Transcript Continental Drift Notes

Earth Shaping
Chapter 16
Earth Shaping Theory
 It
was a gradual change over time.
 In early 1900’s Alfred Wegener proposed the
theory of continental drift.
 Scientist DID NOT support his theory
because at that time he could not explain his
theory.
Current Continental Drift
Theory
The
earth is constantly changing. In
addition to the effects of weathering
and erosion, there are much larger
scale changes occurring due to the
movement of large plates in the
lithosphere.
HOW DO WE KNOW
THIS?

Wegener developed his idea based upon 4 different
types of evidence:

1. Fit of the Continents

2. Fossil Evidence

3. Rock Type and Structural Similarities

4. Paleoclimatic Evidence
Earth’s
Layers
Inner Core - made of iron
Outer Core–molten(liquid)
Mantle – most of Earth’s mass
Crust- rocky and brittle, can fracture
How do we know?
 Measuring
seismic waves
 The
speed of the wave determines the type
of rock it is traveling through
 Do
waves travel faster in solids or liquids?

TWO TYPES OF CRUSTS:

Oceanic – thin, dense rock

Continental- thick, low density
LITHOSPHEREOuter part of the
crust; divided into
tectonic plates
ASTHENOSPHEREthe tectonic
plates are on the
asthenosphere
Plate Movement
 Continental
Drift – the movement of the
tectonic plates
Theory




that continents drift apart
*Proposed by Alfred Wegner
*Fossil evidence
Sea Floor Spreading
 Magma
Rises in mid –ocean ridges or cracks
called fissures
 1. Forms new crust
 2. Moves horizontally
 3. Older crust moves further out
Magnetic Reversals

Earth’s north and south
magnetic poles change
places

Can be seen in the
oceanic crust

Magnetic minerals align
with magnetic field
Supercontinent

Pangea – all of the
continents were
joined together

Gradually drifted
apart over time.
Plate Tectonic Theory
3 Possible Forces
Ridge
Push
Convection
Slab pull/Subduction
Ridge Push –
gravity
causes
oceanic crust
(lithosphere) to
sink, subsidence
Convection
Hot rock rises while
cool rock sinks
 Causes the
lithosphere to move
sideways

Slab Pull
Subduction
Zone- when
oceanic lithosphere (crust)
is more dense causing the
edge to sink and pull the
rest of the plate with it
7 Tectonic Plates

African, North American, South American, Eurasian, Australian,
Antarctic, and Pacific plates. Several minor plates also exist,
including the Arabian, Nazca, and Philippines plates.
MOVEMENT:
*Different
directions &
speeds
*2-10cm per year
(the speed your
fingernails grow)
Plate Boundries

Convergent – come together

Divergent – pull apart

Transform – slide past each other
Review
convection
Magma moves in _______
 currents due to change in
temperatures.


 When
rock layers come together it is a
________
convergent

boundary.
 When
they pull apart it is a
 _________ boundary.
divergent
 boundary.
Tectonic
plates are large pieces of
___________lithosphere
A rock
is made of 2 or more
____________
minerals
What rock type is at 1?
What rock type is at 2?
What rock type is at 3?
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