Continents may reflect conditions in the Earth’s core

Position of the continents with their "convex envelope" (red line) at various periods of time: (a) present time, (b) 65 million years ago, (c) 200 million years ago, (d) 260 million years ago.

In bold new research, a group of scientists in France believes that it has established a link between two of the great discoveries in 20th-century geophysics – plate tectonics and the fact that the Earth’s magnetic field has reversed direction many times throughout the planet’s history. The researchers from Ecole Normale Supérieure, CNRS and Institut de Physique du Globe in Paris, argue that during a given geological period the location of continents is linked with the frequency of magnetic field reversals. The findings have been met with cautious excitement by other geophysicists in the field.

The Earth’s magnetic field is produced by the flow of molten iron in the planet’s outer core – the Coriolis force helps to create a convection pattern in this zone, leading to a geodynamo.

By studying the orientation of magnetic minerals in rocks at the Earth’s surface, geophysicists know that the main dipolar component of the field has reversed direction many times since the field became established early in Earth’s history.

It has long been recognized, however, that the average rate of these magnetic field reversals has varied throughout the past. For example, during the last 25 million years the average reversal rate has been once every 250,000 years; compared with once every 600,000 years during the preceding 25 million years. Most geophysicists agree that the frequency of reversals must be related to slow changes in the conditions at the boundary between the outer core and the overlying mantle – a region some 2900 km beneath the Earth’s surface. Modelling work has shown that more reversals occur when there is an asymmetry between conditions in the outer core in the northern hemisphere and those in the south.

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4 Responses to Continents may reflect conditions in the Earth’s core

  1. Megapixel says:

    The French scientists are not the first to claim a relationship between continental plate movement/position and magnetic reversal rate.

    The Gravity Theory of Mass Extinction is the first theory to do so.

  2. alfy says:

    Could megapixel give us a link of some kind, to follow up this theory with further reading, please?

  3. Megapixel says:

    alphy,
    The early (2004) basics of the theory canbe found on http://www.dinoextinct.com.

    The broader theory is in book form: ‘The Gravity Theory of Mass Extinction.’
    This theory, GTME, posits the relation between continental plate movement/displacement and the movement of the core elements (inner/outer and densest part of the lower mantle).

    Unlike the CNRS theory, which might have been inspired by GTME, GTME claims that when continental plates move ladiitudinally, they would alter the Earth’s angular momentum; something that could not happen because of the Law of Conservation of Angular momentum. Therefore, movement of the core elements was the compensating factor.

    Once the core elements move, surface gravity also changes. This is why dinosaur gigantism occurred when Pangea formed. It also posits that the magnetic reversals are dependent on the movement of the inner core relative to the outer core, not on descending slabs of subducting plates, which would take many millions of years to reach the core mantle boundary.

  4. alfy says:

    Thank you for the link, megapixel. I have not heard of this theory of mass extinctions before and shall read the details with great interest.

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