To understand plate tectonics, the different ways of classifying the layers of the earth-by composition and by mechanical behavior-must be kept in mind. The layer beneath the lithosphere is the weak, soft asthenosphere, which is roughly 300 to 400 km thick. In those terms, the outer layer of the earth is the lithosphere, which is a rigid layer that is broken up into tectonic plates and averages about 100 km (60 miles) thick. The earth is also layered in terms of physical or mechanical behavior. The core consists of a mixture of iron and nickel.The mantle consists of dense, ultramafic rock.Continental crust is thick (25-50 km thick), low in density, and has an intermediate average composition oceanic crust is thin (typically 5-10 km thick), higher in density, and has a mafic average composition. The earth is layered in terms of chemical composition as follows: The foundation for the new way of comprehending earth processes is the understanding that the outer layer of the earth is the lithosphere rather than simply the crust. By 1970, college geology majors were taught a set of ideas that were unheard of by most geology students prior to 1960. The theory of plate tectonics revolutionized geology in the 1960s. Deep Earthquakes (Subduction Earthquakes).Ocean-Continent Convergent Plate Boundaries.Ocean-Ocean Convergent Plate Boundaries.Continent-Continent Convergent Plate Boundaries.What are the different types of plate boundaries?.
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