CompuServe Messages

Hi, Kamron– Deep quakes were supposed to be impossible because mantle material at such depths is too plastic (not liquid – see the subduction thread) for ordinary faulting to occur. Only solid-state phase changes offer much of an explanation for how quakes could occur so deep (remember, olivine under pressures approaching these, where it ceases to be olivine, has been observed in the lab; this is not just theory). Given the plastic nature of the mantle, more or less all stresses dating back to Tertiary age events should have long since been erased at these depths. Even if the Earth's magnetic field was flipflopping madly over a span of days instead of centuries, the stripes of magnetization on the seafloor still record the order in which the seafloor rocks solidified (dropped below the Curie temperature if you want to be precise). Why would they freeze in zones parallel to the ridge? Your explanation makes a prediction: since the sea floors would have cooled from the surface down, there should also be _frequent_ magnetic inversions as one drills deeper into them. I think we would have heard by now if such a thing were there. Movements of a single hot spot might be explained by movements of the source rather than movements of the crust, but what about many hot spots all "moving" in directions consistent with plate movements proposed for other reasons, and few or none "moving" in "wrong" directions? In originally forming plate tectonics theory, some data were surely "set aside" (_not_ discarded) because a spot could not be found for them. But the theory would have remained merely one among rival theories unless almost all of these data eventually found a home in the theory – and more are being snapped into place each day. When it became clear that the ocean floors were relatively young, past theories had indeed to be revised to fit this fact, but not necessarily by proving renewal and consumption of the seafloors. I have a notion that was still in the time when "continental drift" was a maverick idea, when many scientists had as much or more stake in proving an all-at-once resurfacing as in proving a conveyor-belt renewal. Radioactive datings, paleomagnetic stripes, and so on must have forced them to cave in when they could not come up with answering evidence of comparable strength. Consider how bubbles group together atop boiling water, and then tell me again why Earth's surface must have been uniform when it first solidified. I don't know that it wasn't, so tell me also why various geological processes could not have made it non-uniform later. Where was all the water before oceans were opened up? –Doug