[Beijinger]

I had a look into his book. It is not written very scientifically. From a review: "A true academic work would have been far more careful to distinguish between what is hard evidence and what is inference, assumption, and hypothesis."

But it is a fact that America was known and had settlements before Columbus https://en.wikipedia.org/wiki/L%27Anse_aux_Meadows

[Cthulhu_]

Known by Europeans; it's been "known" / inhabited for at least 10.000 years. As far as I'm aware there's no records of other major players visiting / "discovering" it though besides the Norse.

[benxh]

It was known by Polynesians for at least 1000 years before Columbus. See sweet potatoes.

[coldtea]

Where do you think the Native Americans came from?

They are not exactly descendants of the Norse.