The Physical EarthThe Physical Earth

The Solar SystemThe Solar System SunSun

–– Terrestrial planets (small, dense, rocky,Terrestrial planets (small, dense, rocky,thin atmosphere)thin atmosphere)»» Mercury, Venus, Earth, MarsMercury, Venus, Earth, Mars

–– Jovian planets (large, light, gaseous, thickJovian planets (large, light, gaseous, thickatmosphere)atmosphere)»» Jupiter, Saturn, Uranus, NeptuneJupiter, Saturn, Uranus, Neptune

–– PlutoPluto

A View of EarthA View of Earth EarthEarth’’s four spheress four spheres

»» Solid EarthSolid Earth(lithosphere)(lithosphere)

»» HydrosphereHydrosphere

»» AtmosphereAtmosphere

»» BiosphereBiosphere

Formation of EarthFormation of EarthEarth is 4.6 billion years old.Earth is 4.6 billion years old. Same age as all other planets and the sun.Same age as all other planets and the sun.Earth formation.Earth formation. Nebular hypothesis. Diffuse cloud of matterNebular hypothesis. Diffuse cloud of matter

rotating in space, formed a disk shaped body, whichrotating in space, formed a disk shaped body, whichlater formed into sun and planets. Planets arelater formed into sun and planets. Planets arecooled and condensed gases that surrounded thecooled and condensed gases that surrounded thesun.sun.

Core DevelopmentCore Development Earth was a homogeneous planet immediately afterEarth was a homogeneous planet immediately after

formationformation But then, a profound reorganization as Earth initiallyBut then, a profound reorganization as Earth initially

heated up due toheated up due to–– collision with other rocky bodiescollision with other rocky bodies–– heat of compressionheat of compression–– Radioactive decay of elementsRadioactive decay of elements

Earth heated up such that much of the interior meltedEarth heated up such that much of the interior melted–– causing dense elements like iron and nickel to sink to the corecausing dense elements like iron and nickel to sink to the core–– lighter elements like silicon and aluminum float to the crustlighter elements like silicon and aluminum float to the crust–– Resulted in a stratified Earth - core, mantle, crustResulted in a stratified Earth - core, mantle, crust

Distribution of ElementsDistribution of Elements More than 100 elements in entire Earth, butMore than 100 elements in entire Earth, but

99% of Earth's mass is made up of only 899% of Earth's mass is made up of only 8elementselements

Whole Earth:Whole Earth: Fe>O>Si>Mg>Ni>S>Ca>Al Fe>O>Si>Mg>Ni>S>Ca>Al (others constitute < 1%)(others constitute < 1%)

Earth's crust Earth's crust O>Si>Al>Fe>Mg>Ca>K>Na O>Si>Al>Fe>Mg>Ca>K>Na (other constitute <1%)(other constitute <1%)

Composition of EarthComposition of Earth’’s Crusts CrustEarthEarth’’s Crusts Crust

Oxygen 46.6%Oxygen 46.6%

Silicon 27.7%Silicon 27.7%

All others 1.5%All others 1.5%

Magnesium 2.1%Magnesium 2.1%

Potassium 2.6%Potassium 2.6%

Sodium 2.8%Sodium 2.8%

Calcium 3.6%Calcium 3.6%Iron 5.0%Iron 5.0%

Aluminum 8.1%Aluminum 8.1%Fig. 10.4, p. 213

Formation of AtmosphereFormation of Atmosphere

Initial atmosphere - HInitial atmosphere - H22, He, N, He, NCurrent atmosphere - NCurrent atmosphere - N22 (78%) (78%)

and Oand O22 (21%), Others (Ar, CO (21%), Others (Ar, CO22,,etc)etc)

Problem - How do we get from initial toProblem - How do we get from initial tocurrent atmosphere?current atmosphere?

4.6 b.y.a. - H4.6 b.y.a. - H22 and He escape into space, and He escape into space,volcanoes provide source of other gasesvolcanoes provide source of other gases

3.5 b.y.a. - O3.5 b.y.a. - O22 appears: Appearance of single- appears: Appearance of single-celled organisms. COcelled organisms. CO22 + sunlight changes to C + sunlight changes to C(in form of sugar) + O(in form of sugar) + O22

0.6 b.y.a. - Atmosphere similar to today0.6 b.y.a. - Atmosphere similar to today(multi-celled organisms appear)(multi-celled organisms appear)

Formation of AtmosphereFormation of Atmosphere

Formation of OceansFormation of Oceans Oceans consist of water (96.5%) and salt (3.5%,Oceans consist of water (96.5%) and salt (3.5%,

mostly dissolved halite, Namostly dissolved halite, Na++, Cl, Cl--)) Sources of waterSources of water

–– volcanic eruptions (water is the major gas released)volcanic eruptions (water is the major gas released)–– water from comets (bodies of ice and rock that collidedwater from comets (bodies of ice and rock that collided

with the Earth)with the Earth)

