CompuServe Messages

Doug >> Convection in a solid, with spherical geometry, is too foreign to our experience to be so dogmatic about.<< A solid does not have convection. >>There is no reason to assume plumes would arrive in subduction areas.<< I'm not sure what you mean by this. Let me explain again my position here. Convection flows like smoke rises…. if it meets a slanted surface it will seek to move up the slant until it is as cool as the surrounding material. It would not flow downward while it is still warmer than its surroundings. The force it would exert on the plate would be in the opposite direction than is required to move the plate because the plates generally slant upward towards the rise. >>Assume only plumes at first – then a plume might break the single world-plate in the beginning (a common pattern in such sheet breakups is to crack in three pieces, with the three cracks meeting at the dome over the plume), causing the three or so new plates to start subducting at some far edge (they were unstable and "itching" to do this anyway, being cold dense material atop warmer lighter material). Now they are moving, and the rollers may become organized by the motion.<< I buy the first part with a great stretch but the the last >> being cold dense material atop warmer lighter material<< this would not occur. First of all the material is atop because it was lighter as a liquid and/or solid than the liquids below it otherwise it would have sunk upon solidification. The crust material is not as heavy as the material it is floating on. It rose to the top in the liquid state and then solidified when the temperature of the material below cooled enough to allow it. IT did not sink after solidification because it is lighter. >> How can convection be less than furious in a magma ocean with savage temperature differentials? << There would be turbulent convection in the beginning but this would slow eventually. The materials in the deep ocean of magma would stratify out with the cooling into the condition we have now …floating continents and after the catastrophe floating ocean plates. >>It is a relative thing. I cast 1 and 2 as going in opposite directions, but that is from the viewpoint of an observer traveling at an average of their velocities. Let 1 and 2 go in the same direction with 1 pulled harder and faster, and the moving observer will see what I described.<< I have more problems here, if you look at the shifted sections and consider the section that has shifted more is traveling faster…. you have a situation where each section is moving a little faster than its partner ending with a big difference in the speeds of motion all in the same plate. Taking the Mid Atlantic Ridge as an example and looking at the section between the latitudes of Florida and the eastern most tip of S. America the distance covered would show that the plate has shifted nearly two thousand miles more than its counterpart or it has nearly double the speed. That is clearly impossible since the plate is a single mass how can it travel at different speeds? You still have not solved the problem of the shift faults extending into the opposite side of the Rise matching the pulled side. >> The shift faults are parallel to the _relative_ motions of the two plates involved – this is predicted by plate tectonics.<< Ok so this is agreed…. this is one of my points for revising the motions into a single event. >> I see no proof of rapidity here, especially not in the light of paleomagnetic markings. Above I describe how the regular behavior of the ridges are predictable from plate tectonics – I find it hard to imagine them so regular with so much as you would have going on. << It is much easier to reconcile the regularity of the markings into a single event than to get these markings from various merging and diverging of plates. For example where is the evidence that South America has moved upward to meet North America in the last 40 million years? Not only is there a lack of evidence there are actually deep trenches in between the crustal fragments of the Antilles. Why would trenches open up in an area being crushed together? >>Traces of iridium are _far_ less than one would expect with whole continents literally flying about. Can you not show us even a small jumble of weird rocks between K and T layers? How can that boundary be so thin nearly everywhere? << Iridium is very dense and rare. It would be one of the first gases to condense into liquid then solids out of all the elements. It came from deep within the earth where it collected in the original formation of the planet. Actually it isn't thin everywhere I have read it is as wide as 30 centimeters in some areas. The entire planet has much regularity below the KT boundary area and is much more variable above the area. There are also other weird things like the Deccan Traps which were tremendous lava flows over a short period of time. There is also very little gravel below this boundary aside from faults that were back filled. Hows that for weird? Kamron