If the earth were twice as big, the earth would have eight times as much mass and gravity would be twice as strong. Your weight would also be doubled, and it would be much harder for you to walk because you’d feel like you were giving another version of yourself a piggyback ride all day, every day. And what else? Trees would collapse. Gravity determines how tall a tree can grow – so any new trees that grow in their place wouldn’t grow as tall.

THIS IS COOL. I WANT TO LEARN SOMETHING ELSE, TOO!

Video via – Life Noggin
Further Readings and References @ LiveScience, Gizmodo, EarthSky