Source of salt = chemical weathering (dissolution)Source of salt = chemical weathering (dissolution)of rock Earth's oceans probably reached the currentof rock Earth's oceans probably reached the currentamounts of salt and water by 3.5 b.y.aamounts of salt and water by 3.5 b.y.a

Earth StructureEarth StructureCompositional layersCompositional layersCoreCore - Fe,Ni. - Fe,Ni.MantleMantle - compositionally homogenous, - compositionally homogenous,

made up of peridotite rockmade up of peridotite rockCrustCrust - compositionally heterogeneous, - compositionally heterogeneous,

lots of rock typeslots of rock types

Earth StructureEarth StructureMechanical layersMechanical layers Inner and outer coreInner and outer coreMesosphereMesosphere (lower mantle) (lower mantle)AsthenosphereAsthenosphere - warm, ductile, weak, - warm, ductile, weak,

mantle beneath lithospheremantle beneath lithosphereLithosphereLithosphere - cold, brittle, strong, - cold, brittle, strong,

uppermost crust and mantleuppermost crust and mantle

EarthEarth’’s Internals InternalStructure:Structure:

CompositionalCompositionalLayersLayers

Crust:Continental crust (20-70km)Oceanic crust (~6 km)

MantleUpper mantleLower mantle (660km -2900 km)

CoreOuter core (liquid)Inner core

Geological CycleGeological Cycle Earth is an active planet in a constant state ofEarth is an active planet in a constant state of

change.change. Geological processes - continually modify theGeological processes - continually modify the

EarthEarth’’s surface, destroy old rocks (create soil),s surface, destroy old rocks (create soil),create new rocks and add to the complexity ofcreate new rocks and add to the complexity ofground conditions.ground conditions.

Encompasses all the major processes, whichEncompasses all the major processes, whichmust be cyclic.must be cyclic.

Earth movements are vital to the cycle.Earth movements are vital to the cycle.

http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html

IgneousIgneous Rock formed by cooling andRock formed by cooling and

crystallization of magmacrystallization of magma If the cooling occurs at the surface, it is called If the cooling occurs at the surface, it is called extrusiveextrusive

igneousigneous If the cooling occurs in the Earth, it is called If the cooling occurs in the Earth, it is called intrusiveintrusive

igneousigneous Extrusive igneous usually cools fairly rapidly andExtrusive igneous usually cools fairly rapidly and

therefore has smaller crystals than intrusivetherefore has smaller crystals than intrusive Examples: Granite, Basalt, Quartz, Mica, Feldspar,Examples: Granite, Basalt, Quartz, Mica, Feldspar,

ObsidianObsidianhttp://hvo.wr.usgs.gov/hazards/dds24167_L.jpg

Sedimentary RockSedimentary Rock Rock formed by the piling of materialRock formed by the piling of material

over timeover time Sediment is compressed, heated andSediment is compressed, heated and

chemically changed over long periodchemically changed over long periodof timeof time

Examples: Sandstone, Shale, Gypsum,Examples: Sandstone, Shale, Gypsum,Limestone, ChalkLimestone, Chalk

http://realgar.mcli.dist.maricopa.edu/alan/pix/grand-canyon.jpg

Metamorphic RockMetamorphic Rock

Igneous orIgneous orsedimentary rocksedimentary rocksubjected tosubjected totremendoustremendouspressure and heatpressure and heat

Examples: Slate,Examples: Slate,Marble, QuartziteMarble, Quartzite

LithosphereLithosphereLithosphere is divided intoLithosphere is divided into

plates (about 13 major platesplates (about 13 major platesand several smaller ones).and several smaller ones).

Consists of rigid, brittle crustConsists of rigid, brittle crustand uppermost mantle.and uppermost mantle.

History of Continental DriftHistory of Continental DriftHypothesisHypothesis

1596 Abraham 1596 Abraham OrteliusOrtelius: fit of South American & African coasts: fit of South American & African coasts 1620 Francis Bacon: noted same fit1620 Francis Bacon: noted same fit 1782 Benjamin Franklin: suggested that crust of Earth "floated"1782 Benjamin Franklin: suggested that crust of Earth "floated"

on fluid interior (crust broken and disordered by movement ofon fluid interior (crust broken and disordered by movement offluids)fluids)

1885 Edward 1885 Edward SuessSuess–– Similarities between Late Paleozoic plant fossils of Africa, India, SouthSimilarities between Late Paleozoic plant fossils of Africa, India, South

America, Australia & AntarcticaAmerica, Australia & Antarctica–– Carboniferous glaciers on Africa, S. America, Australia, IndiaCarboniferous glaciers on Africa, S. America, Australia, India–– Southern supercontinent of Southern supercontinent of GondwanaGondwana–– Gondwana Gondwana named after province in India where there was glacial andnamed after province in India where there was glacial and

plant evidence (plant evidence (Glosopteris Glosopteris flora)flora)–– LandbridgesLandbridges, which sank beneath the sea, connected present continent, which sank beneath the sea, connected present continent

