Continental Drift Theory. What is Continental Drift Theory? Continental drift theory: Proposed by Alfred Wegener that all the continents were once together as one super continent named… Pangaea (1 Earth / Land). Continental drift theory. How long ago was Pangaea last together.
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Pangaea was last together 250 Million Years ago
How did they break up?
Wegener could never show how it broke up, he thought they floated apart on the ocean like boats on the water (they drifted with help from waves)
1) Continents fit together like a puzzle
Then when you line them up:
2) Mountains match up
3) Rock types match up
4) Plant fossils match up (Glossopteris)
5) Animal fossils match (Mesosaurus)
6) Glacial deposits match
7) Past climates match
(1 large Ocean)
Pangaea's first split was North and South (like the U.S.)
Data – Map of Pangaea (label its parts)
What is CDT (continental drift theory)?
Research Wegener (find new info).
What were his proofs?
What was Pangaea ?
(give its parts: Northern, southern, large ocean)
How long ago was it last together?
What was Wegener missing?CDT lab
Plotting Earth quakes revealed the Earth was not 1 solid outer crust. It is made of plates.
(Most appear at plate boundaries, so do volcanoes)
What are plates?
Plates are Large broken up pieces of the Earths crust (Lithosphere).
~ 8 major plates and several minor
Zebra banding: Iron acting as a compass in rock shows the North and South pole have been flipping.
They also appear in a matching pattern on both sides of the AtlanticOther Discoveries
Using Sonar a Large Mt. Range is found to run down the center of the Atlantic. (Mid Atlantic Ridge)
Rock close to the ridge (in the center of Atlantic) is newest. Far rocks (on both sides by the continents… S. America/Africa) are 250 million years old.
Sea floor spreading: theory by Hess (A geologist in the Navy) that the Sea floor is young rock <250 million years old.
Rock is getting created in the center at the Mid Atlantic Ridge and is being pushed outwards.
This is growing the Atlantic Ocean.
Sea floor spreading proves the plates are moving apart
Plates move due to convection currents in the mantle.
Continents move because they ride on top of the plates.
called plastic mantle because it flows like heated plastic (continents ride on this)
3) Lithosphere – The crust & Rigid Mantle
Ocean crust – Basalt (bass, salt)
Continental crust – Granite (counter tops)
Ocean crust is more dense
What clues do we have about the inside of the Earth if we have never been down there?
To infer about the interior of the Earth we use:
They have iron & nickel cores.
If we started from the same
materials we should have
an iron and nickel core too.
*Shows compositionThe Earths interior
Earthquakes send seismic waves through the Earth. Based on their actions, we can infer a solid and liquid core.
*shows state of matter
By studying lava you are studying material that was inside the Earth.
*shows hot interior
At a divergent boundary:
1) Plates move apart
2) Plates grow (addition of Lava)
3) Ridges are pushed up
4) Rift valleys are created (Rift ~ Ripped)
These occur on continents too
When 2 continental plates with the same density converge they buckle up and make mountains like the Himalayas, (Everest is where India collided).
What happens when a Denser Oceanic plate converges with a less dense continental plate?
When an ocean plate collides with a continental plate it goes under due to density.
This creates a deep trench in the ocean where the plates meet.
Coastal mountains form where the continental plate rides over and buckles.
The subducted oceanic plate melts, creates magma and volcanoes form.
The oceanic plate is destroyed.
Many plates slide slowly past each other unfelt. Over time land forms may no longer match up.
If plates get stuck, they will build pressure until they slip and create an Earthquake
(California San Andreas Fault).
Divergent Boundaries: Plates move apart, new ocean plates created, Mid Ocean Ridges, Rift Valleys.
What happens at Convergent Boundaries?
Convergent Boundaries: Plates crash, Mountains, Ocean Plate destroyed, Deep ocean Trenches, Volcanoes.
What happens at Transform Boundaries?
Transform Boundaries: plates slide past each other, Earthquakes.