Editing Gold (section)

=== 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" />