Answer to Question 1
Answer: Convergent plate boundaries strongly contrast with divergent boundaries in three major ways.
1. Plates move toward one another at convergent boundaries and apart at divergent boundaries.
2. Subduction destroys lithosphere at convergent boundaries whereas lithosphere is created at divergent boundaries.
3. Convergent boundaries are asymmetrical, with one plate angled downward beneath its neighbor. Divergent boundaries are vertical, symmetrical boundaries between plates.
Answer to Question 2
Answer: Plates move apart at divergent plate boundaries by the process of seafloor spreading, which creates a new, mafic oceanic crust and mantle. Abundant earthquakes, basaltic volcanic activity, high heat flow, high seafloor elevation, and a seismically slow upper mantle confirm plate tectonics predictions for mid-ocean ridges. As predicted by the seafloor spreading hypothesis, magnetic polarity of seafloor crust, along with radioactive isotope ages, demonstrates that oceanic crust is progressively older at greater distances from mid-ocean spreading ridges. Divergent plate boundaries can originate within continents to form rift valleys. Persistent extension along a rift valley causes the lithosphere to break into two continental fragments. Not all rift valleys extend sufficiently to form new continents and plate boundaries.
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