Question

Explain how the earth is round and not flat

Answer 1

Aristotle (who made quite a lot of observations about the spherical nature of the Earth) noticed that during lunar eclipses (when the Earth orbits places it directly between the sun and the moon, creating a shadow in the process), the shadow on the Moon's surface is round.

Answer 2

It is a conglomeration of rock that collected together over time, and it rotating in a spinning ball that is orbiting a sun that is in the middle of our solar system. 

You should look at a picture of the earth from a satellite.<span />