Continental Drift
How many continents are there?
7- North America, South America, Africa,
Europe, Asia, Australia, Antarctica
Have the continents always looks
like this?
Were the continents always located
in the same position?
http://www.youtube.com/
watch?v=WaUk94AdXPA
&feature=related
Puzzle Activity
• Cut the continents apart (do not cut the dots
off!)
• Try to reassemble the puzzle using the key.
• What clues did you use to help you put it
back together correctly?
A continental puzzle
Discovering Earth’s Past
• Using your textbook (pages 98-104)
complete the worksheet on continental drift
and seafloor spreading.
• Worksheet is due Tuesday
Continental Drift
• Who?
– Alfred Wegener
(German
meteorologist)
• When?
– 1912
• He noticed the
puzzle-like fit of the
continents
http://maps.google.com
• He proposed that the continents were joined
together in the past, in a large land mass called
Pangaea.
Describe it
• Over time, the continents drifted (moved) apart
– Wegener named his theory “Continental Drift”.
He supported his theory with four
pieces of evidence.
1. Animal Fossil Clues
• Matching fossils of animals on once connected
land areas.
2. Plant Fossil Clues
Fossils of the plant Glossopteris are found in rocks
in South Africa, India, Australia, South America,
and Antarctica
•
3. Climate Clues
Glacial evidence in Africa, South America,
Australia
• Fossils found in Antarctic soil indicate that the now frigid
continent was once lush with trees and ferns, and home to
dinosaurs, amphibians, and later, marsupials.
4. Rock Clues - similarities and ages
Mountains in South America and Antarctica are
believed to have formed as part of the same
mountain chain.
Wegener’s theory made sense, but no one
wanted to accept it until they knew HOW the
continents moved.
Years later someone came up with an
explanation of HOW the continents
moved
Seafloor Spreading
• Who?
– Harry Hess (A Princeton
University scientist)
• When?
– 1960’s
Using new technology, they looked
at the ocean floor
• Hess and other
scientists mapped the
ocean floor using
sonar
• They detected
underwater mountain
ranges
• Further examination of
the ocean floor with a
submarine showed
underwater volcanoes.
• A variety of life living
near the warm vents
of the volcanoes was
found
• Sampling the rocks near the volcanoes
revealed that there was a pattern to their
formation.
Describe Seafloor Spreading
• Magma in the mantle rises and pushes the
plates apart, forming new oceanic crust.
http://www.absorblearning.com/media/item.action?quick=12n
http://education.sdsc.edu/optiputer/flash/seafloorspread.htm
Now we could explain HOW the continents moved:
Seafloor Spreading causes
Continental Drift
He supported his theory with two
pieces of evidence.
1. Rock ages
Youngest rocks are found at the mid-ocean ridges
and they become increasingly older farther from the
edges.
2. Magnetic Clues
• Magnetic iron particles
record the time of the rock
formation.
• When the magnetic north
pole switched places, iron
in the rocks recorded this
information
http://labspace.open.ac.uk/file.php/4462/S279_b1_c3_f37.swf?d=590x40
5
http://www.absorblearning.com/media/attachment.action?quick=12w&at
t=2789
A map of the ocean floor provides
even more evidence
http://maps.google.com/
Iceland shows seafloor spreading
above the water, which makes it
easier to study
Plate Tectonic Theory
• Theory of Plate Tectonics -Earth’s crust is
broken into plates which float and move.
Earth’s crust made of many plates is
similar to the shapes on a outside of
a soccer ball.
There are about 13 plates covering
Earth’s surface
Two Types of Plates
• Continental Plates – lighter, thicker, made of
granite
• Oceanic Plates – heavier, thinner, made of
basalt
Plate Boundaries (edges)
When the plates move, their
boundaries, or edges, can scrape each
other or collide.
Convergent or Destructive
Boundary
• Plates move toward each other
Convergent or Destructive
Boundary
• When two continental plates move into each
other, the plates combine and form
mountains. (India into Asia)
http://www.absorblearning.c
om/media/attachment.action
?quick=12t&att=2783
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1105/es1105page01.cfm?chapter_no=visualization
Convergent or Destructive
Boundary
• When an oceanic plate runs into a continental
plate, the heavier oceanic plate subducts
(sinks) into the mantle and melts back into
magma.
• Volcanic mountains and deep sea trenches are
created along this edge.
http://www.
absorblearn
ing.com/me
dia/attachm
ent.action?
quick=12s
&att=2781
Oceanic plate into continental
• Example: Pacific plate (oceanic) subducts
(sinks) under Japan (continental).
http://maps.google.com/
Divergent or Constructive
Boundary
• Plates move apart
When both diverging plates are oceanic,
it is called seafloor spreading
(Mid-Atlantic Ridge)
When both diverging plates are
continental it is called rift valley
formation (Africa)
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0072402466/30425/19_21.swf::Fig.%2019.21%
20-%20Evolution%20of%20a%20Divergent%20Plate%20Boundary
Transform Boundary
• Plates slide past each other
San Andreas Fault
San Andreas Fault, CA
• Each time the plates slide past each other,
an earthquake occurs
Find the three boundaries
http://www.pbs.org/wgbh/aso/tryit/tectonics/shockwave.html
Asthenosphere
• A plastic-like layer found below the lithosphere.
• The rigid oceanic and continental plates of the
lithosphere sit on top
The Asthenosphere is heated by the
hot Outer Core
Convection Current
crust
mantle
core
• Hot material rises, cooler material sinks,
creating a current, called a Convection
Current
When the asthenosphere moves, it carries the
lithospheric plates
Convection currents cause plate motion
http://www.youtube.com/watch?v=ryrXAGY1dmE
http://www.absorblearning.com/media/attachment.action?quick=12p&att=2775
Every time these plates move we get
earthquakes, volcanic eruptions, and
possibly tsunamis