The Earth’s Structure & Plate Tectonics

The Earth’s Interior Composed of 4 layers –Crust –Mantle –Outer Core –Inner Core

Crust 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)

Mantle 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

Core 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 Tectonics The Earth’s lithosphere is made up of tectonic plates Plate tectonics – the movement of these lithospheric plates

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 development PLATETECTONICS 1915 – Alfred Wegener published hypothesis of continental drift existence of single “super-continent” Pangaea ~ 200 million years ago Pangaea broke into smaller pieces, & “drifted” to present positions

200 million years ago P E G N A A GONDWANALAND LAURASIA A

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 ~ million years ago Historical development PLATETECTONICS

Paleoclimate evidence

Monitoring 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: videovideo GPS Facts: Garmin GPS factsGarmin GPS facts

Monitoring 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 Magnetism Certain minerals are magnetic -They loose magnetization when heated above Curie point (580 o C for iron) -When cooled below Curie pt, magnetic grain aligns w/ Earth’s magnetic field

n animation:sea floor spreading animationsea floor spreading animation nocean ridges are above mantle upwellings, which cause seafloor to spread, like a conveyor belt n magma replaces seafloor as it moves away, becoming new oceanic crust n deep ocean trenches are locations where oceanic crust dives back into planet Sea Floor Spreading

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

n 1963, Vine & Matthews connected seafloor spreading & continental drift, from magnetic field reversals recorded in cooling lavas of new seafloor n symmetric patterns (“stripes”) on either side of spreading center (mid-ocean ridge) n changes in width of a given stripe indicate changes in spreading rate. Seafloor Magnetic Stripes

nhttp://earthguide.ucsd.edu/eoc/teachers/t_tecto nics/p_seafloorspreading.html

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

Transform Fault Boundaries Plates move past each other at cracks in the lithosphere (called faults) Transform fault boundary – horizontal movement between two plates

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