#### A M

Summary
In my high school lessons, it's always been said "Among 92 naturally occurring elements...", "Only 92 elements can be found in nature", ...
Although this fact seemed to be reliable, there was still one little nagging doubt at the back of my mind. So I searched for the exact number in the internet but found a lot of different numbers; from 88 to 98!
Now my questions are: (Quotes are regular Doubtful answers.)
What exactly is a naturally occurring element?
An element that has at least one isotope that occurs naturally on "Earth".
An element that has at least one isotope that can be found in "Nature".
88, 90, 92, 93, 94, 98
Would you please tell me the exact atomic no range of such elements (with exceptions)?
From atomic no 1 to 92 -written in our books!
I would be really grateful if anyone could answer my questions. (Based on Information from the Latest Observations & Reliable Sources)

#### .Scott

Homework Helper
There is also a difference between "can be found in nature" and "exists in nature". In the immediate aftermath of a supernova, there are likely many elements that have not been discovered - but at present, they cannot be "found".

Using naturally "found on Earth" is probably the easiest discriminator. But even that can be tricky.
Simply looking at the half-life of isotopes might make Technetium (atomic number 43) look as though it doesn't belong on the list. Technetium-99 has a half-life of 211,000 years. That would make the age of the Earth more than 4 million 99Tc99Tc half lives - easily enough time to for all Tc to be eliminated from our planet. But it does occur naturally on Earth - as a fission product of Uranium.

The next trouble maker is Promethium, atomic number 61. 145Pm145Pm is the longest-living isotope of Promethium with a half-life of 17.7 years. But like Technetium, it can be naturally produced from the decay products of long-lasting radioactive isotopes. Still, according to the wiki article: "All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time."

Lead (atomic number 82) is the last completely stable element.

Bismuth (atomic number 83) has a half-life that is much older than Earth (or the universe), so it can be safely counted as "naturally occurring".

Polonium (atomic number 84) is probably the lightest element which might not seriously qualify as naturally occurring on Earth. Per wiki: "Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 (with a half-life of 138 days) in uranium ores, as it is the penultimate daughter of natural uranium-238. Though slightly longer-lived isotopes exist, they are much more difficult to produce." But still, technically it IS naturally occurring on Earth.

Astatine (atomic number 85) per wiki: "Astatine is a radioactive chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours.".

There is an island of stability around Uranium where the half lives are very long - and thus can be naturally occurring on Earth.

Here is a useful link: https://en.wikipedia.org/wiki/List_of_elements_by_stability_of_isotopes

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#### phyzguy

"Nature" is enormous. A supernova explosion is a massive nuclear event that probably produces all known elements, and maybe more. Similarly, in a system of merging neutron stars, there is a large amount of decompressed neutron star matter flung into space. It also probably produces all known elements and probably more that we don't even know about. However, many of them are quite short lived and don't last long.

Even if you restrict yourself to Earth, Earth is large and atoms are small. If a Uranium fission product collides with a surrounding atom and briefly produces an atom of a short-lived trans-uranic element, does this count as "naturally occurring"? Or do you need to be able to dig up a macroscopic quantity of the element before you count it as "naturally occurring"?

#### A M

Thank you for the replies.
In the immediate aftermath of a supernova, there are likely many elements that have not been discovered - but at present, they cannot be "found".
But my point of view is a little different. For example, we call an element stable if its decay has never been observed (although it can theoretically go under rare decays).
Therefore naturally occurring elements are those that have been observed depending on our latest information.
So let me ask: In accordance with latest observations, what is a natural occurring element?
"Nature" is enormous.
What is the explanation of "Nature" in scientific terminology? Universe?

#### .Scott

Homework Helper
What is the explanation of "Nature" in scientific terminology? Universe?
Yes. So anything produced in a supernova is "naturally occurring". That would include elements that have not yet been discovered - perhaps many with half-lives in the femtosecond range. So it's not a very good term to use in this context.

More appropriate is "naturally occurring on Earth". I have edited my original post to include more details about which elements might be included in that list.

#### A M

So anything produce in a supernova is "naturally occurring". That would include elements that have not yet been discovered - perhaps many with half-lives in the femtosecond range.
So, how many elements are observed (both directly & indirectly) to be created during Supernovae?

#### A M

Note that I said "observed".

#### .Scott

Homework Helper
So, how many elements are observed (both directly & indirectly) to be created during Supernovae?
The Earth's crust is an example of what was left behind in the aftermath of a Supernova. So that would count as an observation.
Neptunium (the first trans-Uranium element) can be found in trace amounts in Uranium ore - but not the same Neptunium that was created in a supernova, so that would not qualify as an observation of Neptunium in a supernova. ($^{237}Np$ has a half life of 2.14 million years).
Beyond that, there are spectral measurements that can reveal elements - but I don't think you can find a new trans-Uranium element that way.

#### phyzguy

So let me ask: In accordance with latest observations, what is a natural occurring element?
There is no universally agreed-upon definition of what constitutes "naturally occurring". So you need to tell us your definition before the question can be answered.

