I’ll have to make a blog with all the reasons I can think of sometime. For now I’ll give you the first that comes to mind that anyone can try.
Mountains (Or just the horizon). For two reasons:
- [Smart-ass logic:] A flat earth lies in one plane with two dimensions so it can’t have bumps. Mountains are bumpy.
- [Empirical logic:] Look at a mountain afar and you see mostly the top but as you get closer you see more and more. That suggests a curving of the land — a convex curvature. Same logic applies for the horizon and how clouds far away are apparently touching the ground.
Just look near and far and you’ll fail to see flatness.
It’s interesting that for nearly all of human history, most people believed the earth to be flat.
And dust to pop up from sun beams. Knowledge makes the world simpler so you can become more complex, I reckon.