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Plate Tectonics
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Plate Tectonics
Alfred Wegner- 1912 proposed that all continents were one land mass
continents seemed to fit together
Continental Drift
continents collided and separated as they moved over the surface
if North and South America moved across Atlantic Ocean
fit together
continental rocks match
tectonic structures match up; folding, faulting
Pangea- ancient continent
Alfred was not taken seriously, he could not prove how the continents could move
he did not know the role of density and convection currents
ocean floor mapping geology
Tectonics
12 major plates
contain low density-continental rock(granite); high density-ocean rock (basalt)
Plate Boundaries
where plates meet and interact
when plates move = crustal change
volcanoes
earthquakes
mountain building
trenches
Additional Evidence
mapping ocean floor
rock formations
fossil remains
mineral formation
magnetism in rocks
90% of earthquakes and volcanoes occur in the Pacific Rim or the Ring of Fire
Plate Boundaries
Convergent Boundary
when two plates come together
subduction- dense oceanic plate dives beneath lighter continental plate, ocean trench, volcano
if two continental plates converge, resist subduction, leads to folding and faulting mountains
Diagram
heat and action between plates
ocean/continent- forms subduction and trenches
continent/continent- forms mountains
ocean/ocean- forms mountains
Divergent Boundary
when plates move apart
forms mid ocean ridges
newest crust on earth
sometimes called rifts
Diagram
convection currents
new crust near ridge/rift
heat rises; heat = less dense
cool sinks; cool = more dense
no subduction
forms ridges and volcanoes
Magnetic Polarity
reversals causes the stripes to point north
mirror image
Transform Boundary
when plates slide or twist past each other
no subduction
forms earthquakes
Oceanic Plates- thinner and more dense
Continental Plates- thicker and less dense