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Harry Hess proposed the seafloor spreading hypothesis in 1960 (published in 1962 [1]); the term "spreading of the seafloor" was introduced by geophysicist Robert S. Dietz in 1961. [2] According to Hess, seafloor was created at mid-oceanic ridges by the convection of the Earth's mantle, pushing and spreading the older crust away from the ridge. [3]
Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. (The rate at which new oceanic lithosphere is added to each tectonic plate on either side of a mid-ocean ridge is the spreading half-rate and is equal to half of the spreading rate). Spreading rates determine if the ridge is fast, intermediate, or slow.
The second piece of evidence in support of continental drift came during the late 1950s and early 60s from data on the bathymetry of the deep ocean floors and the nature of the oceanic crust such as magnetic properties and, more generally, with the development of marine geology [57] which gave evidence for the association of seafloor spreading ...
If new crust were being formed at the ridges and moving away, as Hess theorized, then reversals in the Earth's magnetic polarity would result in just the kind of parallel, symmetrical anomalies that Matthews' survey had found. The ocean crust would in effect act as a kind of giant tape recorder of magnetic anomalies over time.
The discovery of mid-ocean ridges and the process of seafloor spreading allowed for Wegener's theory to be expanded so that it included the movement of oceanic crust as well as the continents. [49] Plate tectonics was a suitable explanation for seafloor spreading, and the acceptance of plate tectonics by the majority of geologists resulted in a ...
Why this theory is so significant is the interaction between the tectonic plates explains many geological formations. [8] In regards to marine geology, the movement of the plates explains seafloor spreading and mid-ocean ridge systems, subduction zones and trenches, volcanism and hydrothermal vents, and more.
Continental crust is inherently lighter. Oceanic crust is created at spreading centers, and this, along with subduction, drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas of isostatic imbalance. Mesosaurus skeleton, MacGregor, 1908 Fossil patterns across continents (Gondwanaland)
In 1960, Hess made his single most important contribution, which is regarded as part of the major advance in geologic science of the 20th century. In a widely circulated report to the Office of Naval Research, he advanced the theory, now generally accepted, that the Earth's crust moved laterally away from long, volcanically active oceanic ridges.