Transcript PS 2-6-08 - elyceum-beta

Physical Science
Question: How can magnetism of
rocks provide evidence of
continents moving?
Wednesday
Connecting the rube to the physics assignment
And Answers to 10 class questions
Rube Check
continental drift evidence
Plate Tectonics
Homework assignment
• Use the internet and book to find descriptions of the
following concepts:
Pangaea
Panthalassa
Continental drift
Mesosaurus
Mid-Atlantic Ridge
Magma
Sea-floor spreading
Paleomagnetism
Divergent boundary
Convergent Boundary
Rift Valley
Subduction Zone
Ocean Trench
Transform Boundary
What evidence is there that the
continents have moved in the
past?
In other words, what evidence is
used to support the continental
drift theory
Evidence
1)
2)
3)
4)
5)
Evidence
1)
Physical shape of continents
2)
Rock evidence of change in climate
3)
Fossil evidence, including Mesosaurus
4)
Difference in ages of oceanic crust vs continental
crust
5)
Paleomagnetism of rock on either side of the Mid
Atlantic ridge
Alfred Wegener
Determining the magnetic
orientation of ocean rock
In the 1950’s and 1960’s….
• Used Sonar (invented during WWII) to
map the Ocean Floor
To Produce underwater maps for
Submarines
Found that there was a huge ridge of
mountains in the middle of the Atlantic
ocean
Have found many examples since
• Of these mid Oceanic ridges around the
world
• Volcanically active (but not wholly
destructive)
• Ocean floor is not smooth as once thought
Paleomagnetism
• Study of the Earth’s magnetic record over
time
• Minerals in hot rocks do not have a set
magnetic direction
• As it cools, the magnetic orientation of
those minerals becomes fixed pointing in
the direction of the “North Pole”
This magnetic orientation can
and has be measured
What is magnetic orientation?
Means the direction that the rock makes a
compass point as it passes over
What has been discovered…
Discovered bands of rock with different magnetic
orientation as the ship moves away from ridge
• Evidence that the orientation reverses every
200,000 to several million years
• Matched bands with the same magnetic
orientation are found on both sides of a ridge
Orientation of rocks
around a ridge
Different colors represent rocks of
different geologic age
Iceland on a diverging plate
boundary
Who wants to act?
What is the best explanation for the
matched bands of rock?
• New ocean floor is being produced from
the ridge
• Older material material is pushed away
from ridge by newer material
• This in turn moves the continents apart
Mid ocean Ridges
• Are the place of creation of new plate material
• Boundary between plates
• As plates are created items on the plates are
moved farther away from the ridge
• Divergent boundary
Sea-floor Spreading
• Driven by the introduction of new material
at the ridges, the older sea floor is pushed
away from the ridges.
• The oldest ocean rock is farthest away
from the ridges
• The coldest and most dense rock is
farthest away from the ridges
If new crust material is being
created…
Old material must be destroyed
because the surface area of the
earth is not increasing
Where do plates come together?
• Convergent boundary
• Subduction zones
• Most have a lot of volcanic and
earthquake activity associated with their
interaction
What happens at a subduction
zone?
• The density of material coming together
determines what happens
• The most dense material is pushed under
the least dense material
Variations in Convergent
boundaries
Ocean to continental crust
Continental to continental
Ocean to Ocean crust
Oceanic meets Continental
crust
The west Coast of the US around
Seattle and Portland
West Coast
Ocean-vs-Continent
• More dense ocean crust is push beneath
Continental crust
When it is pushed deep enough it begins to
melt
The melted material is pushed upward,
supplies material for volcanos
Magma and Lava
• Magma
• Lava
Continental material meets
other continental material
The mountains between India and
China
Subduction zone –The Himalayas
Continent –vs-Continent
• Nothing is pushed down much, similar
density
• Build Mountains
• Keep building as long as pushing occurs
• No volcanos
Ocean-vs-Ocean
• All based on age of rock, the oldest
material is pushed under
• Creates volcanic islands, or island ars
Subduction zone - Japan
One final type of boundary
interaction
TRANSFORM BOUNDARY
Southern California
• San Andreas Fault
Transform
• Moves past each
other
• Not creating or
destroying material
• Earthquakes
Plate Tectonics
• Describes continental movement
• Describes why and how continents move
Plates and Continents
Pangaea and Panthalassa