the birth of a theory: continental drift. throughout history, most people believed that the...

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.

http://www.iris.edu/seismon/html/plates.html

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