Physical proof of alien activity.
An object of indeterminate origin has been found. It is sent to a lab for analysis, but the lab cannot identify the material it's made of. Similarly, when the heroes ask the lab to identify the mysterious glowing substance found at the crime scene, the reply may come back: organic-based, but unknown. Sometimes the scientists go so far as to say conclusively that whatever it is, it cannot be found on Earth.
Such substances are something of a MacGuffin. Often they do not possess any special properties or behaviors, although at times they are found to be Unobtainium. The purpose of declaring a substance to be Not of This Earth is to "prove" extraterrestrial origin or activity.
There are several ways to handle this trope plausibly: the substance could be made of known elements that are present on Earth but are far too rare to make an object as big as the one being investigated, or perhaps in isotope ratios not typical of Earth or the Solar System, or else it should be a manufactured substance using techniques beyond Earthly science.
- Not quite aliens, but the trope comes up in Death Note. The police get their hands on a Death Note after the Yotsuba arc, and their lab reports state that the paper matches no known earthly substance.
- Darker Than Black has a lot of this. Besides the Alien Sky and Differently Powered Individuals that suddenly appeared with the Gates, some really weird crap comes out of said Gates. Like stone flowers that grow and can be used to make a drug, a crystal that makes Contractors more powerful, or technology that lets the user alter memories. Even the scientists studying them occasionally have to just give up and say that Reality Is Out to Lunch.
- Witchblade is a strange case. In the original, Witchblade was presented as a reproducing creature (it has parents). Shapeshifting, tank-ripping symbionts have few in common with Terran life. So the creators of the adaptation surrounded it with some alien flora in Dream Within a Dream episode endings — and it doesn't look out of place there.
- When Bulma first examines the namekian spaceship in Dragon Ball Z, she says she's never seen anything like it and that it isn't metal. Her father couldn't build his own ship based on it as he couldn't replicate the materials.
- In Tintin, Flight 714, they find an alloy of cobalt and a few common metals. Cobalt is common enough, but cannot be found in this form, apparently.
- In Superman III, Richard Pryor's character does an analysis of kryptonite, and the results indicate that a certain percentage of it is simply "unknown". Looking at a cigarette package, he writes in "tar".
- In Man of Steel, Jonathan Kent mentions that he had a tiny piece of Clark's ship checked out by a scientist who said that it didn't match anything in the periodic table.
- In Predator 2 the creature's weapons are made of metal that doesn't fit in the description of any known element. For a little extra verisimilitude, we actually see the scientist putting a sample into their Spectroscope, and being totally confused by the results.
- In Clash of the Titans, Ammon says of Perseus's sword:
Ammon: What is this strange metal? It is neither brass nor iron. It is like no metal that I have ever seen... By the gods!... I was right to say "by the gods". Who else could make a sword that slices through solid marble, without leaving the slightest blemish on the blade?
- H.P. Lovecraft:
- One of the earliest examples is "The Colour Out of Space" — where the mysterious Green Rocks are not only an alloy unknown on earth, but of a colour unknown on earth.
- An idol depicting the eponymous Eldritch Abomination appears in "The Call of Cthulhu"; it's made out of stone that scientists are unable to identify. The matter from which it was made was brought to Earth by the Great Old Ones.
- "The Whisperer in Darkness" contains artifacts made of a metal unknown on Earth, mined on the dark planet Yuggoth.
- In Sphere, a sample of the hull of a supposed alien ship is analyzed and found to be made of common elements, but they've been worked into a composite form that nobody yet knows how to duplicate.
- The metal used to make the special swords in Highlander. A scientist studied them and determined there was no metal that behaved like this on earth.
- Plutonium-186 in the Isaac Asimov novel The Gods Themselves. Chemists and physicists are befuddled by an isotope of plutonium whose nuclei shouldn't hold together for more than a trillionth of a trillionth of a second, according to the natural laws of our universe. Then, one scientist realizes that the reason plutonium-186 can be stable is because it brought a bit of the physics of its home universe with it.
- Subversion: In the House episode "Cane and Able," Chase removes a small piece of metal from the shoulder of a boy who claims he has been abducted by aliens.
