Final answer:
The theory of plate tectonics developed from Alfred Wegener's continental drift hypothesis in 1915, supported by evidence like the continents' fit and fossil distribution, and was later expanded by Harry Hess's sea-floor spreading hypothesis in the 1960s.
Step-by-step explanation:
Origin of the Theory of Plate Tectonics
The theory of plate tectonics is one of the fundamental principles of geology, explaining the movement of tectonic plates which compose Earth's lithosphere. This theory originated from the continental drift hypothesis proposed by Alfred Wegener in 1915. Wegener observed the puzzle-like fit of the continents, distribution of fossils, mountain ranges, and paleoclimate evidence to suggest that all continents were once part of a supercontinent called Pangea. Despite the skepticism of his peers due to the lack of a mechanism to support his hypothesis, Wegener's idea laid the groundwork for the theory.
In the 1960s, scientist Harry Hess expanded upon Wegener's idea by proposing the hypothesis of sea-floor spreading. This was the missing piece that explained the movement of continents via tectonic plates that are driven by convection currents in the Earth's mantle. Today, plate tectonics is a unifying theory in geology, essential for understanding the formation of geological features such as mountains, oceans, and the distribution of earthquakes and volcanoes.