Black Adam is finally in theaters and not only is it introducing new characters, such as the heroes of the Justice Society of America, to the DC live-action stage, but other world building details as well including. Among those details is the introduction of the element known as Eternium and while it is something that ends up playing a rather interesting role in Black Adam, it's actually something with its roots in comics history and could end up ultimately being a larger part of the future of the DCEU.
Warning: spoilers for Black Adam below.
Eternium is introduced pretty early on in Black Adam, where it's shown that King Anh-Kot enslaved the people of Kahndaq and forced them to mine for the element so that he could create the Crown of Sabbac. It's also shown that, in modern times, Intergang has been oppressing the people of Kahndaq and mining for Eternium for their own weapons and purposes so it's definitely a very useful element. But what ends up being truly interesting about it is that it's shown in the film that Eternium is the only thing that can harm Black Adam. Think of it as Superman's Kryptonite in a sense.
Eternium in comics
That Eternium can weaken or harm Black Adam much like Kryptonite does Superman is taken right from comics. First appearing in Legion of Super-Heroes (Volume 4) #110 in 1998, Eternium is the name given to shards of matter that were cast when the Rock of Eternity was destroyed by Dr. Savant in his attempts to rid the universe of all magic. Being close to Eternium removes or nullifies Black Adam's powers — and interestingly, does the same for Shazam as well. Actual physical contact with Eternium can also cause injuries to these figures which makes it pretty serious business for both Black Adam and Shazam.
Given that Eternium is significant to both Black Adam and Shazam, its introduction here very much feels like something we will see again especially with how Black Adam ends. Black Adam ends up defending Kahndaq and becoming its champion with both Amanda Waller declaring that Adam can operate only within the borders of Kahndaq and if he steps out of line there will be some major consequences. Given that it's Waller, it isn't too much of a stretch to consider she's got herself a supply of Eternium, just in case.
Interestingly, Black Adam isn't our first live-action reference to Eternium. The element is mentioned in Season 6 of The CW's The Flash when Nash Wells arrived looking for items containing the element as he chased The Monitor across the multiverse.
Black Adam is in theaters now.