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4/19/11
The Dynamic Planet
The Pace of Change Earth’s Structure and Internal Energy The Geologic Cycle Plate Tectonics The Pace of Change Geologic time scale
Uniformitarianism
EARTH’S INTERIOR IS HIGHLY STRUCTURED
UNEVENLY HEATED
SO WE GET A VARIED SURFACE . . .
WITH FRACTURES, EARTHQUAKES, VOLCANIC
ACTIVITY AND MOUNTAINS
THE EARTH IS ABOUT 4.6 BILLION YEARS OLD
OLDEST SURFACE ROCK FOUND IN
NORTHWESTERN CANADA: 3.96 BILLION YRS OLD
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Earth’s Structure and Internal Energy Earth in Cross Section
Earth’s Core Earth’s Magnetism
Earth’s Mantle Earth’s Lithosphere and Crust THE EARTH SOLIDIFIES AND GRAVITY
SORTS MATERIALS BY DENSITY
HEAVIER ELEMENTS LIKE IRON
GRAVITATE TO THE CENTER . . .
LIGHTER ELEMENTS SUCH AS SILICA MOVE
TOWARDS THE SURFACE
SO THE INTERIOR IS SORTED INTO
CONCENTRIC LAYERS, MUCH LIKE THE
ATMOSPHERE
CORE
AN INNER AND AN OUTER CORE
THE INNER CORE IS SOLID IRON BECAUSE
OF IMMENSE PRESSURE
THE OUTER CORE IS MOLTEN AND GENERATES
90% OF THE EARTH’S MAGNETIC FIELD
(PERHAPS BECAUSE IT ROTATES 12 mph FASTER
THAN THE REST OF THE EARTH)
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MANTLE
UPPER AND LOWER
REPRESENTS 80% OF THE EARTH’S VOLUME
RICH IN OXIDES OF IRON, MAGNESIUM, AND
SILICATES
TEMPERATURE INCREASE WITH DEPTH
COLD DENSE MATERIAL SINKS IN THE MANTLE
WARM MATERIAL RISES IN THE MANTLE
ASTHENOSPHERE
WEAK, PLASTIC, LESS RIGID PORTION OF
UPPER MANTLE
43 - 155 MILES IN DEPTH
SLOW MOVEMENT CREATES TECTONIC
ACTIVITY (FOLDING, FAULTING AND
DEFORMATION OF SURFACE ROCK)
LITHOSPHERE AND CRUST
FROM SURFACE DOWN TO 43 MILES
CONTINENTAL CRUST:
GRANITE; HIGH IN SILICA; LOW IN DENSITY; CRYSTALLINE
OCEANIC CRUST:
BASALT; GRANULAR; HIGH IN SILICA;
HIGHER IN DENSITY
CRUST ‘FLOATS’ ON DENSER LAYERS UNDERNEATH
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The Geologic Cycle
Rock Cycle Igneous Processes Sedimentary Processes Metamorphic Processes THE ROCK CYCLE
PROCESSES IN THE ATMOSPHERE, CRUST AND
MANTLE THAT PRODUCE THE THREE BASIC
ROCK TYPES:
IGNEOUS
SEDIMENTARY
METAMORPHIC
99% OF THE CRUST IS COMPOSED OF EIGHT
ELEMENTS AND TWO (OXYGEN AND SILICON)
ACCOUNT FOR 75%
COMMON ELEMENTS IN EARTH’S CRUST
OXYGEN
46.6%
SILICON
27.7 %
ALUMINUM
8.1%
IRON 5.0%
CALCIUM 3.6%
SODIUM
2.8%
POTASSIUM
2.6%
MAGNESIUM
2.1%
ALL OTHERS
1.5%
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A MINERAL IS AN ELEMENT OR COMBINATION OF
ELEMENTS THAT FORMS AN INORGANIC
NATURAL COMPOUND
QUARTZ:
COMBINATION OF
OXYGEN AND
SILICON
SILICATES ARE A WIDESPREAD MINERAL FAMILY
BECAUSE SILICON AND OXYGEN ARE SO
COMMON
INCLUDES QUARTZ, FELDSPAR, CLAYS AND
MANY GEMSTONES
OXIDES ARE MINERALS IN WHICH OXYGEN
COMBINES WITH A METALLIC ELEMENT
CARBONATES FEATURE CARBON IN COMBINATION
WITH OXYGEN AND OTHER ELEMENTS LIKE
CALCIUM, MAGNESIUM AND POTASSIUM
A ROCK IS AN ASSEMBLAGE OF MINERALS BOUND
TOGETHER (SUCH AS GRANITE WHICH CONTAINS
SILICA, ALUMINUM, POTASSIUM, CALCIUM AND
SODIUM)
A ROCK CAN ALSO BE A MASS OF A SINGLE
MINERAL
THERE ARE THREE KINDS OF ROCKS, BASED
ON THE PROCESSES THAT FORMED THEM:
IGNEOUS
SEDIMENTARY
METAMORPHIC
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IGNEOUS
ROCKS THAT SOLIDIFY AND CRYSTALLIZE
FROM A MOLTEN STATE
