to life as we know it? In other words, are there any elements that were utterly unstable as some of the artificial one are, would we not be here today.
All of the transuranic elements are almost certainly unnecessary for the earth to have formed and for life on it. None of them as far as we know have long enough half-lives.
I suppose it might be possible that without uranium, itself, the earth’s core would not have remained hot enough so that there was not enough heat to keep the core still molten so there would be no magnetic field and high-energy solar radiation would destroy life, but that is as close as I can come to thinking of an unstable element that might be necessary.
I’m not sure if you’re asking from a biological or sociological point of view: Would life without atomic bombs count as “life as we know it”? Because without plutonium, it’d be harder (though still not impossible) to make atomic bombs.
Enriched uranium works well enough.
There are four unstable elements below uranium in the periodic scale, and they’re unnecessary to life. As are the rare earths. As are most of what’s left. It’s a far more interesting question to ask, which elements are necessary? It’s a surprisingly short list.
And for most purposes, trans uranic elements and artificial elements are synonyms. I believe that tiny amounts of plutonium have been found in nature and perhaps one or two others, but they were all originally developed artificially, as were the sub-uranic unstables.
Plutonium, Neptunium, and Curium have isotopes with half-lives in the millions of years. Long enough for traces to have survived a billion or two years, well after the formation of the Earth and the origin of life.
Technetium, with no stable isotopes, is not fund on the earth, but is used in a couple of medical diagnostic procedures. But hardly necessary for life. How could it be if there isn’t any?
A thousand half-lives is far too long for traces to have survived, even if by “trace” you mean “one atom in the entire observable Universe”. There are naturally-occurring traces of plutonium, not because it’s lasted that long, but because the processes which produce it are still occurring.
You don’t get to have that many half-lives. Remember that the Earth started with shedloads of the stuff. The mass of the Earth is approx 6x10^24 Kg. If we assume that originally a mere 1% of that was transuranics, that’s still 6x10^22 Kg. Take the half-life of 80MY for Plutonium and you’re left with about 1.5x10^19 Kg after a billion years (12 half-lives) and 1.8x10^15 Kg after 2 billion (another 13 half-lives). Even if you assume 0.1%, then you’re still looking at a very large mass of transuranics.
Yeah, I was looking at the figure in that post of “millions of years”, and didn’t look it up. Billions of years divided by millions of years is about a thousand half-lifes, but I wouldn’t describe nearly a hundred million as just “millions”.
They are ALL necessary.
All of them, even the most unstable & thus temporary ones, have to be there at the appropriate spot in the periodic table. Otherwise it would mean that atomic structures & physics as we understand it is wrong. Though that probably would not qualify as “we not being here today”. Except maybe if some atomic scientist tried an experiment based on an incorrect understanding of atomic physics – that might result in us not being here!
Ah yes…neither the transuranics nor the suburanics but that small group known as “the uranics,” composed of one known element. 
With Earth having coalesced approximately 4600 million years ago, you can figure out the requisite information by calculating, first, k/4600 = n, where k is the half-life in millions of years, then, second, p=1/2[sup]n[/sup], n being the result from the first equation and p becoming the proportion of the original amount of that isotope left.
Do not forget that nothing heavier than Lead-208 is stable, though Bismuth-209 has a half-life of 1.9x10[sup]19[/sup] years – a billion times longer than the age of the Universe, and Thorium-232 has a half-life only slightly shorter than the presently estimated age of the Universe – nearly half of all the primordial thorium-232 still exists as thorium. However, the decay cascade from thorium and the two isotopes of uranium mean that radioactive isotopes of elements from plutonium to polonium, plus radioisotopes of bismuth, lead, thallium, and mercury, exist in nature in at least trace quantities owing to breakdown of the three long-lived “:metastable” radioisotopes.
Only six elements are absolutely essential to life: carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, though most lifeforms require a wide variety of others for particular uses: sodium and chlorine for normal salinity of body fluids, calcium for shell or skeletal formation, magnesium and potassium for calcium metabolism, iron for hemoglobin, cobalt for Vitamin B-12, copper for hemocyanin, iodine for thyroxin, etc. Over half the lower half of the periodic table is required by at least some creatures.
Building a shirtsleeves environment calls for even more of the periodic table, as people hav e noted above. And there’s a rather metaphysical but scientifically valid point that, for life as we know it to exist and function as it does, the universe must follow the known laws of physics, which entail the existence of most known elements. For example, for a concentration of non-H/He elements to exist sufficient to build the Earth, supernovae had yo occur, with the nuclear-physics reactions and products that entails, seemingly inclyuding californium, one of the higher transuranics.
OK well let me kind of reverse this question. What do we currently use the transuranic elements for today? Is there any practical use? If not what do we use them for?
I came into this thread to post a somewhat similar assertion;
If these elements didn’t exist, the fundamentals of physics would be different, and probably incompatible with life as we know it in this universe.
[Dr. Magnus Pyke]Science![/Dr. Magnus Pyke]
Some models of smoke detector use a small amount of americium, atomic bombs generally use plutonium, breeder nuclear reactors (which aren’t used in the US, but are elsewhere) reprocess spent fuel into plutonium for energy generation, and I’m pretty sure some transuranics are used in medicine for things like killing cancers, but I don’t know the details there.
Well, it’s found around molybenum and uranium as they decay but the lack of it has put a big crimp in the medical diagnostic business of late with all the shortages.
That is a much better way of saying what I meant. Congratulations!
Semi hijack - I’ve heard that somesuper heavy elementsmay be stable. Any truth to this? If true, why wouldn’t elements that heavy be found on earth? I understand the unstable super heavies might have existed but would have decayed long ago.
ETA: By ‘truth’ I meant more than at the purely theoretical level. IIRC one past claim of a new element being produced didn’t pan out.