Download Action Comics #252
Supergirl, or Kara Zor-El, first appeared in Action Comics #252 (May 1959), in a story called “The Supergirl From Krypton!” written by Otto Binder, who would go on to pen a number of Supergirl stories, and drawn by Al Plastino (although Jim Mooney would become the artist most associated with the early Supergirl).
The story begins with Superman spotting a rocket crashing to Earth with his telescopic vision. He expects the inhabitant to be dead when he reaches the rocket, but to his surprise, the perky blonde teenager inside is not only very much alive, she’s wearing a costume like his and appears to know all about him. Her story, as she tells it, goes like this:
When Krypton exploded, a large chunk containing Argo City drifted into space, surrounded by a bubble of air (later changed to a protective dome so as to be slightly more plausible). When the ground turned to kryptonite, as every piece of the doomed planet eventually does, scientist Zor-El (brother to Jor-El, Superman’s father) laid down a sheet of lead to protect the survivors. Years passed, and Zor-El and his wife Allura2 had a baby, named Kara Zor-El in the patriarchal, vaguely Russian Kryptonian tradition.
When Kara was fifteen, a meteor shower pierced holes in the protective lead covering and exposed the Argonauts3 to deadly kryptonite radiation. Thinking fast, Zor-El and Allura used their telescopes to discover the whereabouts of their nephew Kal-El, then sewed Kara a costume resembling Superman’s and placed her in a rocket, which they sent to Earth in the nick of time.
*courtesy of It's a bird! It's a plane! It's Supergirl!