Transcript File - Down To Earth Science

Drifting Continents
Did Pangaea Exist?
The Theory of Continental Drift
 A German scientist named
Alfred Wegener formed
the hypothesis that the
continents had moved!
 He proposed that all the
continents had once been
joined together in a single
landmass and have since
drifted apart.
The Theory of Continental Drift
 Wegener’s idea that
the continents slowly
moved over the earth
became known as
continental drift.
 Unfortunately Wegener
could not provide a
satisfactory explanation
for the force that
pushed or pull the
continents. Therefore
most geologists
rejected his idea.
Evidence of Continental Drift
 Evidence from
landforms:
 Mountain ranges and
other features on the
continents provided
evidence for
continental drift.
 Mountain ranges in
South Africa line up
with mountain ranges
in Argentina (South
America).
Evidence for Continental Drift
 Evidence from fossils
 A fossil is any trace of
an ancient organism
that has been
preserved in rock.
 Glossopteris fossils
have been found in
rocks in Africa, South
America, Australia,
India, and Antarctica.
Evidence for Continental Drift
 Evidence from climate
 Fossils of tropical
plants have been
found too far north or
south to have survived.
 Glacier deposits are
found too close to the
equator.
 These clues provide
evidence that
continental drift really
happened.
Rejection!!
Even with the evidence, most
scientists rejected Alfred Wegener’s
theory for about a half a century, from
the 1920s to the 1960s.
Let’s See What Wegner Thought
Really Happened!
 http://www.suu.edu/faculty/colberg/Hazard
s/PlateTectonics/18_Pangaea.html
 http://www.exploratorium.edu/origins/antar
ctica/ideas/gondwana2.html
 Energy is constantly
on the move!
 The movement of
energy from warmer
object to a cooler
object is called a heat
transfer
 There are three types
of heat transfer:
radiation, conduction,
and convection.
Radiation
 Radiation is the
transfer of energy
through empty space.
 Heat transfer by
radiation takes place
with no direct contact
between a heat
source and an object.
Conduction
 Heat transfer by direct
contact of particles is
called conduction.
 When your hands
touches a metal spoon
sitting in a boiling pot of
soup, the heat from the
bottom of the pot is
transferred to your
hand by conduction.
Conduction
Convection
 Convection is the
transfer of heat by
the movement of a
heated fluid.
 Convection deals
with density.
 Density is the
measure of how
much mass is there
in a certain volume of
a substance.
Convection
 When a liquid or gas
is heated, the
particles move faster
and the density
decreases.
 As the fluid becomes
cooler, its density
increases.
 As density increases,
the fluid sinks.
 Heat Rises!!
Convection
 The heating and cooling of
the fluid, changes in the
fluid’s density, and the
force of gravity combine to
set convection currents in
motion.
 Without heat, convection
currents will eventually
come to a stop.
Convection Currents in the Mantle
 The heat
source for
these
convection
currents in the
mantle comes
from the heat
of the Earth’s
core.
Convection in the Earth’s Mantle
 The crust “floats” on the
mantle, just like
Cheerios float on the
surface of milk. The
convection currents in
Earth’s mantle cause the
crust to move ever so
slightly, therefore,
allowing continents to
drift.
Plate Tectonics
 Based on the knowledge that the lithospheric
plates float on the asthenosphere, the theory
of plate tectonics was developed.
Radiation, Conduction, and
Convection