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Evolution of the Earth
http://static.neww
orldencyclopedia.org/f/fe/Geologic_clock.jpg
http://www.geosociety.org/science/timescale/timescl.pdf http://www.geosociety.org/science/timescale/timescl.pdf
Evolution of the Earth• Solar system, 4.6 byr
• Proto-earth– Homogeneous composition, partially melted
Smaller concentrations ofmatter coalesce
Collapse of anebula
Star forms asgravityconcentratesmaterial atcenter of cloud
Eventually underwentdensity stratification
Highestdensitymaterial
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Crustal composition(percent by weight)
Oxygen 46.6%Silicon 27.7%Aluminum 8.1%Iron 5.0%Calcium 3.5%Sodium 2.8%Potassium 2.6%Magnesium 2.1%All others 1.5%
Evolution of the Earth: plate tectonics• Thin, rigid blocks of lithosphere move horizontally• Interactions of plates build major features of Earth’s crust
1. Puzzle-like fit ofcontinents
2. Matching rocks andmountain chains– Structures– Rock types– Rock ages
Plate tectonic theory: evidence3. Magnetic polarity reversalsPlate tectonic theory: evidence
3. Magnetic polarity reversals- changes in Earth’s magnetic polarity arerecorded in the rocks as seafloor is created
Plate tectonic theory: evidence
Animation: seafloor magnet
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4. Age of ocean floor: youngest at mid-ocean ridgeSeafloor spreading: Evidence
5. Heat flow: highest at mid-ocean ridge crestSeafloor spreading: Evidence
6. Earthquakes: most occur along plate marginsSeafloor spreading: Evidence Evolution of the Earth: plate tectonics
• Thin, rigid blocks of lithosphere move horizontally• Interactions of plates build major features of Earth’s crust
Evolution of the Earth: seafloor spreading• Rising heat pushes and pulls tectonic plates• Crust created at mid-ocean ridges• Crust destroyed at oceanic trenches
2. Convergent2. Convergent
1. Divergent
3. Transform3. Transform
Evolution of the Earth: plate boundaries
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Convergent: oceanic-continental plate– Oceanic plate subducted– Oceanic trench– Continental arc
Evolution of the Earth: plate boundaries
Convergent: oceanic-oceanic plate– Oceanic plate subducted– Oceanic trench– Island Arc
Evolution of the Earth: plate boundaries
• Divergent: plates move apart
Evolution of the Earth: plate boundaries
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• Divergent: plates move apart
Evolution of the Earth: plate boundaries
Juan de Fuca ridge
• Divergent: plates move apart– Hydrothermal vents: seawater migrates through
cracks in ocean crust
Evolution of the Earth: plate boundaries
Black smoker
White smoker
Oceanic transform fault
• Segments of plates slide past each other• Occur between two segments of mid-ocean ridge• Shallow but strong earthquakes
Evolution of the Earth: plate boundaries
Continental transform fault
Evolution of the Earth: plate boundaries
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Evolution of the Earth: hotspots
Volcanic peaks
Source: Prentice Hall
Evolution of the Earth: hotspots
Source: Prentice Hall
Evolution of the Earth: seafloor spreading• Rising heat pushes and pulls tectonic plates• Crust created at mid-ocean ridges• Crust destroyed at oceanic trenches
Rock cycle and plate boundaries• One or more minerals held together by a matrix
Rock types: Igneous• Form from the solidification and crystallization of
-magma (molten rock below ground)-lava (molten rock above ground)
• Most common examples-Basalt-Granite
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Igneous• Four types of igneous rocks
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Bowen’sreactionseries:
arranged bytemperatureof formation
Mafic mineralsContain iron and magnesium
Felsic mineralsNo iron and magnesium
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Rock types: Igneous• Classified by texture and color/composition
“slow” = thousands to millions of years“fast” = days to weeks
Any aphanitic rock with theword “porphyry”
Two stage cooling; one slowunderground creating visiblephenocrysts, the second fast atthe earth's surface producing afine grained groundmass.
Porphyritic (two grain sizes)
Granite, diorite, gabbroVery slow cooling; crystalsgrow to visible size.
Phaneritic (coarse grained)
Rhyolite, andesite, basaltSlow cooling; microscopiccrystal growth.
Aphanitic (fine grained)
Pumice, scoriaVery fast cooling with rapidgas escape forming bubbles inthe non-crystalline rock.
Vesicular
ObisdianVery fast (hours) cooling; non-crystalline.
GlassyExamplesCooling HistoryTexture
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Igneous rock distribution
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Sedimentary• Loose, unconsolidated accumulation of minerals or rocks
• Sedimentary processes-weathering-transportation/sorting-deposition to
limestone (CaCO3)
Rock types: Sedimentary• Loose, unconsolidated accumulation of minerals or rocks
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Sedimentary• Compounds that weather and do not dissolve in seawaterform clastic rocks
Classified by1. Texture2. Composition- Quartz- Feldspar- Lithic fragments- Fine-grained matrix
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
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Rock types: Sedimentary• Compounds that weather and do not dissolve in seawaterform clastic rocks
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Sandstone (quartz sand)
Shale (clay)
Rock types: Sedimentary• Compounds that weather and do not dissolve in seawaterform clastic rocks
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Breccia(angular particles)
Conglomerate(rounded particles)
Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form:
• Chemical rocks-Precipitate directly from seawater
• Biochemical rocks-Plant or animal derived
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Sedimentary
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
• Compounds that weather and dissolve in seawater willeventually form:
• Carbonates (CaCO3)
-Dolomite (Mg)-Chalk
• Chert (SiO2)
• Evaporites-Halite (NaCl)-Gypsum (CaSO4H2O)
Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Carbonates (CaCO3)
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Oolitic limestone
Dolomite crystals (Mg)
Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Carbonates (CaCO3)
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Fossiliferous rock (coquina)Chalk
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Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Silicate
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Chert (SiO2)
Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Salts
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Gypsum (CaSO4H2O)
Halite (NaCl)
Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Accumulation of plant material
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Peat
Coal
Rock types: Metamorphic• Rocks that have experienced heat and pressure
• Classified by texture1. Granular
-Quartz > quartzite-Calcite > marble
Rock types: Metamorphic• Rocks that have experienced heat and pressure
• Classified by texture2. Foliated
-amount of temperature, pressure, recrystallization
Slate
Phyllite
Schist
Gneiss
Rock types: Metamorphic processes• Hydrothermal metamorphism
-low T, low P-associated with water near igneous intrusions-examples: pegmatite, serpentinite, soapstone
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
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Rock types: Metamorphic processes• Contact metamorphism
-high T, low P-associated with igneous intrusions-examples: hornfels, marble, quartzite
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Metamorphic processes• Regional (Barrovian) metamorphism
-Low-high T, intermediate P-associated with orogenic events (mountain building)-examples: slate, phyllite, schist, gneiss
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Metamorphic processes• Blueschist
-high T, low P-associated with subduction zones-examples: blue color from mineral glaucophane
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Metamorphic processes• Eclogite
-moderate T, very high P-metamorphism occurs in the mantle (rarely outcrops)
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html