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GEOLOGY
Chapter 10 Plate Tectonics
10.3 The Changing Continents
10.3 The Changing Continents
Objectives
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Identify how movements of tectonic
plates change Earth’s surface.
Summarize how movements of
tectonic plates have influenced
climates and life on Earth.
Describe the supercontinent cycle.
Reshaping Earth’s Crust
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Cratons are large areas of stable rock
older than 540 million years that exist on
all continents today.
Cratons that have been exposed at the
Earth’s surface are called shields.
Cratons are the cores around which the
modern continents are formed.
Rifting is the process by which Earth’s
crust breaks apart and it can occur within
continental crust or oceanic crust.
Reshaping Earth’s Crust
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Continental crust is thicker than oceanic
crust and has a high silica content –
making continental crust act as an
insulator.
Heat from the mantle builds up under the
continent causing the lithosphere to
become thinner and weaken.
Eventually a zone of weakness breaks
forming a rift.
Reshaping Earth’s Crust
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Continents can change shape by breaking
apart and gaining material.
A terrane is a section of geologic lithosphere
that has a unique geologic history that is
different from that of the surrounding
lithosphere.
Three characteristics can be used to identify
terranes.
• Contains rocks and fossils that differ from those of
surrounding terranes
• Major faults at the boundaries of a terrane
• Magnetic properties of a terrane are generally
different from those surrounding it
Reshaping Earth’s Crust
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Terranes become part of a continent at
convergent boundaries.
Accretion is the process in which a terrane
becomes part of another continent.
When a terrane is scraped off of a
subducting plate, it may form mountains
or just add to the surface area of the
continent.
Terranes can be small volcanic islands,
atolls, sea mounts, large chunks of
continent.
Reshaping Earth’s Crust
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Large mountain
chains form
when large
terranes collide,
such as the
Himalaya
Mountains –
when India
began colliding
with Asia about
45 million years
ago.
Effects of Continental Change
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The past movements of tectonic plates have an
impact on modern climate.
Latitude and longitude (both determined by
continental movement) of a continent have an
effect on climate as well as ocean currents and
proximity to other landmasses.
Mountain ranges affect airflow and wind patterns
as well as whether or not moisture makes it from
one region to another.
Shifts in ocean currents and air and moisture flow
have a major impact on climate change.
Effects of Continental Change
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Most landmasses
on Earth have been
covered by glaciers
at some time in the
past.
At one point, a
global ice sheet
formed when the
continents were
amassed near the
South Pole.
Effects of Continental Change
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Populations of organisms are formed
as mountain chains are uplifted and
rift valleys form.
New species may evolve when an
existing species is separated into
different populations.
Isolation may also protect
populations from predators or
competitors.
The Supercontinent Cycle
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The supercontinent cycle is the process by
which supercontinents form and break
apart over millions of years.
As continents move about through the
process of plate tectonics, they converge
every so often creating a cycle.
The movement of continental plates
toward convergent boundaries cause
inevitable collisions.
Over time the continents collide to form a
giant supercontinent.
The Supercontinent Cycle
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Since continental crust does not subduct
(it buckles up to form large mountain
chains), convergent boundaries where
continents collide often become
geologically inactive and spreading centers
must form elsewhere.
This creates rifts elsewhere in the
supercontinent.
Pangaea is the supercontinent that formed
about 300 million years ago and began to
break up about 250 million years ago.
The Supercontinent Cycle
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The Appalachian Mountains of North
America and the Ural Mountains of Russia
formed during the collisions of continents
during the formation of Pangaea.
The Tethys Sea cut into the eastern edge
of the supercontinent.
The large, global ocean that surrounded
the rest of Pangaea was Panthalassa.
Pangaea broke up into two continents,
Laurasia and Gondwanaland about 250
million years ago.
The Supercontinent Cycle
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The large east-west rift that split Pangaea sent
Laurasia drifting and spinning slowly northward.
Another rift (eventually becoming the North
Atlantic Ocean) then separated Laurasia into
North America and Eurasia.
The Tethys Sea closed during the rotation of
Laurasia and eventually became the
Mediterranean.
About 150 million years ago, a rift (eventually
becoming the South Atlantic Ocean) developed
between Africa and South America.
The Supercontinent Cycle
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Australia, India, and Antarctica then broke
apart and drifted away.
India would later collide with Eurasia (Asia) to
form the Himalaya Mountains.
Slowly, since the breakup of Pangaea, the
continents have drifted to their current
positions, sometimes picking up terranes
along the way.
With the knowledge of current tectonic
movement and past patterns, we can predict
what the next supercontinent will look like.
References
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Rift Formation - http://wwwgeol.unine.ch/Petrology/Research/theme1.ht
ml
India/Asia Convergence - http://wwwclass.unl.edu/geol101i/15c_glaciers.htm
Late Permian South Pole View http://www3.interscience.wiley.com:8100/lega
cy/college/levin/0470000201/chap_tutorial/ch
09/chapter09-5.html
Paleomaps of Continental Movement http://scotese.com/late.htm