Crust: thinnest layer, least dense

Mantle: upper most part is able to flow very slowly (asthenosphere)

Core: Lower area is a solid and outer areais a liquid. Makes up 1/3 of Earth’s mass.The hottest layer with the most pressure.

Key conceptsEarth Composition

starryskies.com/.../Earth/ under_the_surface.html

Evidence of “continental drift”—.

•Physical fit of continents•Fossil evidence•Measurements of movement•Rock layer sequences•Glacial evidence

Key concepts

Alfred Wegener

What is the theory of continental drift?

• the idea that the continents were once all joined together in one super-continent called Pangaea and slowly moved to their current positions

http://wrgis.wr.usgs.gov/docs/parks/animate/A08.gif

What evidence supports the theory of continental drift?

http://www.abdn.ac.uk/zoohons/lecture1/img008.GIF

Shoreline Fit of the Continents

Fossil Evidence

The fossils from the exact same animals are found on continents separated by vast oceans.

Matching Rock Layers

Glacier Evidence

Glaciers scars are found on continents which are today too warm for glaciers.

How fast are the plates moving?

You may wonder…

Why are the continents moving?

Seafloor Spreading

The oceans are widening along the mid-ocean ridges.

Volcanoes located along ocean ridges erupt, creating new ocean floor.

Plates—continental crust, oceanic crust

Features—faults, trenches, mid-ocean ridges, folded mountains, hot spots, volcanoes

Related actions —earthquakes, volcanic activity, seafloor spreading, mountain building, convection in mantle.

Key concepts

The earth’s lithosphere is broken into huge sections called plates that are in constant motion.

What are the plates made of?

• Ocean plates are made of basalt.

• Continental plates are made of granite.

Divergent Plate Boundaries

Two land or ocean plates move apart in opposite directions. Magma flows to the surface between

them creating new crust.

Mid-Atlantic Ridge = Divergent Boundary

http://www.geo.lsa.umich.edu/~crlb/COURSES/270/Lec12/spreexamples.jpeg

Iceland – a continent directly over the Mid-Atlantic Ridge

Subduction Zones

• An ocean plate and a continental plate hit head-on. The ocean plate subducts under the continent forming a trench. The subducting plate melts. Magma rises to the surface creating a string of volcanic mountains parallel to the shoreline.

Andes Mountains

Subduction zones form chains of volcanic mountains along the shoreline.

Collision Zones

Two continents hit head-on, crinkling up the land into a high mountain chain.

India’s Collision with Asia

Himalayas

The Himalayas Are Born…

Island Arcs

Two ocean plates hit head-on. One ocean plate is forced to subduct under the other forming an ocean trench.

The subducting plate melts. Magma rises to the surface forming a string of volcanic islands parallel to the trench.

The Aleutian Islands

Forces—tension, compression shearing

Key concepts

Ask a Geologist

Ask an earth scientist

How does tectonic activity affect the earth’s crust?

• Builds mountains• Creates deep ocean trenches• Causes earthquakes• Create volcanoes

Ocean Trenches

http://www.nhusd.k12.ca.us/ALVE/wow/Ocean/seafloor.gif

Volcanoes

Most volcanoes occur at plate boundaries…

http://www.thirteen.org/savageearth/hellscrust/assets/images/ringoffire.jpg

Recent patterns of earthquake and volcanic activities; maps showing the direction of movement of major plates and associated earthquake and volcanic activity

Compressional boundaries: folded mountains, thrust faults, trenches, lines of volcanoes (e.g. Pacific “ring of fire”)

Tensional boundaries: mid-ocean ridges, rift valleys

Shearing boundaries: lateral movement producingfaults (e.g. San Andreas Fault).

Real-world contexts:

http://www.gfz-potsdam.de/pb2/pb22/projects/mamba.html

Resources• http://www.calstatela.edu/faculty/acolvil/plates/pangaea.jpg• http://platetectonics.pwnet.org/img/wegener.jpg• http://home.tiscalinet.ch/biografien/images/wegener_kontinente.jpg• http://library.thinkquest.org/17457/platetectonics/comic.jpg• http://www.soc.soton.ac.uk/CHD/classroom@sea/carlsberg/images/fossil_c

orrelation_lge.jpg• http://earthobservatory.nasa.gov/Library/Giants/Wegener/Images/plate_bou

ndaries.gif• http://www.calstatela.edu/faculty/acolvil/plates/atlantic_profile.jpg• http://pubs.usgs.gov/publications/graphics/Fig16.gif• http://cps.earth.northwestern.edu/SPECTRA/IMG/basalt.png• http://cc.usu.edu/~sharohl/granite.jpg• http://tlacaelel.igeofcu.unam.mx/~GeoD/figs/tgondvana_ice.jpg• http://www.physics.uc.edu/~hanson/ASTRO/LECTURENOTES/F01/Lec11/

Pangaea.gif• http://www.poleshiftprepare.com/glacial_striation.jpg

• http://www.ggs.org.ge/plates.jpg• http://earth.geol.ksu.edu/sgao/g100/plots/1008_world_volc_map.jpg• http://www.aeic.alaska.edu/Input/affiliated/doerte/personal/aleutians/ak_map

_big.jpg• http://www.4reference.net/encyclopedias/wikipedia/images/

Aleutians_aerial.jpg• http://www.avo.alaska.edu/gifs/2-3/02-95-03.jpg• http://www.soc.soton.ac.uk/CHD/classroom@sea/carlsberg/images/

island_arc.jpg• http://nte-serveur.univ-lyon1.fr/nte/geosciences/geodyn_int/tectonique2/

himalaya/images/Fig5a_inde.gif• http://terra.kueps.kyoto-u.ac.jp/~sake/himalaya.jpg• http://www.andes.org.uk/peak-info-5000/sabancaya.jpg• http://www-step.kugi.kyoto-u.ac.jp/~keizo/photos/andes.JPG• http://www.letus.northwestern.edu/projects/esp/top10/andespage/

andesphysical.jpg• http://www.soc.soton.ac.uk/CHD/classroom@sea/carlsberg/

images/atlantic_tectonics%20.jpg