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(11) Solid Earth. The student knows that the geosphere
continuously changes over a range of time scales involving
dynamic and complex interactions among Earth's
subsystems. The student is expected to:
(b) explain how plate tectonics accounts for geologic surface processes and
features, including folds, faults, sedimentary basin formation, mountain
building, and continental accretion;
•Students understand how tectonics affect topography
(c) analyze changes in continental plate configurations such as Pangaea and
their impact on the biosphere, atmosphere, and hydrosphere through time;
(d) interpret Earth surface features using a variety of methods such as
satellite imagery, aerial photography, and topographic and geologic maps
using appropriate technologies
Vocabulary: Orogeny
As you have already learned, tectonic processes originate within the planet and
produce movements of the Earth's crust.
There are basically two types of pressures exerted on the crust:
• Compression
has a tendency to shorten the Earth's surface ,resulting in the wrinkling of the
crust. What type of plate boundary may this process occur at?
• Tension
causes the crust to crack or fracture, while pulling it apart. Tension tends to
stretch or expand the surface. What type of plate boundary may this process
occur at?
Folding refers to the wrinkling of the crust which occurs because of slow lateral
compression. When layered flat strata are subjected to compressional forces, they are
bent and deformed. Too much bending creates a break, or a fault.
By far, most of the Earth-forces are compressional.
Fold patterns may be simple or very complex in form, due to the varying intensity of the
tectonic forces that produced them. Either way, they leave clues behind for geologists to
interpret and discover their origins.
What are the two types of forces at work on the planet’s surface?
What types of plate boundaries do you associate with
compression forces?
What types of plate boundaries do you associate with tension
forces?
Compression forces cause f__________ of sediment, and
f__________ appear when too much of this occurs.
Various shapes and forms of folding are the following:
Monocline:
The simplest type of fold. It involves only one inclination of the rocks. In a monocline the
fold is bent in one direction only.
Anticline:
When the pressure exerted on a rock is not great, a series of simple folds are produced.
In such folds the arches or up-folds, or crests, are called anticlines.
Syncline:
In a simple fold, the troughs or down-folds are called synclines. The sides of the folds
between the anticlinal crests and synclinal troughs are called the fold limbs.
Recumbent Fold:
A fold in which the limbs (waves) are largely horizontal. Geologically speaking, it is
inferred that these folds were at one time vertical, and through extreme geologic
upheaval, have been “upended”.
When rock strata are strained beyond their ability to fold, and retain their solid state as a
unit, they fracture, or break. When a fracture occurs and the rocks are displaced on
either side of it relative to one another, the result is known as a fault, and the process is
faulting.
•Faults often occur in groups
along a fault zone. Some faults
displace rocks up and down. This
is called vertical displacement.
•Some faults cause lateral
displacement or sideways
movements.
When there are sudden slippage
movements, it generates
earthquakes.
A single fault movement may result in slippage ranging from a centimeter to about 15
meters. Such slippage may occur in quick succession or may occur after gaps of several
decades or centuries. The cumulative displacement may involve as much as hundreds
of kilometers.
Type of fold represented
in this photo:
The crests of this fold are
known as:
The troughs in this fold
are known as:
The simplest fold is
known as a:
The tension fault or normal fault:
A normal fault occurs where tension causes fracture in rocks that are being pulled apart.
The rock above the fault plane moves down relative to the rock beneath the fault plane.
The reverse fault or thrust fault:
Reverse fault occurs where compressional force causes the upper block of rock to be
pushed over the lower. As a result of compressional forces there is shortening of the
crust.
The strike-slip fault:
A strike-slip fault is a fault on which the two blocks slide past one another. These faults
are identified as either right-lateral or left lateral depending on whether the displacement
of the far block is to the right or the left when viewed from either side. The San Andreas
Fault in California is an example of a right lateral fault.
A _________ fault, or normal fault is caused by tension forces,
pulling the pieces apart.
A ________ fault, is the result of compression forces, pushing the
pieces together.
The _____________ fault is the result of lateral movement.
Strike-slip faults form along ____________ plate boundaries.
SEDIMENTARY BASIN FORMATION
Sedimentary basins are created by depressions (dips) in the surface of the lithosphere
associated with tectonic processes. These topographic and bathymetric (beneath the
water) basins are subsequently filled by sediment, leading to further subsidence and
sediment accumulation.
Sedimentary basins are
important, because
petroleum is most often
found in such locations.
A sedimentary basin is
a depressed area of
the Earth’s crust where
tiny plants and animals
lived or were deposited
with mud and silt from
streams and rivers.
These sediments eventually hardened to form sedimentary rock. The soft parts of plants
and animals, exposed to heat and pressure over millions of years, gradually changed to
oil and natural gas. Coal is formed from the remains of ancient fern-like trees that died in
swamps, and were compressed over the millennia. Temperature, pressure and
compaction of sediments increase at greater depths.
