Answer:
Continental drift; Mid-ocean ridges
Explanation:
Hess expanded on Wegener’s theory of continental drift.
Continental drift was a theory that explained how continents shift position on Earth's surface i.e how it moved over geologic time relative to each other. This theory was developed in the early part of the 20th century, mostly by Alfred Wegener.
Hess described how hot magma would rise from under the crust at the Great Global Rift as the ocean crust spreads and cools over millions of years, it becomes denser and eventually sinks down into oceanic trenches, which explained how the once joined continents had separated into the seven that exist today .
Hess proposed the idea that mid-ocean ridges are places where crust is created.
