Download Continental Drift and Plate Tectonics

Continental Drift and Plate Tectonics
good resource http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor15039288
I.
Continental Drift
A. Proposed by Alfred Wegener in 1912
1. Theory that Earth’s continents were once joined in a large landmass
that broke apart. The continents drifted to their current locations.
(they drift a few centimeters each year)
2. Named the giant landmass Pangaea- Greek word that means “all
Earth”
3. Fossils and rock formations found on the different continents
support his theory.
4. Theory was not readily accepted because he couldn’t explain how it
happened.
II.
Plate Tectonics Theory A. The theory is that the Earth is divided into lithospheric or tectonic plates
that move about the Earth (like slabs of ice on a lake) “tekton” is a Greek
word that means “to build”. They move at a rate of 1-10 cm per year.
B. Lithosphere - (lithos is Greek root for rock or stone)
1. Outermost layer of Earth’s surface
2. Includes the crust and the rigid portion of the upper mantle
3. Composed of tectonic or lithospheric plates (7 major platescorresponding w/ the continents and 7 minor plates)
4. Part of the Earth where all geological events take place: earthquakes,
volcanoes, mountain formation, tsunamis, geysers, erosion, and rock
formation
III.
Convection Current
A. Hypothesis to explain how plates move
B. Asthenosphere – this is the upper part of the mantle that is partially molten
in places. Convection current takes place in this layer.
C. Hot molten material in the mantle becomes less dense and rises
D. Material nearer to Earth’s surface spreads out, cools and becomes denser.
Then it sinks below the hotter, less dense material.
E. Uneven heating causes material in the mantle to constantly and slowly rise
and fall, resulting in convection current.
F. As the currents move molten material sideways, large portions of crust
(plates) “ride” on top across the Earth’s surface.
IV.
Plate Boundaries –
A. The place where the edges of tectonic plates meet.
B. Types of boundaries depend on whether the plates forming them are
moving toward each other, separating or sliding past each other.
C. Geologic events happen along these different boundaries
D. Three Different BoundaryTypes:
i. Convergent Boundary - Forms where plates collide. 3 possibilities:
1. Continental Plate to Continental Plate: the two plates just fold
together and keep pushing on each other. Mountains are
formed.
(example: Himalayas)
2. Continental Plate to Ocean Plate: two plates come together
and the oceanic plate slides underneath the continental plate.
The lower one starts being melted back into magma. This is
called subduction. (example: Andes Mtns.)This molten
material, which is under great pressure can escape through
weak spots in the Earth’s crust. What can happen? Erupting
volcanoes.
3. Ocean Plate to Ocean Plate: two plates come together and one
slides under the other (subduction) When this happens in the
middle of the ocean, strings of volcanic islands are formed.
(example: Hawaii)
ii. Divergent Boundary
1. Forms when 2 plates diverge, or move away from each other.
This usually happens on the ocean floor.
2. A space is created where magma comes through, forming new
crust. The creation of new ocean floor is called seafloor
spreading.
3. They build under sea mountain ranges (example: Mid-Atlantic
Ridge which is longest mountain range in world)