When we say "discovered " in such cases we usually have in mind a special meaning of the word.
We want to say that people from one civilization came to an area where no one from their neighborhood had not been.
As you probably know, the explorers often encounter people and a civilizations that are already in place which he "discovered".
So why we don’t we say that these people found these places first?
From the standpoint of western civilization, we say that Columbus discovered America because after his discoveries in the “New World”, people from the “Old World” began to settle there.
But another 500 years before the birth of Columbus, the old Normans from Scandinavia - the Vikings also found one " piece " of the New World .They sailed west and discovered Iceland, then Greenland , and then later the U.S. mainland.
And did you know that there is a Chinese folk legend about an even earlier trip, when Chinese sailors discovered today’s California?And people from Pacific Ocean islands still sing about famous people from their history, who sailed to South America long before white people arrived to South America and to their island.
As we know , they could be many research era thousands of years ago.
And certainly it was before Columbus.
We could possibly say that neither they nor Columbus, neither Normans had "discovered" America. Native Americans - Indians were living there for centuries before the white man came.
And who can say that they have not arrived in America after such a research endeavor?
It is believed that the Indians came from Asia, but no one knows when and how.
They must have settled over many centuries in different ways.