GEOG 1 Lecture Notes - Lecture 9: Continental Crust, Continental Drift, Oceanic Crust
Document Summary
The processes involved in changing landforms have been in operation for so long that any given location was most likely the site of ocean and land at a number of different times in the past. Continental drift - landmasses were once united in one supercontinent which slowly broke away from one another, drifting to their current positions. Above the earth"s interior is a partially molten layer called the asthenosphere. It supports a thin but strong solid shell of rocks called lithosphere, of which the outer, lighter portion is the. Lithosphere is broken down into 12 large and many small, rigid plates which slide and drift over the semi-molten asthenosphere according to the theory of plate tectonics. Lithospheric plates move because heat and heated material from the earth"s interior rise by convection into particular crustal zones of weakness (sources for the divergence of plates). The cooled material then sinks downward into subduction zones.
