Drifting Continents
Did Pangea 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.
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 south to
have survived.
 Glacier deposits are
found too far north to
have existed.
 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.
Convection Currents in the Mantle
 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 you 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 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 in the Earth’s Mantle
 The heat
source for
these
convection
currents in the
mantle comes
from the heat
of the Earth’s
core.
Radiation, Conduction, and
Convection
Now for Something Completely
Different! AND
CREEPY!
Source: http://cdn.ebaumsworld.com/picture/gionet2454/SeaCreature1.jpg;
(2007) Discovery Education.com, Steve Dembo.