Inside Earth Continental Drift Sea Floor Spreading Plate Tectonics - PowerPoint PPT Presentation

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Title: Inside Earth Continental Drift Sea Floor Spreading Plate Tectonics


1
Inside EarthContinental DriftSea Floor
SpreadingPlate Tectonics
2
The Earths Layers
  • The Earth is made of many different and distinct
    layers. The deeper layers are composed of heavier
    materials they are hotter, denser and under much
    greater pressure than the outer layers.
  • Natural forces interact with and affect the
    earths crust, creating the landforms, or natural
    features, found on the surface of the earth.

3
  • Before we start to look at the forces that
    contribute to landforms,lets look at the
    different layers of the earth that play a vital
    role in the formation of our continents,
    mountains, volcanoes, etc.

4
Crust
Mantle
Outer Core
Inner Core
5
Crust
  • crust - the rigid, rocky outer surface of the
    Earth,
  • The crust is composed of two rocks. The
    continental crust is mostly granite. The oceanic
    crust is basalt. Basalt is much denser than the
    granite. Because of this the less dense
    continents ride on the denser oceanic plates.

6
The Crust
  • The Earth's Crust is like the skin of an apple.
    It is very thin in comparison to the other three
    layers. The crust is only about 3-5 miles (8
    kilometers) thick under the oceans (oceanic
    crust) and about 25 miles (32 kilometers) thick
    under the continents (continental crust).

7
The Lithospheric Plates
  • The crust of the Earth is broken into many pieces
    called plates. The plates "float" on the soft,
    semi-rigid asthenosphere.

8
The Lithosphere
  • The crust and the upper layer of the mantle
    together make up a zone of rigid, brittle rock
    called the Lithosphere.

9
The Mantle
  • The Mantle is the largest layer of the Earth.
  • The middle mantle is composed of very hot dense
    rock that flows like asphalt under a heavy
    weight. The movement of the middle mantle
    (asthenosphere) is the reason that the crustal
    plates of the Earth move.

10
The Mantle Composition
  • mantle - a rocky layer located under the crust -
    it is composed of silicon, oxygen, magnesium,
    iron, aluminum, and calcium.

11
Convection Currents
  • The middle mantle "flows" because of convection
    currents. Convection currents are caused by the
    very hot material at the deepest part of the
    mantle rising, then cooling and sinking again
    --repeating this cycle over and over.

12
The Outer Core
  • The core of the Earth is like a ball of very hot
    metals.
  • The outer core is so hot that the metals in it
    are all in the liquid state. The outer core is
    composed of the melted metals of nickel and iron.

13
The Inner Core
  • The inner core of the Earth has temperatures and
    pressures so great that the metals are squeezed
    together and are not able to move about like a
    liquid, but are forced to vibrate in place like a
    solid.

14
DID YOU KNOW?
15
Land and Water
  • Photographs of the earth taken from space show
    clearly that it is truly a watery planet.
  • More than 70 percent of the earths surface is
    covered by water, mainly the salt water of oceans
    and seas.

16
  • Continental Drift
  • and
  • Seafloor Spreading

17
Continental Drift Theory
  • In the early 1900s a German explorer and
    scientist (Alfred Wegener) proposed the
    continental drift theory.
  • He proposed that there was once a single super
    continent called Pangaea.
  • He believed that the continent floated on the
    oceanic crust (like an iceberg in the ocean).
  • Most scientist rejected his theory due to lack of
    evidence.

18
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19
Evidence of continental drift
  • Continents fit together like a jigsaw puzzle
  • Fossils match across oceans
  • Rock types and mountain ranges match across
    oceans
  • Climate Evidence (Glacial Deposits)

20
Puzzle Pieces
  • Continents look like they could be part of a
    giant jigsaw puzzle

21
Distribution of Fossils
  • Plant and animal fossils found on the coastlines
    of different continents

22
Sequence of Rocks
  • Same rock patterns found in South America, India,
    Africa, Antarctica and Australia

23
Climate
  • Tropical plant remains (coal deposits) found in
    Antarctica
  • Glacial deposits in Africa, South America, India,
    and Australia during the same time

24
Sea-Floor Spreading
25
  • Ocean floor moves like a conveyor belt carrying
    continents with it.
  • New ocean floor forms along cracks in the ocean
    crust as molten material erupts from the mantle
    spreading out and pushing older rocks to the
    sides of the crack. New ocean floor is
    continually added by the process of sea-floor
    spreading.

26
EVIDENCE OF SEA-FLOOR SPREADING
27
Sea-Floor Spreading
1. Evidence from Molten Material Rocks shaped
like pillows (rock pillows) show that molten
material has erupted again and again from cracks
along the mid-ocean ridge and cooled quickly
28
Mid-Ocean Ridge
  • The mid-ocean ridge system is the most extensive
    chain of mountains on earth, but more than 90 of
    this mountain range lies in the deep ocean. The
    mid-ocean ridge wraps around the globe for more
    than 65,000 km like the seam of a baseball.

