Transcript Introduction to Plate Tectonics

Developing the Theory of
Plate Tectonics
8.9A describe the historical
development of evidence that
supports plate tectonic theory
Pangaea: a supercontinent
• Alfred Wegener (1912)
proposed that Earth’s
continents fit together like a
puzzle at one time but has
since broken apart.
• This was known as
continental drift.
Mountain ranges aligned, which
supported continental drift.
What caused the continents to drift?
• Wegener was unable to explain the
cause of continents moving apart.
• He proposed maybe Earth’s rotation
“spun” the continents away.
• The scientific community dismissed this
explanation.
• Continental drift was not universally
accepted.
Movement in Earth’s mantle
• Geologist Arthur Holmes proposed that continents sit
on top of Earth’s mantle which is fluid.
• Convection currents move through the mantle.
• The currents have enough force to move continents.
Action of Convection Currents
• Where currents rise, continents will break
or push up.
• Where currents fall, continents would
crumple and form mountains.
Big shift in idea
• Where scientists once believed that the
continents were too big to move, evidence
showed that continents move constantly.
• This is the theory of plate tectonics.
– Plate = large, rigid slab of solid rock
– Tectonics = from the Greek meaning “to
build”
The theory of plate tectonics suggests that the
Earth’s surface is made of plates (rock layers).
Evidence for
Plate Tectonics
Continental drift
Evidence for Plate Tectonics
• Related fossils found that match up with
idea of continental drift
Evidence for Plate Tectonics
• Mid-Atlantic Ridge separating
Evidence for Plate Tectonics
• Mountain ranges forming where plates collide