Krypton was one of the few worlds capable of defending itself from all conquerors. The planet was home to the most advanced civilization in all the universe but these people kept themselves isolated. They had long since banned all off world travel. For years they kept to themselves to the point of refusing to even acknowledge life away from Krypton, when a respected scientist called Jor-El began desperately trying to warn the planet of the coming of the world devourer Galactus he was scoffed at and threatened to keep his mouth shut. He began work on a space craft to take his family away and had just finished his test shuttle when the Herald arrived. The Kryptonian army attempted to fight but it was for not as it's master arrived.
Jor-El knowing he had no more time loaded his son Kal-El into the craft along with a small device containing the sum total of Kryptonian knowledge and launched just as Galactus began his meal. The shuttle traveled far beyond the speed of light allowing it to transverse galaxies in seconds before coming in contact with a world that would be habitable by a Kryptonian. The craft landed in a field outside the small town of Hope, Kansas. Jonathan and Martha Kent were sitting on the back of their truck star gazing, Jonathan was trying to comfort Martha who'd been told earlier that week that she was incapable of bearing children by a fertility specialist. She was the first to notice the landing craft and talked Jonathan into investigating it with her.
Hours later the were back at home, Jonathan had hid the craft in their barn and a representative from child services was called. They told her the baby had been abandoned in the field. She was an old friend of Martha's and was more than happy to recommend them as foster parents for the child and after a few months of what the Kents knew would be a futile search for the birth parents they adopted the child they now called Clark.