29
Mid-Ocean Ridge
  • Mid-ocean ridges occur along the kind of plate
    boundary where new ocean floor is created as the
    plates spread apart. "divergent plate boundary."
    The plates spread apart at rates of 1 cm to 20 cm
    per year. As oceanic plates move apart, rock
    melts and wells up from tens of kilometers deep.
    Some of the molten rock ascends all the way up to
    the seafloor, producing enormous volcanic
    eruptions of basalt, and building the longest
    chain of volcanoes in the world!

30
Sea-Floor Spreading
2. Evidence from Magnetic Stripes Rocks that
make up the ocean floor lie in a pattern of
magnetized stripes which hold a record of the
reversals in Earths magnetic field
31
Sea-Floor Spreading
32
Sea-Floor Spreading
3. Evidence from Drilling Samples Core samples
from the ocean floor show that older rocks are
found farther from the ridge youngest rocks are
in the center of the ridge
33
Sea-Floor Spreading
Sea-Floor Spreading Harry Hess in the 1960s
the process that continually adds new material to
the ocean floor while pushing older rocks away
from the ridge
34
  • Plate Tectonics

35
  • Most of these changes in the earths surface
    takes place so slowly that they are not
    immediately noticeable to the human eye.
  • The idea that the earths landmasses have broken
    apart, rejoined, and moved to other parts of the
    globe forms part of the
  • plate tectonic theory.

36
Plate Tectonic Theory
Along the mid-ocean ridge the seafloor is pulling
apart and the two parts are moving in opposite
directions, carrying along the continents and
oceans that rest on top of them. These pieces of
Earths top layer are called tectonic plates.
They are moving very slowly, but constantly.
(Most plates are moving about as fast as your
fingernails are growing -- not very fast!)
Currently Earths surface layers are divided into
nine very large plates and several smaller ones.
37
  • According to the theory of plate tectonics, the
    earths outer shell is not one solid piece of
    rock. Instead the earths crust is broken into a
    number of moving plates. The plates vary in size
    and thickness.

38
  • These plates are not anchored in place but slide
    over a hot and bendable layer of the mantle.

39
  • As mentioned earlier, those tectonic plates are
    always moving.
  • pulling away from each other (Divergent)
  • crashing head-on (Convergent)
  • or sliding past each other. (Transform)

40
Divergent Boundaries
  • Boundary between two plates that are moving apart
    or rifting
  • ? ?
  • RIFTING causes SEAFLOOR SPREADING

41
Theyre Pulling Apart!
  • When plates pull away from one another they form
    a diverging plate boundary, or spreading zone.

Thingvellir, the spreading zone in Iceland
between the North American (left side) and
Eurasian (right side) tectonic plates. January
2003.
42
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43
Features of Divergent Boundaries
  • Mid-ocean ridges
  • rift valleys
  • fissure volcanoes

44
Convergent Boundaries
  • Boundaries between two plates that are colliding
  • ? ?
  • There are 3 types

45
Ocean to Continent
  • Ocean plate colliding with a less dense
    continental plate
  • Subduction Zone where the more dense plate
    slides under the less dense plate
  • VOLCANOES occur at subduction zones

46
Continental/Oceanic Crush
Subduction Process by which the ocean floor
sinks beneath a deep-ocean trench and back into
the mantle allows part of the ocean floor to
sink back into the mantle
47
Subduction zone
Deep-Ocean Trench Occurs at subduction zones.
Deep underwater canyons form where oceanic crust
bends downward
48
Subduction Zone
49
Andes Mountains, South America
50
Ocean to Ocean
  • Ocean plate colliding with another ocean plate
  • The more dense plate slides under the less dense
    plate creating a subduction zone called a TRENCH

51
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52
Converging... They crash! And theyre both ocean
plates!
  • When both are oceanic plates, one slides under
    the other. Often an island group forms at this
    boundary.

53
Aleutian Islands, Alaska
54
Continent to Continent
  • A continental plate colliding with another
    continental plate
  • Have Collision Zones
  • The plates push against each other, creating
    mountain ranges.

55
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56
They Crash and are both continental plates!
  • Earths highest mountain range, the Himalayas,
    was formed millions of years ago when the
    Indo-Australian Plate crashed into the Eurasian
    Plate. Even today, the Indo-Australian Plate
    continues to push against the Eurasian Plate at a
    rate of about 5 cm a year!

57
Transform Fault Boundaries
  • Boundary between two plates that are sliding past
    each other
  • EARTHQUAKES along faults

58
San Andreas Fault, CA
  • For example Here, the San Andreas Fault lies on
    the boundary between two tectonic plates, the
    north American Plate and the Pacific Plate. The
    two plates are sliding past each other at a rate
    of 5 to 6 centimeters each year. This fault
    frequently plagues California wit hearthquakes.
  • These areas are likely to have a rift valley,
    earthquake, and volcanic action.

59
  • All graphics were taken from Google Images,
    enchanted learning, boom zone, and other
    educational sites.
  • All written information was taken from Prentice
    Hall, World Geography, PBS.org, and other
    educational websites.
  • A good website for a deeper understanding is
    www.observe.arc.nasa.gov/
  • Animations of sea-floor spreading at the
    mid-oceanic rifts
  • Image http//www2.nature.nps.gov/geology/usgsnps/
    animate/pltecan.html
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