Transcript Slide 1

Thursday 9/5/13
• LT: I can set reasonable goals for my
grade in this class.
• I can describe continental drift
• BR: How do you think you did on the test
yesterday?
1
Plate Tectonics is one of the most
exciting recent theories in Earth Science.
It began with an idea based on
observations made 400 years earlier.
2
• 400 years ago, early explorers like
Magellan and Columbus brought
back information about new
continents and their coastlines.
•Cartographers charted those new
discoveries and produced the first
reliable world maps.
3
In 1912,
Alfred Wegener,
a German scientist,
proposed the hypothesis
of
CONTINENTAL DRIFT
“clearly an idea before its time”
4
1.The continents used to be a
single landmass, or
supercontinent called
= PANGAEA [all lands]
2.This supercontinent was
surrounded by a huge ocean
called
= PANTHALASSA [all seas]
5
6
Pangaea app.
250M yrs ago
7
3.About 250M years ago,
Pangaea began to break up
4.The continents slowly drifted
to their actual locations.
8
•Pangaea is not the only “super continent”
that ever existed.
•Rodinia is another “motherland” that
formed more than 1100M years ago.
•It is to be understood that the separation
and coming together of landmasses
always occurred, and are still happening.
This is known as the:
•Supercontinent Cycle.
9
Pangaea was surrounded by all
seas called:
A.
B.
C.
D.
Oceanographia
Panthalassa
Antarctica
Ishoudinotha
10
The continents used to be a
single landmass called:
A. Hugeenaea
B. Panthalassa
C. Pangaea
D. Americeuropa
11
Who was the first to propose the
hypothesis of the Continental Drift?
A. Robert Wagener
B. Louis Pasteur
C. Alfred Wegener
D. Andrija Mohorovicic
12
EVIDENCE 1
FIT OF THE CONTINENTS
Continental shorelines on either sides
of the Atlantic ocean had such
similarities that they looked like parts
of a giant
JIGSAW PUZZLE:
13
 Bulge of Africa fits the shape of North America
 South America fits along the coast of Africa
beneath the bulge
 Greenland seems to fit between North America
and north western Europe.
14
Untold tragedies of
Continental Drift. .
15
According to the “jigsaw puzzle” evidence, the
bulge of the African coast fits the contour of :
A. East coast of North America
B. West coast of South America
C. Greenland
D. Europe
16
EVIDENCE 2
FOSSILS MATCH
The presence of identical fossil
species [animals and plants] on
now widely separated coastlines
support the theory that those
continents were once joined.
17
LOCATION OF VARIOUS DISCOVERIES
Madagascar
18
EVIDENCE 2
FOSSILS MATCH
Glossopteris  a fern found in
Australia and Antarctica
19
Madagascar
land reptile
land reptile
freshwater reptile
20
Permian ferns
Mesosaurus, a freshwater reptile,
could not have been able to swim across the Ocean,
and no evidence of land bridges.
21
EVIDENCE 3
GEOLOGICAL MATCH
Rock layers’ sequence [structure],
age and types [basalt, sandstone],
are identical on opposite sides of
the Atlantic Ocean.
 Appalachians Mtns [North America]
and mountains in Scotland and
Scandinavia.
22
Matching of mountain ranges
on different continents
23
When the continents are reassembled, the mountain
chains form a continuous belt —
having the same rock types, structures and rock ages.
24
EVIDENCE 4
PALEOCLIMATIC MATCH
Scientists found glacier
evidence in places that are now
warm (Africa) and tropical plant
fossils in areas that are now
cold (Antarctica). This couldn’t
be possible…..
25
EVIDENCE 4a
PALEOCLIMATIC MATCH
Unless:
1) the Atlantic ocean did not exist,
2) the continents were joined AND
3) they were all close together near the
South Pole of Pangaea.
26
Pangaea with
SAfrica centered
over the South Pole
accounts for
glacial ice in the
Southern continents
27
EVIDENCE 4b
PALEOCLIMATIC MATCH
Discoveries of large concentrations of
fossils of tropical plants [in the form of
coal deposits] in eastern US, Siberia,
Antarctica suggest that they were
once situated closer to the Equator, in
a more tropical climate where lush,
swampy vegetations could grow.
28
Now cooler
climate regions
that used to be
at the Equator
Glaciers
movement
centered over
South Pole
29
• Despite all the evidences
– Jigsaw puzzle [cartography]
– Fossils [paleontology]
– Geological match [geology]
– Climatic patterns [paleoclimatology]
• Wegener’s hypothesis was
rejected because he could not explain:
– What forces could move the continents
– How continents could plow through the
stationary ocean floor without crumbling.
• He died in 1930 before finding the ultimate
answer
30
What kind of fossil evidence supported
Wegener’s hypothesis?
