Download Ch. 13 Seafloor Spreading

A ball of glass will bounce
higher then a ball of
rubber.
Harry Hess was
the first man to
study the sea
floor. After
he believed
that Wegener
was correct.
(1960’s)
He noticed that the rocks were
younger near the mid-ocean
ridge than the rocks closer to
the continents.
He noticed that as it moved, it
was being replaced by magma
that cooled and solidified into
rock; therefore, the ocean
floor must be moving.
When the spreading of the
ocean floor reaches a
barrier, such as the edge of
a continent, the oceanic
crust goes under the
continental crust due to
density.
This subducting and
melting of the crust
causes the plate to be
pulled down into the
mantle.
Hess suggested that if
the ocean floor was
moving, the continents
must also be moving.
There still needed to be more
research of the ocean floor
before seafloor spreading
was accepted.
With the discovery of
Magnetic Polarity, Seafloor
spreading was accepted
in 1969.
Scientists discovered
that the Earth’s
lithosphere is broken
into moving plates.
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These plates are ridged
blocks of the earth's outer
crust and are about 31-93
mi. thick.
Scientists have divided
the world into 8 major
plates and 12 minor
plates that are moving
toward or away from
each other.
The heat inside the Earth
causes a convection current
in the mantle.
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A convection current is
the movement of
material caused by
different temperatures,
and is the driving force
of plate tectonics.
You can have me but you can't
hold me; you can gain me
quickly and lose me even
faster. If treated with care I
can be great, and if betrayed I
will break. What am I?