Summary
Highlights
The idea of continents drifting has existed for over 200 years, but it wasn't widely accepted by geologists until the 1960s when overwhelming evidence confirmed that Earth's crust is fragmented into moving tectonic plates. This movement is now tracked with millimeter precision from space.
The common explanation for plate movement involves them being carried by currents in the upper mantle. While hot mantle rock does rise and sink, plates are not just passively riding these currents. Some plates, like the Nazca plate, move faster than the underlying mantle currents, indicating additional forces are at play.
A significant driving force for some plates is 'slab pull.' When an oceanic plate collides and slides beneath another plate (a process called subduction), the sinking edge of the seafloor pulls the rest of the plate along, much like a chain sliding off a table. The deeper the sunken portion, the stronger the pull and faster the plate moves.
Deep ocean trenches visible on Earth mark these subduction zones where oceanic crust plunges downward. These sinking slabs also influence mantle convection, blocking sideways flow and forcing material to sink, eventually breaking off and creating a suction force that pulls mantle material behind them. This highlights that seafloor crust is an active part of the conveyor belt, unlike continents which are more passive.