1) They all lived before Ussher. 2) Kepler's an Astronomer, Scaliger's a writer, Newton was a physicist, I never hears of any of there vast studies of history. Newton, for your sake, I have heard of, and he gives 4000 BC, so round and without further chronology, we all know it was an estimate, the precise number given by Ussher, who was among the great revival of history in the Renaissance.