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Part 3, What does Plate Tectonics
have to do with Climate?
• Changes the topography
• Changes the ocean circulation
• Affects the re-cycling of volatiles
– re-cycling of water vapor is particularly important on
planets besides Earth, such as Mars, Venus & Io
• In turn, climate affects the creation of
continental crust & the long-term evolution
of a planet
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 24
Changes in Ocean Circulation
Earth: today - relatively cool • the arrangement of the
continents affects
circulation of the oceans
• a different configuration of
the continents leaves larger
Earth: Cambrian Era
or smaller spaces in which
Earth: Jurassic - water can circulate
relatively hot • more (less) efficient
note: take a look at
Windows page circulation may result in
on Geologic Time either cooler or (hotter)
global weather
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 25
Little Ice Age Example
• Ice sheets used to cover the Great
Lakes region
• In the14th century the last of the
retreating ice sheets freed the Lawrence
waterway, allowing cold, glacial ice to
drain into the North Atlantic
• The influx of cold water decreased the
average temperature in the North
America and northern Europe by
several degrees for a few centuries.
• freezing temperatures at Valley
Forge, Pennsylvania, for example
note: take a look at Windows page on Geologic Time
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 26
Slippery Continents, a specialty of Earth,
contributes to a recycling of volatiles
• Hydrated minerals, such as
kyanite, a biproduct of the
breakdown of granite, help
make the crust of the Earth
“slippery”, and so facilitate
the subduction of the plates
– (unique to the Earth)
• subducted plates are re-
melted and returned to the
surface as volcanoes
• these re-release volatiles
during eruptions
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 27
Plate Tectonics also forms New
Crust
• Over an extremely long time, plate
tectonics forms the crust and shapes
the surface of a planet. This process
affects:
(1) topography, as mentioned before
(2) recycling of volatiles
• In earliest days, Earth resembled
Jupiter’s moon Io. The slow buildup
of continental crust over Earth’s
history shaped the course of its
evolution.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 28
How does That Work?
• Silicate rocks are about
90% of the Earth’s
surface.
• They evolve in the magma
chamber of a volcano.
• (The exact chemistry will
depend upon the pressure
and temperature inside the
chamber).
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 29
The Bowen Series shows the
evolution of minerals in the chamber
• The progression tend to
T he Bow en Se r i e s
Quartz
separate light materials
Olivine A ci di c
Mi ner al s
Muscovite
Mica
(silica-rich) from heavy
K-
Pyroxene
Felds par materials (silica-poor).
intermediate
ultrabasic
• The progression is well
Na-
Basi c Felds par
Ca-
Felds par Biotite
Amphibole Mica
understood for the Earth.
or der of condensat i on of
cr yst al s out of a mel t , or
Efforts are underway to
magma chamber .
Ther e i s a def i ni t e sequence
understand the
as t he magma chamber cool s.
progression for Mars.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 30
Granite vs. Gabbro
• Thus, the continental crust
of the Earth is formed of
light weight rocks such as
granite (silica-rich).
• The crust of the moon is
made of more silicate-poor
rocks such as gabbro.
• The crust of Mars is made of
basalt of an as-yet unknown
silica %.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 31
Subduction helps create new crust
• The scraping of the crust as
it subducts also creates a
lightweight component of
the crust which does not
further subduct.
• The lightweight component
forms the continental crust of
the Earth, crust which does
not sink in the subduction
process.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 32
The Earth’s Surface has Evolved
• Earliest Earth had no ocean, no continents, and an
unknown atmosphere.
• Continents grew, changed composition, and
oxygen grew in the atmosphere.
• Gradually the oceans have increased in saltiness as
weathering of the surface proceeds. Earth: Jurassic -
Earth: Cambrian Era relatively hot
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 33
Summary
• Changes in topography and/or ocean
circulation affect the way cooling and
warming mechanisms of a region “work”.
• Because climate affects the creation of
continental crust, and vice-versa, a planet
can get stuck with a single climate if there is
no plate tectonics.
• Can you name a few examples?
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 34
Part, 4; Plate Tectonics on Other
Planets - Venus
Venus - a thick atmosphere,
no present-day plate
tectonics
– continents, volcanic rises,
coronae
– thick lithosphere (maybe)
– lithosphere = frozen (maybe)
– plate tectonics is not
understood
• there is some evidence of
rifting & faulting
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 35
Cratering History
& theories of catastrophic turn-over of the surface
• The surface of Venus has just as few
craters as does the Earth. This
means that the surface is just as
young as Earth’s surface!
• Plate tectonics does not exist as it
does on Earth, however.
– Lithosphere is probably thick, not thin
– Plates do not move.
• Suggests a cataclysmic turn-over
process may be at work.
• The inside heats up until, POW! The
whole surface melts.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 36
Coronae & Island Arcs
• There are features
on the surface of
Venus called
“coronae” which
strongly resemble
terrestrial island
arcs - a
manifestation of
plate tectonics
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 37
Volcanic Rises & Islands
• On Earth, over a hot spot deep
within, lava rises and creates a
volcanic “island”.
• Because of plate tectonics, the
“island” moves away from the
hot spot, gradually erodes away,
and a new island takes its place.
• On Venus, because of no plate
motion, volcanic islands keep
Hot spot! growing, and create giant
(deep inside the Earth) continents instead.
• These are called Volcanic Rises.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 38
Mountains
• Mountains of Venus are small, but
the rock may be very dense. The
crust may be very thick in order to
support the weight.
• On the other hand, the crust may
be thin.
• The uncertainties imply that the
surface of Venus may turn over in
a manner which is completely
unlike that of the Earth.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 39
Venus Climate
• Venus has a thick, massive atmosphere.
• Doesn’t seem capable of changing.
• Theoretical work is on-going to
test ideas of a changing climate.
• What happens if there is a
cataclysmic turn over of the
surface - does that affect the
atmosphere?
• New results may suggest ways of
measuring surface rock
composition to seek evidence of
climate change.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 40
Mars
Mars - a thin atmosphere, no
present-day plate tectonics
– continents, volcanic rises,
magnetic stripes
– thick lithosphere (maybe)
– lithosphere = frozen in place
– plate tectonics may have
taken place in the past
• there is some evidence of
rifting & faulting
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 41
Volcanic Rise
• The presence of a
volcanic rise suggests
a thick, and immobile
lithosphere.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 42
Magnetic Stripes
• On Earth, the biggest
proof of the mechanism
of plate tectonics, sea-
floor spreading, is in
the striped ocean floor.
• Mars has been found to
have similar stripes,
indicating plate
tectonics in the past.
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 43
Martian “Geologic” Time
associated with past Martian Plate Tectonics
Like the Earth, Mars
experienced “epochs” in its
past history (like the
Jurassic, or Cambrian), and
these epochs have names!
– Hesperian
• When the super continent at the
southern hemisphere formed
– Something
• 90% of the rest of martian
history, when the cratering eased
off
Plate Tectonics Throughout the Solar System C. Alexander 7/25/02 pg 44
