011 |work=[[BBC]] }}</ref>

Gold which is reachable by humans has, in one case, been associated with a particular asteroid impact. The asteroid that formed [[Vredefort impact structure]] 2.020&nbsp;billion years ago is often credited with seeding the [[Witwatersrand basin]] in [[South Africa]] with the richest gold deposits on earth.<ref>{{cite web |url=http://superiormining.com/properties/south_africa/mangalisa/geology/ |title=Mangalisa Project |publisher=Superior Mining International Corporation |access-date=29 December 2014}}</ref><ref>{{cite journal |last1=Therriault |first1=A. M. |first2=R. A. F. |last2=Grieve |first3=W. U. |last3=Reimold |title=Original size of the Vredefort Structure: Implications for the geological evolution of the Witwatersrand Basin |journal=Meteoritics |volume=32 |pages=71–77 |date=1997 |bibcode=1997M&PS...32...71T |name-list-style=amp |doi=10.1111/j.1945-5100.1997.tb01242.x|doi-access=free }}</ref><ref>[https://web.archive.org/web/20120327184158/http://www.cosmosmagazine.com/news/2101/meteor-craters-may-hold-untapped-wealth Meteor craters may hold untapped wealth]. Cosmos Magazine (28 July 2008). Retrieved on 12 September 2013.</ref><ref>{{Cite journal |last1=Corner |first1=B. |last2=Durrheim |first2=R. J. |last3=Nicolaysen |first3=L. O. |title=Relationships between the Vredefort structure and the Witwatersrand basin within the tectonic framework of the Kaapvaal craton as interpreted from regional gravity and aeromagnetic data |doi=10.1016/0040-1951(90)90089-Q |journal=Tectonophysics |volume=171 |issue=1 |pages=49–61 |year=1990 |bibcode=1990Tectp.171...49C}}</ref> However, this scenario is now questioned. The gold-bearing [[Witwatersrand]] rocks were laid down between 700 and 950&nbsp;million years before the Vredefort impact.<ref name="McCarthy-2005">McCarthy, T., Rubridge, B. (2005). ''The Story of Earth and Life''. Struik Publishers, Cape Town. pp. 89–90, 102–107, 134–136. {{ISBN|1 77007 148 2}}</ref><ref name="Norman-2006">Norman, N., Whitfield, G. (2006) ''Geological Journeys''. Struik Publishers, Cape Town. pp. 38–49, 60–61. {{ISBN|9781770070622}}</ref> These gold-bearing rocks had furthermore been covered by a thick layer of Ventersdorp lavas and the [[Transvaal Basin|Transvaal Supergroup]] of rocks before the meteor struck, and thus the gold did not actually arrive in the asteroid/meteorite. What the Vredefort impact achieved, however, was to distort the [[Witwatersrand basin]] in such a way that the gold-bearing rocks were brought to the present [[erosion surface]] in [[Johannesburg]], on the [[Witwatersrand]], just inside the rim of the original {{cvt|300|km|adj=on}} diameter crater caused by the meteor strike. The discovery of the deposit in 1886 launched the [[Witwatersrand Gold Rush]]. Some 22% of all the gold that is ascertained to exist today on Earth has been extracted from these Witwatersrand rocks.<ref name="Norman-2006" />

=== Mantle return theories ===
Much of the rest of the gold on Earth is thought to have been incorporated into the planet since its very beginning, as [[planetesimals]] formed the [[Mantle (geology)|mantle]]. In 2017, an international group of scientists established that gold "came to the Earth's surface from the deepest regions of our planet",<ref>{{cite web |author=University of Granada |title=Scientists reveal the mystery about the origin of gold |website=ScienceDaily |date=21 November 2017 |access-date=27 March 2018 |url=https://www.sciencedaily.com/releases/2017/11/171121095128.htm}}</ref> the mantle, as evidenced by their findings at [[Deseado Massif]] in the [[Argentinian Patagonia]].<ref>{{cite journal |last1=Tassara |first1=Santiago |last2=González-Jiménez |first2=José M. |last3=Reich |first3=Martin |last4=Schilling |first4=Manuel E. |last5=Morata |first5=Diego |last6=Begg |first6=Graham |last7=Saunders |first7=Edward |last8=Griffin |first8=William L. |last9=O’Reilly |first9=Suzanne Y.|last10=Grégoire|first10=Michel |last11=Barra |first11=Fernando |last12=Corgne |first12=Alexandre |title=Plume-subduction interaction forms large auriferous provinces |journal=Nature Communications |volume=8 |issue=1 |pages=843 |year=2017 |issn=2041-1723 |doi=10.1038/s41467-017-00821-z |pmid=29018198 |pmc=5634996 |bibcode=2017NatCo...8..843T}}</ref>{{clarify|reason=this directly contradicts the first paragraph of the next section|date=April 2019}}