Editing Astatine (section)

== Natural occurrence ==
[[File:Decay Chain(4n+1, Neptunium Series).svg|thumb|upright=0.7|alt=a sequence of differently colored balls, each containing a two-letter symbol and some numbers|Neptunium series, showing the decay products, including astatine-217, formed from neptunium-237]]

Astatine is the rarest naturally occurring element.{{efn|Emsley<ref name="Emsley">{{cite book|last=Emsley|first=J.|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|year=2011|publisher=Oxford University Press | isbn = 978-0-19-960563-7 |pages=57–58}}</ref> states that this title has been lost to [[berkelium]], "a few atoms of which can be produced in very-highly concentrated uranium-bearing deposits"; however, his assertion is not corroborated by any primary source.}} The total amount of astatine in the Earth's crust (quoted mass 2.36 × 10<sup>25</sup> grams)<ref>{{cite book | title = CRC Handbook of Chemistry and Physics | edition = 85th | year = 2004 | pages = [https://archive.org/details/crchandbookofche81lide/page/14 14–10] | publisher = CRC Press | isbn = 978-0-8493-0485-9 | editor-first = D. R. | editor-last = Lide | url = https://archive.org/details/crchandbookofche81lide/page/14 }}</ref> is estimated by some to be less than one gram at any given time.<ref name="MoreAtIC" /> Other sources estimate the amount of ephemeral astatine, present on earth at any given moment, to be up to one ounce<ref name="Stwertka" /> (about 28 grams).

Any astatine present at the formation of the Earth has long since disappeared; the four naturally occurring isotopes (astatine-215, -217, -218 and -219){{sfn|Lavrukhina|Pozdnyakov|1970|p=228–229}} are instead continuously produced as a result of the [[decay chain|decay]] of radioactive [[thorium]] and [[uranium]] ores, and trace quantities of [[neptunium-237]]. The landmass of North and South America combined, to a depth of 16 kilometers (10 miles), contains only about one trillion astatine-215 atoms at any given time (around 3.5 × 10<sup>−10</sup> grams).<ref>{{cite book| url = https://books.google.com/books?id=1RMLAAAAMAAJ | title = Only a Trillion| first = I.| last = Asimov | author-link = Isaac Asimov | publisher = Abelard-Schuman | year = 1957 | page = 24}}</ref> Astatine-217 is produced via the radioactive decay of neptunium-237. Primordial remnants of the latter isotope—due to its relatively short half-life of 2.14 million years—are no longer present on Earth. However, trace amounts occur naturally as a product of transmutation reactions in [[uranium ore]]s.<ref>{{cite encyclopedia |editor-last1=Kolthoff |editor-first1= I. M.|editor-last2=Elving |editor-first2=P. J. |title=Treatise on Analytical Chemistry |date=1964 |publisher=Interscience Encyclopedia |series=Part II: Analytical Chemistry of the Elements|volume=4 |location=New York |pages=487}}</ref> Astatine-218 was the first astatine isotope discovered in nature.{{sfn|Kugler|Keller|1985|p=4}} Astatine-219, with a half-life of 56 seconds, is the longest lived of the naturally occurring isotopes.<ref name="Audi2003" />

Isotopes of astatine are sometimes not listed as naturally occurring because of misconceptions<ref name="Aten" /> that there are no such isotopes,<ref>{{cite journal|last1=Maiti|first1=M.|last2=Lahiri|first2=S.|year=2011|title=Production cross section of At radionuclides from <sup>7</sup>Li+<sup>nat</sup>Pb and <sup>9</sup>Be+<sup>nat</sup>Tl reactions|journal=Physical Review C|volume=84|issue=6|pages=07601–07604 (07601)|arxiv=1109.6413|bibcode=2011PhRvC..84f7601M|doi=10.1103/PhysRevC.84.067601|s2cid=115321713}}</ref> or discrepancies in the literature. Astatine-216 has been counted as a naturally occurring isotope but reports of its observation{{sfn|Greenwood|Earnshaw|2002|p=796}} (which were described as doubtful) have not been confirmed.{{sfn|Kugler|Keller|1985|p=5}}