Answer: Sea Floor Spreading theory was proposed by Professor Harry Hess in the 1960s. In the 1940s and 1950s, mapping of the ocean floor and paleomagnetic studies of rocks from oceanic regions revealed many facts which were used as prominent evidence in support of the theory of SeaFloor Spreading.

Seafloor Spreading

• The constant volcanic eruptions due to upwelling magma at the mid-oceanic ridges cause a rupture in the oceanic crust. The new lava wedges into it and thus pushes the oceanic crust on either side. This process is termed seafloor spreading.
• The seafloor is also destroyed in subduction zones, where oceanic crust slides under continents or other oceanic plates and sinks back into the mantle.
• Example, The East Pacific Rise is a site of major seafloor spreading in the Ring of Fire. It is located on the divergent boundary of the Pacific Plate, the Cocos Plate (west of Central America), the Nazca Plate (west of South America), the North-American Plate and the Antarctic Plate.

Prominent Evidence in its Support of seafloor spreading: 

• Lava at the Mid Oceanic Ridges: It was observed that volcanic eruptions are common, and they bring huge amounts of lava to the surface. As molten material erupts from the mantle, it spreads out and pushes older rocks to the sides of the fissure, a new ocean floor forms along cracks in the ocean crust. 
• Similarity in Rocks: The rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities in terms of period of formation, chemical compositions and magnetic properties.  
• Paleo-magnetism: When molten rock cools and hardens, it aligns its magnetic field with the Earth's. However, if the molten rock is formed in a location separate from the existing seafloor, then its magnetic field will be opposite that of its surroundings. This creates an alternating pattern of magnetic stripes in the ocean crust. This was the first direct evidence for seafloor spreading. 
• Age of Rocks: The ocean crust rocks are much younger than the continental rocks. Moreover, the age of the rocks increases as one moves away from the mid oceanic ridge. This means that new rocks are formed at the mid oceanic ridge. 
• Depth of Earthquake: The deep trenches have deep-seated earthquake occurrences while in the mid-oceanic ridge areas, the quake foci have shallow depths. This means that upwelling of lava displaces the rocks on the surface of the ocean floor. Further, the ocean floor is forced to expand. 

The theory of SeaFloor Spreading was an improvement over Wegener's Continental Drift theory. It paved the way for the development of new theories (like Plate tectonic theory) to explain the distribution of Oceans and Continents.