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.|
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 and continents.)
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 average Crust density is 2-3 gm/cc, 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 has a substantial Iron content, 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 the present premise suggests that a substantial part of that heat is carried by convective action.
This substantial heat represents a strong driving force which causes the formation and maintenance of a number of convection cells inside the Core. In some locations the Core material, including the Iron, rises (very slowly) toward the surface. When near the outer edge of the Core it moves laterally for some (random) distance as it gives up its convective heat (by conduction and radiation) to the Mantle above it and and the Core material therefore cools. Having cooled, it sinks back down toward the center of the Core to replace the heated material 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 are carrying Iron in a closed loop. At least some of those Iron atoms become charged by a variety of natural physical phenomena. The closed loop of circulating Iron has the effect of being like a loop of wire that is carrying electric current. These Core convective cells, therefore, represent a variety of separate very low voltage, VERY high current electric currents in the Core. Each of these loops has its own dynamics and its own orientation. Every circulating electric current creates a resultant magnetic field. The sum total of all these resultant magnetic fields is the magnetic field that we measure at the surface of the Earth.
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. Much of the strength of the magnetic fields that are created by the individual Core convection loops tends to get cancelled out by other loops that happen to be creating magnetic fields of the opposite polarity. At the surface, our instruments sense and record a single net magnetic field for the Earth, which is (generally) much weaker than the intensity of its individual components.
Over geologic times of hundreds of thousands of years, variations in the individual Core convection cells occur. A specific reason why this would happen is that the heat generating Uranium near the center of the Core must necessarily be jostled around by the actions of the convective sell motions that it causes. 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 apparently drastic 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. It also allows explanation for the fact that the Earth's magnetic field doesn't actually have TWO poles (dipole), but it also has characteristics of being a quadrupole, and even an octopole. Prevailing theories attempting to explain the source of the Earth's magnetic field often seem to overlook the complexity of its presence.
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. These facts explains the variety of movements seen in tectonic activity.
The Hawaiian chain is also explained. The bulk of the Pacific Ocean (currently) appears to be riding on one very large plate. Its bottom surface is rather smooth, so it is not directly dragged very much by whatever disparate Mantle flows are beneath it. There is certain to be quite a lot of slippage at the Mohorovicic Discontinuity where the Crust and the Mantle are in contact. The Pacific Plate is more likely to be affected (pushed) by the motions of surrounding plates. The whole Pacific Plate is thereby (currently) moving slowly northwest, at the rate of a few inches a year. There is a weak spot near its middle. A specific point of upwelling in the Mantle (between two convection cells) is clearly near that area. There are two effects of that. The upward motions of the Mantle materials must certainly apply some physical stress on the Crustal material right above the upwelling area. In addition, the excess heat from the hotter upwelling material must certainly be supplying extra heating there from the Mantle to the Crust. That one hot spot has existed 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.
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 (as suggested from some of the previous comments about India and Hawaii), sizes and velocity profiles. Precise magnetic field vectors and their changes and distributions may give some information on the component magnetic fields in the Core, and therefore the convection cells locations and parameters there.
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 is completely solid and that it rotates as a unit, and that it somehow is able to rotate at this angle tp the Earth's rotational motion without substantial friction. The absolute certainty of friction between the Core and Mantle, and the 4.5 billion year age of the Earth, would certainly not allow such a situation to be true for very long, and that, by now, the rotation axis of the Core must certainly be virtually co-axial with the Earth's rotational axis.
This theory easily explains the (present) 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 likely 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 proximity of Mercury to the Sun may add enough internal heat (or equally retard formation internal cooling) to keep Core materials more fluid, and therefore more able to have numerous, active convective Core cells.
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.
This same argument also explains why the source of the Earth's magnetic field does not appear to be centered at the center of the Earth. (The point halfway between the North Magnetic Pole and the South Magnetic Pole is quite distant from the exact center of the Earth). The multiple convection cell source easily explains that fact.
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.
The present theory can clarify this situation. The movement of the continental plates seems presently constant to human observers, but it has not always been so. Since these plates are dragged by the lateral flows in the top portions of Mantle convection cells (which will change from time to time), 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 (or even geologically 'suddenly') reversed, India would head south and separate from the Asian continent. 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. (This could also explain some geologic records of large areas of subsidence, where a mountain chain effectively collapsed under its own mass to achieve isostasy with the Mantle after such shearing action.) Finally, if a new (volcanic) mountain chain were to develop 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 initiating a clockwise rotating to the Indian sub-continent.
These various scenarios would cause the continents to move in fits and starts, rather than uniformly as presently assumed. In addition, the possibility that a continent could ROTATE is realistic, although probably unlikely. As a continental plate moved from one climate to another, all existing life forms on that plate would be stressed with the necessity to evolve. Life generally has the capability to evolve rather quickly. But some species would not be adaptable enough to be able to succeed in the new environment.
