Question

when earth was dicovered

Answer 1

when we are not alive

Answer 2

Early Greek philosophers alluded to a spherical Earth, though with some ambiguity. Pythagoras (6th century BC) was among those said to have originated the idea, but this might reflect the ancient Greek practice of ascribing every discovery to one or another of their ancient wise men.

By Aristarchus of Samos, and later in Nicolaus Copernicus' heliocentric system (De Revolutionibus Orbium Coelestium, 1543), the Earth came to be considered a planet revolving with the other planets around the Sun, in the following order of distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, and Saturn.