Download Chapter 1, Section 5 – The Theory of Plate Tectonics

Chapter 1, Section 5 – The Theory of Plate Tectonics
*J. Tuzo Wilson: proposed that the lithosphere is broken into sections called plates
*Plates carry continents or parts of the ocean floor as they move
I.
How Plates Move
a. Theory of plate tectonics:
i. Movement of plates in lithosphere powered by convection currents
ii. Plates collide, pull apart, or grind past each other = changes in
Earth’s surface
1. creates volcanoes, mountain ranges, and deep ocean trenches
iii. plate movement is incredibly slow – only 1 – 24 cm. per year!
II.
Plate Boundaries
a. Extend deep into lithosphere
b. Three types:
i. Divergent boundary: place where two plates move apart
1. Usually found at mid-ocean ridges where sea-floor spreading
occurs
2. Sometimes form a rift valley on land
ii. Convergent boundary: place where plates come together/collide
1. density determines which plate slips below the other
a. oceanic crust is more dense than continental crust
(subduction will occur)
b. two plates carrying continental crust will collide and
form mountains
iii. Transform boundary: two plates slip past each other (moving in
opposite directions)
1. earthquakes often occur here