Download Plate Motion and Convection Currents

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Experiential Science 10—Terrestrial Systems
The Franklin and Mackenzie mountains in the NWT are part of the continuous chain of mountains extending through the western
part of North and South America. These mountains formed when island chains and small continents collided with the ancient
North American plate about 185 million years ago and again about 100 million years ago.
Plate Motion
and Convection Currents
The Earth’s lithosphere (the crust and the outer
layer of the mantle) is thin, cool, and strong
compared to the molten layer of the asthenosphere below it. Inside the asthenosphere,
magma is slowly heated by the Earth’s hot core
or by radioactive decay. As it is heated, the asthenosphere rises up away from the Earth’s core.
When it nears the lithosphere it flows sideways,
becomes heavier, and sinks again. This change
in movement creates swirling currents of heat in
the asthenosphere called convection currents.
Scientists know that convection currents in
the Earth are at least partially responsible for the
movement of plates, but there is still much to
find out about how the plates move and how convection
currents work. For example, it is known that sometimes
heat from the molten asthenosphere does not move
evenly in convection currents but comes to the surface
as gushes of hot material that melts through the middle
of plates, rather than escaping out from the edges. These
are called mantle plumes. The plume melts the plate
like a blowtorch, and a volcano forms above it. As the
The Hawaiian Islands are an example of a chain of volcanic
islands produced by plumes of molten material erupting from
the asthenosphere.
SCIENTIFIC TERMS
convection current: a current caused by the difference in
temperature from the bottom to the top of the Earth’s mantle,
which in turn causes plate movements.
Chapter 1 Geologic Time and Earth Dynamics67
plate slowly moves, the plume
melts through another part of
the plate, producing a chain of
volcanic islands. This is called a
hot spot. Hawaii is an example of
a chain of islands caused by hot
spot activity.
The Earth’s plates move at
different rates, but in continuous
directions, not randomly.
Asthenosphere
Lithosphere
(crust and
upper mantle)
Figure 1.22 Convection currents
in the asthenosphere. The red
arrows show the movement of
the convection currents while the
white arrows show the Earth’s
plates moving due to the convection
currents below.
Activity 13
field activity
4 lab activity
library activity
classroom activity
chapter activity
4 research team activity
Convection Currents
SAFETY
PRECAUTION
Be sure to wear
safety goggles when
handling the oil, since
you will be heating it.
Purpose
To investigate convection currents and how they play a role in
plate motion.
Materials and Equipment
• 300 ml oil
• 1 tablespoon dried spices such as basil or oregano
• 1-litre heat-proof clear beaker
• ring stand with ring holder
•candle/matches
• safety goggles
Procedure
1. In your research teams, pour the oil into the beaker and
sprinkle the spices on top of the oil. Place the candle
on the base of the ring stand and the beaker on the ring
holder. Position the ring so that it is just above the flame
level of the candle.
2. Light the candle and wait for several minutes while the
oil heats up. Remember to wear your safety goggles! As
the oil heats, describe the movement of spices in the oil.
The oil represents the molten mantle and the spices are
used to show the movement of convection currents in this
molten material.
3. Record your findings and explain how this experiment
simulates convection currents in the asthenosphere.
Conclusions
1. What are 3 everyday examples of convection?
2. Describe the ways in which the lithosphere interacts with
convection currrents in the asthenosphere.