Continental Drift & Seafloor Spreading

Honors Marine Science

Chapter 3

Continental Drift: What is it? Idea that all the continents were once

joined together. Who came up with the idea?

Alfred Wegener

Was he the 1st to think of this? No

Why did they come up with this idea?

Pangaea Theory of Continental Drift Maps- “puzzle pieces” could make

Super-continent Wegener called it Pangaea Ocean called Panthalassa He thought it might have taken 200 million years

for the continents to split and drift apart to today’s position

Animation

Is there Evidence? Maps available in 1600’s pretty accurate 1855 Edward Suess of Germany found

fossils of Glossopteris (ancient fern) South America Africa Australia India Antarctica

How did they get there? Too heavy to travel w/wind, Too fragile to survive sea voyage

Is there more? Critters too !!! Animal fossils found on opposite continents

Ocean too far for ocean travel

Today we also look to Biogeography Like species living on separate continents, but

adaptations have changed do to environmental conditions

Still more? Coal 1908, Ernest Shackleton discovered coal in

Antarctica. How is coal formed? Antarctica MUST have moved

Coal formed from vegetation being buried in warm, swampy climates faster than it could decompose

What is the temperature like in Antarctica today?

Evidences: 3 Jigsaw puzzle Fossil remains (both plant and animal) Coal found in Antarctica

Wegener’s Flaw No mechanism for the drift

Wegener’s theory did not include a strong enough account for how the continents could move

He suggested Earth’s rotation & tides moved them Calculations would prove otherwise

No credibility He was a meteorologist, not a geologist

Jigsaw puzzle theory had gaps He died B-4 theory was accepted

Disappeared in 1930 in Greenland

Lab “Dance of the Continents”

Read as a class Work in pairs Turn in when complete

Theory of Seafloor Spreading

Chapter 3

Meteor- German expedition Mid-Ocean Ridges

Mountain ridges on bottom of ocean

Rift Valleys Deep valleys running through mid-ocean ridges

Trenches Ravines in seafloor

Patterns were revealed……….

Hess and Deitz- 1960 SFS Seafloor is constant state of creation and

destruction New crust emerges at the mid-ocean ridges

Magma pushes up through rift and solidifies into new crust

New sea floor forms at the ridges, and is then subducted at the trenches (goes back into the rock cycle)

What are the evidences? If this is true, where would you find older

rock; trenches or ridges? Radiometric dating Older is farther away from ridges- trenches

If this is true, where is the more dense rock? Newer rock will have less deposits on it- more

dense, more layers, older rock is at the trenches

If this is true, magnetism should be symmetrical Huh?

Plate Tectonics combines Continental Drift and Seafloor Spreading P.T. state that Earth has over 12 plates that float

on top of the Asthenosphere 2 different types of plates

Oceanic; more dense Continental; less dense

These plates interact in 3 different ways: Divergent Boundaries- Convergent Boundaries- Transform Faults-

Marianna’s Trench

So what happens? Divergent boundaries- Plates move away

from one another- Constructive Boundaries Ridges, valleys, new seafloor; much activity here

Mtns can form higher than sea level Iceland

Transform (fault) boundaries- Plates slide past each other- Earthquakes prevalent San Andreas Fault in Ca; Pacific/N. American

Plates

Divergent Boundary- Constructive

Transform Fault/Boundary

Cntd Convergent Boundary Convergent boundary- 2 plates meet; collisions-

Destructive Boundaries Type 1: 2 ocean plates; 1 subducts under the other

Island arcs result Japan, Aleutian Islands

Type 2: Ocean and continental: more dense oceanic subducts under less dense continental

Subduction occurs in trenches Range of vocanic mtns: Benioff’s Ring of Fire, Andes Mtns,

Cascades (Mt St Helens) Type 3: 2 continental plates: equal densities push mass

together and up Himalayans

2 Oceanic Plates

Oceanic meets Continental

Continental meets Continental

Plate Movement What is the mechanism behind continental drift? Convection!-

Warm air rises, then falls as it cools, rises at it warms, etc. etc.

Convection currents exist w/in mantle; moves plates away from each other at divergent boundaries, towards each other at convergent boundaries, past each other at transform boundaries

Second mechanism is seafloor spreading- plates slide away from ridges

Animation

Hot Spots? Activity: Grab a Text; w/partner (no more than 2) How did volcanoes arise away from plate

boundaries? Why are the Hawaiian Islands not 1 continuous land mass?

White board The creation of the Hawaiian Islands List the names of Earth as it progresses through time,

along with dates and define the differences of each.

Lab Day: Computer Time Type the websites listed on the lab sheets Answer the questions Continue until lab is complete

Wrap it Up!!Continental Drift to Plate Tectonics Video

Study Guide Tomorrow

Video ClipDance of the Plates Lab