1. Mid-Ocean Ridges: He observed that mid-ocean ridges, underwater mountain ranges, were sites of active volcanism. He theorized that molten rock from the Earth's mantle rose up at these ridges, creating new oceanic crust.
2. Magnetic Stripes: Hess noticed alternating patterns of magnetic stripes on the ocean floor. He realized these stripes represented the Earth's magnetic field flipping over time. As new crust formed, it locked in the magnetic orientation of the time, creating the striped pattern.
3. Sea-Floor Spreading: Hess proposed that the new crust created at the ridges pushed older crust away from the ridge, like a conveyor belt. This movement, he argued, was the driving force behind the movement of tectonic plates.
4. Subduction Zones: Hess also recognized that ocean trenches marked places where oceanic crust was being pulled back down into the mantle, a process known as subduction. This process, he argued, balanced the creation of new crust at the ridges.
Hess's theory, supported by the evidence he gathered, revolutionized our understanding of Earth's geology and the movement of continents. It provided the key to explaining continental drift, the formation of mountains, and the distribution of earthquakes and volcanoes.