Early hypotheses to explain this difference. Pacific ocean formed as a scar from where the moon separated after a large asteroid impact. Expanding Earth Model 1925, Earth has doubled its size, oceans are scars where continents were rifted apart by expansion. Both of these hypotheses assume an originally uniform continental crust that has undergone a catastrophic incident. Continental drift - the fit of the continents indicate they were once joined and have since drifted apart.
Continents plow their way through ocean crust.
Proposed that continents were once fit together. Himalayas as cont-cont collision. Tidal forces moved continents. The theory of continetal drift based on distribution of fossils, rock types, and paleoclimate evidence. Holmes and Taylor 1929 proposed a configuration and movement of the continents that is very similar to the proposed today for the last 250 my.