Final answer:
Continents move on a conveyor belt, which is explained by the mechanism of plate tectonics, not just drifting as Wegener originally hypothesized. It was the discovery of seafloor spreading and mantle convection that provided the necessary mechanism for this movement.
Step-by-step explanation:
Continents are said to move across the ocean basins on a conveyor belt rather than drifting because of the underlying mechanism of plate tectonics. Initially, Alfred Wegener's idea of continental drift, proposed in 1915, suggested that continents moved due to a lack of explanation for the mechanism involved. It wasn't until the development of plate tectonics in the 1960s that a plausible mechanism was understood, which involves rigid tectonic plates (including continental and oceanic crust) gliding over the malleable asthenosphere beneath them.
Wegener's hypothesis was supported by evidence such as the jigsaw fit of continents, matching fossils on separate continents, and similar mountain ranges across oceans, but it lacked a scientific explanation for how continents could move over the Earth's surface.
The concept of plate tectonics provided this explanation, with the discovery of mid-ocean ridges and the process of seafloor spreading establishing how new oceanic crust is constantly created and pushed away from these ridges, carrying continents along like on a giant conveyor belt. This movement is driven by convection currents in the mantle, caused by the Earth's internal heat.