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III. Plate Tectonics
A. Definition: the idea that the Earth’s crust is
broken into rigid blocks called plates and these
plates move.
B. History:
1.
1801 – Alexander Von Humboldt
Said that the coastlines of the continents show that
they fit together like pieces of a puzzle. (Ex: Africa &
South America)
2. 1858 – Antonio Snider-Pellegrini
Said that all the evidence you need to agree with Von
Humboldt is a map. Just look at it and you can tell that
the continents fit together.
3. 1908 - Frank Taylor (from the U.S.)
Said there is a crack in the Earth where new crust is
being formed each day. The crack is located in the
middle of the Atlantic Ocean. He called that crack the
Mid-Atlantic Ridge.
4. 1912 - Alfred Wegener (German meteorologist
Developed the Theory of Continental Drift. This
theory states that all the continents were once
together forming a supercontinent, which he
called Pangaea. His proof was that he found
fossils on the west coast of Africa and the east
coast of South America of the same plants and
the same reptiles. Plant is called Glossopteris;
Reptile is called Lystrosauris. He also found the
same type of rock on the two coasts.
5.
1960’s – Wegener’s Theory of Continental
Drift becomes widely accepted by the
scientific community. WHY? Because of
advances in technology. More fossils found,
dated the age of rocks as the same age.
Boats & submarines could look at the MidAtlantic Ridge.
6. Today –The Theory of Plate Tectonics states:
a.
b.
c.
d.
Earth’s crust divided into pieces
Pieces called plates
Plates move a few cms each year.
Driving force behind the plates movement is
convection currents in the mantle.
e. At plate boundaries:
1) New crust is made
2) Plates slide past each other
3) Plates crash into each other
4) Subduct under
5) Plates buckle
C. Plates – pieces of Earth’s crust
1. Sit on top of Mantle
2. Oceanic vs. Continental plates/crust
a. Oceanic crust is very thin
b. Continental crust is thick
c. When two type of crust meet:
Oceanic crust subducts under continental
crust
3. New Crust
a. Formed at Mid-Atlantic Ridge
b. New crust pushes plates apart
4. Old Crust
a. Destroyed at subduction zones
b. Oceanic crust subducts under
continental crust
c. Two plates are colliding with each
other
5. Boundaries
a. Transform fault
1) Crack in Earth’s crust
2) Plates slide past each other
3) Ex: San Andreas Fault, New
Madrid Fault
b. Divergent Zones
1) Boundaries where the plates move
away from each other
2) Example: Mid-Atlantic Ridge
c. Convergent Zones
1) Boundaries where plates come
towards each other
2) Example: India slamming into the
Eurasian Plate (makes the Himalaya
Mountains taller each year by
approximately 1”)
3) Subduction zone
Plate Tectonics Video