Mechanism Behind Plate Tectonics

also explains the source of the Earth's magnetic field,
Variations in the Earth's magnetic field,
Dinosaur extinction,
Non-constant species evolution,
the Species Explosion Events,
and more!

In the 1960s, scientists found various types of evidence which suggested that the continents are slowly moving (inches per year) relative to each other. Careful investigation since then has confirmed this and even precisely determined the movement velocities of most areas of the Earth's surface. The pattern seems relatively random. It is not.

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Some of the most compelling evidence regarding this is the magnetic banding in the Earth's Crustal rock near the Atlantic's Mid-Atlantic Ridge, where new Crust is being volcanically inserted between the two plates that are separating. This banding indicates that the Earth's magnetic field has changed tremendously, and even regularly reversed, in relatively short geologic time periods. No good theory had been presented to explain how these drastic magnetic changes occur.

The Earth's Crust is relatively quite thin. Out of the 8,000 mile diameter of the Earth, the 5-40 mile thickness of the Crust is amazingly thin. This also makes it very much less massive than the Mantle or Core, especially since its density is also much lower. The underside of the Crust is quite irregular, due to isostatic equilibrium. Wherever tall mountains extend above outer surface, similar extension of the Crust down into the Mantle also exist on the Crust's underside. (For short [dynamic] periods, this is not necessarily true but for longer [static] periods, it must be, to properly support the extra mass of the mountain ranges.)

These irregularities on the bottom side of the Crust are important.

The earth's composition is primarily compounds of a few elements, like oxygen, iron, silicon, aluminum, etc. However, it also contains smaller amounts of nearly all the other elements as well. Some are naturally radioactive, the most common of which is Uranium.

The elements and compounds within the Earth have basically been there since the Earth was formed about 4.5 billion years ago. For quite a while, the entire contents were in fluid (semi-liquid) form, both from the heat of initial formation and from the presence of much more radioactive elements than are now present. During that time, stratification gradually occurred, with the more dense elements and compounds settling toward the center and the less dense materials rising toward the surface. This is the explanation why the Crust density is 2-3, the Mantle 4-5, and the Core probably around 12 gm/cc.

This reasoning assures us that the very dense radioactive elements, including Uranium, are necessarily in the inner Core. As the nuclear fission of the Uranium occurs, the atoms break apart into different elements, giving off quite a bit of energy. Trapped inside the Earth, this energy necessarily becomes heat energy.

The Core is primarily Iron, in a very viscous semi-liquid state. The heat from the centrally occurring radioactive fission must pass through this thick layer of Iron Core. Some of the heat is conducted through it, since Iron is a reasonably good conductor of heat. But some of that heat is carried by the Iron in convective action.

This convection causes a variety of convection cells inside the Core. In some locations the Iron material rises (very slowly) toward the surface. When near the top of the Core it moves laterally for some (random) distance as it gives up its convective heat to the Mantle above and cools. At this point, it sinks back down toward the center to replace the Iron materials now convectively rising from there.

The result of this is an assortment of individual circulations of the Iron materials in the Core. Each of these circulations' flows represent separate very low voltage, very high current electric currents in the Core. And every circulating electric current creates a magnetic field.

Therefore, complex motions in the Earth's Core create MANY separate magnetic fields. Far above, at the Earth's surface, our instruments just sense the net effect of the sum of all of them, many of which cancel each other. We apparently record a single magnetic field for the Earth.

Over geologic times of hundreds of thousands of years, variations in the individual Core convection cells occur. As those cells fluctuate, the resultant magnetic field contributions also change. Since we only register the sum of all of those contributions, fairly subtle flow changes (which mostly cancel each other) can cause reversals and strength changes in the Earth's magnetic field as recorded in Crustal rocks.

This complex situation also explains the irregular movement of the Earth's magnetic poles and variations of the intensity of the Earth's magnetic field. It might also explain localized magnetic anomalies found in certain areas of the Earth's surface.

As described above, the radioactivity generated heat created in the Earth's Core has now entered the inner portions of the Mantle. Again, the heat can be transported outward by conduction and by convection. Both actually occur. The materials of the Mantle have lower heat conduction coefficients that those of the Core, so more of the heat is carried by convection. Again, this causes a variety of convection cells, this time in the Mantle. The warmer materials rise toward the exterior, and then move laterally while losing heat to the Crust. Then, the cooled Mantle materials sink back in toward the Core, to complete the convection cell.

The lateral movement of Mantle materials near the top of the Mantle is important. Remember that the Crustal materials above it are very thin, low density, and of low relative mass. Remember also that the bottom surface of that Crustal material has a variety of irregularities. This explains the variety of movements seen in tectonic activity.

The strengths of the Crustal materials are minimal in relation to the forces of the moving Mantle materials which drag them around. This explains the Indian sub-continent continuing to crash into Asia which is creating the Himalayas.

