Transcript Ch 4 Plate Tectonics

Plate Tectonics
Make up of the Earth
Earth’s Interior
(Composition Layers)
• Crust - Layer of thin & solid rock that forms Earth’s
outer skin.
• Ranges from 5 to 100 km in thickness
• Split into 2 layers: continental (less dense) & oceanic (more
dense)
• Mantle - Layer of Hot Rock
• Roughly 2900 km thick
• 67% of Earth’s mass
• Core – innermost layer(s) {outer & inner core}
• Made mostly of iron & nickel
• Radius is 3,430 km
Layers of the Earth
http://my.hrw.com/tabnav/controller.jsp?isbn=003030492x
Draw & Label
the layers of the Earth
Physical Layers
• The less familiar layers are the physical layers. They are
based on how the layer looks or acts.
– Lithosphere “rock sphere” (15-300 km)
• The tectonic Plates
• A combination of crust and the upper region of the mantle
• Cold and brittle (easily broken)
– Asthenosphere “weak sphere” (250 km)
• Hard rock that acts like warm tar or honey
- Mesosphere “middle sphere” (2250 km)
–
–
Rest of the mantle
Much stronger & hotter than asthenosphere
– Outer Core (2200 km)
• Liquid layer
– Inner Core (diameter= 2456 km)
• Solid, dense core of the planet
Lithosphere & Asthenosphere
Tell your neighbor:
•Which physical layer is rigid?
lithosphere
Write
these 3
definitions
in your
notes.
#14
#15
Now, add in
asthenosphere,
lithosphere, &
mesosphere to
your drawing
Continental Drift
• Continental Drift – the hypothesis* that states that
the continents once formed a single landmass,
broke up, and drifted to their present locations.
Review of hypothesis*, facts,
theories, & laws
• Hypothesis: This is an educated guess based upon
observation. It is a rational explanation of a single event or
phenomenon based upon what is observed, but which has
not been proved. Most hypotheses can be supported or
refuted by experimentation or continued observation.
• Theory: A theory is more like a scientific law (what) than a
hypothesis. A theory is an explanation (how & why) of a set of
related observations or events based upon proven hypotheses
and verified multiple times by detached groups of
researchers. One scientist cannot create a theory; he can only
create a hypothesis.
• Any scientific theory must be based on a careful and rational
examination of the facts.
• A fact is something that is supported by unmistakable
evidence. For example, the Grand Canyon cuts through layers
of different kinds of rock, such as the Coconino sandstone,
Hermit shale, and Redwall limestone. These rock layers often
contain fossils that are found only in certain layers. Those are
the facts.
• Scientific Law: This is a statement of fact meant to explain, in
concise terms, an action or set of actions. It is generally
accepted to be true and universal.
• In general, both a scientific theory and a scientific law are
accepted to be true by the scientific community as a whole.
Both are used to make predictions of events. Both are used to
advance technology.
•
An analogy can be made using a slingshot and an automobile.
•
A scientific law is like a slingshot. A slingshot has but one moving part--the rubber
band. If you put a rock in it and draw it back, the rock will fly out at a predictable
speed, depending upon the distance the band is drawn back.
•
An automobile has many moving parts, all working in unison to perform the chore
of transporting someone from one point to another point. An automobile is a
complex piece of machinery. Sometimes, improvements are made to one or more
component parts. A new set of spark plugs that are composed of a better alloy
that can withstand heat better, for example, might replace the existing set. But the
function of the automobile as a whole remains unchanged.
•
A theory is like the automobile. Components of it can be changed or improved
upon, without changing the overall truth of the theory as a whole. Theories can
be tweaked, but they are seldom, if ever, entirely replaced.
Continental Drift
•Pangaea- Supercontinent that existed 300
million years ago. (see slide)
•Alfred Wegener - Scientist (1915) who came
up with the hypothesis of Continental Drift.
Plate Tectonics
Look in your book, find
and write down the
definition for:
• Tectonic Plates: (#16)
• Pieces of the lithosphere that move around on
top of the asthenosphere
Plates
Are tectonic plates neatly
divided along continental
lines?
Continental Drift
Restless Continents
• Have you ever looked at a map of the world
and noticed how the coastlines of continents
on opposite sides of the oceans appear to fit
together like the pieces of a puzzle? Is it just
coincidence that the coastlines fit together
well? Is it possible that the continents were
actually together sometime in the past?
Where does it seem like
the continents “fit”?
Evidence of drifting continents
1. Rock landforms match on different continents.
2. Fossils - Trace of ancient organisms preserved in rock.
– Same ancient reptiles and plants found on different continents.
