Operation Hitchhiker

Operation Hitchhiker, as it was called by Robin, refers to an incident involving the destruction of Krypton, when one particular chunk of Krypton, called the sky stone, was sent hurling in the direction of Earth from the massive explosion, and it was likely caught in the warp field of the Kryptonian Space Ark.

The Kryptonite that eventually reached Earth had traces of Kryptonian mushroom spores on it, which hitched a ride to Earth on the Kryptonite.