What is Continental Drift?
A hypothesis that the continents have moved slowly to their current locations
Where did it come from?
Section 1: Continental Drift
The hypothesis was the work of a German scientist named Alfred Wegener
Wegener said that all the continents were once connected as one large landmass now called Pangaea
The land mass broke apart, and the continents drifted to their present positions.
Section 1: Continental Drift
Is there evidence for Wegener’s Continental Drift hypothesis?
Yes!
The puzzle-like fit of the continents
Similar fossils have been found on different continents.
Remains of warm-weather plants in Arctic areas and glacial deposits in tropical areas suggest that the continents have moved.
Similar rock structures are found on different continents.
Section 1: Continental Drift
At first continental drift was not accepted because nobody could explain how or why continents had moved.
Section 1: Continental Drift
Why is the fact that similar fossils have been found on different continents considered evidence for continental drift?
If fossils of similar plants and animals are found on widely separated continents, it is more likely that the continents had once been joined than that the plants and animals migrated.
Section 1: Continental Drift Discussion Question
Using sound waves, scientists discovered a system of underwater mountain ranges called the mid-ocean ridges in many oceans.
In the 1960s, Harry Hess suggested a theory of Seafloor Spreading to explain the ridges
Section 2: Seafloor Spreading
The Seafloor Spreading theory of Harry Hess said:
Hot, less dense material below Earth’s crust rises upward to the surface at the mid-ocean ridges.
Then, it flows sideways, carrying the seafloor away from the ridge.
As the seafloor spreads apart, magma moves up from the cracks, cools, and forms.
Section 2: Seafloor Spreading
Evidence for Seafloor Spreading:
Youngest rocks are located at mid-ocean ridges.
Reversals of Earth’s magnetic field are recorded by rocks in strips parallel to ridges.
Section 2: Seafloor Spreading
How could seafloor spreading be related to continental drift?
If the seafloor is constantly spreading apart and moving, it will affect and move the continents as well.
Section 2: Seafloor Spreading Discussion Question
http://www.extremetech.com/wp-content/uploads/2012/10/earthcut.jpg
Section 3: Theory of Plate Tectonics Plate Movements
Earth’s crust and upper mantle are broken into sections.
The sections are called plates that move on the plasticlike layer of the mantle.
The plates and upper mantle form the lithosphere.
The plasticlike layer below the lithosphere is called the asthenosphere
Section 3: Theory of Plate Tectonics Plate Movements
http://www.physicalgeography.net/fundamentals/images/lithosphere.gif
Section 3: Theory of Plate Tectonics Plate Movements
1 km = .6 miles
1 mile = 1.6 km
You do the math!
Section 3: Theory of Plate Tectonics Converting km to miles
Plates moving apart – divergent boundaries
Plates moving together – convergent boundaries Denser plates sink under less dense plates
Newly formed hot magma forced upward forms volcanic mountains
Plates collide Plates crumple up to form mountain ranges
Earthquakes are common
Plates slide past – called transform boundaries Their sudden movement can cause earthquakes
Section 3: Theory of Plate Tectonics Plate Boundaries
https://www.youtube.com/watch?v=dkELENdZukI&index=3&list=PLRot3FlJRMWm8Azy4oIvK9sVs77wDMPam
Section 3: Theory of Plate Tectonics Plate Boundaries
Convection inside earth is thought to be the force behind plate tectonics
The cycle of heating, rising, cooling, and sinking of material inside the earth produces that force
Section 3: Theory of Plate Tectonics Convection
Faults and rift valleys.
Mountains and volcanoes
Strike-slip faults – cause of earthquakes!
Section 3: Theory of Plate Tectonics Features Cause by Plate Tectonics
Faults and rift valleys. http://mvsdperiod6.wikispaces.com/file/view/c02244.jpg/45490523/c02244.jpg
Section 3: Theory of Plate Tectonics Features Cause by Plate Tectonics
Mountains and volcanoes http://www.mountainprofessor.com/images/osorno-volcano-Chile2.jpg
Section 3: Theory of Plate Tectonics Features Cause by Plate Tectonics
Strike-slip faults http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Strike-slip+Fault+Flash+Animation&flash_file=strikeslip&flash_width=240&flash_height=310
Section 3: Theory of Plate Tectonics Features Cause by Plate Tectonics
Scientists use tools to measure plate movements
These movements can be as little as 1cm per year!
http://oceanlink.island.net/SOLE/tectonics/WCDA.html
Section 3: Theory of Plate Tectonics Testing for Plate Tectonics
What will happen if a continental plate collides with an oceanic plate? A continental plate with a continental plate? Why?
The denser plate will always subduct, or bend under, the less dense plate. Oceanic plates are denser than continental plates, so the oceanic plate will sink under it. When two continental plates collide, neither will subduct because they are both less dense than the asthenosphere beneath them. Instead, they will crumple up and form mountain ranges.
Section 3: Theory of Plate Tectonics Discussion Question