Transcript Plate Tectonics - Awtrey Middle School

Earth’s Structure and Pangaea
RE-Quiz first thing though!!!
20 min video clip to get us started!
Inside the Earth
The Earth has 3
layers.
1. Crust
2. Mantle
3. Core
Continental Drift
• Continental Drift states
that the continents were
once a single landmass,
broke apart, and “drifted”
to their current locations.
• Proposed by Alfred
Wegener.
He had evidence that
Pangaea existed…
Video Clip!!
Pangaea
•
•
Large landmass that existed 245 m.y.a.
Evidence that Pangaea existed
1. Continents fit together like puzzle pieces (mountain
ranges lined up)
2. Mesosaurus – Reptile fossil found on South America
and Africa – It couldn’t swim!
3. Glossopteris – Tropical plant fossil that was found in
Antarctica!
The continental drift theory
was NOT accepted
because Wegener could
not explain WHY the
continents were moving.
Video Clip!!
Why WERE the continents
moving??
…because of sea-floor spreading!
Two oceanic plates pull apart, magma rises
through the gap in the middle, the magma
cools and forms new seafloor.
Continents are connected to
the sea-floor. When the seafloor moved, so did the
continents!
Check these sites out!
• http://www.wwnorton.com/college/geo/ege
o/flash/2_5.swf
• http://education.sdsc.edu/optiputer/flash/s
eafloorspread.htm
Sea-Floor Spreading Evidence
1. Brand new rock was found at the midocean ridge.
2. Rock got older and older the farther you
got away from the ridge. Oldest rocks
were found at the trenches.
3. Magnetic Reversals – Iron in the rocks
switched directions every time the
Earth’s polarity switched.
Sea-Floor Spreading in detail…