The Earth’s Structure &The Earth’s Structure &Plate Tectonics Plate Tectonics

The Earth’s InteriorThe Earth’s Interior

• Composed of 4 layers– Crust– Mantle– Outer Core– Inner Core

CrustCrust

• Temperature: Over 175 ºC (347 ºF)

• Topmost layer of the Earth

• Relatively cool

• Made of rock

• 2 types of crust– Oceanic (5-10 km thick)– Continental (30-50 km thick)

MantleMantle

• Temperature: Over 1250 ºC (2282 ºF)

• Makes up about 80% of the Earth’s volume

• ~ 2900 km thick

• Lithosphere - rigid upper layer of the mantle and the crust

• Asthenosphere – “plastic-like” lower layer of the mantle

CoreCore

• Temperature: Over 6000 ºC (10,832 ºF)

• Outer core – liquid– Pressure from the mantle & crust do not allow

the metals in the outer core to become gasses

• Inner core – solid– Pressure from the mantle and crust do not

allow the metals to become liquid

Plate TectonicsPlate Tectonics

• The Earth’s lithosphere is made up of tectonic plates

• Plate tectonics – the movement of these lithospheric plates

Why do the plates move?Why do the plates move?

• One theory suggests that plates move due to the convection currents in the asthenosphere (“plastic” inner portion of the mantle)

Historical developmentHistorical developmentPLATEPLATETECTONICSTECTONICS

• 1915 – Alfred Wegener published hypothesis ofcontinental drift

• existence of single “super-continent” Pangaea • ~ 200 million years ago Pangaea broke into

smaller pieces, & “drifted” to present positions

200 million years ago

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• Evidence supporting continental drift– Fossils: Strikingly similar fossils found on

different continents– Rock Formations: Mountain belts on one

continent match up with another– Paleoclimates: Ice sheets covered big areas

of southern hemisphere ~ 220-300 million years ago

Historical developmentHistorical developmentPLATEPLATETECTONICSTECTONICS

Paleoclimate evidence

Monitoring Plate MovementMonitoring Plate Movement

• The Global Position System (GPS) is used to monitor the movement over time of the plates

• GPS measurements are used to record recent and current plate movement

• How GPS Works: video

• GPS Facts: Garmin GPS facts

Monitoring Plate MovementMonitoring Plate Movement

• Sea-Floor Spreading– This is used to measure plate movement prior

to GPS technology– Geologists look at the magnetic patterns of

oceanic crust (crust below the ocean) to determine the age of the rock and movement of plates

Rock MagnetismRock Magnetism

Certain minerals are magnetic -They loose magnetization when heated above

Curie point (580oC for iron)-When cooled below Curie pt, magnetic grain

aligns w/ Earth’s magnetic field

animation:sea floor spreading animation

ocean ridges are above mantle upwellings, which cause seafloor to spread, like a conveyor belt

magma replaces seafloor as it moves away, becoming new oceanic crust

deep ocean trenches are locations where oceanic crust dives back into planet

Sea Floor SpreadingSea Floor Spreading

Earth’s magnetic field “reverses” recorded in lava flows

Geomagnetic ReversalsGeomagnetic Reversals

1963, Vine & Matthews connected seafloor spreading & continental drift, from magnetic field reversals recorded in cooling lavas of new seafloor

symmetric patterns (“stripes”) on either side of spreading center (mid-ocean ridge)

changes in width of a given stripe indicate changes in spreading rate.

Seafloor Magnetic StripesSeafloor Magnetic Stripes

http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_seafloorspreading.html

Divergent Plate BoundariesDivergent Plate Boundaries

• 2 plates move apart at a mid ocean ridge(the divergent plate boundary)

• Magma fills the gap created from this movement

• Magma cools as it reaches the Earth’s surface making new oceanic crust

• Rift Valleys form when the divergent boundary is below a continent

Divergent Plate BoundariesDivergent Plate Boundaries

• When a divergent plate boundary is beneath a continent, the lithosphere of the continent bulges up and is stretched sideways

• The continent forms a crack at the boundary, creating a rift valley

• This rift valley eventually becomes a new ocean

Convergent Plate BoundariesConvergent Plate Boundaries

• Two plates move towards each other

• Oceanic plates dive beneath continental or oceanic plates (called subduction)

• Creates deep ocean trenches

Wall diving- coral reefs form over time on the “walls” of deep sea trenches. Many are thousands of feet deep.

Convergent Plate BoundariesConvergent Plate Boundaries

• Mountains form at the convergent plate boundaries one of two ways:– as magma from the mantle rises, continental

crust is pushed upward– Plates collide and great masses of rock pile

on top of each other (Himalayas)

Convergent Plate BoundariesConvergent Plate Boundaries

• Volcanoes form at the convergent plate boundaries as magma rises to the surface and cools

Transform Fault BoundariesTransform Fault Boundaries

• Plates move past each other at cracks in the lithosphere (called faults)

• Transform fault boundary – horizontal movement between two plates

EarthquakesEarthquakes

• Occur at plate boundaries– Plates slide past each other creating pressure– Rocks break along the fault line– Energy is released, called seismic waves