While it's hard to pinpoint a single person as the "discoverer" of seafloor spreading, Harry Hess is generally credited with proposing the theory in the 1960s.

Here's a breakdown:

* Harry Hess: In the 1960s, Hess, a geologist, studied the ocean floor using sonar data. He observed mid-ocean ridges and deep-sea trenches, and proposed the concept of seafloor spreading. He suggested that new oceanic crust is formed at mid-ocean ridges and then spreads outwards, pushing older crust away from the ridge.

* Others who contributed: While Hess is the most recognized, other researchers like Robert S. Dietz, Bruce Heezen, and Marie Tharp also made significant contributions to the understanding of seafloor spreading.

It's important to remember that scientific discoveries rarely happen in isolation, and seafloor spreading was built upon the work of many scientists who contributed to our understanding of Earth's processes.