Continental drift and plate tectonics « KaiserScience
“From Continental Drift to Plate Tectonics: The Evidence
The described below had quite literally fallen into place by ~4.4 Ga, butplate tectonics has operated on planet Earth only in thelast ~2.0 Ga (from 13:20 hours on). Prior tothat, a much hotter earth lacked the crustal and upper mantle strength to support discretecontinents standing high above ocean basins, and very different surfaceprocesses applied. If you're interested in pre-plate details, take a side trip to or a .
Physical Science Concepts by Mason, Griffen, Merrill and Thorne
Pressure gradients inthe earth are also fairly well worked out, at least at some depths. At alldepths, the pressure is largely —i.e., simply due to thecombined weight of all overlying materials. In the and , plate tectonic processes can vary pressurea bit around lithostatic values—not by much, but enough to make a difference,particularly vis-à-vis the asthenosphere's very tenuous hold on solidity. Theunthinkable lithostatic pressures found at depths severely suppress convection but foster chemical stratification.
What Causes An Earthquake - Geography Site
Sooner or later, all oceanic crust . Theoldest dated continental crust on earth contains ~4.2 Ga zircons, whereas theoldest crust on the ocean floor today is only ~180 Ma old. The averagesurface dwell time for oceanic crust is a mere ~100 Ma. Satisfactorilyexplaining these vast age differences was an early plate tectonic triumph.
In the Beginning: Compelling Evidence for Creation and …
In aggregate, the plates form a self-organizing, far-from-equilibriumdissipative system driven only by gravity and the top-down cooling of the earth,subject to spontaneous reorganization without notice on long and short timescales and on large and small distance scales. In other words, the plates behave in the mathematical sense of the term. The moves primarily in response to the motions of the plates, not theother way around, as . Interestingly, therealways seem to be about 12 roughly pentagonal major plates, with many minorplates filling in the gaps.