Consider for a moment that some present Tectonic Plates appear to be moving at nearly a foot per year. What if the swamp that some Brontosauri lived, with the adjacent Palm trees, had been at 30 degrees Latitude (like Northern Florida). If the Plate on which that swamp existed started moving northward at even one foot per year, it would be 1000 miles farther north (like part of Ontario, Canada), just 5 million years later! Whether swamp creatures or plants could survive the harsh Canadian winters is a moot point. Smaller creatures, that are more mobile and/or more adaptable, might have a better chance of survival in such circumstances.
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. There has been an implied microscopic evolution in every generation.
But consider that domestic dogs have (although artificially accelerated) been evolved into all the hundreds of present breeds in only a few hundred years (about 100 generations). Given significant environmental changes, many plant and animal species CAN evolve in just a very few generations.
Thus, major increases in species counts appeared (seemingly overnight) at various times in geologic history. These episodes 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 or longer), the great diversity of existing plants and animals would allow continuation of many of the life forms 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 animals and plants that were seemingly new species popping up after the 50,000 years, and 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 (suddenly) 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. The term (suddenly) is obviously used in a geologic sense and not in a traditional sense.
This suggests the very logical premise that biological evolution is generally stress driven, by significant changes in the environment, and that, without such environmental stress, evolution would occur extremely slowly. The continuous success of sharks and a few other species, for hundreds of millions of years, attests to this idea.
Some amount of gradual, continuous evolution would also occur, but with stable environmental conditions, species would tend to multiply rapidly and succeeding generations would very closely 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. The current premise suggests that this was in response to some recent substantial movement of most of the continental plates. Then they dominated the Earth for an amazingly LONG time (160 million years). That's quite a success story! This incredibly long dynasty would have been possible only in response to fairly slow movement, or movement primarily east- or west-ward of the plates they inhabited, or by species that retained a lot of adaptability. Finally, about 65 million years ago, Mantle convective flows must have rearranged, moving the continents to areas of rather differing climates. By then, many of the dinosaur species had become extremely specialized, and in many cases, quite large.
Very large, evolutionally advanced (specialized) species tend to become so adapted to specific environmental conditions that they don't adapt easily 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 (and any other highly specialized species as well) would die out in just a few hundreds of thousand years, and that apparently new species would rapidly appear (to fill the competitive vacuum). 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 seemed to start appearing 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 easily 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, the present premise suggests that 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 certainly 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 certainly 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. Finally, convection cell flow rates are driven by the amount of heat that is present, so that also would make the Core convective cells and the Mantle convective cells much more active and much more dynamically unstable than today.
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 would be natural because of 'drag' at the Core-Mantle and Mantle-Crust boundaries. 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. Significant angles can occur between the rotational axis and the magnetic axis, but averaged over long times, these two axes should be nearly co-axial.
The following was added 10/8/97
The initial inspiration for this theory was the numerous gaps in prevailing theories for the phenomena discussed.
Plate tectonic theories often seem to treat the plates as massive entities, but they are relatively insignificant in mass when compared to the Mantle. They are almost as paper boats on a pond. Studying the boats' movements may not say much about the boats' capability of moving as the water currents and winds which move it.
Many theories seem to have ignored much about the activities deep within the Earth, opting for the simplest descriptions. An example is a common assumption that the heat moves out through the 'solid' Mantle exclusively by conduction. This oversight of convective flow and even the fact that 'solid' rock DOES still flow (very slowly), seemed to initiate some of the logical gaps in extant theories.
These are the two primary areas which initiated the creation of this theoretical explanation of the phenomena discussed here. Additional subject areas showed potential resolution as progress developed.
The following was added 3/8/99
An analogy exists for the movements of Tectonic Plates upon the Mantle convective flows. It is a large kettle of water on a kitchen stove, with a variety of pieces of tissue paper floating on the water.
As heat is applied under the kettle, a variety of random convection cells form in the water. As more and more heat is applied, the water gets hotter and hotter, and the convection cells each have much more rapid mass flow rates in them. They also become much more unstable, with each convection cell only lasting a fraction of a second, with another one quickly replacing it. This instability is very logical, since at the bottom of the kettle, as a particular convection cell develops, it acts to remove heat from that specific location on the bottom, but tends NOT to do so for adjacent areas. Very quickly, the one area is cooled (because of the effectiveness of the convection cell) and the adjacent areas get hotter (because they do NOT have an effective way of releasing their heat). Obviously, new and different convection cells MUST quickly develop.
The net effect on the wisps of paper floating on the top of the water is to be continuously be jostled around, as a result of the unstable, turbulent flows which are the tops of the various convection cells. The individual pieces of paper move, back up, rotate, and crash into each other, in a seemingly random dance, but those movements are merely evidence of the hidden convective flows beneath.
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