MOST ROCKS IN THE EARTH’S CRUST ARE
IGNEOUS
IGNEOUS ROCKS FORM FROM MAGMA
(MOLTEN ROCK BENEATH THE SURFACE)
LAVA IS MAGMA THAT HAS EXTRUDED ONTO
THE EARTH’S SURFACE
HOW FAST THE ROCK COOLS DETERMINES
THE TEXTURE AND STRUCTURE OF IGNEOUS
ROCKS
COARSE-GRAINED, LARGE CRYSTAL ROCKS
COOL SLOWLY
FINE-GRAINED AND GLASSY ROCKS COOL FASTER
ROCKS CONTAINING SILICA, SODIUM, ALUMINUM
ETC ARE LIGHT IN COLOR AND DENSITY ROCKS HIGH IN IRON AND MAGNESIUM ARE
DARKER AND HAVE GREATER DENSITY
SEDIMENTARY ROCKS
FORMED FROM PREEXISTING ROCKS
FORMED FROM ORGANIC MATERIALS:
BONE AND SHELL FORM LIMESTONE
MUD BECOMES SHALE
ANCIENT PLANT REMAINS BECOME COAL
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SEDIMENTARY ROCKS
WEATHERING AND EROSION GENERATE
SEDIMENTS NEEDED TO FORM ROCKS
SEDIMENTS ARE TRANSPORTED AND DEPOSITED
SOME MINERALS DISSOLVE INTO SOLUTION AND
THEN FALL TO THE BOTTOM, ESPECIALLY IN
OCEANS
SEDIMENTS THEN CEMENT, COMPACT, HARDEN
INTO SEDIMENTARY ROCKS
METAMORPHIC
EXISTING IGNEOUS OR SEDIMENTARY ROCK THAT
HAS UNDERGONE PHYSICAL AND CHEMICAL
CHANGES UNDER INCREASED TEMP AND PRESSURE
MORE COMPACT , HARDER, MORE RESISTANT TO
WEATHERING AND EROSION
SUBSURFACE ROCK IS SUBJECTED TO HIGH TEMP
AND HIGH COMPRESSION OCCURRING OVER
MILLIONS OF YEARS
ANCIENT ROOTS OF MOUNTAINS; SEDIMENTS
COLLECT IN DEPRESSIONS AND TRANSFORM UNDER
OWN WEIGHT Plate Tectonics   Brief History
A
 Seafloor Spreading and Production of New Crust
 Subduction of the Crust
 The Formation and Breakup of Pangaea
 Plate Boundaries
 Earthquake and Volcanic Activity
 Hot Spots
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CONTINENTAL DRIFT
PROPOSED BY ALFRED WEGENER IN 1912
THE EARTH’S LANDMASSES HAVE MIGRATED OVER
THE PAST 225 MILLIONS YEARS FROM A
SUPERCONTINENT CALLED PANGAEA TO THE
PRESENT CONFIGURATION
WEGENER COMPARED FOSSIL RECORD AND
GEOLOGIC RECORD AND CLIMATE RECORD FOR
SOUTH AMERICA AND AFRICA CAUSED BY PLATE TECTONIC PROCESSES:
CONTINENTAL DRIFT, SEA FLOOR SPREADING, AND
RELATED ASPECTS OF CRUSTAL MOVEMENT
SEA-FLOOR SPREADING
THE MECHANISM DRIVING THE MOVEMENT OF
THE CONTINENTS
ASSOCIATED WITH UPWELLING FLOWS OF MAGMA
ALONG THE WORLDWIDE SYSTEM OF MID-OCEAN
RANGES (A SUBMARINE MOUNTAIN RANGE THAT
EXTENDS MORE THAN 40,000 MILES WORLDWIDE
AND AVERAGES MORE THAN 600 MILES IN WIDTH)
CENTERED ALONG THE SEA-FLOOR SPREADING
CENTERS: AS CONTINENTS MOVE AWAY, MAGMA
UPWELLS, CREATING MOUNTAINS
SUBDUCTION
WHEN TWO PLATES OF CRUST COLLIDE AND THE
DENSER OCEANIC CRUST DIVES BENEATH THE
LESS DENSE CONTINENTAL PLATE DEEP OCEANIC TRENCHES AND SEISMICALLY
ACTIVE REGIONS ARE FORMED
SUBDUCTED CRUST IS DRAGGED DOWN TO
MANTLE, MELTED AND RECYCLED AS MAGMA SUBDUCTION ZONES ARE AREAS OF VOLCANO
AND EARTHQUAKE ACTIVITY
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THREE TYPES OF PLATE BOUNDARIES: PRIMARY
LOCATION OF EARTH’S EARTHQUAKE AND
VOLCANO ACTIVITY
DIVERGENT: CRUSTAL PLATES SPREAD APART:
CHARACTERISTIC OF SEA-FLOOR
SPREADING CENTERS AND THE
GREAT RIFT VALLEY OF EAST AFRICA
CONVERGENT
COLLISION ZONES
CONTINENTAL AND OCEANIC CRUST COLLIDE
WEST COAST OF SOUTH AND CENTRAL
AMERICA
ANDES MOUNTAINS
TRANSFORM
PLATES SLIDE LATERALLY PAST ONE ANOTHER
AT RIGHT ANGLES TO A SEA-FLOOR
SPREADING CENTER
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