GEOLOGY

Detailed explanation-1: -Hess discovered that the oceans were shallower in the middle and identified the presence of Mid Ocean Ridges, raised above the surrounding generally flat sea floor (abyssal plain) by as much as 1.5 km.

Detailed explanation-2: -As people mapped the ocean floor after World War II, new evidence was discovered that led to a new understanding of how the earth’s crust was put together. This included the discovery of a mid-ocean ridge, underwater volcanoes, magnetic stripes in volcanic rock and seafloor spreading.

Detailed explanation-3: -Harry Hess was a geologist and Navy submarine commander during World War II. Part of his mission had been to study the deepest parts of the ocean floor. In 1946 he had discovered that hundreds of flat-topped mountains, perhaps sunken islands, shape the Pacific floor.

Detailed explanation-4: -That enabled Hess to understand his ocean floor profiles in the Pacific. He realized that the Earth’s crust had been moving away on each side of oceanic ridges, down the Atlantic and Pacific oceans, that were long and volcanically active.

Detailed explanation-5: -During the 1940s and 1950s, scientists began using sound waves on moving ships to map large areas of the ocean floor in detail. Sound waves echo off the ocean bottom-the longer the sound waves take to return to the ship, the deeper the water is.