In 1975 Forsyth and Uyeda used the inverse theory method to show that, of the many forces likely to be driving plate motion, slab pull was the strongest.
[4] Carlson et al. (1983)[5] in Lallemand et al. (2005)[6] defined the slab pull force as: Where: The slab pull force manifests itself between two extreme forms: Between these two examples there is the evolution of the Farallon Plate: from the huge slab width with the Nevada, the Sevier and Laramide orogenies; the Mid-Tertiary ignimbrite flare-up and later left as Juan de Fuca and Cocos plates, the Basin and Range Province under extension, with slab break off, smaller slab width, more edges and mantle return flow.
However, most scientists working today believe that the asthenosphere does not directly cause motion by the friction of such basal forces.
[citation needed] The North American Plate is nowhere being subducted, yet it is in motion.
The subducting slabs around the Pacific Ring of Fire cool down the Earth and its core-mantle boundary.