evolution of earth - seattle central collegefaculty.seattlecentral.edu/kgagnon/env170/evolution of...

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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


Convergent: oceanic-oceanic plate– Oceanic plate subducted– Oceanic trench– Island Arc


• Divergent: plates move apart


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• Divergent: plates move apart


Juan de Fuca ridge

• Divergent: plates move apart– Hydrothermal vents: seawater migrates through

cracks in ocean crust


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


Continental transform fault


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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


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


Rock types: Igneous rock distribution


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


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


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Sandstone (quartz sand)

Shale (clay)



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


Rock types: Sedimentary


• 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)


Oolitic limestone

Dolomite crystals (Mg)

Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Carbonates (CaCO3)


Fossiliferous rock (coquina)Chalk

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Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Silicate


Chert (SiO2)

Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Salts


Gypsum (CaSO4H2O)

Halite (NaCl)

Rock types: Sedimentary• Compounds that weather and dissolve in seawater willeventually form: Accumulation of plant material


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


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Rock types: Metamorphic processes• Contact metamorphism

-high T, low P-associated with igneous intrusions-examples: hornfels, marble, quartzite


Rock types: Metamorphic processes• Regional (Barrovian) metamorphism

-Low-high T, intermediate P-associated with orogenic events (mountain building)-examples: slate, phyllite, schist, gneiss


Rock types: Metamorphic processes• Blueschist

-high T, low P-associated with subduction zones-examples: blue color from mineral glaucophane


Rock types: Metamorphic processes• Eclogite

-moderate T, very high P-metamorphism occurs in the mantle (rarely outcrops)


evolution of earth - seattle central collegefaculty.seattlecentral.edu/kgagnon/env170/evolution of...

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