The answer to the question of how many objects on the periodic table of the elements are naturally occurring is actually a bit complicated. Conventional wisdom says that the first 92 elements, from element one, hydrogen, to element 92, uranium, are all naturally occurring, but in fact some of these elements are highly unstable, and have only been observed when they have been created artificially. Some people believe that elements 93 (neptunium) and 94 (plutonium) should also be included on a list of naturally occurring elements. As a result, anywhere between 94 and 88 elements are “naturally occurring,” depending on the definition one is using.

Elements are considered to be “naturally occurring” when they can be found in nature, rather than needing to be created in a laboratory, and many representations of the periodic table of the elements include a dividing line between natural and artificially produced elements. Some naturally occurring elements have very unstable isotopes or short half-lives, so they exist only intermittently and in very small quantities on Earth. Some people believe that when thinking about the periodic table of the elements, elements such as these should not really be considered “naturally occurring,” especially since they are only observed as a direct result of human activity. Others argue that while only small amounts are observable at any given time, they are “natural” because they can occur spontaneously.

The questionable elements are: element 43, technetium; element 61, promethium; element 85, astatine; and element 87, francium. Elements 43 and 61 are somewhat unusual, as they are surrounded by stable elements, but they have only been observed in controlled laboratory conditions. Elements 85 and 87 do appear in nature, but only briefly, and very rarely, making it tough to pin down an actual natural appearance for these shy members of the periodic table of the elements.

If all four questionable elements are struck from the list of “naturally occurring” elements, you end up with either 90 or 88 naturally occurring elements, depending on whether or not you think neptunium and plutonium belong on the list. Some people include astatine and francium on the list of naturally occurring elements, raising the total to 92 or 90. The most-commonly cited number is “92,” which could be viewed as the first 92 entries on the periodic table of the elements, or the first 94 minus elements 43 and 61, depending on how complicated you feel like being.

It it is important to remember that when looking at the periodic table of the elements, “naturally occurring” does not necessarily mean “abundant.” Many naturally occurring elements are in fact quite rare, although some were once more abundant. Levels of elements also change depending on where you are: helium, for example, is rare on Earth, but abundant around the Sun.