Notes

Courtesy of your kind & intelligent teacher, Mr. Whallen

Section 4.1

Alfred Wegener born 1880 Germany

proposed continents were once together.

He Said:

• 250million years ago (Mesozoic Era) Pangaea began breaking up & continents drifted to current locations. He Gave this a name…

Continental Drift• Which is the apparent movement of

the continents relative to one another over the Earth’s crust.

He did research to come up with PROOF for this!

• A.  1st evidence:   Fit of the continents. – He cut out and pieced together a crude map – He called the great ocean Panthalassa (meaning all

seas)

• The continent was called Pangaea (meaning all lands)

• Continental drift animation

B. 2nd body of evidence: Matching rocks:Found on the following continents.1. North Eastern N. America & Western Europe.2. Southern N. America & North Africa.3. South America & Africa.4. Not enough proof!!

C. (3rd body of evidence) Identical fossils found all over the world:

• 1. East South America & West Africa.

• 2.  Southern North America & Northern Africa.

• 3. Northern North America and Europe.

D. 4th evidence Climate

• 1. He found tropical fern fossils in Antarctica.

• 2. Found many fossils in climates opposite to what they would have lived.

• SO… He began to develop . . .

Plate Tectonics• Study of, the formation and movement of

rigid crustal plates across the surface of the Earth. (this movement driven by . . . )

• He never found out, died on trek to Greenland in 1930.

Later in the 1960s and 70s

Plate Tectonics Truly Developed

Scientists discoveredConvection currents – movement of partly

molten rock in the Asthenosphere, driven by, heated, rising material from mantle.

The currents put friction on overlying layers of crust & cause plates to move.

Plate Boundaries Divergent

Divergent BoundaryDivergent Boundary– where 2 plates are pulled

apart. In this picture 2 ocean crusts.• Here hot less dense magma rises up through the

asthenosphere toward surface, causing the convection currents, & undersea EQs

• MID-OCEAN RIDGE -string of undersea divergent boundaries where new ocean crust is formed.

• Called spreading centers & are associated with mountainous areas on ocean floor

Plate Boundaries Convergent

Plate Boundaries Convergent• Where 2 plates collide by moving together.• SUBDUCTION ZONE area where an ocean plate

dives or sinks under another ocean plate, or continental plate.

• Old crust is subducted and destroyed here.• Dives into the Asthenosphere, melts then rises and

circulates again.• Volcanic islands & trenches are the most common

landforms. EQ of all depths occurs.• This is 2 Ocean crusts.

Plate Boundaries Convergent

Plate Boundaries Convergent • This is an oceanic and continental plate

subduction zone. • The plates move toward each other. • Volcanoes & trenches are most common

landforms. • Magma is generated at all subduction zones where

dense oceanic plates are pushed under lighter continental plates, melted, and rises back up through the crust.

• Shallow, intermediate and deep EQ occur

Plate Boundaries Convergent

Plate Boundaries Convergent

• This convergent boundary is where 2 continental crusts collide.

• The rock layers are folded and bent forming mountains.

• The plates move toward each other.

• Mountains and Valleys are the common land forms

Plate Boundaries Transform

Plate Boundaries Transform• This boundary is a lateral boundary where two

plates slide past each other. • Earthquakes occur frequently at these

boundaries. • The plates can move in same direction but at

different rates. • Many rolling hills and shallow trenches are

common. • ANY TYPE OF CRUST can have be transform,

its most common on earth.

Causes of Plate Motion1. Convection – is why plates move,

grow, get subducted.– It is the transfer of heat energy from

inside (e) to surface. Hot less dense rock material rises while cool more dense rock material sinks.

Causes of Plate Motion• 2. This convection movement pulls

plates along breaking &bending them.– Causes magma to rise to surface at pulled

apart locations called ridges.

• 3. This makes new ocean crust.

• 4. At same time old crust is being subducted and melted at subduction zones.

Growth and Change Continents

• Two ways continents grow– Microplate Terranes

– Volcanic Eruptions

• Microplate Terranes- Section of crust formed elsewhere then scraped off ocean crust as plate gets subducted

  Each Terrane has 3 characteristics:– 1. Contains rock & fossils different from

surrounding rock.

– 2. 3 major faults at boundaries of terrane

– 3. Magnetic properties of terrane do not match surrounding areas.

• *California has 10 in the San Francisco Bay area

This Has Been A Mr. Whallen Production

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