Editing Chemical element (section)

==== Occurrence and origin on Earth ====
{{Main|Abundance of elements in Earth's crust}}
Chemical elements may also be categorised by their origin on Earth, with the first 94 considered naturally occurring, while those with atomic numbers beyond 94 have only been produced artificially via human-made nuclear reactions.

Of the 94 naturally occurring elements, 83 are considered primordial and either [[stable isotope|stable]] or weakly radioactive. The longest-lived isotopes of the remaining 11 elements have [[Half-life|half lives]] too short for them to have been present at the beginning of the Solar System, and are therefore "transient elements". Of these 11 transient elements, five ([[polonium]], [[radon]], [[radium]], [[actinium]], and [[protactinium]]) are relatively common [[decay product]]s of [[thorium]] and [[uranium]]. The remaining six transient elements (technetium, promethium, astatine, [[francium]], [[neptunium]], and [[plutonium]]) occur only rarely, as products of rare decay modes or nuclear reaction processes involving uranium or other heavy elements.

Elements with atomic numbers 1 through 82, except 43 (technetium) and 61 (promethium), each have at least one isotope for which no radioactive decay has been observed. Observationally stable isotopes of some elements (such as [[tungsten]] and [[lead]]), however, are predicted to be slightly radioactive with very long half-lives:{{NUBASE2016|ref}} for example, the half-lives predicted for the observationally stable lead isotopes range from 10{{sup|35}} to 10{{sup|189}} years. Elements with atomic numbers 43, 61, and 83 through 94 are unstable enough that their radioactive decay can be detected. Three of these elements, bismuth (element 83), thorium (90), and uranium (92) have one or more isotopes with half-lives long enough to survive as remnants of the explosive [[stellar nucleosynthesis]] that produced the heavy elements before the formation of the Solar System. For example, at over 1.9{{e|19}} years, over a billion times longer than the estimated age of the universe, [[bismuth-209]] has the longest known [[alpha decay]] half-life of any isotope.{{r|Dume2003}}{{r|Marcillac2003}} The last 24 elements (those beyond plutonium, element 94) undergo radioactive decay with short half-lives and cannot be produced as daughters of longer-lived elements, and thus are not known to occur in nature at all.