Evolution of Rotation Structures in the Earth’s Geological History

Abstract

The behavioral study of the Earth’s magnetic moment or palaeointensity, inversion frequency and other geomagnetic field characteristics in the remote past could have provided the basis for estimation of the time taken by global space and intraterrestrial processes. However, at many international conferences earth scientists are not unanimous as to whether endogenic and cosmic processes are interrelated. In the past few years, the Research Team of the Geophysical Observatory at the Institute of Physics of the Earth, RAS, headed by V.V. Shcherbakova has developed a global IAGA Palaeointensity Database and obtained new extensive reliable data on the magnetic virtual dipole moment (VDM) of the Earth by estimating the degree of validity of each value. The database is available at the website: ftp://ftp.ngdc.noaa.gov/Solid_Earth/Paleomag/access/ver3.5/access2000/PINT00.MDB. It contains about 3900 VDM values and more geomagnetic field palaeointensity values from 3 billions of years ago (Ga) to the present, but most of the data are confined to the last 100 million years (Ma). This work provides an impetus to the palaeomagnetic study of the oldest localities. New evidence for the Earth’s evolution, the timing of internal core formation etc. can be obtained by studying geomagnetic field intensity in the geological past. One of the Earth cooling models shows that the Earth’s internal core could be younger than it has been assumed earlier (Labrosse et al., 2001). Obviously, voluminous data on geomagnetic field intensity in Palaeoarchaean-Proterozoic time are needed to check this and other hypotheses. However, slightly more than 30 intensity determinations, consistent with modern reliability criteria, are available for this time span of about 3 Ga in geological history. Some determinations have been made by the authors under INTAS Project 03-51-5807 at the Salmi suite and at the Ropruchei sill on the Fennoscandian Shield (Pavlov et al., 2004; Shcherbakova, Pavlov et al., 2006). An interesting hypothesis of periodical variations in the Moon’s orbit radius and tidal forces during the Phanerozoic was proposed by Y.N. Avsyuk (1993). Variable tidal forces would have made the Earth rotate now rapidly, now slowly. If this hypothesis is valid, the retardation and acceleration of the Earth’s rotation also could have affected the behaviour of the main geomagnetic field and folding phases. Variations in palaeointensity, geomagnetic field inversion frequency and Bertrand cycles were correlated with the phases of variations in the Moon’s orbit radius after Avsyuk, but no significant correlations have been revealed (Kurazhkovskii et al., 2008), although in the same publication the authors have concluded