North Pole, South Pole: The Epic Quest to Solve the Great Mystery of Earth's Magnetism by Gillian Turner

Author:Gillian Turner [Turner, Gillian]
Language: eng
Format: azw3
Publisher: The Experiment
Published: 2011-01-11T05:00:00+00:00

The formation of a seismic shadow zone. Waves entering the core are slowed down and refracted so they reappear at the surface further from the source than they would have otherwise, leaving a shadow zone in which no waves are detected. In the Earth the shadow zone is observed between 105 and 143 degrees from the source of an earthquake.

It would be 1926 before a pronouncement by a noted British geophysicist would finally settle the argument. Harold Jeffreys, the author of the famous and much reprinted textbook The Earth, had improved Wiechert’s calculations and eventually come to the conclusion that Wiechert’s discontinuity in density and Gutenberg’s seismic discontinuity were one and the same. Furthermore, the discontinuity corresponded to changes both in composition (from rocky to iron-rich material) and in phase (from solid to liquid). He therefore declared that Earth’s core was “truly fluid.”

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