It was a fraction separated from liquified air, which when placed in a Plücker tube connected to an induction coil yielded a spectrum with a bright yellow line with a greener tint than the known helium line and a brilliant green line that corresponded to nothing seen before. link Phantom Girl finds an ancient tablet at an archaeological project on a little island in the Atlantic Ocean in the 30th century, the LSH split into two teams & set off in Time Bubbles to Earth & Krypton's “remote past” to investigate “The War Between Krypton and Earth”.
As it turns out a group of Kryptonian scientists set up shop on Earth because they were persecuted back home.
Too bad the uninhabited Earth had already been colonized by the Vruunians who had established a town called Atlantis. After the "Civil War of the Legion" that saw the two teams taking sides with their new friends, came this inevitable ending after Brainiac 5 uses "artifical evolution" to turn the Atlanteans into mermen:
LSH & Superboy © DC Comics