topic vi: the dynamic earth

Topic VI: Topic VI: The Dynamic EarthThe Dynamic Earth

Earth’s Four Zones: Earth’s Four Zones: 1.1. CrustCrust: the outside or surface—made up of : the outside or surface—made up of

mostly igneous rock with a thin shell of mostly igneous rock with a thin shell of sedimentary rock on the outsidesedimentary rock on the outside

a.a. Oceanic CrustOceanic Crust: only about 5 miles thin—: only about 5 miles thin—made up of made up of basaltbasalt (dense) (dense)

b.b. Continental CrustContinental Crust: about 30 miles thick—: about 30 miles thick—made up of made up of granite granite (less dense)(less dense)

Crust types….Crust types….

2.2. MantleMantle: the middle layer that the crust : the middle layer that the crust “floats” on—divided into 3 parts:“floats” on—divided into 3 parts:

a. Rigid Mantleb. Asthenospherec. Stiffer Mantle

**the **the LithosphereLithosphere is the crust AND rigid mantle is the crust AND rigid mantle

**the MOHO—boundary between the crust and mantle**the MOHO—boundary between the crust and mantle

3.3. Outer CoreOuter Core: liquid : liquid nickel & ironnickel & iron

4.4. Inner CoreInner Core: solid because of high : solid because of high pressure / made of pressure / made of nickel and ironnickel and iron

Why Nickel & Iron?.....Why Nickel & Iron?.....Meteorites!Meteorites!—more dense, sank to “center” —more dense, sank to “center”

of young molten Earthof young molten Earth

What happens the deeper you go in the Earth?What happens the deeper you go in the Earth?

Density, temperature, pressure all Density, temperature, pressure all increaseincrease

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How do we know what Earth’s interior looks like?How do we know what Earth’s interior looks like?

Study Earthquake waves (like an ultrasound)Study Earthquake waves (like an ultrasound)

What does the heat from the core cause? What does the heat from the core cause?

Continental DriftContinental Drift: the : the lithosphere (crust)lithosphere (crust) is made up of solid is made up of solid platesplates that move ( that move (plate plate tectonicstectonics) )

Plates move because of Plates move because of heat that risesheat that rises in the in the AsthenosphereAsthenosphere due to density due to density differences—called differences—called convection convection currents or cellscurrents or cells

More Convection Currents….

Even More Convection Currents:

Plate BoundariesPlate Boundaries: areas on Earth where : areas on Earth where two plates are interacting with each othertwo plates are interacting with each other

**this isWhere mostVolcanoes /EQ’s / and MountainsOccur

Three Types of Plate Boundaries:Three Types of Plate Boundaries:1.1. ConvergentConvergent: plates collide (subduction : plates collide (subduction

zone—plate moves under another)zone—plate moves under another)

2. Divergent: plates move apart

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3. Transform: plates move side to side

USA

HotspotsHotspots: places in Earth’s crust with an : places in Earth’s crust with an unusually high heat flow (Hawaii) unusually high heat flow (Hawaii)

**plates move only a few centimeters per **plates move only a few centimeters per year—about as fast as your fingernails year—about as fast as your fingernails growgrow

Evidence of Plate Motion:Evidence of Plate Motion:

1.1. Deformed (messed up) Rock Strata (layers)Deformed (messed up) Rock Strata (layers)

**because of gravity, all **because of gravity, all sedimentary rockssedimentary rocks formed in horizontal layers (formed in horizontal layers (law of original law of original horizontalityhorizontality) )

If not horizontal, the layers can be…If not horizontal, the layers can be…

a.a. TiltedTilted: force pushes rock layers from 1 : force pushes rock layers from 1 side side

Force

b.b. FoldedFolded: forces push on rock layers from : forces push on rock layers from 2 sides (rocks are not broken) 2 sides (rocks are not broken)

Force Force

c.c. FaultedFaulted: a break in the earth’s crust : a break in the earth’s crust where movement occurswhere movement occurs

Force Force

Williamsport, PAWilliamsport, PA

2.2. Displaced FossilsDisplaced Fossils: marine fossils found : marine fossils found in rock layers several hundred feet above in rock layers several hundred feet above sea level (uplift)sea level (uplift)

3.3. SubsidenceSubsidence: sinking of rock layers : sinking of rock layers (fossils being found deep underground)(fossils being found deep underground)

4.4. Continents Fit together like a puzzleContinents Fit together like a puzzle

5.5. Rock layers and fossils may be Rock layers and fossils may be correlated (matched-up) across oceanscorrelated (matched-up) across oceans

6.6. Continuation of mountain chains from Continuation of mountain chains from continent to continentcontinent to continent

7.7. Evidence (fossils / rock) indicates that Evidence (fossils / rock) indicates that the climate was much different (coal the climate was much different (coal found in Antarctica)found in Antarctica)

Coal forms in a tropical swamp

New York: Salt and Marine Fossils

Evaporated Ocean

8.8. Sea Floor Spreading (Divergent Plate Sea Floor Spreading (Divergent Plate Boundary)Boundary)

Evidence of Sea-Floor Spreading:Evidence of Sea-Floor Spreading:

a.a. Radioactive DatingRadioactive Dating found that as rocks found that as rocks get closer to the continents they get older get closer to the continents they get older

**more on this later

b.b. Reversal of Magnetic PolarityReversal of Magnetic Polarity: the : the Earth’s magnetic poles switch from time Earth’s magnetic poles switch from time to time—this can be seen because of to time—this can be seen because of iron in basaltic ocean rocksiron in basaltic ocean rocks

