Download Notes: Seafloor Spreading In the early 1900`s, the

Notes: Seafloor Spreading
 In the early 1900’s, the ________________ floor was believed to be _____________.
 Scientists thought that ____________________ crust was unchanging and was much
____________________ than the ____________________ crust.
 Technological Advance and Seafloor Mapping
 Advances in ____________________ allowed scientists to see what the ocean floor truly looked
like:
 Sonar uses ______________________________to measure ____________________ by
measuring the ____________________ it takes for sound waves sent from a
____________________ to bounce off the ____________________ and return.
 A magnetometer is a device that can ____________________ small changes in
______________________________. It is towed behind a ____________ and records the
____________________ fields produced by the ocean ____________.
 Mid-Ocean Ridges and Trenches
 Of all of the features discovered, ____________________ridges and ____________________
puzzled them the most. They wondered what could have caused them.
 A mid-ocean ridge is a long chain of underwater ____________________ contain active
and extinct ____________________.
 Deep-sea trenches are elongated, arc-shaped ____________________ in the seafloor
that are several kilometers ____________________ that the abyssal plain.
 They are the ____________________ part of the oceans.
 Many lie near _______________ islands and volcanic island chains
 Abyssal Plain: the ____________________ part of the ocean
 covered with hundreds of meters of fine, muddy ____________________ on top
of____________________volcanic rocks (which are made from dark, dense,
___________-rich lava)
 Scientists later discovered that ____________________ and ____________________ were
common along mid-ocean ridges and trenches.
 Oceanic Rocks and Deep-Sea Sediment
 Analysis of deep-sea ____________________ and the oceanic crust beneath it revealed:
 The rocks____________________to mid-ocean ridges are ____________________than
rocks located farther away.
 ____________________of oceanic crust was ____________________ near the midocean ridges.
 Paleomagnetism
 Earth has a ____________________ field generated by the flowing
________________________________________________in the outer core.
 This magnetic field causes ______________ to align itself like the needle of a
____________________ aligns to point north.
 Periodically, the north and south poles ____________________ because the flow of the iron and
nickel switches. This is called a magnetic reversal.
 During a magnetic reversal, the _______________ magnetic pole is over the _______________
pole and the south magnetic pole is over the north pole. A compass will point
____________________.
 Paleomagnetism is the study of the Earth’s ___________________________________.
 Scientific studies of continental ____________________ revealed that when lava that contains
iron cools, the iron ____________________ itself with the ____________________ (like a
____________________).
 When there is a magnetic reversal, the ____________________ of the iron in the rock of
continental crust ____________________ too.
 Oceanic crust is formed from ____________________ lava (like the lava from mid-ocean ridges).
It contains a lot of ____________________.
 Scientists hypothesized that magnetic reversal would ____________________ 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 ____________________ allowed scientists to analyze the magnetic fields of
the oceanic crust.
 Surprisingly, the magnetometer revealed that regions of
____________________________________________________________and regions of
____________________________________________________________formed a series of
____________________ along the ocean floor that run ____________________ with the midocean ridge.
 Even more surprising was that the ____________________ and ____________________ of the
stripes matched from one side to the other.
 The oceanic crust that is ____________________ the mid-ocean ridges is
____________________while the crust ____________________ the trenches is
____________________.
 Seafloor Spreading
 Seafloor-spreading is the idea that explains how new oceanic crust is formed at
________________________________________and destroyed at
________________________________________.
 ____________________ that is hotter and less dense ____________________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 ____________________.
 Remember; ____________________ could not explain ____________ continents moves.
 ________________________________________was the missing link that he needed to complete
his idea of ________________________________________.

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.