Seafloor Spreading, Part 1
The Keys to Seafloor Spreading
There are four key pieces of evidence that helped to prove the theory of seafloor spreading. Each of these keys was documented and studied by independent researchers, some prior to Hess's book being published, and each was critical in helping to prove the theory.
Age of the Ocean Floors
Throughout most of the science of geology geologists thought the Earth was static, the continents having remained as they are seen today from the beginning of time. In this view, the ocean floor is just as old as the rest of the rock on the planet. In the years after World War 2 geologists used piston-coring devices to sample areas of the ocean floor. Many geologists were puzzled since the oldest rocks found in the cores were Cretaceous in age. It was thought that the ocean sediments were very thick, having accumulated over millions of years, and that the piston corers were unable to sample the deeper sediments. In the late 1960s the research vessel Glomar Challenger began to take deep core samples across the ocean basins. Cores taken from the ocean floors by Glomar Challenger have shown that the oldest rocks recovered in either the Atlantic or Pacific Oceans is Late Jurassic in age. Another piece of evidence was that rocks nearer the mid-oceanic ridges are younger than rocks found further from the ridges. The first cornerstone for the seafloor spreading theory had been laid.
Magnetic Anomalies
Research vessels based around the magnetometer, a device designed to locate submarines by the deflection of the magnetic field the submarine causes, began to ply the waters of the Atlantic and Pacific in the 1950's. These ships noticed the presence of north-south trending magnetic anomalies in the ocean. The anomalies were areas with a higher magnetic intensity than the average Earth magnetic field that alternated with areas with a lower magnetic intensity. It was found that these magnetic anomalies were symmetrical, centered along the mid-oceanic ridges. For years these magnetic anomalies puzzled scientists when two researchers proposed a reason for their presence.
In 1963 Fred Vine and DH Matthews proposed that the magnetic anomalies were the result of reversals in the Earth's magnetic field. Studies of magnetic reversal had been shown for continental rocks, now Vine and Matthews proposed that the positive anomalies showed time when the Earth had a normal polarity and the negative anomalies were the result of time when the Earth's
Latest Articles