Kryptonian civilization is at least 100,000 years old and many millennia more advanced than human civilization on Earth, and had begun exploring the Milky Way Galaxy. Kryptonians later abandon these projects in favor of isolationism and artificial population control, engineering newborns for pre-determined roles in society. The planet's resources were strained, and the stability of the planet was threatened by careless mining of the planet's core. As Jor-El attempts to warn the Science Council of their folly, General Zod stages a coup. In hopes of preserving the Kryptonian race, Jor-El steals the genetic Codex of the planet (a list holding the DNA pattern of everyone yet to be born on Krypton) and infuses it into the cells of Kal-El, the first natural-born child on Krypton in centuries, and sends his son to Earth. Zod kills Jor-El and is arrested by the authorities. He and his followers are banished to the Phantom Zone shortly before Krypton is destroyed.