Earth's Magnetic Field, Plate Tectonics, Magnetic Banding

The source of the Earth's magnetic field may be slightly more complex than previous theories have suggested. Instead of one circulation of ionized iron in the Core, there may be two or four counter-rotating circulations. To a great extent, their effect at the surface tends to therefore cancel out, but any variation in either of a matching pair of circulations could cause EITHER a North or South orientation of the surface field. A proposed simplified mechanism is presented here. The consequences of this modification of existing theory can help explain a number of other mysteries of the Earth's history and present state.

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The three phenomena of the source of the Earth's magnetic field, Plate Tectonics and Magnetic Banding are usually considered separately in theories. They may be three different aspects or consequences of a single phenomenon, convective circulations inside the Earth. A variety of other of Earth's mysteries may also be associated with this same concept, possibly even including non-continuous biological evolution and mass extinctions.

General Structure of the Earth

The general structure of the Earth is usually described as being a central Iron Core surrounded by a Mantle surrounded by a relatively thin Crust. The Iron Core is generally considered solid and rotating. It is considered solid primarily because of the "shadowing" effect of it on certain types of earthquake shock waves. The Core is assumed to have significant Iron content because the Earth clearly has a lot of Iron as constituent parts of it, because Iron has fairly high density which would have tended to settle toward the center when the young Earth was more liquidy and fluid, and because moving Iron is one of the only ways we know of that could explain being a source of the Earth's magnetic field.

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Rotation of a solid Core that contains a lot of Iron in it, some of which is naturally ionized (for a variety of reasons as result of physical phenomena), effectively causes very high amperage electric currents which effectively "flow" within the Earth. This has traditionally been the explanation of the source of the Earth's magnetic field. The Mantle is considered fluid, with motions driven by heat generated by radioactive decay (both within itself and from within the central Core). Until the 1960s, the Crust was considered solid and continuous. Since then, it has been considered as a jigsaw puzzle of about 20 tectonic plates which slowly and methodically move around, explaining continental drift.

The new premise does not contradict any of these thoughts. It is primarily intended as an enhancement of them.

Theoretical ideas about the vertical distribution of elements in the Earth has always been primarily based on the behavior of earthquake S- and P- waves, on the total mass and rotational inertia of the Earth, and on the composition of extra-terrestrial meteorites found on Earth. These empirical results have been combined with the concept of vertical segregation of minerals and elements by weight, to suggest that the heavy elements (including mostly Iron) would have migrated (in an earlier, more molten Earth) toward the center Core and the lighter elements and minerals (including gases) would migrate toward the outer Crust.

The Core

The opinion that the Core is solid is primarily based on a shadow-effect on earthquake-generated waves. The concept of solid is somewhat a relative term. Very tall mountains are considered solid, even though they have clearly documented very slow flow rates, so, in some sense, those mountains are fluid, and the flow rates have even been measured. Thus, a solid Core can generally be said to be true while still involving relatively slow flow rates. This circumstance would have the effect of acting as solid for the earthquake generated shock waves, but would still allow fluid flow. Such slow flow would cause two additional consequences. First, the very heavy elements could migrate even more centrally, to the Inner Core, including the primary sources of long-term natural radioactivity (such as Uranium). This new perspective puts the Earth's primary inner heat source farther toward the middle of the Earth. Second, this situation would certainly drive (rather slow) convective movements in the Core.

This Core convection would probably tend to stir up the very heavy elements in the center of the Core, so the vertical segregation may not be as distinct as it could otherwise be. More importantly, this slow convection would create a variety of randomly oriented convection cells in the Core. These cells would be somewhat dynamic and fluctuating, in various locations and of variable number. Each such cell would effectively generate an electric flow in a circuit, and would thus create a magnetic field. These convectively created magnetic fields would generally NOT be co-axial with the rotation of the Earth itself!

The individual magnetic fields created by the individual convective Core cells would not be easily noticed or measurable from our perspective at the surface of the Earth. The net, measurable Core magnetic field would be a combination of all of these cell-based magnetic fields. MUCH of the effects of the magnetic fields due to specific Core convective cells would be cancelled out by the magnetic fields created by OTHER Core convective cells with opposite circulation flows. For example, two exactly identical convective cells on opposite sides of the Core, would, (due to the Right-Hand Rule of magnetic field orientation as a result of an electric current) cancel each other out! There would be no net di-pole effect of the magnetic fields generated by these two Core convective cells. (There WOULD, however, be a quadru-pole magnetic field present, because the two sources were spatially separated from each other)

The net effect of a multitude of Core convective cells would thus have a VERY complex nature, and would certainly NOT act like a simple magnetic dipole. During short time intervals, this net Core magnetic field would create a measurable Earth magnetic field that seems stable and relatively constant. But small, continuous variations of field intensity and effective magnetic pole location would be expected, as are observed. This premise would also explain the quadrupole, octopole (and higher) components empirically measured in the Earth's magnetic field.

