Simplify the following text for a Grade 10 native English-speaking person.
Original: The idea that the seafloor itself moves ( and carries the continents with it ) as it expands from a central axis was proposed by Harry Hess from Princeton University in the 1960s .
Simplified: The idea that the ocean floor itself moves and carries the continents with it as it expands from a central axis was by Harry Hess of Princeton University .