Download Plate Tectonics

11/12/15
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Pieces of lithosphere
that move around on
top of asthenosphere
Act like pieces of a
jigsaw puzzle that fit
together to form
lithosphere
Not all tectonic plates
are the same

Differences in size and
shape


North American plate
versus Cocos plate
Parts of crust they
contain:
Cocos and Nazca plates:
only oceanic crust
 North plate: continental
and oceanic crust

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Continental drift:
theory that continents
can drift apart

Proposed by Alfred
Wegener

Originally rejected
because of lack of
evidence

Fossil findings

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Mesosaurus (reptile)
Glossopteris (plant)
 Found on four different
continents

Glacier activity

Grooves created over
time match up when
continents once fit
together

Pangaea: “all earth”

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Began over 225-245
million years ago
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
Panthalassa: “all sea”
Both Greek terms
Laurasia
Gondwana
65 million years ago

Further breakup
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Process by which new
oceanic lithosphere is
created
Occurs at mid-ocean ridges

Mid-Atlantic Ridge
Underwater mountain
chains that run through
Earth’s ocean basins

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Sea floor spreads as
tectonic plates spread
apart
Magma rises to fill gap
newly created gap
Newest crust is found
along ocean ridges

Oldest found near
edges of continents
New lithosphere

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Process in which Earth’s magnetic poles
change place
Provides evidence of sea-floor spreading
Molten rock contains tiny grains of magnetic
minerals (act like compasses)

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Once molten rock cools minerals are “set in stone”
Magnetic fields reverse each time a new band starts