Download plate tectonics - mfischerscience

PLATE TECTONICS
or: Why Earth Farts
CHAPTERS 1 & 17
How old is
the Earth?
• Recall that Earth is 4.6 billion
years old.
• Earth has changed a lot in
that time.
• http://www.wwnorton.com/college/
geo/egeo/flash/2_1.swf
What is
continental
drift?
• Earth’s continents had once
been joined in a single
landmass.
• The continents drifted to their
present locations.
• http://www.wwnorton.com/college/
geo/egeo/flash/2_1.swf
What is the • Early observations of drifting
evidence for
continents
• Starting in the 1500’s, people
continental
noticed that the continents had
drift?
matching coastlines.
• Alfred Wegener came up with the
first real theory of continental drift
in 1912. He proposed:
• The idea of Pangaea, a single
landmass.
• That the continents began to split
apart 200 million years ago
(MYA).
• That continents slowly moved to
their present positions.
• Rock formations
• Rocks from far apart lands are
made of similar material and are
similar ages.
• This is because mountains and
other rock formations split apart.
• Ex. Similar rocks in the
Appalachian Mountains in the U.S.
and in Greenland & Europe.
• Fossils
• Fossils from related plants &
animals were found far apart.
• This is because animals living on
joined land masses died, and their
fossils spread apart over time.
• These animals could NOT have
swam such long distances.
• Ex. Kannemeyerid,
Labyrinthodont, & Glossopteris
• Climatic patterns
• Coal deposits were found in
Antarctica.
• Coal forms in ancient swamps,
and Antarctica used to be nearer
to the equator, which made it a
swampy habitat.
• Glacial deposits were found in
Africa, India, Australia, & South
America.
• This is because these continents
used to be closer to the poles.
• There are no present glaciers
there.
What is sea
floor
spreading?
• Seafloor spreading is the idea
that new ocean crust is
formed at ocean ridges and
destroyed at deep-sea
trenches.
• This involves continuous
movement of magma, like a
conveyer belt.
What is the • Underwater topography
• Sonar showed that the sea floor is
evidence for
not flat.
seafloor
• Underwater mountain ranges and
spreading?
deep-sea trenches were
discovered and were made
through seafloor spreading.
• Earthquakes and volcanoes occur
there.
• Ocean rocks & sediments
• Rocks on the sea floor are NOT all
the same age.
• Rocks near ridges were younger
because new magma formed
them.
• Rocks near trenches were older
because they were pushed away
from ridges and toward trenches.
• Sediments on the sea floor are not
as thick as expected.
• Sediments get thicker as they get
farther away from ridges because
they accumulate over time.
• Paleomagnetism: study of the
earth’s magnetic record
• Iron is in basalt, the rock that
makes oceanic crust.
• Iron orients parallel to earth’s
magnetic field as it cools.
• So, the seafloor shows a record of
magnetic reversals.
• A magnetic reversal is a change
in Earth’s magnetic field.
• There are parallel stripes of
magnetic material on either side of
a ridge.
• This shows that new rock was
coming from the ridges.
What is the
theory of
plate
tectonics?
• Plate tectonics is the theory
that Earth’s crust and upper
mantle (lithosphere) are
broken into moving plates.
• There are 12 major plates and
several smaller ones.
• Plate boundaries are the
places where tectonic plates
meet.
What are the • Divergent boundaries
• Two plates are moving APART
types of
• New crust forms there
plate
• Most form ridges on the sea floor
boundaries?
• On continents they form rift valleys
Rift Valley in Africa
Mid Ocean Ridge in the Atlantic Ocean
• Convergent boundaries
• Two plates are coming
TOGETHER
• Old crust is destroyed there at a
subduction zone
• Can be classified as:
• Oceanic-oceanic: form trenches
& island arcs
• Oceanic-continental: form
trenches & volcanic mountains
• Continental-continental: form
folded mountains
• Oceanic crust sinks below
continental crust because it is
more dense.
Aleutian Islands
Marianas Trench
Cascade Mountain Range & Mt. Saint Helens in
Washington State
Himalayas
• Transform boundaries
• Two plates SLIDE PAST each
other
• Crust is deformed there
• These boundaries form faults
San Andreas Fault
in California
What
causes
plate
tectonics?
• The mantle is made of
magma, which is mostly liquid.
• Plate tectonics is caused by
mantle convection.
• Hot magma moves up, and when
it cools it moves down.
• This is because hot magma is less
dense (floats) and cool magma is
more dense (sinks).
• This creates currents.
• The currents cause the plates
on top to move.
http://education.sdsc.edu/optipu
ter/flash/convection.htm