Download Notes: Plate Tectonics - Riverdale Middle School

I. Plate Tectonics
A. ___Continental Drift______
1. Many early scientists have noticed
that the Earth’s continents seemed
to fit together.
2. ___Alfred Wegener____- proposed
the theory of continental drift
a. _Permian Period_ - about 225
million years ago
1.) all the continents formed a
supercontinent called
Pangaea
2.) ____Panthalassa____ was
the major ocean
b. __Triassic Period____ - Pangaea
was split in two
1.) _____Laurasia_____ in the
north (North America, Eurasia)
and Gondwanaland in the
south ( India, Africa, and
South America)
2.) Panthalassa broken in two,
one part becomes the
____Tethys Sea______
pg. 77
c. Wegner theorized that continents
moved horizontally to their present
location.
B. Evidence of Continental Drift
1. Fossil and Climate Clues
a. The reptile ___Mesosaurus____
1.) fossils found in South America
and Africa
2.) lived on land and water but
would have been impossible for
this animal to have swam across
an entire ocean
b. A fern _____Glossopteris________
1.) fossils found in Africa, Australia,
India, South America, and
Antarctica
2.) found in areas that vary greatly
in climate, scientists believe
these regions once were
connected and had similar
climates
c. Fossils of warm weather plants were
found in Arctic Ocean Islands
d. Glacial deposits have been found
where no glaciers exist today
2. Sea-floor Spreading
a. ___Mid-Ocean Ridge____1. using sound waves, scientists discovered a
system of underwater mountain ranges in
many oceans
2. The peaks of some of these mountains can
form an island
b. 1960’s scientist, _Harry Hess_, suggested a
theory of ___sea-floor spreading___
1. Magma gets forced upward through
cracks in the ocean floor
2. As new material comes up it pushes
sections of the sea floor away from the
ridge.
3. The magma solidifies and creates new sea
floor
c. Evidence for Sea-floor Spreading
1. Youngest rocks are located at the midocean ridge
2. Reversals of Earth’s magnetic field are
recorded by rocks in strips parallel to
ridges
Harry Hess
C. Plate Tectonics
1. Earth’s crust and upper mantle are broken
into sections called __plates_____
a. The crust and upper mantle are called
the ______lithosphere_________
b. Middle layer of the mantle is the
_asthenosphere__ - semi-molten rock,
very plastic-like
c. __Convection Currents__ inside Earth
cause plate tectonics – the cycle of
heating, rising, cooling, and sinking of
material inside Earth
2. Plate Boundaries
a. Divergent Boundary - two plates move
away from one another; ex. Sea-floor
spreading
b. Convergent Boundary -two plates move
toward each other, there are three types:
1.) subduction zone- dense ocean plate sinks
under light continental plate
ex: deep sea trench, volcanic mountain
chains
2.) two ocean plates collide
ex: deep sea trench, volcanic island chain
3.) two continental plates collide
ex: mountains, earthquakes common
c. Transform Fault Boundary two plates slide past each other; they can
move in opposite directions or in the same
direction