What was the major weakness of Wegener's theory of continental drift

Alfred Wegener proposed the continental drift theory in four reasons. One, he hypothesized that the continents were once a giant continent. Two, he observed that there are fossils found of the same kind in the different locations. Three, he found that the edge of opposing continents somehow fits if they are combined, almost like a puzzle. And four, there are glacial scars that are left behind by a larger glacial continent. His greatest weakness of Alfred Wegeners’ continental drift theory was he could not explain what kind of force that caused this continents to move far from each other.