Fossil Evidence
More Evidence
3. Climate
(Glaciers used to be on parts of continents
that are now found in the tropics.) Tropical
plant and animal fossils found in arctic areas.
4. Some continents’ coastlines fit like
puzzle pieces. (ex. South American and
Africa.)
Clues to the forces that move
continents
Sea-Floor Spreading (1960’s)
– At mid-ocean ridges, molten material rises from the
mantle and erupts. This new rock spreads out, pushing
older rock to both sides of the ridge.
Sea-floor spreading
Sea-floor spreading evidence
Sea Floor Spreading
Mid-Ocean Ridges
Sea Floor Spreading
Draw simple picture of
sea floor spreading
Magnetic Reversals – evidence for sea floor
spreading
• Differences in magnetism throughout history are recorded on the
ocean floor.
• Differences in polarity show that the sea floor has been spreading.
The Theory of Plate Tectonics
Finding a mechanism
What is a mid-ocean ridge?
Lithosphere Plates
Heat Transfer
• Heat Transfer - Movement of energy from warmer object
to cooler object.
• Radiation- Transfer of Energy through empty space.
• Conduction- Transfer of energy by direct contact.
• Convection - Heat transfer involving fluid motion.
Radiation
Conduction
Convection
Possible causes of tectonic
plate motion
• The solid rock of the asthenosphere flows very
slowly
• This movement occurs because of changes in
density within the asthenosphere.
• Hot rock from deep within the Earth rises, but
cooler rock near the surface sinks.
• Think lava lamp
Convection Currents
The heating and cooling of the fluid, changes the fluid’s density, and causes
convection currents in the Asthenosphere. The lighter Lithosphere float on top
and move along with these currents
Draw a side view of the Earth
with convection currents.
Putting it all together
•As scientists’ understanding of mid-ocean ridges and
magnetic reversals grew, they formed a theory to explain how
tectonic plates move.
•PLATE TECTONICS is the theory that the Earth’s lithosphere
is divided into tectonic plates that move around on top of the
asthenosphere.
•TECTONIC PLATE BOUNDARIES – a place where tectonic
plates touch – 3 types
Convergent Motion
• Convergent Boundary: A
plate boundary where the
plates are moving toward
one another. (#17)
• Convergent Motion:
Motion along a plate
boundary where the
plates are moving towards
one another.
• Subduction Zone: Area
where a plate sinks
beneath another plate.
(#20)
Convergent Boundary
Drawings
Divergent Motion
• Divergent Boundary:
A plate boundary
where the plates are
moving away from
one another. (#18)
• Divergent Motion:
Motion along a plate
boundary where the
plates are moving
away from one
another.
Examples of land diverging
Divergent Boundary
Drawings
Divergent & Convergent Boundaries
Transform Motion
• Transform fault
boundary: A boundary
between two tectonic
plates where the motion
of the plates is to slide
past one another. (#19)
• Transform Motion: The
motion of transform fault
boundaries which is to
slide past one another,
usually in the opposite
direction.
Transform fault
All faults
Transform Boundary
Drawings
Deforming the Earth’s Crust
In your text (pg. 112)
write down the
definition of
deformation.
The process by which the shape of a rock changes because of stress
• _______________ stress occurs when forces act
to squeeze an object (#21)
• _______________ stress occurs when forces act
to stretch an object (#22)
Folding
The bending of rock layers because of stress in
the Earth’s crust is called _______________.
(#23)
Folds can be large or small – as seen in the
pictures below.
Faulting
Fault – the surface along which rocks
break and slide past each other (#24)
• There are 3 types of faults:
1.normal – rocks are pulled apart
2. reverse - rocks are pushed together
3. strike-slip – opposing forces cause
rock to break and move horizontally
(San Andreas)
Have you ever seen this?
Plate Tectonics
& Mountain Building
• Folded Mountains
• Where is an
example? How
were they formed?
Plate Tectonics
& Mountain Building
• Fault-Block
Mountains
• Where is an
example? How
were they formed?
Plate Tectonics
& Mountain Building
• Volcanic Mountains
• Where is an
example? How
were they formed?
Stop! Add drawings of the 3 types of faults
Review Questions
1. Which part of the Earth is molten? (crust,
mantle, outer core, inner core?
2. The part of the Earth on which tectonic
plates move is the ___________.
3. What is magnetic reversal?
4. If a piece of sea floor has moved 50 km in 5
million years, what is the yearly rate of seafloor motion?
5. In your own words, write a definition for plate
tectonics.
6. Draw arrows to describe convergent,
divergent, & transform movement
7. T/F There is only one major way that
mountains are made.