I'm not sure there is a universally agreed value even now. It comes down to "decay", half-life, etc. (and, potentially, how far out into space you look). Basica

I'm not sure there is a universally agreed value even now. It comes down to "decay", half-life, etc. (and, potentially, how far out into space you look). Basically, depends on how you define "natural". You get numbers like 94, 98, etc. https://depts.washington.edu/eooptic/linkfiles/The%20Elements.pdf https://depts.washington.edu/eooptic/linkfiles/The%20Element... This many-page PDF, with actual references (to CRC etc. - lots of stuff that comes up for this question just has bare numbers, ugh), for example, points out that trace amounts of plutonium etc. occur in nature. This is from late 1997, I believe, but gives an idea of what factors lead to different numbers and which elements actually do show up naturally, even if not stable enough to exist "forever" independently. Also, note that there are some low atomic number elements that are unstable enough and without enough "feedstock" to be found only in trace amounts (and were considered potentially not "naturally occurring" when discovered by scientists in the first place) - like "Technetium." One last note: I just came across something in past couple weeks discussing Bismuth 209 - originally thought to be heaviest "stable" nucleus, turns out it decays in the exayears or something - https://en.m.wikipedia.org/wiki/Bismuth-209 https://en.m.wikipedia.org/wiki/Bismuth-209 Nuclear physics is ... not so straightforward.