Although water covered 70% of the earthÕs surface, because of technical difficulties it had been virtually unexplored. With increased technical sophistication and interest scientist began charting out the ocean floor with some surprising discoveries.
In 1934, four years after Wegener had died, Maurice Ewing began plumbing the bottom of the ocean floor with explosives. His first discovery was that the continental shelf was not permanent but merely sedimentary rock up to 12,000 feet deep. This small fact flew in the face of the preconception that the continents had been fixed and immovable since the beginning of the earth. By and of itself, it was only considered an interesting anomaly.
Because of the submarines of World War II, all the scientists directed their energy towards detection and the charting of the ocean floors. With the Cold War after W.W.II, the US Government invested huge sums of money into charting the ocean floor for the submarines, which they considered to be the weapons of the future.
Ewing in the meantime had been commissioned to study the Mid-Atlantic Ridge. In dredging up samples, the scientists of the world expected to find a complete record of history written in sedimentary layers. Instead Ewing found a layer of recent sediment on top of a 20 million year old ocean floor. There was no sediment in the intervening time between sediment and ocean floor. Next he found that this layer of recent sediment, which should have been up to 12 miles thick if it had been accumulating for about 3 billion years, was only a few thousand feet thick, representing sedimentation only 100 to 200 million years old.
Next when Ewing reached the center of the Mid Atlantic Ridge, he first discovered that the sediment narrowed as he went up the ridge. Then he pulled up some pillow lava, molten lava quenched in water. It pointed to a recent volcanic origin. The surprises continued. While the granitic crust underlying the continents is up to 25 miles thick, the ocean floor was only 3 miles thick and made up of basalt a different material altogether.
The next step occurred in 1953 when drawing up a topological map of the ocean from all the data that had been accumulated. The scientists noticed a rift down the center of the North Atlantic Ridge. While plotting all the Atlantic earthquakes, it was noticed they always occurred within the rift valley. Then in gathering more data on oceanic earthquakes it was found that they occurred in the middle of the oceans all over the world.
Ewing presented his findings in 1956. But they were rejected because they implied that the earth was growing - not shrinking, as the geologists still assumed. But then another group of scientists found that the heat generated from the ridge was 8 times greater than the base of the ocean floor. It was obvious that this ridge was atop a Ōgreat crack in the earthÕs crust where new, hot material was rising to the surfaceÕ. In 1959 a map was published showing Ōa 40,000 mile long mountain range that curls through all the oceans of the world, encircling the planet like the seam of a baseball.Õ (Continents, p75) This was revolutionary because it linked ridges, which had been considered separate.
Next Harry Hess discovered that some old volcanic peaks, that he named guyots, seemed to drifting away from these ridges. Cautiously avoiding WegenerÕs fate, he tentatively proposed, in ŌgeopoeticalÕ terms, that the ocean floor might be a type of conveyor belt, moving things away from the ridges. This idea explained many of the mysterious phenomenon that had been discovered. He published this paper in 1962. Hess was glad that he had presented it in geopoetical terms because, while intrigued, most geologists still rejected the theory.
From another scientific discipline, paleomagnetism, came evidence that the magnetic orientation of certain rocks in the British countryside deviated as much as 30% from the modern magnetic orientation of the Poles. The obvious conclusion was that the island had shifted and had not been permanently there. Mindful of WegenerÕs fate the scientists were quick to point out that it did not indicate continental drift. But as they gathered more and more evidence which indicated that the land had moved, they began to start considering continental drift. But as paleomagnetism is an inexact science, the rest of the scientific establishment was not impressed.
By 1964 however a symposium on continental drift was held in London. There another scientist showed a map of Africa and South America hooked up by their more permanent continental shelves rather than by their more changeable coastlines. This map, combined with all the other evidence that was available at the time, converted many more scientists to the theory of continental drift, The tide had changed. Things moved even more rapidly from this point.
More data came in linking other continents. In the race to discover the South Pole Robert Scott in 1911 had discovered coal. Coal comes from the disintegration of living remains. Where was the life on the South Pole to generate coal? In 1969, using radar, which doesnÕt see ice, they were able to chart the bedrock under the glacial ice sheets. They discovered geological formations, which linked East Antarctica geologically with South Africa, Australia, and peninsular India. Furthermore West Antarctica was linked geologically with South America. It seems that its mountain range was at one time linked with the Andes.
