Title: Inside Earth Continental Drift Sea Floor Spreading Plate Tectonics
1Inside EarthContinental DriftSea Floor
SpreadingPlate Tectonics
2The 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.
4Crust
Mantle
Outer Core
Inner Core
5Crust
- 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.
6The 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).
7The Lithospheric Plates
- The crust of the Earth is broken into many pieces
called plates. The plates "float" on the soft,
semi-rigid asthenosphere.
8The Lithosphere
- The crust and the upper layer of the mantle
together make up a zone of rigid, brittle rock
called the Lithosphere.
9The 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.
10The Mantle Composition
- mantle - a rocky layer located under the crust -
it is composed of silicon, oxygen, magnesium,
iron, aluminum, and calcium.
11Convection 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.
12The 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.
13The 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.
14DID YOU KNOW?
15Land 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
17Continental 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.
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19Evidence 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)
20Puzzle Pieces
- Continents look like they could be part of a
giant jigsaw puzzle
21Distribution of Fossils
- Plant and animal fossils found on the coastlines
of different continents
22Sequence of Rocks
- Same rock patterns found in South America, India,
Africa, Antarctica and Australia
23Climate
- Tropical plant remains (coal deposits) found in
Antarctica - Glacial deposits in Africa, South America, India,
and Australia during the same time
24Sea-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.
26EVIDENCE OF SEA-FLOOR SPREADING
27Sea-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
28Mid-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.
29Mid-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!
30Sea-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
31Sea-Floor Spreading
32Sea-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
33Sea-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 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.
36Plate 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)
40Divergent Boundaries
- Boundary between two plates that are moving apart
or rifting - ? ?
- RIFTING causes SEAFLOOR SPREADING
41Theyre 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.
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43Features of Divergent Boundaries
- Mid-ocean ridges
- rift valleys
- fissure volcanoes
44Convergent Boundaries
- Boundaries between two plates that are colliding
- ? ?
- There are 3 types
45Ocean 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
46Continental/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
47Subduction zone
Deep-Ocean Trench Occurs at subduction zones.
Deep underwater canyons form where oceanic crust
bends downward
48Subduction Zone
49Andes Mountains, South America
50Ocean 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
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52Converging... 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.
53Aleutian Islands, Alaska
54Continent to Continent
- A continental plate colliding with another
continental plate - Have Collision Zones
- The plates push against each other, creating
mountain ranges.
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56They 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!
57Transform Fault Boundaries
- Boundary between two plates that are sliding past
each other - EARTHQUAKES along faults
58San 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