If there is one thing I have learned from comic books, it is that the law of physics and reality do not apply. The impossible is possible and the improbably is probable.
Anyway, this guy didn't do his research completely. Thor's hammer, Mjolnir is made from Uru a mystical (fictional) substance that is both stone and metal, only the intense heat of a star, or the Asgardian forges can shape the metal. The dwarfs used the inner core of a star to as a mold, while they were shaping the hammer from Uru inside the star it went supernova (killing the dinosaurs).