While in high school In the late 60Õs, I was still taught that scientists suspected that the moon had emerged from between the Africa and South America and that was why their coastlines were such a remarkable fit. It seemed a little loony to me because something that emerges from between two things does not leave a similar edge on both sides. But it was a revelation that they fit so well together. However our teacher and textbook were quick to point out that the two continents had not drifted apart. Just to show the lag between education and research, by this time in the late 60Õs the scientific community had begun a wholesale shift to the side of continental drift and ocean spreading. The cooling and contracting earth theory with its artificial land bridges was dead and WegenerÕs theories had been resurrected.
By the late 1990s the generally accepted version of the geological movement of the earth is that in the center of the earth, it is very hot, filled with molten rock. The heat and pressure increases and is released through the continuous volcanic ridge that rings the Earth in its oceans. This movement equalizes. Hence the earth is neither shrinking nor growing. This mid-oceanic rift is there to release pressure from the interior. It probably emerged along with the coagulation of the earthÕs surface in the first billion years of the EarthÕs existence. The way the Earth breathes, equalizing internal and external pressure, is through a continuous release of energy through these rifts. The lava flow causes ridges on both sides of the rift. This is the Mid-Atlantic Ridge.
Another way that the Earth deals with pressure is its cross-stitch fault structure. There is the Ridge itself, which releases heat and pressure from the interior, but it also translates any north south pressure through the fault that lies up its center. There are also small fault-like stitches, which run perpendicular to the Ridge Fault. These translate any east-west pressures into oceanic earthquakes to relieve the stress. Hence the Earth is stitched up like a huge baseball. Its oceanic fault lines are in place to translate any stress into motion through earthquakes. One can envision the Earth as huge teakettle set at boiling. It is wheezing through the crack between the lid and the pot, unpredictably rattling around. (This recalls the lattice crevasses in the glaciers designed to relieve lateral and downward stress.)
The volcanic lava spreads out of the rift at the center of the volcanic ridge. Many scientists believe that the ocean flow is like a convection current. The hotter material flows to the surface and out through the rift. Then it flows slowly down hill towards a deep trench, which takes the cooled magma back underground to repeat the cycle again.
When I say slowly, it is 10,000 times slower than the hour hand of a clock. However this means that an entire cycle could occur within 58 million years. This means that the oceans could have gone through 80 such revolutions since the Earth began. Significant in geological time - insignificant in human time.
Remember that the ocean floor is like a conveyor belt transporting anything on top of it including mountains and continents slowly away from the spreading center, even if it is into another land mass. When they collide mountains are formed. These oceanic conveyor belts have also slowly separated Africa and South America and India. The conveyor belt also slammed India into the Asian continent creating the Himalayas.
According to this theory the ocean floor moves just the way glaciers move through internal deformation called creep. If enough pressure and heat are upon a solid then it can ooze along, like silly putty or a cake piled too high. The oceanic plate has pressure from the water and heat from the interior to put it in that state. Heat causes it to rise to the ridge. Then gravity pulls it towards the trenches.
Internal deformation, or creep, is how glaciers and the ocean floor move. This is when the solid is close to its melting point with lots of pressure. It then moves downhill, the direction that gravity pulls it. Just as glaciers spread from an ice reservoir, the ocean starts from the spreading center. In both cases an artificial elevation is created which pulls the solid down and creates the flow. A glaciers begins to flow when excessive snowfall at one location creates an altitude. The ocean floor moves downhill to the trenches when magma creates ridges.
The area from the volcanic ocean ridge to the trench is called the tectonic plate. These tectonic plates grow, are consumed and also break apart. There is nothing permanent about them, except in the human time scale.
When the subduction trench forms next to a continent then the friction of plate against plate will melt the crust. Sometimes this produces volcanoes overhead to release the stress through the land. This is what happened in the Sierras with the appearance of the Pacific Plate. It is happening in the Cascades right now. Sometimes the subduction just melts the crust, creating a huge block of melted material. This type of subduction from the Sonomia and Smartville Blocks was what created the Sierras before they rose.
Sometimes the trench occurs mid ocean. Then the heat of the friction might create an underground volcano that if it continues growing might even emerge above the surface of the water. Iceland is one such island. If it grows big enough it might become a continent. However most island arcs dock onto continents. The suture is where they join.
