Seafloor Spreading, Part 1

Earth's magnetic field was reversed. Vine and Matthews said the alternating anomalies were the result of volcanism and the symmetry seen would only result if the volcanism occurred at the mid-oceanic ridges and that the seafloor was moving when the Earth's magnetic field switched between normal and reversed polarity and back again. When the magnetic stripes of the ocean floor are compared with the time of the Earth's period of normal and reversed polarity the two show a great degree of similarity. Today, the Vine-Matthews explanation for the magnetic anomalies is one of the cornerstones of the seafloor spreading theory.

The age of the ocean floors and the discovery and interpretation of the magnetic anomalies around the mid-oceanic ridges were the stepping-stones for other discoveries that together became the theory of seafloor spreading. Next time we'll explore the remaining two keys that led to Hess's theory of seafloor spreading.

References and Sources:
Kious, W. Jacquelyne and Tilling, Robert I.; This Dynamic Earth: The Story of Plate Tectonics, 1996.

Seyfert, Carl and Sirkin, Leslie; Earth History and Plate Tectonics: an Introduction to Historical Geology; 1973, Harper & Row Publishers.

Winchester, Simon; Krakatoa: The Day the World Exploded: August 27, 1883; 2003 Harper Collins.

Atlantic seafloor map courtesy of National Geographic Maps at www.nationalgeographic.com.

Seafloor spreading image is reprinted from the online edition of This Dynamic Earth

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