The exploded parts of Krypton circled the sun for years in the form of asteroids. This one eventually came within the Earth's gravitational pull.
8 seconds sound clip from Superman (1948) - The Reducer Ray (Chapter 3).
You can hear this line at 00:17:23.877 in the Blu-ray version of the episode.
Quote context
[...]
- Morgan has already made a test. The meteorite contains nothing dangerous to us.
- Is there anything wrong, Mr. Kent?
- I don't know. I don't think so, please go on.
- Now, you'll see what I mean when I say this meteorite is different.
- The fragment glows with its own inner light. We don't know why.
- Operator. Get me the car. Clark Kent just died in my office.
- Is it possible that Clark Kent, mighty Superman, can really be dead?
- What terrible power does this strange metal wield over the Man of Steel?
- Be sure to see Man of Steel, the fourth action chapter of Superman at this theater next week.
[...]