Alfred Wegener
1912
Proposed idea (hypothesis)
of “CONTINENTAL
DRIFT”
Evidence for Wegener’s Idea
Continents fit together like puzzle pieces
Evidence for Wegener’s Idea
Continents fit together like puzzle pieces
Fossils found on different continents were
identical…separated by thousands of
miles…how’dey do dat?
This is a freshwater reptile called a Mesosaurus.
Look at the distribution of fossils….hmmmm
Wegener compiled information about fossil discoveries from around the
world. He felt this evidence was compelling.
Assorted Fossil Evidence
Evidence for Wegener’s Idea
Continents fit together like puzzle pieces
Fossils found on different continents were
identical…separated by thousands of
miles…how’dey do dat?
Dey ustabe neighbors
Evidence for Wegener’s Idea
Continents fit together like puzzle pieces
Fossils found on different continents were
identical…separated by thousands of
miles
Evidence from Glaciers: Marks in
bedrock left behind by glaciers located on
AFRICA, SOUTH AMERICA, INDIA, and
AUSTRAILIA indicate that portions of
these continents must have been
CONNECTED in polar regions far from
their present positions.
Marks from ice
movement
striations
Evidence for Wegener’s Idea
Rock types on the east coast of North
America MATCH EXACTLY the rocks in
the British Isles, Scandinavia, and Africa
Continental Drift Hypothesis
The continents were all connected at one
time
Supercontinent was called Pangaea
Pangaea broke apart up into two
continents call Laurasia and
Gondwanaland
Continents are still moving today
No one believed Wegener…..
…because he could not explain what
hidden mechanism might be
responsible for the movement of an
entire continent!!!
1930
Wegener leaves for Greenland
to seek more evidence to test
his hypothesis.
He is never seen again. Some
speculate that he ate his own
dogs before he froze to death.
The last photo him…
Yummy
His hypothesis is “hotly”
debated for the next 30 years
Cut and Paste Playtime
Plate Tectonics
A.K.A.
“What Wegener Wished He Knew”
(animations from USGS)
Current Scientific Theory
“Plate Tectonics”
1. The Earth’s crust is composed of about
22 plates
2. The plates are rigid and may contain
CONTINENTAL or OCEANIC crust, or
BOTH
3. CONTINENTAL CRUST is mostly Granite
4. OCEANIC CRUST is mostly Basalt
What Makes the Plates Move?
This question drove Wegener mad!
1. The plates move due to the transfer of
HEAT energy from the Earth’s core
2. Heat leftover from Earth’s formation and
produced by radioactive decay creates
DENSITY differences in the mantle
3. This causes the “plastic” mantle to flow.
4. The flow of mantle material pulls on the
lithosphere above it…like a leaf on a
stream
How do density differences
cause fluids to move?
Watch THIS!
Complete the Demo Analysis
Sheet
The THEORY of Plate Tectonics
Evidence:
Convection currents in the mantle move
the plates around…and have been doing
so for more than 4 billion years (1:10)
Convection cell movement causes plates
to collide, rip apart, and plunge back into
the mantle
This current model (A) predicts
that convection cells are
limited to the outermost plastic
mantle.
This current model (B) predicts
that convection cells extend
through the mantle toward the
Lehmann discontinuity.
We’re not sure
Don’t you
just LOVE
which
model
is the
uncertainty of Science?
correct.
Work hard like INGE, and maybe, someday,
you’ll be the first to figure it out…and have a
convection cell named after YOU…that is, if
they truly exist!
Which model has the New York
State Ed Dept selected for you?
Evidence for Plate
Tectonics
1. Location of earthquakes
and volcanoes
Map of earthquake foci for the last 30 days
Pacific Ocean Floor:
Evidence for plate
tectonics
1. Location of earthquakes
and volcanoes
So, how would you characterize
the distribution of earthquakes and
volcanoes around the world?
Random?
Patterned? Isolated?
Evidence for plate
tectonics
1. Location of earthquakes
and volcanoes
The distribution of earthquakes
and volcanoes is not random.
They occur TOGETHER in narrow
bands under the oceans and along
the edges of some continents.
Evidence for plate
tectonics
…turns out…these locations
are the edges of plates
called “Plate Boundaries”
The Plates…IN COLOR
Evidence cont’d
2. Age of seafloor
Oceanic igneous rock is much
younger than continental igrox
Oceanic rock gets younger as you
approach the mid-ocean ridge
(mountain range which runs through
all world’s oceans)
Map showing
Ages of
oceanic crust
Reading Passage
Please open your review book to page 80
and read the passage titled “Evidence
from the Oceans”
Magnetic pattern in rocks
– Earth’s magnetic pole reverses
– Magnetic crystals line up with earth’s poles
when the magma hardens
– Patterns in ocean rocks show parallel strips
on either side of the ridge that match in width,
age, distance from the ridge, and magnetic
polarity
What pulls the lithosphere apart?
Types of Plate Boundaries
Divergent / Rift
Convergent/ Subduction
Transform
Divergent/ Rift
Plates move apart from one
another
New basaltic crust is formed
Mid-ocean ridge: volcanic
mountain range which circles
the earth beneath the oceans
Mid-ocean ridge
Volcanic eruption in Iceland.
March 21, 2010
Rift valley
Black
Smoker,
East Pacific
Rise
Marie Tharp & Bruce Heezen used echo soundings to build up a
picture of the ocean floor
Continent
Mid-ocean
ridge
Continent
Sea mount
Central rift zone
trench
Mid-ocean ridge
seamounts
Convergent Boundary
Plates collide
Continental/ oceanic crust
Oceanic/ oceanic crust
Continental/ continental
crust
Mountains grow: Volcanoes, or
continental ranges
Ocean- Continent collision with subduction
Ocean- Continent collision with subduction
Andes Mountains
Ocean-ocean collision with subduction
Ocean-ocean collision with subduction
Hugo Benioff suggested that this Earthquake pattern shows a plate
subducting (sinking) into the mantle (1940s discovery)
Continent-continent collision (Subduction has ended)
Continent-continent collision (Subduction has ended)
1963 Tuzo Wilson
Developed the hypothesis of hot spots to explain islands like Hawaii
& a third kind of plate boundary called a transform plate boundary
Transform Boundary
Plates slide past one another
–Ex. San Andreas fault
Crust is neither created nor
destroyed
Hot Spots
Places where magma
reaches earth’s
surface
Typically not
associated with plate
boundary
As plate moves over
hot spot, island
chains form
Example: Hawaii
So by the mid-60’s all the evidence came together to form the
Theory of Plate tectonics
This theory states that the Earth crust is broken into a series of
plates which are constantly on the move.
Convection
computer model.
The most current
understanding.