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 continents1. 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 mechanismWhat 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.

RadiationConduction 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 BoundaryDrawings

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)

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.

Folding

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 apart2. reverse - rocks are pushed together3. 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 Questions1. 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 sea-floor 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.