What set the Earth’s plates in motion?

What set the Earth's plates in motion? 17 September 2014 - An 87 million year long story. This shows an early buoyant continent slowly spreading toward the adjacent immobile plate (blue). After 45 million years, a short-lived subduction zone, where the plate goes under, develops. This allows the continent to surge toward the ocean, leading to the detachment of a continental block, the starting step in the movement of the continental plates. The mystery of what kick-started the motion of our earth's massive tectonic plates across its surface has been explained by researchers at the University of Sydney. "Earth is the only planet in our solar system where the process of plate tectonics occurs," said Associate Professor Patrice Rey , from the University of Sydney's School of Geosciences. "The geological record suggests that until three billion years ago the earth's crust was immobile so what sparked this unique phenomenon has fascinated geoscientists for decades.