Download Sea-Floor spreading

Lesson Objective
• Explain how sea-floor spreading provides a
way for continents to move.
• Describe how new oceanic lithosphere forms
at mid-ocean ridges.
• Explain how magnetic reversals provide
evidence for sea-floor spreading.
Sea-Floor Spreading
• supports the continental drift hypothesis
• Sea-Floor spreading
process by which new oceanic
lithosphere forms as magma rises
toward the surface and solidifies.
Sea-Floor Spreading
• Mid-Ocean Ridges
Mid-ocean ridges are underwater
mountain chains that run through
Earth’s ocean basins.
• Mid-ocean ridges are located where
sea-floor spreading takes place.
Sea-Floor Spreading
• Moving Sea-floor collides into continental crust
• Subduction
occurs when a denser (oceanic) crust moves
under a less dense (continental) crust
Subduction occurs at a “convergent” boundary
Sea-Floor Spreading
• Subduction form “trenches”
• Trench
• hemispheric-long, narrow depressions of the sea
floor.
• deepest parts of the ocean floor! Some not
measurable
• 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.
(higher than Mt. Everest)
Sea-Floor Spreading
• What: mid-oceanic ridges, trenches, guyots
• Where: oceanic crust
• When: 1957-1963
• How??? What data or evidence?
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 the planet.
• 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
Magnetic Stripes
Alignment pattern of magnetic grains
in the sea-floor crust that change over time
based on the Polar direction (N v S)
Every 100 K years the magnetic poles change
direction (magnetic reversal)
Magnetic Strips along
the Mid-Ocean Ridge
The older crust moves outward.
Dates are confirmed by the Magnetic
Reversal of the crust.
Animation link
How do…
• Magnetic Stripes relate to Sea-floor Spreading?
• What is Geomagnetic Reversal?
• Magnetic Anomalies relate to Continental Drift?
What is…
• Paleomagnetism
the Earth’s record of magnetic fields in rocks,
clay or bricks, by direction and intensity
“Guyot” (gee-oot)
• Tabletop mountain, under the sea
that stretches for miles
• Cooled, flattened seafloor as it moves away
from the mid-ocean ridge
• Today, see old plateaus in mid West
(UT, NM, CO)
Mt. Roraima
Earth Today
Earth tomorrow
RESOURCES
• http://images.yourdictionary.com/pangaea
• Magnetic Reversal animation
• 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/.../3
-Continental_Drift.pptx