Eur. Phys. J. Plus (2011) 126: 31
https://doi.org/10.1140/epjp/i2011-11031-y

Regular Article

The D” layer’s key position in the long-term electromagnetic core-mantle coupling and observational evidence

¹ Department of Physics, Peking University, 100871, Beijing, China
² Key Laboratory of Orogenic Belts and Crustal Evolution, Peking University, 100871, Beijing, China
³ Committee of Yuanpei Honors Program, Peking University, 100871, Beijing, China
⁴ Department of Geology, University of California, California, 95616, CA, USA
⁵ Department of Electronics Engineering and Computer Science, Peking University, 100871, Beijing, China

^* e-mail: yuanlinsun@gmail.com

Received: 17 October 2010
Accepted: 18 February 2011
Published online: 28 March 2011

Abstract

Based on Holme’s electromagnetic coupling torque, calculations reveal that a long-term electromagnetic coupling might be triggered when the D ^′′ (Double Prime) layer thickness passes a threshold, which could result from the decompressional effect of a global supercontinent, such as Pangaea. When the D ^′′ layer thickness exceeds this threshold, the conductance increases and the electromagnetic core-mantle coupling torque would strengthen to overcome the damping torque and accelerate the Earth’s rotation. This process is accompanied with a redistribution of mass in the core-mantle system. Meanwhile, when the D ^′′ layer thickens, the Earth’s magnetic field would also experience a series of dramatic changes, including a decrease in the intensity of the dipolar field and frequent reversals. Both could have negative effects on the biosphere. New palaeontological clock data, together with previous studies support the prediction of a long-term acceleration of the Earth’s rotation in the Early Mesozoic following the assembly of Pangaea. Since Pangaea existed more than 100Ma, the D ^′′ layer remained above the threshold for a very long time leading to a long-term acceleration of rotation. The observed acceleration took place near the Permo-Triassic boundary, a peculiar period in which the Pangaean Supercontinent reached its zenith and the biosphere underwent the largest known mass extinction, and ended during the Late Jurassic when Pangaea began to disperse rapidly and the Atlantic Ocean began to open quickly. Available palaeomagnetic evidence, including the frequent reversals from late Permian to Triassic and a long-term dipolar intensity low in Early Mesozoic, corroborates the predictions made by the model presented here.