Transcript Evidence of continental drift

Plate Tectonics
Will California really ever fall off
into the ocean?
You should be able to answer this question by the end of the
power-point.
Continental Drift
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Developed in 1912 by Alfred
Wegner, a German
meteorologist.
Continental Drift proposed that
Earth’s continents had once
been joined as a single
landmass that broke apart and
sent the continents adrift.
Wegner called the
supercontinent Pangaea which
means “all the earth” in Greek.
Pangaea broke up 200 mya.
The northern half of Pangaea
was referred to as Laurasia
and the southern portion is
known as Gondwanaland.
Evidence from rock layers
• When examining
the rock layers of
where the
continents were
connected during
Pangaea, it was
discovered that
the rocks were of
the same TYPE
and AGE!
Fossil Evidence
•Wegner found similar
fossils of several different
animals and plants that
once lived on or near land
had been found on widely
separated continent.
• The dinosaurs found
could NOT swim across
oceans, therefore
continents had to be
connected!
The Continents fit together like puzzle pieces:
Climatic Evidence:
•Coal deposits, made
accumulation of swamp
plants, were found on
Antarctica.
•Glacier deposits were found
on Africa, India, South
America and Australia.
•For example, the
Glossopteris was a fern-like
shrub and was found in South
America, Antarctica and India.
•This plant grew in Temperate
Climates, which were places
closer to the equator.
Seafloor Spreading
• Sea-floor spreading is the
process in which the ocean floor
is extended when two plates
move apart.
• As the plates move apart, the
rocks break and form a crack
between the plates.
• Earthquakes occur along the
plate boundary.
• Magma rises through the cracks
and seeps out onto the ocean
floor like a long, thin, undersea
volcano or magma slowly come
up and cools forming NEW
OCEAN FLOOR!
Paleomagnetism
• Paleomagnetism is the study
of the record of the Earth’s
magnetic poles preserved in
various magnetic minerals,
such as hematite in the ocean
floor, through time.
• This supports the theory of
continental drift because it
demonstrates that periods of
pole reversals align perfectly
on the ocean floor. It
demonstrates an identical
pattern on both sides of the
spreading centers.
• This demonstrates plate
motion!
Evidence of continental drift (Summary)
1. Plates/continents fit together like puzzle pieces
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5.
Fossil evidence- dinosaurs and plants on Antarctica
Same type and ages of rocks found on Africa and South America
Seafloor Spreading- new rock created along the ocean floor
Paleomagnetism- shows a pattern of identical pole reversal on both
sides of a spreading center.
The Dwyka Tillite (rocks layers
shown) correlates with similar
rocks in South America, India,
Australia, and Antarctica. Alfred
Wegener considered this
uplifted rock layer to be
evidence of continental drift.
Layers of the Earth
A. Crust- solid, 5-70 km thick
Two Types of Crust:
Oceanic- ocean floor,
more dense then
because of more iron
Continental-dry land
B. Moho- boundary between
mantle and crust
Lithosphere- upper part of the
mantle, almost like crust
Asthenosphere- softer layer
under lihtosphere
C. Mantle-(lower) melted,
“plastic” magma
D. Outer Core- liquid metal
E Inner Core- solid metal
(iron and nickel)
Convection currents in the mantle
-The “plasticity” of the mantle allows the plates to glide and move along
the mantle creating mountains, trenches and new land.
-Heat from the core and the mantle itself causes convection currents
to be created in the mantle.
-The warmer magma at the bottom of the thick mantle is warmer
because it is closer to the core. Warm magma is less dense and rises
to the top of the mantle, then it cools and sinks again, creating a
constant circulation in the mantle.
This diagram shows how the moving plate
boundaries move and create different landforms.
Convection
Currents
Which plate
do we live
on?
Divergent
creates new
ocean floor!
Convergent
creates
mountains and
volcanoes!
Plate Tectonics- the study of the movement of
thin slabs of crust called tectonic plates.
Three types of plate
boundaries:
1. Convergent- two plates
coming together
2. Divergent- two plates
separating
3. Transform- two plates
sliding past each other.
http://www.msnbc.msn.com/id/7807001
California lies on a
strike-slip fault. So,
will it ever fall off
into the ocean?
NO!
The only possibility is
that the western half
of California will float
north (up the coast of
the U.S)
Three Types of Convergent Plate
Boundaries
A. Continental-Continental- Creates
Mountains. (Example ?)
Oceanic crust sinks,
why?
B. Oceanic-Oceanic- More dense plate
sinks & melts. Magma rises up and
creates island volcanoes. (Ex: Fiji)
C. Continental-Oceanic-oceanic sinks and
comes to the surface and creates land
volcanoes.(Example: ???)
Volcanoes and Plate Tectonics
Volcano- a weak spot in
the crust where magma
comes to the surface.
There are about 600
active volcanoes on land
and many more beneath
the sea.
- Ring of Fire: an area of
active volcanoes that form
along the Pacific Plate
boundary.
The Tectonic Plates of the World
Tectonic Plates of the World