Final answer:
J. Tuzo Wilson theorized plate tectonics based on three primary observations: the existence of cracks in continents similar to those on the seabed; the occurrence of sea-floor spreading which forms new crust; and the theory of continental drift which posits that continents were initially unified and have since drifted apart.
Step-by-step explanation:
J. Tuzo Wilson, a Canadian geologist formulated the theory of plate tectonics based on three major observations. The first observation was that there were cracks in continents akin to those found on the ocean floor. This signified that the Earth's crust was not a single immovable mass, but was constituted of multiple plates. These plates could move independently, thus causing the cracks.
The second observation was based on the phenomenon of sea-floor spreading. Seafloor spreading refers to the process in which new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. This led him to the theory that newer crust is continuously created at the mid-ocean ridges by upwelling of magma as the tectonic plates diverge, while older crust is destroyed at the deep-sea trenches as tectonic plates converge.
Lastly, continental drift, a theory originally proposed by Alfred Wegener, was another pillar of Wilson's theory of plate tectonics. Records of equivalent fossils found on separate continents that are physically separated by vast oceans today, constitute evidence supporting this theory. As certain animal and plant species could not have naturally migrated across these vast water bodies, it suggested that these continents were once unified and have since drifted apart.
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