Each of the various Core convective cells would create quite a strong magnetic field. On opposite sides of the Core, the convective cells may generally be rotating in opposite directions, thus creating opposing magnetic dipoles. Even two adjacent convective cells on the same side of the actual center might circulate in opposite directions, having this same effect. This situation would have the appearance to us at the surface, as a net reduced strength dipole (with net polarity of whichever of the two was then creating a stronger field, since the dipole effect of the two would be somewhat subtractive) and at the same time would exhibit quadrupole field effects.

Of course, many other opposite pairs and generally randomly oriented convective cells would exist at various other angles around the circumference of the Core. Keep in mind that this situation is true in three dimensions, so that there are convective cells completely surrounding the center of the Core. The net magnetic field of the Earth, as measured at its surface, would be the sum of all these constituent components, making for a measured magnetic field with a LOT of fine detail.

The rotation of the Earth itself would certainly have some effect on the formation and durability of the various constituent Core convective cells. Internal friction would certainly have caused a "general" rotation of the Core that would be moderately co-axial with the rotation of the physical body of the Earth itself. This logic would imply that there would likely be a tendency (but not a necessity) for the axis of the Earth's Magnetic Field to be generally co-axial or anti-axial with the Earth's rotation axis. Further study would be necessary to determine which orientations of Core convective cells would become preferred and which would quickly disappear. This effect should tend to cause the empirically identified Reversals of the Earth's magnetic field, rather than just causing random orientation of it.

Over longer time periods, say thousands of years, the effect of stirring up some of the central radioactive heat sources would cause changes in the locations of some of the Core's the heat sources, which would have considerable effects on changing the Core's convective cells flow patterns. Even fairly minor changes in a few of these convective cells might change the NET effect (at the surface of the Earth) so much so as to reverse the Earth's effective magnetic field. Think about the theoretically identical Core convective cell pair mentioned above. EACH of their individual magnetic fields is quite substantial in strength, possibly much in excess of the total measured effect of the whole Core, but they totally cancelled out their dipole effect. Now say that one of the pair got just a few percent stronger, due to a variation in the Core convective flow in its cell. This relatively minor change could drastically affect the net effect of the whole Core and might even cause a Reversal of the measured Earth's magnetic field. Again, the (net) total field measured at the surface of the Earth is the sum of the magnetic fields of many such pseudo-randomly oriented convection cells, so that the total net measured effect could fluctuate erratically and quickly. It is important to note that the magnetic field strength of an individual Core convective cell is FAR larger than the net effect of an opposing pair. The present premise suggests that this is what allows the rapid, large, erratic fluctuation in the net Earth's magnetic field, both short-term (which we new continuously measure) and long-term (as recorded in magnetic banding in sea floor spreading).

This premise also explains the heretofore unexplained quadrupole and octopole magnetic moments of the Earth's magnetic fields, and suggests that thorough analysis of those effects might give some insight into the actual distribution and orientation of the Core's constituent convective cells.

This explains the relatively rapid and extreme changes which must have occurred in the Earth's magnetic field to explain the magnetic banding first noticed in recently formed Crust near the Mid-Atlantic Ridge in the Atlantic Ocean. Previous explanations of these polarity shifts have always required mechanisms which disobey conservation of rotational inertia or other basic laws of science. (Such as regular reversal of rotation of the Core or its physically flipping North to South). It also explains the short term variations observed in the location of the North and South Magnetic Poles, and various slight variations and complexities in magnetic field intensity. It also explains the apparently non-central location of the rotating central Core which has long confounded theorists. (The point halfway between the North and South Magnetic Poles is not very close to the actual center of the Earth.) If movement of some of the central radioactive element heat source was such that even one of the Core's convective cells materially changed, the NET magnetic field of the Earth could be significantly altered. Even if it wasn't reversed, the Poles might suddenly (over a few hundred years?) jump thousands of miles.

