Embed Size (px)
Citation preview
The Birth of a Theory:
Continental Drift
Throughout history, most people believed that the continents had always been in the same
positions that they are today.
In 1915, a German scientist, named Alfred Wegener,
proposed the idea of “Continental
Drift”.
Alfred Wegener
Alfred Wegener
1. The earth is always changing, land masses (continents) are constantly moving.
What is the theory of continental drift?
The hypothesis:
What is the theory of continental drift?
2. Originally all of the continents were joined together in one super-continent called Pangaea and slowly moved to their current positions.
http://www.auburn.edu/academic/science_math/res_area/geology/camp/Pangaea.jp
g
What evidence did Wegener use to support his theory
of continental drift?
http://www.abdn.ac.uk/zoohons/lecture1/img008.GIF
1 - Earth’s landmasses—especially South America and Africa—fit together
like a jigsaw puzzle.
Fossil Evidence
2 - The fossils from the exact same land-living animals and plants are found on continents now separated by the Atlantic Ocean.
http://wrgis.wr.usgs.gov/docs/parks/animate/A15.gif
Matching Rock Layers
3 - The rocks of South America match the rocks of Africa in age and layers.
Matching Mountains
4 – The Appalachian Mountains match the mountains in Ireland and Scotland.
Fossils
5 – Fossils of tropical swamp plants were found in the eastern United Sates, Europe, and Siberia.
Glacier Evidence
6 - Glaciers scars are found on continents such as Asia,
India, and Australia which are too warm for glaciers today.
Panthalassa
Evidence of “continental drift”—.
•Physical fit of continents•Fossil evidence•Rock layer sequences•Glacial evidence•Matching mountain ranges
Key concepts
Alfred Wegener
Was Wegener’s theory believed?
• Scientists did not believe Wegener’s ideas because he couldn’t explain HOW the continents moved!!!
NO
Harry Hess
Harry Hess was a navy sea captain and scientist that
proposed the idea of seafloor
spreading.
A bit of history…
Sonar was developed during World War II to locate German submarines.
After the war, sonar was used to map the ocean floor.
Many new features were discovered…
1 – a huge volcanic mountain range in the middle of the Atlantic Ocean (M.A.R.)
M.A.R.
2 – deep trenches in the Pacific Ocean
http://www.harcourtschool.com/glossary/science/images/gr6/trench6.jpg
Hypothesis:
The ocean floor is getting bigger at the ridges and smaller at
the trenches.
Evidence:•The newest rocks are on the ocean floor along the Atlantic Ridge.
oldest
youngest
oldest
•The oldest rocks are on the continents.•The continents are much older than the
ocean floor!
Volcanoes located along ocean ridges erupt, creating new ocean floor.
Iceland’s Volcanoes
http://www.navis.gr/photos/images/iceland.jpg
http://www.sas.upenn.edu/African_Studies/Map_Satellite/World_Map1_11218.gif
World Earthquake Data
http://www.sas.upenn.edu/African_Studies/Map_Satellite/World_Map1_11218.gif
The earth’s lithosphere is broken into huge sections called plates that are in constant motion.
Plate Tectonics
Plate Tectonics – The idea that the earth’s surface is broken into huge pieces called
plates. These plates are constantly moving and bumping into each other,
carrying the continents and ocean floor to new locations.
How fast are the plates moving?
You may wonder…
How are the continents moving?
Convection Cells!
Magma circulates under the ground, pushing around the plates. (Convection Cells)
What are the plates made of?
• Ocean plates are made of basalt.
• Continental plates are made of granite.
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
Divergent Plate Boundaries
Two land or ocean plates move apart in opposite directions. Magma flows to the surface between
them creating new crust.
ocean floor
M.A.R.granite granite
basalt
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.
trench volcanic mountains
basalt
granite
What are the plates made of?
• Ocean plates are made of basalt.
• Continental plates are made of granite.
Andes Mountains
Subduction zones form chains of volcanic mountains along the shoreline.
Pacific Ocean
Cascade Mountains
The Cascade Mountains
Collision Zones
Two continents hit head-on, crinkling up the land into a high mountain chain.
granitegranite
mountains
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.
basalt basalt
The Aleutian Islands
Island ArcDivergent Boundary
Subduction Zone
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_correlation_lge.jpg
• http://earthobservatory.nasa.gov/Library/Giants/Wegener/Images/plate_boundaries.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/ima
ges/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
• http://wrgis.wr.usgs.gov/docs/parks/animate/A08.gif
• http://jan.ucc.nau.edu/~rcb7/230NAt.jpg
• http://pubs.usgs.gov/publications/graphics/hess.gif
• http://www.minerva.unito.it/sis/hess/Image20.gif
• http://atlas.geo.cornell.edu/education/instructor/tectonics/images/divergent_small_white.gif
• http://www.thepubliccause.net/LoudSONAR/Active%20SONAR%20Graphic.jpg
• http://chartmaker.ncd.noaa.gov/HSD/images/sonar.gif
• http://www.glossary.oilfield.slb.com/files/OGL98090.jpg
• http://www.innovations-report.com/bilder_neu/20175_Pacific_basin.jpg
• http://pao.cnmoc.navy.mil/pao/Educate/OceanTalk2/images/image19a.gif
• http://www.bedford.k12.ny.us/flhs/science/kwoodell/iceland/thingvellir2.jpg
• http://www.christiananswers.net/q-aig/contdrift1.gif
• http://www.tulane.edu/~sanelson/images/iceland.gif
• http://images.google.com/images?hl=en&lr=&q=volcanic+areas+of+Iceland&btnG=Search
• http://www.seismo.unr.edu/ftp/pub/louie/class/plate/harvard-map.GIF• http://www.kidscosmos.org/kid-stuff/mars-trip-graphics/mt-st-helens-before.jpg• http://www.serve.com/wizjd/pics/rain01_m.jpg• http://academic.emporia.edu/aberjame/tectonic/cascade/plates.gif• http://www.kidscosmos.org/kid-stuff/mars-trip-graphics/volcano-map-2.jpg• http://www.yenwen.net/CraterLake01/WatchmanTop01_2.JPG• http://www.crater.lake.national-park.com/crat1.htm
Lithosphere
