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Transcript
Sci. 4-2
Restless Continents
Pages 95-98
A.Continental Drift- a theory that continents can
drift apart from one another and did so in the
past
1)Alfred Wegener wrote this theory
2) evidence that supports continental drift
a)The puzzle- like fit of the continents
b)Fossils of the same species found on
opposite sides of the ocean
c)The pattern of grooves left by glaciers
B. Pangaea- large supercontinent
1) broke into 2 pieces called Laurasia and
Gondwana
2) Then broke into our current 7 continents
C. Sea-Floor Spreading
1) Mid Ocean Ridges- a chain of underwater
mountains in the Atlantic Ocean
2) Sea-Floor Spreading- the process by
which new oceanic lithosphere is created as older
material pulls away
3) spreading happens at the Mid Ocean
Ridges
4) The newest crust is at the Ridge on both
sides and the oldest is at the edges of the
continents
D. Magnetic Reversals- when Earth’s magnetic
poles change place
1)This is evidence of sea-floor spreading
2) Molten rock comes up at the Mid Ocean
Ridge. This molten rock has grains of magnetic
minerals in it.
3) The grains of magnetic material acts like
a compass pointing to the North Polarity. When
the rocks cools, the grain is pointing in that
direction permanently.
4) The changing polarity of the Earth’s
magnetic poles causes the new oceanic crust to
have alternating bands of normal and reverse
polarity.