The Hawaiian chain is also explained. The bulk of the Pacific Ocean is one large plate. Its bottom surface is rather smooth, so it is not directly dragged very much by whatever Mantle flows are beneath it. It is more affected by the surrounding plates' movements. It is thereby moving slowly northwest. There is a weak spot near its middle, where the Crust has a weakness or fault. A specific point of upwelling in the Mantle is near that area, supplying extra heating there from the Mantle to the Crust. That one hot spot has been present for several million years. As the Crustal plate moves northwest above it, the hot spot keeps creating new islands in the Hawaiian chain. The oldest islands are at the northwest end of the chain. The youngest at the southeast. Another one is now forming undersea, but it won't break the ocean's surface and become an island for thousands of years.

The amount of radioactive material inside the Earth is fairly well known. The amount of heat created, and the amount rising to the surface if known. The conduction and viscosity coefficients of the various materials of the Earth's Core and Mantle are known. Calculations can be done to establish Mantle movement rates. Preliminary results suggest speeds on the same scale as the speeds of movements of tectonic plates.

Some predictions may be possible due to this theory. Computer analysis of all the present movement velocities of known plates may suggest the actual Mantle convection cell locations, sizes and velocity profiles. Precise magnetic field vectors and their changes may give some information on the component magnetic fields in the Core.

Since the tectonic plates are dragged primarily by their extensions sticking down into the Mantle, they are subject to variations in the flow in those vicinities. Consider a continental plate, which sticks down some to start with. Say it has two main mountain chains, like North America. Say that the convection cell(s) beneath one of those mountain ranges reverses lateral direction. This would cause an opposite drag on that one chain, which could cause the whole continental plate to rotate. In a few thousand years, the continent could be turned completely north to south. This action could also affect adjacent oceanic plates, pushing them around to change their motions. This phenomenon, in combination with conventional continental drift, can explain tropical fossils in Antarctica and Alaska.

This theory explains several phenomena much more completely than existing arguments have. Geomagnetic reversals, magnetic pole migration, geomagnetic anomalies, the Hawaiian chain formation, tectonic plate movement, climate changes in geologic time are all explained.

The following is added 7/97

This theory also offers explanation for a number of other phenomena which have heretofore resisted analysis.

The fact that the Earth's magnetic axis is tilted about 11 degrees from its rotational axis has traditionally frustrated theorists. Most previous theories have assumed that the Iron Core of the Earth rotates as a unit, and with the Earth's rotational motion. That situation would necessarily cause the magnetic axis to be virtually identical with the rotational axis.

This theory easily explains the 11 degree difference. It also explains short-term and long-term anomalies in the location of the North and South magnetic poles. The fact that the measured geomagnetic field is the sum of many magnetic dipoles of various Core convection cells at different orientations explains this. Most of the magnetic flux densities vectors of these randomly oriented magnetic dipoles tends to cancel out. In the event that they would ever all circulate such to add their magnetic field fluxes, the measured Earth's magnetic field could be hundreds of times as large as we now measure it. The fact that the (relatively large) magnetic fields developed by various Core convective cells mostly cancel out (add to zero) causes measurable changes in the sum in response to minor changes in those inner Core convective flows.

This same reasoning also explains the tilted magnetic fields of the planets Uranus, Neptune, and Jupiter, and explains the existence of a magnetic field in Mercury, which rotates so slowly.

The net effect we measure is the sum of many stronger but randomly oriented, convection-cell caused, magnetic dipoles. The magnetic pole axis of this sum does not necessarily line up with the planet's axis of rotation IN THE SHORT TERM. Averaged over millions of years, it should line up fairly well. This could suggest that planets where the magnetic axis and the rotational axis nearly line up, might have stabilized Core convection flows, where planets with more shifted axes might have more turbulent (and therefore changing??) flows in the short term.

During 1995 and 1996, science has determined that the evolution of animal and plant species on the Earth advances in spurts, rather than methodically and slowly as was previously believed. This has troubled most previous theories regarding the mechanisms of such evolution.

This theory clarifies this situation. The movement of the continental plates is presently constant, but it has not always been so. Since these plates are dragged by the lateral flows in the top portions of Mantle convection cells, and since the areas of best 'grip' between the Crust and Mantle is under mountain chains, extremely variable continental movements could occur. For example, the Indian sub-continent is presently moving northward, effectively crashing into Asia. Presumably, this is due to northward flow in Mantle material in a convective cell below. Over time, that cell flow can (and will) change. If it gradually reversed, India would head south. Also, if the bottom surface of the Crust became ground smooth (by the dragging force and the resistance of the impact with Asia), India could just stop moving, even if the Mantle convection cell flow remained. Finally, if a new (volcanic) mountain chain developed near the west edge of India, an additional drag point would develop under it, adding northward drag on that western part while not doing so for the rest, thereby rotating India clockwise.