Sometimes a trench is blocked, then a fault appears. This is what happened in the relation between the Pacific and North American Plates. The trench between them was sealed up as the growing San Andreas Fault. The triple conjunction of plates, called the Mendocino Triple Conjunction is where the zipper of the fault meets the still open trench. A trench canÕt exist between two landmasses. Thus when two landmasses, which are sitting atop plates, collide, the trench is swallowed up.
When two landmasses dock the momentum both melts the crust and crushes the existing land, crumbling it. This is what happened when the island arc called the Santa Ynez Mountains crashed into the coast of California crumbling the sedimentary land in front of it into the Sierra Madre Mountain Range. While many island arcs are volcanic, this island arc is merely the accretion of sediment along the subduction zone between the Farallon Plate and the North American Plate. This occurred before the larger Pacific Plate moving from the west subsumed the Farallon Plate.
In erratic places, the magma from the interior burns through the tectonic plate. If this hot spot is in the middle of the ocean, which many are, then they can create a series of volcanoes, which also become an island arc. This is the case of the islands of Hawaii. If the hot spot breaks through the tectonic plate under a continental landmass, then it could eventually split apart the continent. This process takes quite a few years. No one has ever seen it happen before. But theoretically a hot spot formed in the middle of Panagea, the super continent that preceded our present organization. It split Panagea into many parts, including the continents of Africa, South America, Australia, Antarctica, and India.
The theory is that the hot spot burns a continuous hole in the crust first creating volcanic ridge, but then eventually opening up into a rift with a volcanic ridge on both sides. Because of the melting action, eventually it melts through the landmass onto the ocean floor. The cracks in the middle are filled in with water. Et voila. We have the beginnings of an ocean and the beginning of an oceanic ridge.
No one saw this happen. But we have found coal on Antarctica indicating lots of life. We have seen parallel land formations and life forms upon the continents that made up Panagea. Additionally we can trace the supposed path of prehistoric creatures from one to the other. Hence this theory explains a lot of mysterious facts, which would remain mysteries if the continents had always been in the present position.
All of these ideas are counter-intuitive, with respect to our day-to day existence. We donÕt see ocean floors move, continents split and drift apart, or continental plates collide and wrinkle. While our intuitions tell us that we live in a fixed world, the fixed world theory doesnÕt explain many of the facts that derive from this fixed world. In the constant relentless examination of our underlying assumptions against seeming facts, we must throw away our intuitive assumption that the world is a fixed entity. Similarly we must constantly examine our underlying assumptions against the facts of existence in order to constantly modify and refine our worldview. We need to be alert to the idea that our intuitive conception of reality is many times based upon cultural conceptions rather than a rigorous examination of facts.
Plate tectonics, subduction zones, and transverse faults are buzzwords that are bandied about in a self-knowing semi-scientific way. A prominent geologist, who was instrumental in identifying and charting out the San Andreas Fault, says that she has never really seen a tectonic plate and doesnÕt really know what they are. This is no amateur. This is a Ph.D. specialist on plate tectonics. What does she mean? She means that plate tectonics are a useful way of explaining certain phenomenon but that theyÕve never seen one. It is like electrons. Everyone visualizes electrons like microscopic planets revolving around their proton nucleus. Every school child knows this but no scientist has ever seen an electron revolving around a nucleus. It is a useful mind image but is not reality.
No one has ever seen a tectonic plate, neither has anyone seen a continent drift, nor an ocean floor spread, nor have they seen subduction zones. Scientists and others have seen volcanoes. Many have experienced earthquakes. Almost all of us have seen a mountain. There have been pictures taken of the Mid-Atlantic Ridge. Scientists have seen the volcanic rift in the center of the oceanic ridge. Anyone can look on a map and see island arcs. There has also been much data that scientists have interpreted from their instruments to indicate such things as age, depth, density, and substance of the ocean floor. Although we have mountains of data, personal experience, and volumes of paper written about the above phenomenon, the theory has only created constructs to enable us to understand the data. Hence remember much that follows are mind puns or metaphors that enable us to understand certain facts, but arenÕt real in themselves. Beware of attributing reality to the theoretical constructs that exist only to service the data. With this in mind proceed cautiously and with humility.