Download Seafloor Spreading

Earth Today
PBS: Sea-Floor Spreading
Word: Continental Drift Hypothesis
Word: Continent
Word: Sea-floor Spreading
Word: Tectonic Plate
Word: Magma
Word: Magnetic anomaly
Word: magnetic reversal
Word: paleomagnetism
Word: Mid-ocean ridges
Word: Rift (valley)
Word: Subduction
Word: Trench
Magnetic Reversals in Oceanic Crust: Draw & Label
Seafloor Spreading
•
supports the continental drift hypothesis
process by which new oceanic
lithosphere forms as
magma rises toward the surface
and solidifies.
Subduction
supports the continental drift hypothesis
Two major processes of plate tectonics
•Seafloor spreading
•Subduction
Seafloor Spreading
Mid-Ocean Ridges
Mid-ocean ridges are underwater
mountain chains that run through
Earth’s
ocean basins.
•
● location where seafloor spreading
takes place.
Subduction
•
Moving seafloor collides into continental
crust
•
Subduction
occurs when a denser (oceanic) crust
moves under a less dense (continental)
crust
● occurs only at “convergent” boundaries
Seafloor Spreading
•
Subduction forms “trenches”
•
Trench?
hemispheric-long, narrow depressions of
the sea floor.
deepest parts of the ocean floor!
Some not measurable
most important natural boundaries
formed between two lithospheric plates.
•
•
•
•
Subduction form “trenches”
●
A trench marks the position at which the
denser slab begins to descend beneath
another lithospheric slab (less dense).
●
3 to 4 km (1.9 to 2.5 mi) below the level
of the surrounding oceanic floor.
●
The deepest ocean depth to be sounded is
Mariana Trench at a depth of 10,911 m
(35,798 ft) below sea level.
Seafloor Spreading
•
Who
•
How
•
Where
•
When
study the Earth's
ancient magnetic
field
Has magnetic field
always pointed
North?
Magnetic Anomaly
Fluctuations or
variations in the
intensity of the
magnetic field
Magnetic Reversals
On seafloors:
at the boundaries between New
& Older sections seafloor
Magnetic Field is Reversed in
Direction
On Continental Crust:
Lots of magnetic anomalies,
no set pattern or prediction
Direction of N-S Polarity changes ~ +100 000 y
MAGNETIC FIELDS
A field of attraction or repulsion to another
substance based on its composition
MAGNETIC FIELDS
●
Outer core of the Earth
The molten iron flows
creates an electric current
(flow of electrons) &
a magnetic field that surrounds Earth
●
The magnetic field created in the center
of the planet makes your compass point
north
Protects the Earth from solar winds.
MAGNETIC FIELDS
MAGNETIC FIELDS
Who
• How
• Where
• When
•
The older crust moves outward.
Dates are confirmed by the Magnetic
Reversal of the crust.
Magnetic Strips along
the Mid-Ocean Ridge
Why does “Seafloor Spreading”
support CD hypothesis?
How does “Subduction” fit with
“Seafloor Spreading” ?
Earth’s Lithospheric Plates
In the Future?
RESOURCES
• http://images.yourdictionary.com/pangaea
• http://www.sciencebuddies.org/science-fairprojects/project_scientific_method.shtml
• http://www.sciencedaily.com/articles/o/oceani
c_trench.htm
• www.appstate.edu/~marshallst/GLY1101/.../3Continental_Drift.pptx
RESOURCES
●
●
http://www.sciencebuddies.org/science-fairprojects/project_scientific_method.shtml
http://www.sciencedaily.com/articles/o/oceanic_t
rench.htm
● www.appstate.edu/~marshallst/GLY1101/.../3Continental_Drift.pptx