MOUNTAIN BUILDING: OROGENY
The terms orogeny and orogenesis involve tectonic processes that result in the
formation of mountain chains. Mountain building most commonly involves the collision
between two continental lithospheric plates. Because continental plates are of relatively
equal density, when they converge, they crinkle up. These are known as “folded
mountains”. When the plates carrying Africa and Saudi Arabia, along with other smaller
plates, collided (from the south) with Eurasia in the north, the Alps formed.
When these boundaries
form subduction zones,
most often, volcanic
mountains arise, such as
the Andean orogenics. It
results from the
subduction of the oceanic
Nazca plate underneath
the South American
continent. Collision
follows subduction of
oceanic lithosphere
beneath one continent.
Topographic features are found ___________
___________ means the “origin” of mountains.
Bathymetric features are found____________
Describe the two different types of mountains, and what types of
plate boundaries they may form along. Give examples of each.
Sedimentary basins are especially important because this is
where ________________ form.
CONTINENTAL ACCRETION
Accretion is a process by which material
is added to a tectonic plate or a
landmass. There are two possible ways
Amazon Alluvial Deposit
this may happen.
•Tectonic Accretion:
 Volcanic island arcs or seamounts may collide
with the continent, and as they are of relatively
light material, they will often not be subducted, but
are thrust into the side of the continent, thereby
adding to it.
•Landmass Accretion:
This involves the addition of sediment to a
coastline or riverbank, increasing land area via
erosion and deposition. The most noteworthy
landmass accretion is the deposition of alluvium,
often containing precious metals, on riverbanks
and in river deltas.
Give an example of tectonic accretion.
Give an example of landmass accretion.
SUPERCONTINENTS
Pannotia; a time of
great glaciation
Formation of supercontinents, such as
Rodinia, greatly influences climate. Climate
influences life.
Since Rodinia formed during a time when
life consisted only of bacterial forms, such as
stromatolites, it must have been a vast and
desolate place. Life had not yet colonized
land.
The eight continents which made up Rodinia
later reassembled briefly into another super
continent Pannotia, and again into Pangaea.
Rodinia produced some significant changes in
the Earth. It was the largest landmass to have
existed up till that time. It significantly
changed ocean currents, which may have led
to snowball Earth later in the Cryogenian.
(850 to 635 million years ago)
ENVIRONMENTS
The formation of a supercontinent can dramatically affect the environment. The collision
of plates will result in mountain building, thereby shifting weather patterns. Sea levels
may fall because of increased glaciation in mountains and continental interiors. They
may also rise if there is excessive glaciation causing isostatic pressure in the mantle.
The rate of surface weathering can rise, resulting in an increase in the rate that organic
material is buried… and the formation of sedimentary basins.
The formation of a supercontinent
insulates the mantle. The flow of
heat will be concentrated,
resulting in volcanism and the
flooding of large areas with basalt.
Increased volcanism leads to
increased greenhouse gases, and
global warming. Notice here that
the hottest areas on the planet
are right over Pangea during this
period.
CAMP, or Central America Magmatic Province
Why didn’t the formation of the supercontinent
Rodinia influence the biosphere as much as
Pangea did?
How does mountain building due to continental
collision affect climate?
BIOSPHERE
Plate tectonics recycles water, carbon and
nitrogen, creating an environment that is
perfect for life.
Land and sea barriers generated by
continental drift have influenced distribution
of life on the Earth by restricting
movements of both plants and animals.
It makes oceans open and close, mountains
rise and fall and continents gather and split. Organisms that arose and diversified on an
ancient landmass, such as Gondwana,
were prevented by large sea barriers from
Every 500 to 700 million years, tectonics
colonizing other landmasses.
brings the continents together to form a
supercontinent.
Diversity of life is a consequence of
isolation. Less isolation, means less
When these supercontinents slowly break
diversification. This occurs during
up,
separating landmasses
forming
Breakup
Formationand
Breakup
of
shallow
seas, evolution
goes into
overdrive, supercontinent formation, producing both
of
of Pangea
Pangea
one continent and one ocean with one
Pannotiacountless new species which
forming
Panthalasacoast. Because genes (heritable units of
colonize the new habitats.
organisms) are allowed to “flow”, evolution
slows down.
Tectonics can move a continent from a
tropical to a polar latitude, where the
organisms will experience new patterns of
competition.
Break-up events result in the tremendous
proliferation of diversity of life forms. Gene
What does each of these
animals have in common?
Not only are they all marsupials, or special
mammals who birth embryos that are nurtured
within pouches, but they all are currently found
in the wild, only in Australia. They began
evolving near the breakup of the supercontinent,
Pangea, which went on to form Laurasia and
Wombat
Gondwana.
BIOSPHERE
During in the Triassic Period and later, the break
up of Pangea played a significant role in the
Devil
evolution of all marsupials, especially those in Tasmanian
the
Americas and Australia. They were unable to
compete in Asia and Europe, and became extinct
there.
