Download compleate chap 10 lecture

Chapter 10
Continental drift- from
controversial hypothesis
to respectable theory.
When conducting a scientific
investigation there are two key
questions that need to be asked-
 What’s
happening?
 What causes this to happen?
To answer this first question
what must the investigator do?
 Look
for patterns.
There are several observed patterns that led
to the theory of continental drift which
include:
Jigsaw-puzzle fit of continents.
 Remarkable similarity of rocks and rock
assemblages on opposite sides of the
Atlantic.
 Remarkable similarity of geologic
structures on the outer continental
margins.
 Similarities of fossils on opposite sides of
the Atlantic.

Jigsaw-puzzle fit of continents.
Jigsaw-puzzle fit of
continents.
 Observable
jigsaw-puzzle fit of the
coasts on both sides of the Atlantic
look as if the Americas, Europe, and
Africa were at one time assembled
together.
 Parallelism of facing shores of the
Atlantic first noticed by Sir Francis
Bacon-an English philosopher-
Remarkable similarity of rocks and
rock assemblages.
Remarkable similarity of rocks
and rock assemblages.
Geographic match up of ancient
crystalline rocks in adjacent regions of
South America, Africa, North America
and Europe discovered.
 Rock units of these adjacent areas were
the same age.
 Rock assemblages of adjacent coastlines
parallel each other.

Remarkable similarity of geologic
structures.
Remarkable similarity of geologic
structures.



distribution of Permian glacier deposits found in
South America, Africa, India, Antarctica and
Australia.Difficult to explain in terms of separate
glaciers- some close to the equator.
A single continental glacier could account for all
these glacier deposits.
Mountain chains that ended at the coastline of
one continent and seemed to continue on the
edge of another continent’s coastline across the
ocean (e.g. Appalachians match up with
mountains in Greenland and northern Europe).
Similarities of fossils on opposite sides of
the Atlantic.
Similarities of fossils on
opposite sides of the Atlantic.
 Fossils
of the late freshwater
Paleozoic reptile Mesosaurus were
found in South America and Africa
and nowhere else in the world.
How could this reptile be found on
opposite ends of the Atlantic?
What is the second question that is
asked during a scientific investigation?
 What
causes these patterns to
happen?
In 1912 a German meteorologist - Alfred
Wegener set out to explain the event that
led to these patterns.
His explanation was a geologic event
known as continental drift.
 Wegener
suggested that
all continents
were once one.
This giant super continent was
called Pangaea (Greek for all lands)*
http://www.uky.edu/ArtsSciences/Geology/webdogs/plates/rec
onstructions.html
Pangaea broke into two parts
 Laurasia
 broke
to the
north
 Gondwanaland
 broke
south
to the
This theory of continental drift
was ignored by most of the
scientific community at this time.
The reason was a plausible
driving force that could split up
Pangaea could not be found.
Plate Tectonics
Chapter 4 Section 2
Plate Tectonics

The study of the movement of the earth’s
surface
Earth structure
Outer Layers
Plate Tectonic Theory


Earth is made up of as many as 30 lithospheric
plates with 7 or 8 major plates which move
slowly on top of the mantle.
There are two types of plates, oceanic and
continental.
lithosphere


from the Greek, lithos, stone
the rigid outermost layer made of crust and
uppermost mantle
asthenosphere


from the Greek, asthenos, devoid of force
the part of the mantle that flows like putty when
put under pressure
Plate Boundaries
Tectonic Plates
2 Types of Crust


1. Ocean Crust
2. Continental Crust
2 Types of Crust
Ocean Crust
Thin
 Dense
 Young


Common rock- Basalt
2 Types of Crust
Continental Crust
Thick
 Not Dense
 Old


Common rock- Granite
Three types of
PLATE BOUNDARIES

Divergent plate boundary
Thingvellir fissure
A
fissure zone (in
shadow) that is
the on-land
exposure of the
Mid-Atlantic
Ridge.
Divergent plate boundaries
(spreading)
 Mid


Mid-Atlantic ridge
Juan De Fuca ridge
 Rift

ocean ridge
valley
Red Sea
nd
2
boundary type
Convergent plate boundary, where one plate
collides with another, of which there are three
possibilities
Convergent plate boundaries
(colliding)

oceanic to oceanic collisions


result in chains of volcanic islands/forms trenches
Aleutian Islands
Convergent plate boundaries
(colliding)
 oceanic
to
continental
 results
in volcanic
mountains; oceanic
plate slides under
Convergent plate boundaries
(colliding)
 Andes
Range
Mountain
Convergent plate boundaries
(colliding)
 continent
to
continent
 collision
results in
nonvolcanic
mountains
 Himalayas
rd
3
type of boundary
Transform plate boundary
Transform plate boundaries
(shearing)
 results
in a lateral
fault
 San Andreas
Francois Gohier
Causes of Plate Motion
 Convection,
the
transfer of heat
through the
movement of
heated material
(think of boiling
water).
Density Changes With
Temperature
Higher temperature =
less dense (rises).
 Lower temperature =
more dense (falls).
 This cycle is called a
convection current.

Mantle Convection

Convection currents in the
mantle rise beneath oceanic
ridges, spread laterally
carrying plates along, and
then decend at subduction
zones where oceanic plates
dive into the mantle.
Continents, being less
dense, are not subducted.
Evidence for this is shown
by higher heat flows
measured at oceanic ridges.
Suspect Terranes

Terranes are pieces of
lithosphere, each with
its own distinct
geologic history. We
think that continents
are formed, and grow
over time, by the
addition of terranes.
Moved by Seafloor Spreading
 Blocks
of
terranes are
then added to
continents
where
subduction is
occurring.
Western North America
 Much
of the
continent is a
patchwork of
terranes.
The End