Transcript Continental Drift and Sea Floor Spreading Notes

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Pangaea
Continental Drift Notes
What Would Wegener Say?
Sea Floor Spreading Notes
Sea Floor Spreading Model
Sea Floor Spreading Notes (Con’t)
 Alfred Wegener
was a German scientist
from 1910 that was very curious about the
relationship of the continents.
 Wegener’s
Hypothesis was:
• That all the continents were once
joined together in a single landmass
and have since drifted apart.
 According
to Wegener, the continents
were once all together forming the
supercontinent called Pangaea.
 Unfortunately, other
scientists didn’t
believe Wegener because Wegener
could not identify the cause of the
drifting continents.
 During WWI
& WWII, scientists
discovered that the ocean floor was not
flat.
• A mid-ocean ridge is an underwater mountain
chain where new ocean floor is produced.
 Scientists
have discovered these midocean ridges by using sonar, which is a
device that bounces sound waves off
underwater objects & then records the
echoes of these sound waves.
The
sea floor spreads apart along
both sides of a mid-ocean ridge –
an underwater mountain chain
where new ocean floor is produced.
• Scientists used sonar to discover the mid-
ocean ridges.
 Harry
Hess was an American geologist
who studied mid-ocean ridges.
 Hess
proposed the idea that the sea floor
spread apart along both sides of the midocean ridge as new crust is added.
Molten
Materials:
• Scientists found strange rocks shaped like
pillows - Such rocks only form when molten
material hardens quickly after erupting
under water.
Magnetic
Stripes:
• Rocks in the ocean floor have a pattern of
“magnetized stripes” – these stripes hold a
record of reversals in Earth’s magnetic field
because the rock contains iron.
Rock
Age:
• The farther away from the ridge the samples
are taken, the older the rocks were and the
youngest rocks are always at the center of the
ridges.
Younger
rock
Older
rock
 Hess's
theory of "seafloor spreading"
offered a compelling driving mechanism
for Wegener's continental drift, but it
needed more proof, soon to be known as
the Plate Tectonics Theory.