House: The results came back. The lab cannot identify the metal. Said it might not even be terrestrial.
Dr. Chase: Really?
House: No, you idiot. It's titanium.
- Cleverly averted in an episode of The Equalizer. The title character helps a street crazy who claims to be an alien; it turns out the man is actually a brilliant research scientist who presumably snapped when corrupt execs forced his invention away from him... however, at the end, he's disappeared, and it's discovered that the metal medallion he left behind "was manufactured in a vacuum." "You mean," the Equalizer demands, "this thing was made in outer space?" His assistant shrugs and grins. "They just don't know." note
- The odd watches carried by angels on Port Charles. Victor's lab cannot identify the metal.
- Silicon-based biotic material or DNA containing more than four bases are sometimes mentioned in The X-Files. For instance in "The Erlenmeyer Flask", a scientist is baffled by Scully's sample. Surprisingly for Scully, it is not monkey pee, but extraterrestrial material.
"A fifth and sixth DNA nucleotide. A new base pair. It exists nowhere in nature. It would have to be, by definition... extraterrestrial."
- Stargate SG-1:
- Done with a Jaffa in the pilot episode.
Doctor: [removing a larval Goa'uld] It's not human!
Jack O'Neill: Ya think?
- Very early episodes treated Naquada like this; before they learned the name, they referred to it simply as "the Stargate element," because it was unknown on Earth.
- There is super-strong/light metal trinium.
- Done with a Jaffa in the pilot episode.
- In several episodes of Doctor Who over the series run. At one point the Third Doctor specifically was testing for something that he knew couldn't exist on earth.
- Occurs in Smallville with kryptonite, various Kryptonian devices, and other alien materials.
- In The Rocky Horror Show, Doctor Scott tries to distract Brad from realizing that Frank has outed him as Nazi by pointing out that a nearby machine is made of a metal that is not of this Earth and probably from another planet.
- Subverted in Condemned 2: Bloodshot. One of the TVs displays an interview with a scientist who has been analyzing samples of the metal that the Oro Invictus use to enhance their powers. When he explains that he cannot place the origin of the metal fragments, the interviewer immediately suggests that the metal pieces fall under this trope. However the scientist shoots this theory down, stating that the pieces are of Earthly origin; they're just made using a previously-unknown manufacturing technique.
- Shin Megami Tensei IV: Neither Sanat nor the Ancient of Days are made of materials native to the Universe, which only further proves how alien they are to it. Scans only end in Error messages.
- X-COM: UFO Defense has both a straight example and a subversion:
- UFOs are powered by Elerium-115, which can only be obtained by capturing ships with their reactor intact.
- UFOs are made of "alien alloys", but once reverse-engineered, it turns out those alloys can be produced using Earth technology.
- Grrl Power: Subverted. Deus (with great difficulty) manages to find the geode that contained the substance that gave Maxima her powers. He didn't find anything particularly interesting, just a few exotic isotopes, "but nothing we've never seen before." The Rant specifically mentions that the idea of elements not on the periodic table is silly, since we have the periodic table pretty well mapped out.
- Superman: The Animated Series: In "Knight Time", Superman and Robin's search for Batman uncovers evidence that he was targeted by mind-controlling nanites. They capture the Mad Hatter, who denies involvement and, when allowed to examine the nanites, declares them to beyond any technology he's seen and suggests an alien origin. Admittedly, alien origin (e.g. Supes himself) is rather less unusual in this universe.
- A standard element in alien crash cover-up conspiracy theory. Some people claim to have found some metal debris near the crash site, allegedly part of the alien ship. Said metal usually is strangely light, yet highly resistant to impact (often said to be bulletproof). To this date, no such metal has been subjected to public scrutiny.
- A historical real life example is Helium — the second most common element in the entire universe as we currently understand it — which was detected and identified as a new element by analyzing the spectrum of the Sun's chromosphere in 1868, fourteen years before the same spectral line would be first detected on Earth as well and twenty-seven before the element itself could be properly isolated here. In fact, all the other Noble Gasses were similarly unknown as elements until well after much rarer ones had been discovered and studied.