In this scene, Tybalt encounters Romeo and Mercutio. He insults them, and attempts to fight Romeo. However, as Tybalt is Juliet's cousin, and Romeo has just married Juliet, he does not want to fight. Nevertheless, Tybalt is short-tempered, and after exchanging offenses, he decides to draw his sword. This causes Mercutio to draw his, as he wants to defend Romeo. The two of them fight, with Mercutio losing his life.
If for whatever reason we are forced to leave Earth there are no other hospitable planets we could live on. By making mars more like Earth we could eventually relocate to mars.
