Other than extinct organisms and species what else animate or inanimate material, element or form has completely disappeared from planet Earth.
What would fit in the ‘animate’ category but not be an organism?
How would elements disappear?
Not sure if this counts, but Technetium (number 43 on ye ol periodic table) does not occur naturally on earth. It forms naturally in stars and would have been present when the Earth was originally formed, but none of its isotopes are stable and all of the Technetium that was present on Earth at its formation has long since decayed.
But… (and this is why it might not count)
We do produce it artificially. It has a lot of uses in things like nuclear medicine scans and some industrial uses, and we end up producing a bunch of it since it is one of the waste products found in spent nuclear fuel rods.
Some of the other rare elements in the periodic table are artificially produced. Off the top of my head I’m not sure if those are produced in stars as well.
Well, before WWII, essentially all the Plutonium that existed when the Earth was formed had disappeared. Not 100%, of course, but 99.99999% or so. Plutonium needs to be created in a reactor, and the only two natural ones (in Africa) stopped working millions of years ago. Some vanishingly small amount might be created by chance, but in quantities too small to detect.
But, if one atom counts, then even Plutonium hasn’t completely disappeared.
Doesn’t helium escape into the atmosphere? I’ve heard both extremes about whether this is a future concern or not, and don’t know the current research.
We lose gases to space constantly. Helium was unknown on Earth before being discovered in the spectral lines in sunlight. There was a lot of it still here, trapped below ground, but any in the atmosphere would escape undetected into space. Is that what the OP was looking for?
Greek fire. A major weapon in the 7th century that changed the course of history. No one knows for sure what it consisted of.
Yes, it does. Helium for balloons and such is created naturally by radioactive decay. Any helium that escapes from balloons or isn’t captured during industrial and other uses ends up in the atmosphere and eventually escapes off into space.
For a while, helium prices were kept artificially low. The federal government had stockpiled a bunch of helium, but had racked up a large debt while doing so. To clear the debt, they sold off a lot of the helium, which kept helium prices artificially low. If I recall correctly, the helium sell-off is set to end within the next few years.
Helium is currently produced as a waste product or by-product of something else. For example, a lot of it is typically collected when companies are actually going after natural gas. Many of the scares reported in the news a few years back were just typical media over-hype. The Earth produces a lot of helium through radioactive decay, and there’s a lot of it trapped in pockets all around the globe. It’s just a lot harder to get to now that the federal government isn’t flooding the market with cheap and easily obtainable helium.
There’s some naturally produced technetium on Earth, although it’s very rare. I believe it’s produced by radioactive decay of some other isotope although I’m not sure what decay chain. There’s also some naturally occuring plutonium on Earth, which is in the decay chain of uranium.
Helium-3 is not produced by radioactive decay, so it’s extremely rare on Earth, but not completely absent. You may have to measure how common it is in parts per trillion or something like that, but it’s not totally absent.
Voyager 2
I’m interpreting your OP as meaning not animals (i.e., no dinosaurs or dodos or what have you).
But I was always intrigued by the story of Silphium - Wikipedia
Replacement parts for my 10-year-old microwave oven.
Atlantis.
It’s there, just under the sea now.
Non-artificial orbital satellites beside the moon? I’ve read speculation that during its early lifetime, the Earth would have been surrounded by an orbital debris field. The formation of the moon either pulled those objects into its gravity well such that they became part of the moon, or the debris’s orbits were destabilised causing them to fall to Earth.
Somewhat supported by the Wikipedia article on the formation of the moon:
Judging from the news, my vote is for common sense.
Just remembered…few languages have disappeared
Also many types of musical instruments have no players or makers.
The Earth does get temporary moons, asteroids that happen to encounter a specific spot where they change from a solar orbit to Earth orbit. I forget if it’s the L1 or L2 spot, but one of those or maybe either. They usually only orbit a few times, before hitting that spot again and leaving Earth orbit. Their periods are generally several months long though. I understand that there may be several around at any one time, although we rarely discover them.
As far as elements go, the only things I can think of are those with very high atomic number, above around 105 or so. They won’t occur naturally, since they require a particle accelerator to be created and only last a few hours at most. However, the OP did not specify that they’re only interested in naturally occuring elements.
Ten zillion books about it, despite being obviously a product of that well known fibber Platos imagination. It was a parable, not a history. No one took it as history then.