Wallaby
Tectonics provides an explanation for the vast
number of different species of marsupials in
Australia, but the relative rarity of marsupials
elsewhere. Marsupials were able to adapt and
compete successfully only in Australia.
Evolutionarily, adaptation is what it’s all about!
Opossum: Only remaining
marsupial in North America
Formation of supercontinents often is accompanied by
_________ diversification of life forms, due to increased gene
flow.
Break-up of supercontinents leads to ___________ , which
influences huge diversification events.
What types of barriers do plate tectonics provide that influence
evolutionary events?
Why are there currently more marsupials on Australia than on any
other continent?
ATMOSPHERE AND HYDROSPHERE
Throughout the Pangea period, due to the reconfiguration of the continents and oceans,
global atmospheric circulation patterns changed. Atmospheric warming was caused by
Atmospheric Circulation:
expansion of magma beneath Pangea.
During Pangea
Carbon is cycled tthrough tectonics as well. Carbon
dioxide is released into the atmosphere by volcanic
activities. CO2 will warm up the air, and cause more
seawater to evaporate.
Acidic rain reduces the amount of CO2 by producing
carbon-containing minerals, which is carried into the
mantle by plate tectonics, and eventually returns to the
atmosphere through volcanoes to repeat the cycle
again.
Interestingly, this planetary self-help method of climate regulation may
not work very well if the CO2 released by human activities becomes too
much for the slow process of plate tectonics to handle!
During the time of Pangea, global circulation patterns were affected. When the
Australian and South American continents broke away from Antarctica approximately 38
mya, oceanic currents in the newly formed Southern Ocean created a circumpolar
current. This in turn led to atmospheric currents that rotated from west to east. Both
these atmospheric and oceanic currents stopped the transfer of warm tropical air and
water to the higher latitudes. This ultimately led to the cooling of the Antarctic continent.
HYDROSPHERE ANDTheATMOSPHERE
thermal plumes that arise during
As you saw on the last slide, there is an unavoidable connection between atmospheric
supercontinent buildup result in:
circulation, and oceanic circulation patterns. They both affect climate greatly. When the
• warming atmospheres, which results in:
North and South American continents joined around 3 mya forming the isthmus of
• sea level rise due to thermal expansion
Panama, (historically known as the Isthmus of Darien) this had the effect of stopping
of water, which results in:
equatorial currents passing from the Atlantic to the Pacific. .
• the melting of the ice sheets, changing
It has been shown that this strengthened the Gulf
the weight on the continents beneath,
Stream by diverting more equatorial (warm)
changing isostatic pressure, which results
currents northwards towards Europe.
in:
In doing so, warm waters at high latitudes led to
• localized sea-level change as the land
increased evaporation and therefore atmospheric rebounded with the removal of ice, which
moisture.
results in:
•increased precipitation as snow and ice
Today, evaporation in the tropical Atlantic and
over Greenland, ultimately leading to a
Caribbean leaves behind saltier ocean waters and
build up of the ice cap, which results in:
puts fresh water vapor into the atmosphere.
• average albedo increase, which leads to
further global cooling.
Trade Winds carry the water vapor westward
across the low-lying isthmus, depositing fresh
This is cyclical in nature, as seen by this
water into the Pacific through rainfall. As a result,
graphic representation of global
the Atlantic is saltier than the Pacific
temperatures through geologic time
Sea level is generally lower during the time of supercontinents, and higher when they break apart.
This is because the age of the oceanic lithosphere provides a major control on the depth of the
ocean basins, and therefore on global sea level. Let’s take a look at the cycle.
THE FUTURE
In the next 50 to 200 million years, all
of Earth’s continents will be once again
pushed together into a supercontinent.
The proposed supercontinent, Amasia,
will be centered around the North Pole.
This conclusion comes from a
computer model that shows the slow
movements of the continents over the
next several millions of years.
How will this supercontinent affect
global circulation patterns, and
climate? Will humans be here to see
it? Considering the fact that the
greatest mass extinction in Earth's
history happened at the same time
Pangaea formed 250 million years ago,
the formation of a supercontinent in the
future may eventually cause extinctions
on a similar scale.
The lessons from these vast geologic and
geographic changes is both simple and
exceedingly complex. As you’ve seen, the
opening and closing of seaways has a
profound influence on the distribution of fresh
water, nutrients, and energy in the global
ocean. The coupling of these changing oceans
with a changing atmosphere inevitably means
a changing climate.
Describe how CO2 is recycled in plate tectonics, and how it plays
a role in planetary temperatures.
What is the danger of increased human CO2 formation?
How did the break-up of Pangea, particularly Antarctica from
South America and Australia, lead to a colder climate for
Antarctica?
How does a strengthening Gulf Stream influence global
temperatures?
Which ocean is saltier, and why? When did this happen?