The Greeks actually knew how the Earth was curved, and you can see it too. Do this: buy some binoculars or a telescope and go to any port where you can watch the ships.
Now: pick a ship leaving port and heading off for the horizon. Now, watch as it disappears, as if it was going down a hill. This is because of Earth's curve-figure it out.
Oh, and by the way: I suppose you've never actually been to the south pole? Despite the fact that we've been all over the globe, and should have long ago seen this mystical ice wall...But, no pictures, no nothing. Just your good faith. THAT IS IT.
You can, indeed, start in North America, take off in an airplane going South, stop over in Antartica to refuel, and continue, now north, on the opposite hemisphere, coming up on India or Africa.
How can we possibly do this? Unless...OMG, you're wrong! :shock:
Besides, as far as we can tell, all other planetary bodies are spherical-including the moon and the Sun-unless it magically rotates so it matches Earth's orbit...unless you're so dense you think Earth is the only true planetary body in the universe...unless...