But, for a time, there were heroes on Earth that predated Superman, but not the younger version of Superman, Superboy.
Here's a quick bit of history on two of DC's founding super-heroes, and a unique thing that links them together!
Superman First Appearance
As the years went by, more details were added to the origin and life of Kal-L of Krypton, and he helped found the Justice Society of America, joined the All-Star Squadron, and even married Lois, as well as meeting many heroes from other worlds as well, as the world which this Golden Age Superman grew up and protected had come to be referred to as Earth-2.
Superboy First AppearanceLegion of Super-Heroes from the future, and eventually being the Superman who helps found the Justice League of America, and meeting even more heroes, as this Superman on the world which was called Earth-1.
Why, Superboy of course!
In the New Adventures of Superboy #15 (March, 1981) by Bob Rozakis, John Calnan and Tex Blaisdell, "Superboy Meets Clark Kent". While fighting a freak tornado in Smallville, Superboy finds himself transported to another Smallville, but earlier in time (the early 1930s), and figures out he has not only transported in time, but to another dimension. While checking around, Superboy meets the young Clark Kent of this world, who has strength and speed beyond those of normal men, but was planning to join the circus.....so, Superboy starts to train young Clark in the use of his powers.