#### A M

There is no universally agreed-upon definition of what constitutes "naturally occurring".
So, I mean the element that at least one of its isotopes has been created in any type of natural (not processed by humans) nucleosynthesis (big bang , star evolution, supernova,...) or as a radioactive daughter of such nuclei.
Note that elements created in any nuclear reactors or their daughters are not included.

#### A M

There is no universally agreed-upon definition of what constitutes "naturally occurring"
I think that could be the reason for that noticeable difference in numbers.

#### phyzguy

So, I mean the element that at least one of its isotopes has been created in any type of natural (not processed by humans) nucleosynthesis (big bang , star evolution, supernova,...) or as a radioactive daughter of such nuclei.
Note that elements created in any nuclear reactors or their daughters are not included.
So, like I said in post #3, by this definition all of the known elements would count as "naturally occurring", plus more that we don't yet know about. I can't prove it by direct observation, but given the size and energy available in a supernova explosion or neutron star merger, I think it's clear that all elements are produced, although some would be produced in realtively small quantities and would decay quickly.

#### .Scott

Homework Helper
Note that elements created in any nuclear reactors or their daughters are not included.
Are you saying that if it can be created in a reactor, then it is automatically not natural.
If so, I am pretty sure that would bring the number to zero.

#### A M

I can't prove it by direct observation, but given the size and energy available in a supernova explosion or neutron star merger, I think it's clear that all elements are produced,
That's only in theory; although there are many properties haven't been observed yet about supernovae. Even extremely high energy released in supernovae is an observed fact. So that's not that simple as you said.
If so, I am pretty sure that would bring the number to zero.
To simplify my definition, just think of a universe without human being and all its change (although difficult to imagine). Then all the elements that can be found in this ideal Universe are naturally occurring.

#### .Scott

Homework Helper
To simplify my definition, just think of a universe without human being and all its change (although difficult to imagine). Then all the elements that can be found in this ideal Universe are naturally occurring.
By that definition, all elements are natural. Nuclear reactors don't manufacture any elements that are not also created in neutron star collisions.

#### A M

Nuclear reactors don't manufacture any elements that are not also created in neutron star collisions.
Yes, but when we say all elements; it is not clear at all.
First, all elements haven't been produced by human yet. Also, they haven't been observed completely.
Second, we don't think of an exact limit of elements (As known); so in accordance with known observations the universe MAY contain some elements haven't been discovered, or there is a possibility for Future discovered elements not to exist in the universe.
That's all about possibility. How can you convince that ALL elements can be created in neutron star collisions?

Staff Emeritus
. For example, we call an element stable if its decay has never been observed (although it can theoretically go under rare decays).
So Vanadium-50 and Bismuth-209 used to be stable, but aren't any more? And Te-123 is stable today but will be unstable in the future? This seems like a very odd criterion.

#### .Scott

Homework Helper
That's all about possibility. How can you convince that ALL elements can be created in neutron star collisions?
I am not necessarily convinced that all elements are created in all neutron star collisions - although the greatest source of my doubt is related to what constitutes an element under those extreme conditions. Neutron starts are not elemental - and the soup that would splash out from them in a collision might defy any definition of what is and isn't an element.

I think the most workable definition of a "natural element" would an element that is present in the Earth's crust from a sources other than technology. So Uranium would be among the "natural elements", but Californium would not.

#### phyzguy

By that definition, all elements are natural. Nuclear reactors don't manufacture any elements that are not also created in neutron star collisions.
I agree with @.Scott . By your definition all elements are naturally occurring, including some that we haven't mangaed to synthesize yet.