The Mantle

An effect of all this dynamically changing Core activity is that the heat rising within the Core is therefore non-isotropic. As this heat gets to the Core-Mantle boundary, some "hot spots" are necessarily created. These "hot spots" will certainly drive and affect convection cells in the Mantle. Since the Mantle is much more fluid than the Core, the physical flow rates can be far more rapid in the Mantle than in the Core. An additional complication on the dynamics of this Mantle convection is that the Core's "hot spots" move around from time to time as the Core's convective cells shift.

Present evidence suggests that is likely that the physical dimensions of these Mantle convection cells is generally on the scale of thousands of miles. This suggests that if we could "peel off" the Earth's Crust, we would see a complex and continuously shifting patterns of turbulent top surface flow. The shifting referred to here is probably on the scale of a few feet per year, over thousands of years.

The Crust

The thin Crust of the Earth is not smooth on its inner surface. Wherever mountain ranges occur on the outside, equivalent structures exist on the inner surface of the Crust directly below the mountains. This is necessary due to the difference of density of Core and Mantle materials, for the Crust to "float" on the Mantle. That concept is called isostasy.

If the inside surface of the Crust is smooth, the convective movement of the Mantle material would not be efficiently transferred to the Crust. There would be some friction between the two media, and a general moderate drag force pulling on the Crust, but no very strong forces would be present that affect the Crust. The presence of downward obstructions under mountain chains and continents create a variety of "gripping points" for the horizontal movement at the top of the Mantle's convection cells to be much more efficiently transferred to the Crust. The Crust would therefore move or otherwise be affected in response to the flow of Mantle material beneath it.

A tectonic plate would therefore move in response to the NET effect of the various Mantle convective cells beneath it. This movement would depend tremendously on the effectiveness of the "gripping points" referred to above. The movement would also depend on the structural integrity of the specific tectonic plate. It might result in a general movement of that tectonic plate, or in a physical distortion or disruption of that plate's physical integrity.

The fact that short-term (hundreds of years?) changes in the Core convective cell flows and in the Mantle convective cell flows are likely, mean that a tectonic plate's movement could reverse or a plate could even rotate or tear apart as a result. Even if we identify present movement rates of all points on the Earth's surface, it is not necessarily possible to extrapolate backwards to predict previous locations of the tectonic plates.

Conclusions

This premise has a variety of consequences. As a new mountain chain develops on the surface, a new "gripping point" develops on the under side of the Crust. If this "gripping point" occurs above a Mantle convective cell whose top is moving "rapidly," tremendous stresses could occur in that continental plate. If the plate's structural integrity is great enough, the plate stays together and then tries to run over or into some other plate. The current motion of the Indian plate might be an example. If the plate's structural integrity is lower, then the plate can be ripped apart. A current example could be Iceland and the Mid-Atlantic Ridge. If the mountain range and the "gripping point" happens to be toward one edge of the plate, a plate rotation could occur as well as the translation motion already addressed.

This could explain both the macroscopic and the microscopic mechanics of plate tectonic movements. It should also be possible to analyze the previous movements of all the plates to determine the probable Mantle flow directions which caused these movements.

It explains the magnetic banding observed in the Central Atlantic by a more reasonable and physically mechanism than previous thought has offered.

It could also add to our understanding of earthquake theory.

The approximate Mantle flow velocities might be determined by accounting for the known net heat flow inside the Earth.

This theory also explains something that no one has seemed concerned about. When the Earth was originally formed, it might have been true that the Core's rotational axis was (briefly) not co-axial with that of the Mantel and Crust. But over the extremely long time the Earth has existed, frictional drag at the Mantel-Core boundary would certainly have caused these axes to have become co-axial long ago. Most competing theories about the source of the Earth's magnetic field have the Core rotating at an angle, such that it is lined up with the present Magnetic Poles. That situation appears to defy the laws of science. The present premise does NOT require this, and includes a mechanism for explaining the separation of the Geographic and Magnetic Poles. This premise allows the much more logical generally co-axial rotation of all the major components of the Earth.

This theory suggests that the complex nature of the Earth's magnetic field would also have a lot of vertical detail out into space. Three-dimensional analysis of all of these empirical results might better identify the more complex components, such as quadrupole and octopole moments of the net Earth magnetic field, possibly giving evidence of the nature of the locations and strengths of the Core's convective cells.


First Developed, Mar 1996,
First Published on the Web: Jun 22, 1997

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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago