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Plate Tectonics
The Earth’s Crust in Motion…
The Theory
In 1910 Alfred Wegner begins to wonder…
What’s the relationship?
Perhaps all these pieces used to be connected.
Continental drift =slow movement over Earth’s surface
(Eventually Theory of Plate Tectonics)
300 million years ago…
Pangaea – all lands
•Reptiles and insects
•Tropical forests
- coal deposits
Tens of Millions of years!
How does it work?
Plates – pieces of the lithosphere
Plates fit closely together along
cracks called
Plate Boundaries
Convection Currents  movement
Evidence of Plate Movement
 If
you bring the coasts of continents on
both sides of the Atlantic Ocean together
you see correlating (matching):
fossil evidence
mountain ranges
glacial striations
rock formations
Evidence of Plate Movement
 In
the oceans:
Scientists discovered features called ridges in
the middle of the Atlantic Ocean.
Radioactive dating shows that as you move
away from these mid-ocean ridges, rocks
become older.
New rock is being formed in the middle
of the oceans at the ridges.
Evidence of Plate Movement
 In
the oceans:
Physicists skilled in magnetism discovered
another piece of evidence.
As you move away from the ridges, you can
see bands of rock with normal magnetic
polarity alternating with bands of rock with
reversed magnetic polarity.
Evidence of Plate Movement