Answer: The theory of plate tectonics has a mechanism for explaining how the continents move, while Wegener's hypothesis of continental drift did not.
Explanation: In the early 20th century, Alfred Wegener proposed the hypothesis of continental drift, which suggested that the continents were once joined together in a single landmass called Pangaea, and had slowly drifted apart over millions of years. However, Wegener did not have a mechanism to explain how the continents moved.
In the 1960s, the theory of plate tectonics was developed, and it provided a mechanism for understanding how the continents move. The theory of plate tectonics suggests that the Earth's lithosphere (which includes the crust and the uppermost part of the mantle) is divided into a series of plates that move relative to each other. The motions of the plates are driven by convection currents in the mantle.
At the boundaries where the plates meet, different phenomena occur. At divergent boundaries (such as the Mid-Atlantic Ridge), new crust is formed as magma rises to the surface and hardens, pushing the plates apart. At convergent boundaries (such as the Andes Mountains), plates collide and one is forced under the other (in a process called subduction). At transform boundaries (such as the San Andreas Fault), plates slide past each other.
The theory of plate tectonics thus provides a mechanism for explaining how the continents move over time. As new crust is formed at divergent boundaries and old crust is destroyed at subduction zones, the plates move apart and the continents drift. This explains why the continents are moving today and have been moving over geological time scales, and how they have been in different positions in the past.
Overall, while Wegener's hypothesis of continental drift was a significant step in understanding the evolution of the Earth's continents, it was the theory of plate tectonics that provided the more complete and explanatory picture, by proposing a mechanism for how the continents move.
Hope this helps, and have a great day!