Transcript Plate tectonics - pams

Plate Tectonics
Plate Tectonics explained by a 7 yr old…
The Claim…
The Earth once had a single landmass
that broke up into large pieces.
 This large continent is called Pangaea
meaning” all Earth”.

Shoulder Partner
How could you go about proving a
theory like this?
 How do you convince people to support
your ideas/thoughts?

The Earth’s Drifting
Continents

Alfred Wegener was not
the first to propose that
the continents had been
joined; however, he was
the first to gather enough
evidence.
Evidence from
fossils…

Glossopteris’ fossils (extinct
plant) located in rocks
about 250 million years old
in South Africa, Australia,
India and Antarctica.
Seeds were too large to
have been carried by wind
and too fragile to have
survived a trip by ocean
waves.
Evidence from Rocks…

An ancient folded mountain chain that
stretches across S. Africa links up with
an equally ancient folded mountain
chain in Argentina.
The Evidence
Face Partner

Can you think of any other type of
evidence that Wegener could use?
The Real Issue………..
How could the continents move through
the solid-rock bottoms of the oceans?
 In the 1950’s, scientists using better
instruments found underwater mountain
chains with rift valleys in their centers

Plate Interactions
Earth’s Spreading Ocean
Floor
Midocean ridges form the
single largest mountain
range in the world
 In between the ridges
are thin cracks called
transform faults.

Midocean ridge
Mid-Ocean Ridges and an Ocean Floor Spreading
How do they prove that
it’s really spreading?
New deep-sea
drilling machines
showed the
following evidence:
 A. rocks next to a
mid-ocean ridge are
younger than the
rocks farther away.

old  young
young  old

B. Magnetic stripes on the ocean floor
showed that the magnetic poles have
reversed themselves nine times in the past
3.5 million years
Tectonic Plates
Without looking…
 What
are the two
things that prove
that the ocean floor
is spreading?
If the ocean floor is being created, is
the Earth getting bigger?


Ocean floor is being destroyed in trenches through
subduction where oceanic crust slides under
continental crust.
The denser ocean crust is pushed downward into
the mantle and melts
Continental vs Oceanic Crust…
The Earth’s Moving Plates

The Theory of Plate
Tectonics links
continental drift and
seafloor spreading and
helps to explain the
formation, movement,
collisions, and
destruction of the
Earth’s crust
Lithospheric Plates



There are seven major
plates (Pacific, North
American, South
American, Eurasian,
African, Indo-Australian,
and Antarctic)
There are also 5 small
plates.
Each plate moves at a
different speed and
direction
3 cm N W per year
Plate Boundaries

Divergent boundaryplates moving apart
Volcanic islands
and activity

Convergent boundaryplates that are moving
together
Mountain building,
Earthquakes,
Trenches, continental
Volcanic activity

Transform boundary,
slip-strike, lateral faultsplates slide past one
another
Earthquakes…and lots
of them…sometimes
severe!
Plate formation
Plate Motion

The power of convection currents in the
mantle is the force that moves the plates
TIME ELAPSED…
Table Talk
How would plate boundaries act
differently if ocean plates hit each other
or if ocean plates hit continental plates?
 Would there be a difference?

OCEAN TO OCEAN
PLATES…

The older oceanic plate is subducted
and melted causing a string of
volcanoes forming islands.
CONTINENTAL TO
CONTINENTAL PLATES

The continents fold upward to form
large mountain ranges. Ex.
Appalachian Mountains from when
Africa collided with N. America.
Ocean to Continental

The oceanic plate is subducted and a
trench is formed. Can form mountains
and volcanoes…
Plate Tectonics
PLATE TECTONICS…
Will the Earth Continue to
Change?
The Earth’s Changing Surface
Stress is what causes the surface of the
Earth to change
 Put simply: It’s what plate boundary
movements do to the land above.

Types of Stresses



Compression –
(convergent) squeezes
the rock
Tension – (divergent)
causes the rocks to
stretch
Shearing –
(transformational)
causes it to twist or
tear
Faults
Before Stress
Tension
Shearing
Compression
Faulting
- A break
or a crack in the
earth’s crust
where
movement
occurs.
Footwall
up
 Fault
Hanging
Wall
up
Faults
Strike-Slip Fault
Reverse Fault
Normal Fault
Mountain Formation…
Folded Mountains


When stress is applied to the rock and it bends
but doesn’t break, folded mountains form.
This process forms an anticline which is an
upward fold and a syncline which is a
downward fold
Anticline vs Syncline…
The “Floating” Crust

Isostasy -the balance between the downward
force of the crust and the upward force of the
mantle
Tectonic Humor and
we’re finally done!