Transcript Evidence for Continental Drift

Aim: What New Evidence is used
to explain Plate tectonics?
Do Now:
What evidence did Wegener use to help explain
his theory of Continental Drift?
(REVIEW) Theory of Plate Tectonics
- the lithosphere is broken
up into many segments
each carrying a continent
or a part of a continent.
(like a cracked egg shell)
- continents are attached to
the lithosphere (crust) which
move on the asthenosphere
I.
Earthquakes and Volcanos
What do you notice about the earthquakes and volcanos on
this world map?
I. Earthquakes and Volcanos
- Occur in specific areas on our planet and create a
pattern around the world.
They outline the boundaries of the plates.
II. Sea-Floor Spreading
Which continents appear to fit best together on the world map?
How have these continents moved relative to each other?
- as magma rises up through the crust
(lithosphere), the sea floor spreads apart and
gets wider.
- rising magma makes
new oceanic crust (young)
- This new oceanic crust pushes continents away
from each other.
Where would the youngest oceanic crust be
located on the diagram?
• at the ridge, where new magma rises and solidifies.
Where would the oldest oceanic crust be located
on the diagram?
• at the edge of the plate closest to the continents
Ridge
III. Paleomagnetism
(ancient magnets)
• Earth’s inner core rotates.
• This rotation creates a magnetic field that extends
out into space.
• The invisible magnetic field…
- Protects Earth from solar radiation
- Creates a North/South magnetic pole (used by
compass)
- Can be studied in rocks on Earth’s Surface
What minerals make up the core and mantle?
- iron in the rising magma aligns
to Earth's magnetic field (like a
compass).
- the magma cools and solidifies
the iron in place within the rock.
The iron in the rock shows the record of
Earth’s magnetic history.
~ 1 MYA
• Normal polarity - when
rocks show the same
magnetism as today
• Reverse polarity - when
rocks show the opposite
magnetism as today
~ 500,000
years ago
Present
Mid- Ocean Ridge
Earth’s Magnetic
poles switch about
once every
500,000 yrs.
The magnetic orientation in the rock creates the
same pattern on both sides of the boundary.
IV. Hot Spots
• Fixed concentrations of magma in the
mantle that rise to the surface as a
plume.
•The Hawaiian Islands
were formed as the
Pacific plate moved
over one of these hot
spots
Push me
Closure 1:
What if the sea-floor
was not spreading?
Evidence that supports
sea-floor is spreading
Age of sea-floor?
- sea-floor shows
different aged rocks
(younger at the ridge
and older at the
continents)
- sea-floor would have
the same age
throughout the entire
ocean.
Paleomagnetism?
- rocks would show the
same magnetism
- rocks show matching
patterns of alternating
magnetism on both
sides of the ridge.
Closure 2:
Review Book
Page 105-107 #1-10
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