http://en.wikipedia.org/wiki/Expanding_earth_theory___________________________
Arguments against subduction
Expanding Earth Theory challenges the existence, or at least the extent, of subduction in global tectonic theory. Exponents contend that in order for subduction to cause the Earth's size to remain fixed, the exact same amount of crustal material appearing at the mid-ocean ridges must be subducted. There is no agreed mechanism for such a correlation between the two processes.
1. The mid-ocean ridges are greater in length and area than the known subduction zones and circle the entire globe in several configurations. Proponents of an expanding Earth argue that in order for the crustal material appearing there to subduct equally into the known zones, some evidence of a bottle-neck pile-up of oceanic crust should be visible nearing these subduction zones. Yet the entire ocean floor is smoothly surfaced, free of oceanic slab irregularities, indicating harmonious spreading unencumbered by such a process.
2. Subduction only occurs on one side of subduction zones, so the "other side" should show evidence of being much older. In some cases (where two oceanic plates come together) no such evidence is visible. However, this is explained in plate tectonics by the assumption that in some cases, the direction of subduction changes.
Arguments for subduction
Since the 1970s, a vast amount of evidence was found in structural geology, seismology, petrology and isotope geochemistry that subduction is at least to some extent taking place. It is still very hard to calculate the global rate with which material subducts. Proponents of the expanding Earth theory claim the existence of subduction does not necessarily rule out expansion of the planet, but the existence of a mechanism by which the Earth can keep its crust size constant is a significant problem for the expanding earth theory and is one of the major reasons why it was abandoned. Observations seen as evidence for subduction include:
1. The existence of Wadati-Benioff zones, elongated regions of high seismic activity within the crust and mantle that are explained as huge shear zones. These zones are located beneath oceanic trenches and seem to indicate a slice of crustal material is moving downward through the mantle. They form one of the best arguments for subduction.
2. 3D models of the mantle made with seismic tomography show cold zones of sinking material exactly in the regions where plate tectonics predicts slabs of crust are subducting into the mantle.
3. Petrologic research of rocks from mountain belts has yielded countless pressure-temperature-time paths. Paths for the axial zones of mountain belts (the metamorphic core) show many mountain chains went through a period of "deep burial". This is explained by plate tectonics (subduction followed by obduction). The existence of eclogite in many mountainbelts indicates material was "pushed" to depths far into the mantle (depths up to over 200 km are found). In plate tectonics this is explained by the slab pull force which occurs at mid-ocean ridges.
4. The existence of major geologic shearzones (sutures) in most mountain belts. Paleomagnetic and mineralogic studies show the rocks that are now lying next to each other were originally thousands of kilometers apart. In other words: a piece of the crust is missing. Structural geology has shown these missing pieces of crust are not located directly underneath the shearzones or laterally. Instead, they seem to have moved along the sutures into the mantle (this is supported by shear indicators in the shear zones). This is again strong evidence that subduction took place and mountains form by the "continental collision" of tectonic plates.
5. Rare earth isotope compositions of volcanic rocks that formed above subduction zones are similar to those of sediments on top of the subducting plate. If there are lateral differences in the isotope composition of sediments on subducting plates, these lateral differences are also found back in the composition of the magma that rose from the deeper part of the subduction zone.
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From what I can tell, the main beef between the two is the rate of subduction/obduction vs rate of crust creation. I compare it to a joke I heard once, about the existence of hell.
I sincerely doubt that the rate of sub/obduction is equal to the rate of creation, simply because perfect is to convenient to accept. So that means that either sub/obduction is occurring at a greater rate, or a lesser rate to creation, meaning it is either growing, or shrinking.
One of the places they went wrong is claiming that the earth's smaller stature allowed for the dinosaurs' large sizes. It seems like the opposite should be true, as gravity isn't calculated by volume alone, its density is a major factor. If the earth had the exact same mass, but displaced a smaller amount of space, then its gravity should be increased. Its core and magma should be hotter as well. (if I'm wrong about this, I'd love to be corrected)
BTW: The joke went (as much as i can remember)
A professor asked a class to use physics to explain the existence of hell. One of the students wrote in...
If hell exists, then it must be expanding in order to accommodate the arrival of new souls. If hell is expanding slower than the arrival of new souls, then it will become hotter and be under greater pressure until all hell breaks loose.
If hell is expanding faster, then it will be under less pressure, and be cooling until hell freezes over.
I am led to believe that hell has indeed frozen over as Jenny Lincoln said "it will be a cold day in hell before I sleep with you Jimmy", and seeing as i hit that, and hit it good, hell must be expanding faster.