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Plate Tectonics Throughout the S

VIEWS: 15 PAGES: 21

									    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

								
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