The Clown Prince of Crime
Super Freak
The codex was just an old Kryptonian skull with the DNA of billions or trillions of Kryptonians imprinted onto/into it. Either no more DNA recombination is being performed, or it's extremely controlled. But the original unaltered DNA of those ancient Kryptonians is imprinted onto that skull, so Jor El decided to put that data inside the one and only survivor from Krypton . So, while the planet is gone, the natural DNA of trillions of Kryptonians still survives, and so there still exists the possibility of recreating the Kryptonian race, if nothing else. It makes sense