#### A M

So Vanadium-50 and Bismuth-209 used to be stable, but aren't any more? And Te-123 is stable today but will be unstable in the future?
Why not?! (They thought to be stable)
"252 nuclides are considered stable. Many of these in theory could decay through spontaneous fission, alpha decay, double beta decay, etc. with a very long half-life, but no radioactive decay has yet been observed. Thus the number of stable nuclides is subject to change if some of these 252 are determined to be very long-lived radioactive nuclides in the future....
Such nuclides are considered to be "stable" until a decay has been observed in some fashion. For example, tellurium-123 was reported to be radioactive, but the same experimental group later retracted this report, and it presently remains observationally stable."
(Wikipedia)
"After being caught suffering a breakdown, the heaviest stable element on the periodic table has just lost its title. Clever new experiments with bismuth-209 have shown that the heavy metal actually does decay, a theoretical prediction that had defied verification by experimenters until now. The technique could help scientists search for dark matter, a fundamental--and fundamentally unknown--component of the universe." (Sciencemag)
"The spectrometer consists of a 4″×4″ NaJ-crystal with a double lead shield — the inner one being of selected lead — and a guard anticoincidence ring in between. The apparatus is situated in a cellar covered by 3 meters of soil. The total background above 0.03 MeV is 120 cpm, being extremely stable with an intrinsic r.m.s. variation below ±2 per mil. The crystal is surrounded by a sample container of volume 1.8 liters. An energy dependent gamma detection limit (2σ) ranging between 0.3 and 0.8 dpm has been obtained. This corresponds to a maximum detectable halflife of 1.0 to 2.7× 1018 years per mole of the radioactive nuclide in the sample container. In the case of vanadium-50 (isotopic abundance 0.25%) a lower limit of the half-life was found to be 9.0×1016 and 6.9×1016 years respectively for the two modes of decay V50-EC-Ti50*-γ(1.58 MeV) — Ti50 and V50-β−-Cr50*-γ(0.78 MeV)-Cr50." That's about you @Vanadium50 (link.springer.com)
There is also a difference between "can be found in nature" and "exists in nature"
When we say "found in nature" we mean observed (directly or indirectly) in the "observable Universe".
But according to information we have, "existence" is much more advanced; acceptable theories come from observational evidence, and acceptable Observations do have many limits. So we do not exactly know what exists in "Present Universe". We just know what we have observed and concluded from observations.
Technetium-99 has a half-life of 211,000 years. That would make the age of the Earth more than 4 million 99Tc99Tc half lives
How did you calculate this number? That would make the age of the Earth more than 20 thousand 99Tc half lives.
There is no universally agreed-upon definition of what constitutes "naturally occurring".
I agree with @.Scott . By your definition all elements are naturally occurring, including some that we haven't mangaed to synthesize yet.
To prove or at least strengthen a theory, your idea should correspond observations; for example the big bang theory wasn't so acceptable at first, but discovering (or analyzing) numerous observational evidence (like CMB, the expansion of space, Primordial gas clouds,...) made "the big bang picture too firmly grounded in data from every area to be proved invalid in its general features." (details beyond the scope)
- Do we have any observational evidence to convince that all (known) elements can be found and exist in supernova explosions or neutron star mergers?
If no, at least how many known elements are observed? (in the Universe)

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#### .Scott

Homework Helper
How did you calculate this number? That would make the age of the Earth more than 20 thousand 99Tc half lives.
You are right:
$(4.543 10^9) / (211,000) > 20,000$ $^{99}Tc$ $half lives$
Still, it only takes about 400 half-lives to eliminate an element from the Earth.

- Do we have any observational evidence to convince that all (known) elements can be found and exist in supernova explosions or neutron star mergers?
If no, at least how many known elements are observed? (in the Universe)
As I stated in an earlier post, I believe the only elements that are observed have been observed on Earth.

#### A M

the only elements that are observed have been observed on Earth
I don't agree.
They can be also observed indirectly in some regions of observable universe by "mass spectrometry" -a special type of indirect observation that can provide data for calculating the abundances of each ion even after supernovae- but as I said these types of observation are facing a lot of limits.

#### .Scott

Homework Helper
I don't agree.
They can be also observed indirectly in some regions of observable universe by "mass spectrometry" -a special type of indirect observation that can provide data for calculating the abundances of each ion even after supernovae- but as I said these types of observation are facing a lot of limits.
I did not say that you couldn't observe elements (such as Hydrogen) using a spectroscope. What I said is that I do not believe that there are elements that you can identify that way that have not already been identified on Earth.

Also, mass spectrometry is not a remote sensing method. If you wanted to use mass spectrometry to identify extraterrestrial elements, you would need to either retrieve samples and bring them back to Earth or launch the measuring device into space.

#### A M

You're right I meant spectroscopy. But I still do not agree. Supernovae -as has already been said- can create a lot of elements. Some of these elements -also as has already been said!- have too short half lives to exist on the Earth. Can't we observe these elements shortly after supernovae by spectroscopy -as you...!- ?

#### .Scott

Homework Helper
In theory, yes. But I believe there are practical issues that would make it very difficult. For one, when you see a supernova or nova collision, you are looking at it after it has had at least several hours to "decay" and you are looking at the outside layer of it. Most of what you see will be common elements. So looking for identifying marks of unknown elements would be challenging.

But suppose you did find a lot of new spectral lines. The next step would be to attempt what elements or molecules created them - and which spectral lines were from the same chemical source. Again, that would seem very challenging to me. There may be methods to accomplish this, but I have never heard of any.

In normal spectronomy, you compare an unknown to the spectrograph of your target molecule - so there had to be a sample of that molecule available to make that spectrograph. In this proposed nova case, you would need to look at a mix of spectral lines, separate them out into known and unrecognized lines, then group subsets of those unrecognized lines into elements according to a model of those elements.

A research chemist would be better at answering how practical that is. As I have said, I have never heard of a nova being measured and analysed that way.

There are enumerable spectroscope studies of novae. Common elements detected are Hydrogen, Calcium, Sodium, Iron, Nitrogen, Helium, and Oxygen.

Neutron star spectrographs are dominated by material orbiting those stars.
https://www.nature.com/articles/nature01159

Here's a super-nova spectrum:

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