Homework – Unit 2, Plate Tectonics (short answer)
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In 3-4 sentences, explain the theory of plate tectonics.
Plate tectonics is the theory that the lithosphere is divided into a number of plates that float independently over the mantle and along whose boundaries occur the formation of new crust, the building of mountains, and the seismic activity that causes earthquakes. When looking at a world map
it appears continental landmasses have matching shaped like the pieces of a puzzle, this is because they once did fit together and began spreading apart due to plate tectonics, and they are still spreading apart to this day. As a whole the plate tectonics theory simply describes the motion of earth’s lithosphere. •
How does mantle convection cause seafloor spreading?
Upwelling flows of magna from hot areas in the upper mantle and asthenosphere and sometimes from
the deeper lower mantle. As the upwelling occurs, the new seafloor then moves outward from the ridge as plates pull apart and new crust is formed causing sea floor spreading. •
How does a convergent boundary differ from a subduction zone?
A subduction zone is when one portion of the lithosphere descends beneath another and dives downward into the mantle, the process is called subduction and therefore this area is a subduction zone. On the other hand, convergent boundaries occur in areas of crustal collision. Where areas of continental and oceanic lithosphere meet, crust is compressed and lost in a process as it moves downward into the mantle. As we can see subduction zones are when one piece of the lithosphere goes
under another piece, while convergent boundaries occur from collisions. Often times convergent boundaries form subduction zones. •
What is the current theory on the driving force behind the movement of lithospheric plates on the Earth’s surface? About how fast do the plates move?
The current theory on the driving force behind the movement of the lithosphere is convection currents. Convection currents in the atmosphere and upper mantle provide upwelling and downwelling forces that push and pull portions of the lithosphere. The plates move roughly 6cm a year.
