How long have humans been on the earth for?

It would very much depend on your point of view and your belief in a deity.

Some religions proclaim mankind has been on earth for about 6000 years, others believe differently.

Scientifically Modern man, Homo Sapiens, is believed to be on the order of 50,000 years old. There were, of course, precursors to the genus. Neanderthals and Cro-magnon for instance. For which there is evidence dating back much longer.