A. Fossils hinting at a land bridge between
South America and Africa
B. Fossils proving Mesosaurus never lived
in Africa
C. Plant fossils showing that cold areas
used to be tropical
D. Sea fossils proving the continents had
plowed through the ocean floor
31
Wegener speculated that over millions
of years smaller landmasses
A. Moved closer together
B. Drifted to their present locations
C. Did not move
D. Drifted to the southern hemisphere
32
Seafloor Spreading:
Harry Hess’s hypothesis
Underneath the ocean, molten magma was
coming through cracks as both sides of the
tectonic plates were moving AWAY from each
other.
The moving ocean floor was replaced by the
rising magma that cooled and solidified into
new rock.
33
Harry Hess’s hypothesis
 ocean crust is formed at ocean
ridges and destroyed at deepsea trenches.
Maybe the ocean floor moving
was the force responsible
for the movement of the
continents
Thus came the idea of
SEAFLOOR SPREADING
34
A REVIEW
Earth’s Magnetic Field
• The Earth's magnetic field produces
invisible lines of force that extend from one
pole to the other.
• A compass needle aligns itself with these
lines of force, meaning that it points toward
the magnetic poles.
35
36
PALEOMAGNETISM
• When igneous rocks containing magnetic
minerals solidify, the crystals align
themselves with the Earth's magnetic field.
• The magnetic field of the rock then points
toward the magnetic pole that existed when
the rock formed.
• If the rock is moved, its magnetic field will
act as a “fossil compass”.
37
• Basalt is rich in iron-bearing materials, like
magnetite.
• As the basalt lava cools, the Fe-bearing
minerals become oriented parallel to the
Earth’s magnetic field.
38
• As the lava hardens, the magnetic
orientation is preserved and provides a
record of the current Earth’s magnetic field.
39
.
40
As new seafloor is created at the ridge, it is added
in equal amounts to both trailing edges of the
spreading seafloor.
The pattern of stripes appear as mirror images on
both sides of the ridge which is the strongest
evidence for seafloor spreading.
41
Magnetic history of the Earth showed a
symmetrical or mirror-image stripes
parallel to the ocean ridges
42
43
Theory of Plate Tectonics
From the hypotheses of Continental Drift and
Seafloor Spreading came the
Theory of Plate Tectonics
44
Theory of Plate Tectonics
The Earth’s crust and rigid upper mantle
are broken into huge slabs or plates.
Those plates are riding/floating on the
mantle [like wood blocks on water],
at different rates and different directions.
45
Directions and rates of plate motions
Subduction
Spreading
46
The oceans and the
continents are carried
as passengers onto the
moving plates.
47
The constant movement of those
plates is responsible for the
changes to the Earth’s surface
by the way of:
48
EARTHQUAKES
49
V
O
L
C
A
N
I
C
E
R
U
P
T
I
O
N
S
50
MOUNTAIN RANGES
51
RIFT VALLEYS
52
Ocean basins
FORMATION / DESTRUCTION
53
8 major plates:
1)
2)
3)
4)
5)
6)
7)
8)
North American
South American
Eurasian
African
Pacific [largest]
Indian/ Australian
Antarctica
Nazca
The minor ones:
Juan de Fuca, Cocos, Caribbean, Scotia,
Arabian, Philippine
54
55
BOUNDARIES
•Tectonic plates interact at places called
BOUNDARIES.
•The continents / oceans do not
necessarily resemble the outline of the
plate boundaries.
•There are three types of boundaries, each
one associated with specific geologic
activities and/or features.
56
Divergent Boundaries
Two plates moving AWAY from each other
and forming a gap or RIFT.
• Mostly associated with OCEANIC crust
[seafloor spreading = Mid-Atlantic Ridge]
– as molten rock [MAGMA] from the mantle
rises the plates move apart, and fills the
space between the plates.
– as it cools, it hardens onto the edges of the
plates and creates new crust.
57
DIVERGENT PLATES
“CONSTRUCTIVE”
58
59
Divergent Boundaries
• Some involve the CONTINENTAL crust
– when it begins to separate, the stretched crust
forms a long, narrow, depression called a
RIFT VALLEY
• it is currently happening between the African and
Arabian plates  Red Sea is therefore widening
60
D IV E R G E N T
61
RIFT VALLEYS
62
Mediterranean Sea
63
Convergent Boundaries
Two plates moving TOWARDS each other.
• Direct COLLISION of one plate with
another one.