These various scenarios would cause the continents to move in fits and starts, rather than uniformly as presently assumed. As a continental plate moved from one climate to another, all existing life forms on that plate would necessarily evolve. Life has the capability to evolve rather quickly. Previous theories assumed that horses needed 53 million years to gradually and continuously evolve from the dog-sized Eohippus. That's about 10,000,000 generations of horses. But consider that domestic dogs have (artificially accelerated) been evolved into all the hundreds of present breeds in only a few hundred years (about 100 generations). Given significant environmental changes, plant and animal species CAN evolve in just a few generations.

Thus, major increases in species counts appeared (seemingly overnight) at various times in geologic history. These periods are not unreasonable. Actually, they are quite reasonable. Even today, if North America would get dragged to a location at the Equator (say, over 50,000 years), the great diversity of existing plants and animals would allow continuation of life there. Some species would die out, probably including Alpine shrubs, Polar bears, and Sequoia trees. But many species would be progenitors of later generations which were slightly more adapted to the new climate, culminating in (seemingly) new species popping up after the 50,000 years which were well adapted to the hot tropical climate. In geologic terms, this 50,000 years is a heartbeat. In such a short interval, few animals and plants would wind up being fossilized, so little record would seem to exist regarding the intermediate stages of this transition. Archeologists in the distant future might just see the existence of cold-weather species disappear and new (unrelated???) hot-weather species suddenly appear. When geologic history is viewed in million year chunks (as it often is), this is how it would look.

Some amount of gradual, continuous evolution would also occur, but with stable environmental conditions, species would tend to multiply rapidly and succeeding generations would quite resemble their progenitors.

This previous discussion of this theory also explains many things about the age of dinosaurs on the Earth. They came into existence, and started multiplying rapidly fairly suddenly (over a few million years) about 225 million years ago. This was in response to a recent substantial movement of most of the continental plates. Then they dominated the Earth for an amazingly LONG time (160 million years). This incredibly long dynasty would be possible only in response to fairly slow movement, or movement primarily east- or west-ward of the plates they inhabited. Finally, about 65 million years ago, Mantle convective flows must have rearranged, moving the continents to areas of rather differing climates.

Very large, evolutionally advanced species tend to become so adapted to specific environmental conditions that they don't adapt well to rapidly changing climatic conditions. Smaller and less evolved species are usually more easily able to make the necessary adaptations.

This would make it very likely that nearly all species of dinosaurs would die out in just a few thousand years, and that apparently new species would rapidly appear. Rapidly is again an overstatement. Evidence is that the last dinosaur fossils are from about 65 million years ago, and that many new species' fossils appeared about 63 million years ago. Popular media make it sound that dinosaurs died out 'overnight' as if on a Tuesday they were there and on Wednesday they weren't. That was not the situation. As presented above, they disappeared over a period which might have been as long as 2 million years, which agrees with the theory presented here.

There appear to be a handful of brief periods in the Earth's distant history where enormous numbers of new species came into existence. Other than at those times, relatively few new species seem to appear in the fossil record. As described above, these situations occurred as a result of substantial north-south movements of the continental plates in response to north-south convective cell flows in the outer surface of the Earth's Mantle.

The amount of radioactive material in the Core was greater in the distant past. That greater amount proportionally created greater heat amounts which had to get to the Earth's surface to be able to be radiated away. One result of this was that the materials of the Core and Mantle were hotter than today, and therefore more fluid. That situation was enhanced by the remaining presence of a substantial amount of heat remaining from the original formation of the Earth.

The result of all this was more heat driving convective cells in materials which were more fluid. This necessarily caused more rapid movements of those materials. This would have created substantially greater geomagnetic field strengths in the distant past. It would also have caused far more rapid lateral flow velocities in the Mantle convection cell tops.

Depending on the 'grip' (or static / dynamic coefficient of friction) between Mantle and Crust, this could enable very rapid tectonic plate movements in the distant past. When that caused substantial north-south movement in the continental plates, strong evolutionary pressure would suddenly exist.

The fossil record seems to suggest that generally the Earth's magnetic field has usually been oriented roughly north-south, and not in other random directions, as might seem expected by the present theory. That is not necessarily a problem. The Earth's Core can be expected to rotate (as a whole) generally with the rest of the Earth. This can both cause a basic dipole field by its motion, and also an added velocity vector to the motions of the materials moving in the convection cells in the Core. These two effects are almost the same. They would create a background field strength to which the sum of the convective cell caused magnetic fields would be added. This could cause directional preference of the resultant magnetic field axis vector to be parallel or anti-parallel to the rotational axis.

There are several associated subject-specific essays on this subject area, specifically:
Earth's Magnetic Field - Source and Logic

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

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Carl Johnson,
Theoretical Physicist, Physics Degree from University of Chicago

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