Continental Drift

Chapter 10 Section 1

Continental Puzzle

• Do the continents fit together perfectly?• What continents fit the best?• What other information would you look for to

provide evidence that continents may have once been part of one large continent?

Alfred Wegener & Continental Drift

• 1912 proposed supercontinent–Pangaea–Continents separated and drifted apart

Evidence

• Coastline similarities• Fossils• Rock formations• Climates

Coastline Similarities

• Continents on either side of Atlantic ocean seem to fit together– Contours of eastern coast of South America fit along the contours of

the western coast of Africa

Coastline Similarities

Fossils

• Mesosaurus – reptile fossils found only in southern South America and western Africa

• Glossopteris – plant fossils found in South America, southern Africa, India, Australia, and Antarctica (Southern Hemisphere)

Mesosaurus Fossils

Fossil Evidence

Rock Formations

• Mountain ranges of eastern South America (Brazilian Highlands) and western Africa (Cape Mountains) are the same

• Mountain ranges in north eastern North America (Appalachian Mts.), Greenland, Scotland and northern Europe (Caledonian Mts.) are the same

Rock/Geologic Formation Evidence

Climates• Glacial evidence in South America, Antarctica,

India, Australia and Africa – When viewed separately, glacial evidence on these

continents suggests that the entire earth was covered with glaciers at one time, but this is contradicted by other evidence from sedimentary rocks

– When continents are placed together, like a puzzle, glacial evidence is not world-wide, which coincides with other evidence

• Tropical plant fossils in Antarctica– No plants currently grow in Antarctica, so plant fossils

found there indicate warmer temperatures at one time

Climate Evidence

Antarctica Fossils

Alfred Wegener and Continental Drift

• Despite the evidence that seemed to suggest Pangaea, Wegener’s continental drift hypothesis was rejected by the scientific community– If the continents were moving apart, why wasn’t the

Earth expanding?– Continents don’t plow through oceanic rock, so how

can they move?• There was no evidence for the mechanism of

tectonic plates or their movement

Evidence for the Theory of Plate Tectonics

• In the mid part of the 20th Century, discoveries were made as a result of Naval technologies that enables the mapping of the sea floor– Hitler had gotten very close to the U.S. in WWII,

via submarines (in the coastal waters of the eastern seaboard)

– U.S. raced to learn more about the ocean floor in order to develop better submarine capabilities

Mid-Ocean Ridges and Rift Valleys

• 1947 mapping project– sonic technology enabled the mapping of the sea

floor– Rift valleys and mid-ocean ridges were discovered

• Rift valley – a rip, or rift, in a tectonic plate at which volcanic activity is found

• Mid-ocean ridge – the mountain ranges found on either side of a rift valley, formed from magma building up on either side of a rift

Mid-Ocean Ridge/Sea-Floor Spreading

Mid-Atlantic Ridge

Features of Mid-Ocean Ridges

Paleomagnetism• Magnetometers developed during WWII to detect

submarine hulls also discovered that Earth’s rock record contains magnetic reversals– Normal magnetism and reverse magnetism alternates

in rocks during specific periods– Magnetic symmetry – magnetic bands (reverse and

normal) are mirror images on either side of mid-ocean ridges

• Suggests that magnetism of Earth changes – Metals in molten magma align with the magnetism at

the time of crystallization– Igneous rocks (basalt) retain the magnetic orientation

at time of formation

Paleomagnetism

Additional observations of Ocean Floors

• Ages of ocean floor features increase in age as distance from the ridge increases– Sediments are thinner and younger nearer ridge– Fossils are younger nearer ridge– Rocks are younger nearer ridge

• All this suggests that new oceanic crust is forming at the rift valleys

Tectonic Plate Boundaries

http://www.bing.com/videos/search?q=volcanoes+and+earth+quakes&FORM=HDRSC3#view=detail&mid=0F70E0C062BAAA8F5BCE0F70E0C062BAAA8F5BCE

Earth’s Active Volcanoes

“Ring of Fire”

• Area of high seismic and volcanic activity outlining the Pacific Ocean

“Ring of Fire”

Conservation of EnergyAccording to the law of conservation of energy, energy can’t be created nor destroyed.

•What is the source of energy that drives volcanoes?

•What energy source produces earthquakes?

Quick Review

Lithosphere

• Crust and upper portion of mantle

Lithosphere

• Broken into blocks called tectonic plates– Each plate may include continental crust,

oceanic crust, or both•Continental crust thicker and less dense than

oceanic crust

Lithosphere• About 15 major tectonic plates

Lithosphere

• Tectonic plates “float” on Asthenosphere – solid, putty-like (“plastic”) rock below lithosphere

• Asthenosphere flows very slowly

Asthenosphere

Tectonic Plates Interact

• The tectonic plates of Earth’s lithosphere form the pieces of a very tightly-fitting puzzle.

• Since plates move over the asthenosphere, they are bound to interact with each other

• Plates interact at their boundaries in 3 major ways

Types of tectonic plate boundaries

• Divergent Plate Boundaries• Convergent Plate Boundaries• Transform Plate Boundaries

Types of tectonic plate boundaries

Divergent Plate Boundaries

• http://www.youtube.com/watch?v=2q4Yqctq6nE

Divergent Plate Boundaries

Boundary between tectonic plates that are diverging (moving apart)•Common features– Mid-ocean ridges– Rift valleys– Seafloor spreading– Volcanic activity– Seismic activity

Divergent Boundary

Examples

1. Mid-Atlantic Ridge2. Red Sea – separation of African and

Arabian plates

Transform plate boundary

• Boundary between plates that slide past each other

• Common features– Earthquakes– Faults– Example: San Andreas Fault

– Offset surface features

Types of Plate Boundaries

Transform Fault Boundary

Offset Surface Features

Offset Surface Features

Fault

Fault and Offset Features

Convergent plate boundary

• Boundary between tectonic plates that are converging

• Three types of collisions1. Oceanic-continental collision2. Oceanic-oceanic collisions 3. Continental–continental collisions

Oceanic-Continental Collisions

•Continental crust collides with oceanic crust•Oceanic crust subducts – dives

beneath the continental crust

Oceanic-Continental Collisions

•Common featuresa) Subduction zones – areas where one

tectonic plate dives beneath another tectonic plate

b) Oceanic trenches – area in the ocean where oceanic plate subducts

– deepest points in Earth’s oceans– Peru-Chile Trench

Oceanic-Continental Collisions, continued

•Common featuresc) Volcanic activityd) Mountain building – volcanic mountain

ranges such as Rocky Mountains– Oceanic plate re-melts and rises to the

surface inland from the boundary, creating mountains

e) Earthquakes

lithosphere

Volcanicmountains

Subduction zone

Ocean trenchOceanic crust

asthenosphere

Continental crust

Oceanic-oceanic collisions

• One plate subducts• Common features– Subduction zones– Oceanic trenches – Mariana Trench (Challenger

Deep – deepest point in the Earth’s ocean)– Volcanic activity– Island arcs – Japan, Aleutian Islands, Mariana

Islands (volcanic mountains)– Earthquakes

Lithosphere

Subduction zone

Oceanic crustOcean trench

Volcanic island arc

Volcano Continental crust

Asthenosphere

Continental-Continental Collisions

• Neither plate subducts• Common features– Mountain building – Uplifted mountain ranges – Himalayan

Mountains– Earthquakes

Continental crust

Uplifted mountain range

Lithosphere

4Asthenosphere

Himalayan Mountains