There's nothing hypothetical about convection currents in a fluid
Current density is the measurement of how many Amps per square meter are flowing through a cross-section of the tube. If the horizontal axis shows current density at a point in the plasma, the vertical axis is then relabeled as being the electric field (V/m) at that point.
The convection current hypothesis, Reviews of …
It was fortunate for Hall's theory that the eastern flank of the Appalachains was deeply buried under later sediments. The Appalachian geosyncline was full of sediments that came from the east in large quantity, not from the sparse rocks of the continental platform to the west. However, there is no land there any more. In the south, the Ouachita geosyncline was filled with dark shales and cherty limestones unlike anything to the north on the platform: it all had to come from high land to the south. There is no land there any more. These are just two examples of a problem that arose with nearly all geosynclines that had later formed mountains. When you read a study in which this occurs, there is usually little more than a plaintive note or two that the source of the sediments cannot be located. We now know that the sediments in the case of the Applalachians came from Africa, and in the Ouachitas, from South America, both of which departed the scene long ago. The geosynclinal concept is one that should vanish from geology texts, but it is deeply embedded in the souls of geologists.
Harry Hammond Hess (1906-1969), a Professor of Geology at Princeton University, and a submarine commander in World War II, used ultrasonic sounding to map the ocean's floor much more accurately than it had been done before, and his and subsequent work have revealed a wonder: the ocean floor is filled with trenches, faults, rises, mountains and all kinds of irregularity. He identified rises, such as the East Pacific Rise, and the Mid-Atlantic ridge, as spreading centres, where Arthur Holmes's convection currents rose to make new ocean crust. It had long been obvious that the trenches were areas in which the ocean floor was diving beneath continental or oceanic crust and disappearing into the mantle. Putting Holmes's convection currents and Hess's spreading centres together, the idea that the continents were riding on the conveyor belts of rigid upper mantle and crust became clear. This, finally, is , in which continental drift has found a mechanism.
Describe the convection current hypothesis for driving earth’s plates
The text remains a celebration of actualism, and it seems to build continually toward the final chapters on earth history. The final chapter is entitled "Continental Drift and Palaeomagnetism." 1965 was the threshold of plate tectonics, and Holmes comes up to the threshold, but does not step over. Nevertheless, it is obvious that he realized his long persistence was finally crowned by success, and that geologists were accepting that the continents moved as a result of mantle convection, and that a "theory" was about to be confirmed by proof. It is very interesting to compare the two editions on this subject. Doris Reynolds published a third edition later, in which plate tectonics was finally present, but we will not consider it here.
Convection Currents: Currents in the Earth's System
The model of turbulent convection in the lower mantle is consistent with localizing a material of high strength and high viscosity in the upper mantle and with the observation that earthquakes are not observed to occur in the lower mantle.
- What is Convection-Current Hypothesis? - Custom …
Plate tectonics indeed marks a revolution in geology, a paradigm change as Thomas Kuhn would say. There is a great amount of complexity, but the basic reason for orogeny is now known, if not understood in detail. The Appalachians and the Ouachitas are the crumpling caused by the assembling of Pangaea. The Rockies are the result of light rock carried beneath the continent by subduction, giving the Miocene uplift as a result of isostasy. There are no real geosynclines in the Rockies, despite valiant efforts to find them. The deep basin of Cretaceous rocks in front of the Rockies was not folded. The whole western part of the continent, from Utah west, is a Mélange carried in on plates subducting to the west, an example of , something previously completely unexpected. As the Rockies rose, the Great Basin was stretched as the deep light rock was shifted eastward, so it subsided from its previously lofty position in the Cretaceous (where it provided sediment whose provanance was problematical) across what would later be the Rockies. These are American examples, but Alpine, African, and Asian examples abound. The Himalayas, for example, have a double thickness of sialic continental crust, 70 km rather than the usual 35 km, giving the gravity low and the high altitude, a result of isostatic adjustment.
Abby's Science blog: Modeling Mantle Convection Currents
The second edition, which Holmes just lived to see, drops the three-fold division explicity, but the 31 chapters are still arranged in the same logical order. It is pleasant to see the many uncertainties and questions left from the first edition resolved by the twenty years' research that intervened. Holmes is not ashamed to admit being wrong, but this happens to be a very rare occurrence. In most cases, he was uncannily correct and far-seeing. With the extensions, the book now runs to 1250 pages of text, so it is not as compact as the first edition, and takes much longer to digest. However, all the additions are valuable and important. There are now many more illustrations, one of the treasures of the book.