Plate Tectonics
What is the
Plate
Tectonic
Theory?
Who
proposed
that Earth’s
surface
 Plate Tectonic Theory=
idea that convection
currents in the mantle
move lithospheric plates
 Lithospheric plate= huge
piece of the crust-cracked
into huge pieces
 Mvmt of plates causes
EQ’s, volcanoes, mtn
ranges, rift valleys, midocean ridges, deep-ocean
trenches
 Mvmt changes the size &
shape of oceans &
continents
 Alfred Wegener (18801930) 1st proposed Earth’s
surface moves
moves?
What
evidence
supports PT
theory?
Proved HAD
moved→
 Thought that the
continents were once joined
together, but drifted apart
 Gathered evidence to
support his idea
1) continents “fit together”
like a puzzle-LAND
FEATURES
 Pangaea=
“supercontinent” that
broke up 300 million yrs
ago
 Coal fields in NA &
Europe line up
 Mtn ranges of SA &
Africa meet up
2) FOSSILS- fossil beds on
diff. continents line up;
fossils of the same
organisms were spread
across continents now
separated by oceans
3) CLIMATE- evidence of
tropical climate in the
Arctic region & Antarctic
glaciers in a warm region
 Scientists rejected
Wegener’s hypothesis b/c
he couldn’t explain the
“pull & push”-the HOW
 Could only explain the
HAD
 Died w/out anyone
believing his hypothesis
 1960 technology advances
led to…
→
↓
Showed
HOW it
4) Sea-floor Spreading=
magma finds a crack in
the sea floor, comes out,
cools into new rock,
spreading the continents
apart (action)-“the push”
 Creates a mid-ocean
ridge= (landform) under
ocean mtn range
5) Subduction Zone= ocean
floor plate sinks into the
mantle under another
plate (densest plate
sinks)-“the pull”
 Creates a deep-ocean
trench= (landform) under
ocean canyon; Marianas
Trench is the deepest
place on Earth (≈ 25 miles
deep)
**subduction & sea-floor
spreading shrink & expand
oceans, moving continents
**convection currents in the
Asthenosphere is the “motor”
that moves the plates
What is a
 Tectonic plate boundary=
tectonic plate
where 2+ plates touch e@
moved
↓
→
boundary?
other
DIVERGENT (spreading/separating)
1a) Mid-Atlantic Ridge & Iceland
1b) Great Rift Valley in E. Africa
CONVERGENT (colliding)
2a) Cascade Mtns in NW NA (Mt.
Saint Helens, Mt. Ranier, Mt.
Olympia, Mt. Shasta)
2b) Indonesian Islands & Marianas
Trench
2c) Himalaya Mtns where Eurasia
meets India
TRANSFORM (“touchy-slidy traveling”)
3) San Andreas Fault in CA where
the Pacific Plate & NA plate slide
by e@ other
**a plate can have all 3 types of
boundary**