• There are three POSSIBILITIES:
– CONTINENTAL – OCEANIC
– OCEANIC – OCEANIC
– CONTINENTAL – CONTINENTAL
64
CONTINENTAL - OCEANIC
• As the plates are colliding, the denser plate will be
forced downwards
• Since the oceanic crust is denser than the
continental crust, the ocean plate is pushed under
continental plate. [crust destruction]
The area is called a SUBDUCTION ZONE, and
forms a deep-ocean trench
• As the plate sinks into the mantle, it melts and
becomes magma. The magma rises through the
continental plate and forms a volcanic chain
65
“DESTRUCTIVE”
OCEANIC   CONTINENTAL
66
M o u n t H o o d n ea r P o rtla n d , O reg o n
C a sca d es ra n g e
67
Mount St. Helens, Washington
Cascades range
68
Volcanic mountains of the Andes,
(Nazca and South American Plates)
69
TRENCH
70
71
OCEANIC – OCEANIC
• The more dense of the 2 will go under and form
a subduction zone / OCEAN TRENCH
• The new mantle material produced from the
melting of the subducted plate will eventually
resurface to produce chain of volcanic islands
on the ocean floor called ISLAND ARCS
• As magma accumulates over time, the
volcanoes may rise above sea level to form
volcanic islands:
Mariana trench and
the Mariana Islands in the west Pacific ocean
72
OCEANIC-OCEANIC CONVERGENCE
“DESTRUCTIVE”
73
74
75
76
CONVERGENT PLATES
“DESTRUCTIVE”
77
CONTINENTAL - CONTINENTAL
• As the 2 continental plates are colliding,
neither plate is subducted i.e. neither plate
goes beneath the other  WHY?
– because the Continental crust is too buoyant to
sink into the mantle.
• The colliding edges buckle and are pushed
upward to form mountain ranges.
Indian/Australian plate collide with the
Eurasian plate to form the HIMALAYAS.
78
CONTINENTAL – CONTINENTAL CONVERGENCE
79
The collision of India and Asia
produced the Himalayas (before)
80
The collision of India and Asia
produced the Himalayas (after)
81
Mountain Building
82
Transform Boundaries
Two plates PASSING each other.
• Plates are grinding past each other and the
crust is either cracked or deformed.
• Motion is not smooth but rather in spurs of
sudden moves generating
 EARTHQUAKES*
• They are followed by periods of low or
no activity  San Andreas Fault
* Earthquakes can occur / are common along all boundaries
83
TRANSFORM
FAULT
“CONSERVATIVE”
Crust is nor created nor destroyed
84
85
Tectonic plates can include
A. only asthenosphere.
B. only oceanic crust
C. only continental crust
D. both oceanic and continental crust.
Features found at divergent boundaries
include ____.
A. ocean ridges
B. deep-sea trenches
C. crumpled mountains
D. island arc volcanoes
Continental-continental plate collisions
produce ____.
A. island arcs
B. rift valleys
C. deep-sea trenches
D. very tall mountain ranges
The theory that explains why and
how continents move is called
A. continental drift
B. paleomagnetism
C. plate tectonics
D. sea-floor spreading
The Himalaya Mountains were
formed in a collision at a
A. divergent boundary
B. convergent boundary
C. transform boundary.
D. fracture zone
Crust is neither destroyed nor formed
along which of the following
boundaries?
A. convergent
B. divergent
C. transform
D. magnetic
SUMMARY
Direction of
movement
Type of
Boundary/
impact on crust
Plates involved
Geological
activities/
features
Examples
92
Importance of plate tectonics
• Theory provides an explanation of Earth’s
major surface processes
• Geologists have found explanations for the
geologic distribution of earthquakes,
volcanoes and mountains and the distributions
of plants and animals fossils.
#1 MATCH
• DIVERGENT
• CONSERVATIVE
• CONVERGENT
• DESTRUCTIVE
• TRANSFORM
• CONSTRUCTIVE
What causes Plate Movement?
While several models have been
proposed to explain the
DRIVING MECHANISM responsible
for their movement,
there is no doubt that the Earth’s
internal heat is the DRIVING
FORCE.
98
DRIVING MECHANISM
Convection Currents 
the rising-sinking action of magma due to the heat in
Earth’s core
 Magma close to the core is heated,
 It expands, lowering its density, and then rises
 Closer to the crust, the magma cools, it contracts, increasing
its density, and then sinks due to gravity
99
Convection currents
100
101
The driving mechanism of
tectonic plates movement are related to
convection currents in Earth’s ____.
A. crust
B. mantle
C. inner core
D. outer core
The downward part of a convection current
causes a sinking force that ____.
A. pulls tectonic plates toward one another
B. moves plates apart from one another
C. lifts and splits the lithosphere
D. creates a divergent boundary
Which of the following is an example of a
divergent plate boundary?
A. [Option 1]
B. [Option 2]
C. [Option 3]
D. [Option 4]
104
At what type of plate boundary
does sea-floor spreading occur?
A. convergent oceanic-oceanic boundaries
B. convergent oceanic-continental
boundaries
C. divergent oceanic-oceanic boundaries
D. transform boundaries
The force behind the movement of
Earth’s plates is
A. cooling of magma cells that rises to
the Earth’s surface
B. magnetic attraction between Earth’s
iron core and its poles
C. temperature differences between
Earth’s oceanic and continental plates
D. the Earth’s internal heat producing
convection currents in the mantle.