* The Earth is a sphere: It's a round object, so there's no edge to reach. If you keep walking in one direction, you'll eventually circle back to where you started.
* The Earth has an atmosphere: This layer of gas surrounds the planet and doesn't have a sharp edge. It gradually thins out until it blends into the vacuum of space.
* Space is vast and continuous: There isn't a clear boundary where Earth ends and space begins.
So, while we talk about "Earth" as a planet, it's really a continuous system with no defined edge.