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Continental Drift
from a Hypothesis by Alfred Wegener and was
developed into a Theory with supporting evidence
Super continent called Pangaea >Greek for “all land”
Began to brake apart over 200 million years ago
Puzzle fit of South America and Africa
Collected evidence in rocks, fossils, and climatic data to
support his hypothesis
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Ancient climates
evidence of coal deposits found in Antarctica
coal is formed from swamp plant or other vegetation that
has decomposed
this meant a temperate rainy climate was once on the
surface of Antarctica
glacial deposits of till and striation scratches on bedrock
found in Afrrica, 290 million year old land formations
today Africa is covered by huge deserts where the
evidence of continental glaciers was documented
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Seafloor Spreading
Technology sonar echo-
location > sound beams /
time returned
WWII submarine warfare
developed technology to
detect more than an
enemy sub
Detailed maps and a safe
way to navigate the
bottom
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Mid Ocean Ridges & Trenches
Ocean ridges are long
mountain ranges
Continuous wrap around
planet
Deepest and longest
mountain range on the
planet
~46,000 miles long (~ 72km)
Mariana Trench
11 km deep deepest
trench in all oceans
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Continental Crust - Oceanic Crust
Oldest age 3.8 BYBP
Billions of years before
present
Less dense than oceanic
crust
Continental mountains
keep getting folded and
faults break up crust
Young age ~ today’s lava
>180 MYBP
Millions of years before
present
More dense than
continental crust
The further away from the
ridge the thicker and
older the oceanic crust
becomes
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Causes of Plate Movement
Mantle convection are thought to be the driving mechanism of plate tectonic
movement
(continental drift caused by seafloor spreading and subduction)
The transfer of heat, called thermal energy is the cause of the movement of
hot matter (magma) moving to cold matter; this is called convection
Warm matter move toward cold matter
Cooler matter sinks because it is more dense
“G force” gravity pulls it down into the mantle
Ridge push and slab pull are the results of this process of heat moving away
from the radiation of the core out towards the crust
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Isochron Map
maps with magnetic fields showing Earth’s polarity for
magnetic north
A line graph defined by data
for rocks of the same age;
With the same isotopic
composition
Polarity event is recorded in
rocks a period of no more
than 100,000 years when
Earth’s magnetic polarity was
opposite to the existing
polarity
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Check out and watch this movie on your iPad
http://science.discovery.com/tv-shows/greatest-
discoveries/videos/100-greatest-discoveries-magnetic-field-
reversal.htm
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Questions?
Going further time for the iPad technology
Do scientist know if convection currents stay in
the same places ?
Are hot spots located in the same places ?
For how long ?
Is Cape Cod located on a hot spot?
What state is located over a hot spot ?
When was the last earthquake Cape Cod felt ?