Continental movement not a new ideaContinental movement not a new idea Wegener developed hypothesis of "continental driftWegener developed hypothesis of "continental drift””.. Proposed "continental drift" - published "Origin ofProposed "continental drift" - published "Origin of

Continents and Oceans" in 1915Continents and Oceans" in 1915–– Pangaea ("all land") existed about 200 MaPangaea ("all land") existed about 200 Ma–– Showed breakup in series of mapsShowed breakup in series of maps–– Few supporters - mostly European and African geologistsFew supporters - mostly European and African geologists–– Ridiculed by American geologistsRidiculed by American geologists–– Can't "sail" continents through oceans (granitic continentsCan't "sail" continents through oceans (granitic continents

too weak to move through stronger basaltic crusttoo weak to move through stronger basaltic crust–– No mechanism to explain movement (Wegener's tidalNo mechanism to explain movement (Wegener's tidal

forces => too weak)forces => too weak)–– Land bridges the answer to explain fossilsLand bridges the answer to explain fossils

Evidence for Continental DriftEvidence for Continental DriftCoastline fitCoastline fitAlignment of mountain rangesAlignment of mountain rangesSimilar Rock SequencesSimilar Rock SequencesFossilsFossilsModern FaunaModern FaunaAncient climatesAncient climates

Idea was revived in 1950Idea was revived in 1950’’s and developeds and developedinto Plate Tectonicsinto Plate Tectonics

Theory of plate tectonics accepted by nearlyTheory of plate tectonics accepted by nearlyall geologists.all geologists.

Plate tectonics explains wide range ofPlate tectonics explains wide range ofgeological phenomenon (volcanism,geological phenomenon (volcanism,earthquakes, earthquakes, orogenesisorogenesis, fossil distributions,, fossil distributions,etc.)etc.)

Plate TectonicsPlate TectonicsBathymetric observations duringBathymetric observations during

WWII and earthquake data setWWII and earthquake data setstage for Plate Tectonics.stage for Plate Tectonics.

These observations are nowThese observations are nowcombined to form the theory ofcombined to form the theory ofplate tectonics.plate tectonics.

Plate BoundariesPlate BoundariesDefined by earthquake data.Defined by earthquake data.

Depths of earthquakes indicateDepths of earthquakes indicatetypes of boundaries.types of boundaries.

Plate BoundariesPlate Boundaries

Plate BoundariesPlate Boundaries Divergent BoundariesDivergent Boundaries

–– Places where plates are coming apartPlaces where plates are coming apart Convergent BoundariesConvergent Boundaries

–– Places where plates crash or crunchPlaces where plates crash or crunchtogethertogether

Transform BoundariesTransform Boundaries–– Places where plates slide past each otherPlaces where plates slide past each other

Earthquakes define zone dipping into mantleEarthquakes define zone dipping into mantle(Benioff zone)(Benioff zone)

Zones around Pacific dipped about 45Zones around Pacific dipped about 45oo toward the toward thecontinentscontinents

Ocean-Continent BoundariesOcean-Continent Boundaries Magmas produced in mantle wedge aboveMagmas produced in mantle wedge above

subducting slabsubducting slab Much ascending magma stalls in continental crust -Much ascending magma stalls in continental crust -

> batholith (roots of volcanic arc)> batholith (roots of volcanic arc)

Transform BoundariesTransform Boundaries Most fracture zones connect segments of mid-ocean ridgesMost fracture zones connect segments of mid-ocean ridges Areas of different water depth on each side of fracture zoneAreas of different water depth on each side of fracture zone Shallow earthquakes occur on transforms between sectionsShallow earthquakes occur on transforms between sections

of mid-ocean ridgeof mid-ocean ridge

Transform BoundariesTransform Boundaries Connect other plate margins (convergent andConnect other plate margins (convergent and

divergent)divergent) San Andreas Fault - on land transform (Pacific plateSan Andreas Fault - on land transform (Pacific plate

sliding north relative to North America)sliding north relative to North America)

Hot SpotsHot Spots Columns of hot material rising throughColumns of hot material rising through

mantle (plumes).mantle (plumes). Source seems to be core-mantle boundarySource seems to be core-mantle boundary

area (D" layer) - low velocity zones inarea (D" layer) - low velocity zones inlower mantlelower mantle

Hot spot fixed in position underneathHot spot fixed in position underneathmoving lithospheric platesmoving lithospheric plates

Hot SpotsHot Spots Islands associated with hot spots (island chains, mid-Islands associated with hot spots (island chains, mid-

ocean ridges, triple junctions).ocean ridges, triple junctions). Iceland (mid-ocean ridge).Iceland (mid-ocean ridge). Galapagos Islands (triple junction).Galapagos Islands (triple junction). Island of Hawaii (mid-plate volcanic chain; hot spotIsland of Hawaii (mid-plate volcanic chain; hot spot

trace).trace). Linear island chains form as plate moves over hotLinear island chains form as plate moves over hot

spot.spot. Hawaiian islands get older in direction of plateHawaiian islands get older in direction of plate

movement (older away from mid-ocean ridge).movement (older away from mid-ocean ridge).