**Iron (magnetic) in the liquid basalt line up like compass needles (stays when it hardens)

Hot ColdCold

YoungOld Old

Mid-Ocean Ridge

EarthquakesEarthquakesEarthquakesEarthquakes: a sudden shaking or : a sudden shaking or

trembling of rock layers along a fault line trembling of rock layers along a fault line or plate boundary (the rock layers slip)or plate boundary (the rock layers slip)

**energy is released and is transmitted by 2 **energy is released and is transmitted by 2 types of wavestypes of waves

1.1. Primary or “P” waves (Compressional Primary or “P” waves (Compressional ))2.2. Secondary or “S” waves (Shear waves Secondary or “S” waves (Shear waves ))

Seismic StationsSeismic Stations: located around the world—: located around the world—used to study earthquake waves.used to study earthquake waves.

SeismographsSeismographs: device that records the : device that records the vibrations of earthquake wavesvibrations of earthquake waves

waves

P-wavesP-waves: travel “: travel “pphastest” so it arrives at hastest” so it arrives at the seismic stations “the seismic stations “pphirst” hirst”

Can travel through Can travel through solid rocksolid rock & & magmamagma (can (can travel through ALL Layers)travel through ALL Layers)

S-wavesS-waves: travels : travels sslower so it arrives at lower so it arrives at seismic stations seismic stations ssecondecond

Only travel through SOLIDS—all layers Only travel through SOLIDS—all layers EXCEPT LIQUID outer core and Solid Inner EXCEPT LIQUID outer core and Solid Inner CoreCore

Origin Time Origin Time (what time EQ began at (what time EQ began at the epicenter)the epicenter)

Epicenter Felt

EpicenterEpicenter: point on the surface (city) : point on the surface (city) directly above the directly above the focusfocus (in the interior (in the interior where the earthquake occurs) where the earthquake occurs)

**P & S waves travelout in all directions

1.1. Get P and S wave arrival times from Get P and S wave arrival times from 33 differentdifferent seismic stations seismic stations

How is an earthquake’s epicenter located on a map?How is an earthquake’s epicenter located on a map?

2.2. Using the ESRT’s, find the distances from the Using the ESRT’s, find the distances from the epicenter for each station epicenter for each station

**The larger difference between P and S wave arrival times means that the seismic station is farther away from the epicenter

3.3. Using the distances and a compass, Using the distances and a compass, draw 3 circles draw 3 circles

**Where the three circles intersect the epicenter is located

**as these P & S waves travel, they change speed **as these P & S waves travel, they change speed and bend (refract) as they enter different and bend (refract) as they enter different substances and / or different densities substances and / or different densities

**remember the ultrasound?

**this is how we knowwhat Earth’s interiorLooks like

Shadow ZoneShadow Zone: a region on the Earth where : a region on the Earth where no P and S waves are recorded (because of no P and S waves are recorded (because of refraction & lack of s-waves)refraction & lack of s-waves)

Earthquakes in NY (rare)Earthquakes in NY (rare)

**Remember Lat / long

Earthquake StrengthEarthquake StrengthRichter Richter MagnitudeMagnitude Scale Scale: measures the : measures the

amount of energy an earthquake releases amount of energy an earthquake releases (uses seismographs)(uses seismographs)

Strong Weak

**1 (little energy) 10 (tremendous energy)

Mercalli Mercalli IntensityIntensity Scale Scale: based on what : based on what damage people observe and shaking felt—damage people observe and shaking felt—can be used for historical earthquakes can be used for historical earthquakes (newspaper articles)(newspaper articles)

Roman Numerals:

I (little) XII (lots)

in the cases of both scales, the closer you are to the in the cases of both scales, the closer you are to the epicenter, the more you will feel the shaking—meaning epicenter, the more you will feel the shaking—meaning the numbers will be higher the closer you are to the the numbers will be higher the closer you are to the quakequake

Does this make sense…..Does this make sense….. The closer you are to the epicenter, both P & The closer you are to the epicenter, both P &

S waves will be found at nearby seismic S waves will be found at nearby seismic stationsstations

Stations on the other side of the world may or Stations on the other side of the world may or may not pick up P & S wavesmay not pick up P & S waves

Earthquakes can cause:Earthquakes can cause:a.a. TsunamisTsunamis: seismic sea waves (oceans): seismic sea waves (oceans)

—can cause severe coastal damage —can cause severe coastal damage

b.b. Landslides / Landslides / avalanchesavalanches

c.c. FiresFiresd.d. Train / Car wrecks Train / Car wrecks

Earthquake Emergency PlanningEarthquake Emergency Planninga.a. Get away from windows, chimneys Get away from windows, chimneys b.b. Get under something strong (doorway) Get under something strong (doorway) c.c. Don’t try to get outside (last < 30 sec)Don’t try to get outside (last < 30 sec)

VolcanoesVolcanoes: mountain composed of : mountain composed of extrusive igneousextrusive igneous rocks that can erupt rocks that can erupt gases, lava, ash, and rocks onto Earth’s gases, lava, ash, and rocks onto Earth’s surfacesurface

Volcanic HazardsVolcanic Hazardsa.a. Ash (buries everything)Ash (buries everything)

b.b. Lava (usually moves slow—people Lava (usually moves slow—people avoid)avoid)

c.c. Shooting, hot rocks (bombs)Shooting, hot rocks (bombs)

d.d. Mudslides (ash mixes with snow and dirt Mudslides (ash mixes with snow and dirt from mountain tops) from mountain tops)