In the comments for my essay on THE GHOST OF KRYPTON PAST, AT-AT Pilot posted the following:
What is the mythical significance of the fire-fall crystals and Kryptonite? Why is it that the remaining fragments of his doomed planet hurt Superman? Is it supposed to be interpreted as a painful reminder of a past that he wishes he could forget? But of course, Superman has been written to be appreciative of his Kryptonian roots, with the Fortress of Solitude serving as a museum for his mementos. (The one time I can recall Superman distancing himself from his Kryptonian self was the last issue of the Byrne series, where--if I recall accurately--Superman asserts that he is now earth's son, not Krypton's.)
Kryptonite may have the most involved backstory of any element in the Superman mythos.
One of the most egregious mistakes about kryptonite is that it was introduced because Superman was so mighty that he had no weaknesses. That may be true of Superman as he had developed in 1949, when kryptonite officially entered the comics-canon in SUPERMAN #61 (1949). However, the Superman who had been produced for DC by the studio of Jerry Siegel and Joe Schuster did not need a specific weakness. Throughout the eight-or-so years that the studio elaborated the nature of the Man of Steel, the hero was occasionally seen being stymied by energy-rays or mental powers. (The moderately famous "Powerstone" story even shows him being briefly mesmerized by the hypnosis of guardian serpents.) I don't know at what point the hero became so godlike that he could fly into the heart of Earth's sun without taking harm, though I'm reasonably sure that it took place after DC kicked Siegel and Schuster to the curb in the late 1940s. But the point is that Siegel himself never thought of his pre-eminent creation as being invulnerable in the way later DC editors defined the term.
And yet, in 1940 Siegel birthed the basic idea of kryptonite in a story rejected by DC's editors and then squirreled away in a vault for the next fifty-plus years. "The K-Metal from Krypton" only came to the light of day because in 1994 Mark Waid, working on staff for DC, encountered the story in the files and made known its contents to comics-fandom. It's been further theorized that though DC never published the story (except for a very brief excerpt in a 1960s annual), Whitney Ellsworth made all Superman material available to the writers of the 1940-51 SUPERMAN radio serial, and that one of those writers used Siegel's K-metal story as a template for the 1943 episode "The Meteor from Krypton," in which the name "kryptonite" was first used for the radioactive mineral that could bring death to Krypton's only surviving son.
Since the Siegel story was not completed at the time of its composition-- though the aforementioned site provided a modern interpretation-- we can't know exactly why Siegel introduced the K-metal. But as I mentioned above, Siegel's Superman did not need a specific weakness, because he was already vulnerable to a handful of esoteric menaces. The most likely reasons are that (a) Siegel wanted to inject a new level of drama into Superman's adventures, in part by revealing his identity of Clark Kent to Lois Lane, and (b) to get that drama, the hero would find his mighty powers endangered by metal from his homeworld. Siegel could have conjured up any kind of power-draining entity or material, but I'm sure that on some level he appreciated the irony of Superman being weakened by a fragment of his own world. Indeed, on page 15 of the modern interpretation, Clark Kent muses that originally he derived "great strength and powers from the planet," which might be the only time Siegel had ever advanced that particular explanation of Superman's powers.
I'm not aware of any examples from folklore or myth in which a hero's strength is either increased or depleted by contact with native soil. The only example in which native soil increases a character's mojo would seem Bram Stoker's 1897 DRACULA. To the best of my knowledge, Stoker made up the idea of the vampire needing to rest in his native Earth out of whole cloth. But there can be no question that Stoker gave the idea special significance, for I just happened to cover the matter in depth in my 2008 AA essay A MOVABLE FEASTER. I wrote in part:
Early in the novel, Dracula tells Jonathan Harker:
"Why, there is hardly a foot of soil in all this region that has not been enriched by the blood of men, patriots or invaders."
Naturally, at that point in the novel, the vampire does not dwell on how this "blood-enriched" earth is going to make it possible for him to pick up stakes (so to speak) and invade merry old England. But much later in the novel, Van Helsing goes into greater detail about Dracula's literal need for earth that has been sanctified (as well as ensanguinated) by the past:
"There have been from the loins of this very one [Dracula] great men and good women, and their graves make sacred the earth where alone this foulness can dwell. For it is not the least of its terrors that this evil thing is rooted deep in all good; in soil barren of holy memories it cannot rest."
So in Stoker's mythos the sacred earth of Dracula's Transylvania is replete with both "the blood of the heroic dead" and "memories of great men and good women." Blood, then, is not just plasma and platelets in Stoker's cosmos, but rather the objective correlate of life itself, a sort of vitality that doesn't vanish with the deaths of individual humans but which seeps into the earth and sustains the life of a vampire quite as much as feeding off the blood of the living. This "sacred earth" explanation may explain how Dracula and his vampire brides managed to survive without exsanguinating every last mortal left in the region, especially given that Stoker's Transylvania often seems like a barren Hades-on-Earth, lacking the vitality that Dracula praises in past generations of his land. Stoker, in formulating this notion of the vampire needing to take his native soil with him when he departed for other climes, was thus overcoming the folkloric notion that a vampire had to return to his grave. Thanks to Stoker, Dracula could take his grave with him as he travelled.
To be sure, Stoker never has any scenes which directly prove Van Helsing's assertion about Dracula's dependence on Transylvanian soil-- that is, scenes like having Dracula try without success to sleep in English soil. But apparently whatever "blood-memories" in Dracula's native soil nourish the vampire, that vitality can be trumped by a greater vitality, as Van Helsing uses holy wafers, presumably blessed by the Catholic Church, to make some of Dracula's earth-filled coffins useless to him. (Side-note: the "holy water" device popular in many later vampire-tales appears nowhere in the original novel.) Still, the original folklore-limitation does crop again with respect to Dracula's only vampiric convert in England, for apparently Lucy Westenra can't just go anywhere she likes, but is obliged to return to her mausoleum at daybreak. Stoker does not emphasize her dependence on being close to English soil, but one must presume that she has some such dependence on returning to her original grave.
I think it's pretty likely that by 1940 Jerry Siegel had read DRACULA, though I don't know that he ever committed to posterity any comment on Stoker's greatest work. A long time ago I read a vampire story Siegel did for his 1930s series DOCTOR OCCULT, but I don't recall any special Stoker quotes therein. But writers are packrats, and I think it very likely that he picked up the symbolism of "beneficial earth" from Stoker and later transformed it into "inimical earth" for his superhero.
Oh, and though it has nothing to do with the derivation of kryptonite, the title of this essay I rook from the King James Bible, wherein God tells the murderous Cain that he's "cursed from the earth"-- meaning not that the earth is literally poisonous to Cain; just that the earth won't give him sustenance. Readers of this blog should know that a day without a myth-quote is like a day without sunshine.