Download Technological Advance and Seafloor Mapping Mid

11/9/2016
Mid-Ocean Ridges and Trenches


mid-ocean ridge is a
long chain of
underwater mountains
contain active and
extinct volcanos.
Scientists thought that oceanic crust was
unchanging and was much older than the
continental crust.
Technological Advance and
Seafloor Mapping

A
In the early 1900’s, the ocean floor was believed
to be flat.
Advances in technology allowed scientists to see what
the ocean floor truly looked like:
 They
exist all over the
world.
Mid-Ocean Ridges and Trenches

 Sonar
uses sound waves to measure distance by
measuring the time it takes for sound waves sent from
a ship to bounce off the seafloor and return.
magnetometer is a device that can detect small
changes in magnetic fields. It is towed behind a ship
and records the magnetic fields produced by the
ocean floor.
A


Mid-Ocean Ridges and Trenches
 The
development of sonar allowed scientists
to map the ocean floor.
 Of
all of the features discovered, mid-ocean
ridges and trenches puzzled them the most.
They wondered what could have caused
them.
Deep-sea trenches are
elongated, arc-shaped
depressions in the
seafloor that are several
kilometers deeper that
the abyssal plain.
They are the deepest
part of the oceans.
Many lie near volcanic
islands and volcanic
island chains
Mid-Ocean Ridges and Trenches

Abyssal Plain: the flattest
part of the ocean
 covered
with hundreds
of meters of fine, muddy
sediment on top of
basaltic volcanic rocks
(which are made from
dark, dense, iron-rich
lava)
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11/9/2016
Mid-Ocean Ridges and Trenches
 Scientists
later discovered that volcanism and
earthquakes were common along midocean ridges and trenches.

Oceanic Rocks and Deep-Sea
Sediment
Analysis of deep-sea sediment and the oceanic
crust beneath it revealed:
1.
2.
The rocks closer to mid-ocean ridges are
younger than rocks located farther away.
Sediment of oceanic crust was thinner near
the mid-ocean ridges.
Paleomagnetism
Earth has a magnetic field generated by the
flowing liquid iron and nickel in the outer core.
 This magnetic field causes iron to align itself like the
needle of a compass aligns to point north.
 Periodically, the north and south poles switch
because the flow of the iron and nickel switches.
This is called a magnetic reversal.
 During a magnetic reversal, the north magnetic
pole is over the south pole and the south
magnetic pole is over the north pole. A compass
will point south.

 Paleomagnetism
is the study of the Earth’s
magnetic field.
 Scientific studies of continental crust revealed
that when lava that contains iron cools, the
iron orients itself with the poles (like a
compass).
 When there is a magnetic reversal, the
alignment of the iron in the rock of
continental crust reverses too.
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11/9/2016
 Oceanic
crust is formed from basaltic lava
(like the lava from mid-ocean ridges). It
contains a lot of iron.
 Even
 Scientists
 Note
hypothesized that magnetic
reversal would affect the alignment of the
iron in the basaltic rock of the oceanic crust
the same way it affects the iron in the
continental crust rocks.
 The
invention of the magnetometer allowed
scientists to analyze the magnetic fields of
the oceanic crust.
 Surprisingly,
the magnetometer revealed that
regions of normal magnetic alignment and
regions of reversed magnetic alignment
formed a series of stripes along the ocean
floor that run parallel with the mid-ocean
ridge.
more surprising was that the ages and
widths of the stripes matched from one side
to the other.
that the
younger rocks are
closer to the midocean ridge.
 The
oceanic crust that
is near the mid-ocean
ridges is newer while
the crust near the
trenches is older.
Seafloor Spreading
 Seafloor-spreading
is the idea
that explains how new
oceanic crust is formed at
mid-ocean ridges and
destroyed at deep sea
trenches.
 Magma that is hotter and less
dense rises at the mid ocean
ridges. As the two sides of the
ridge are forced apart,
magma fills in the space,
cools, and solidifies, creating
new crust.
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 Remember;
Wegener could not explain how
continents moves.
 Seafloor
spreading was the missing link that
he needed to complete his idea of
continental drift.
 We
know that the combination of these
ideas is not the currently accepted model
today, but it was another step along the path
to discovery.
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