Lecture #4
Week #2
Fullerton College
ESC 130F, Lecture #4
A.K. Morris, Ph.D.
Chapter 3
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„1596: Dutch map maker Abraham Ortelius 2
„1620: Sir Francis Bacon also noted continents on opposite Atlantic coasts fit like puzzle pieces
„Postulated that the Americas were torn from
Europe and Africa by earthquakes and flood
The idea was ridiculed
in those days
Ortelius 1596 - Theatrum Orbis Terrarum
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„A fixed Earth
HondiusHondius-Jansson 1629 world map
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1858 – Antonio Snider‐Pellegrini – French geographer
La Création et ses mystères dévoilés
„Continents and Oceans don’t move!
„Topography results from divine guidance
„Chose to ignore the critics
„Found identical plants in
Europe and N. America
„Postulated that the continents
were connected in the past
„Separation was due to the Noah flood and eruptions of material out of Earth’s interior along cracks
Breaking from dogma is hard
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Lecture #4
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1908 – Alfred Wegener – the man who history
“officially” associates with continental drift
1908 – Frank Bursley Taylor
„First proposed continental drift by “Crustal Movement”
„“… great world belt … of Tertiary fold‐mountains almost encircling the earth”.
„Explained mountain formations
„Cites the mid‐Atlantic ridge as the original place of the “great fracture”.
„German meteorologist. Made key observations:
„ Identical fossil flora and fauna in N. America and Europe. Anomalies? „ Identical snail species in Scandinavia and New England
„ Marsupials in Australia.
„World continents must’ve been together in the geologic past
„1915 Published “The Origin of Continents and Oceans”
„Called the landmass “Pangaea”.
„But he was an obscure crackpot American…
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Wegener’
Wegener’s Pangaea
Triassic
250 mya
This explained the fossil anomalies
„Also explained the presence of tropical fossils near the poles
„Still downplayed among scientists!
„WHY???
„Continental Drift had no MECHANISM
Fossil conifer from Antarctica, I. Poole, 1999
Fossil beech wood from Antarctica, R. Hunt, 1999
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Lecture #4
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„Recall sonar developed in WW II
„Could now ‘see’ beneath ocean
„Late 1940s – 1950s HUGE advances in
seafloor mapping
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„Harry Hess – Princeton professor and Navy
„At the same time as Hess…
captain.
„Fathometer used for landing maneuvers. Hess
never turned it off!
„Ocean NOT covered thickly with sediment.
„Huge mountain range down the Atlantic with a
canyon in the middle. Earth is splitting apart!
„He wrote it up and…
„ WAS IGNORED!
„Robert Dietz – Scripps oceanographer
„Described the geology of mid-ocean ridges
„1960s core samples: young rock
at rift, gets older further away.
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„1963!
„Vine and Mathews on the Carlsberg Ridge
Magnetic Polar Reversal
„Morley in the NE Pacific.
„Mobile crust finally an accepted concept.
„1967-68 Named the moving masses “plates”.
„Vine-Mathews-Morley Hypothesis
„Plate Tectonics is born!
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„ Magnetic Polar reversal even debuts in a movie !!!
„ Waterworld – video clip
„Polar Wandering
„Polar Reversal
2050?
2005
1903
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„Oldest rock furthest from ridges
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Mid‐Atlantic ridge runs
through the center of Iceland.
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„
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Crust & upper mantle = rigid
Lithosphere: crust & mantle 70‐100 km layer
Forms several plates that cover earth surface
Floats on asthenosphere, upper mantle “fluid”
Plates move on top of asthenosphere
Spread at spreading zones Crust
Fig. 3.4
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Even more evidence has emerged…
Similarities in:
1. Geology
2. Fossils of
extinct spp.
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Fig. 3.5
•All crusts contain oceanic and continental
•Different proportions
•E.g. Pacific plate vs. Eurasian plate
•Dimensions change. E.g. Indo‐Australian plate split
8-12 larger plates
20 or so smaller plates
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Fig. 3.8.a
y Edges of plates interact in 3 main ways…
• Divergent Boundaries (separating)
• Convergent Boundaries (coming together)
• Transform Boundaries (sliding past)
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Fig. 3.8.b
• We’ve got sea floor spreading
• Is the earth getting bigger?
• What must be occurring elsewhere?
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y As new lithosphere created, old destroyed at trenches
y Formed when two plates collide and one dips below (subduction)
y Trenches = subduction zones
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•Depends on density. Why?
•Explains why never get REALLY old rock in ocean
• Breaks up
• Earthquakes
• Gets hot and melts
• Volcanoes
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• A collision causes development of continental volcanoes
• Forms deep trenches
• May form coastal mountain ranges (Andes of south America).
Fig. 3.10
Chilean Trench
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LEFT OFF HERE 1/29/10
y Causes quakes & volcanoes.
y Volcanoes may rise to create chains of volcanic islands.
y (Aleutian & Mariana Islands)
s
land
tian Is
Aleu
Fig. 3.9
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Mariana Trench
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• Both plates float and neither is subducted b/c of low density. • Causes folding and upward pushing of earth
• India & Asia collide to produce Himalayas
Himalaya Mountain Range
Fig. 3.11
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Plates can’t spread
evenly on spheres
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Northridge Earthquake, January 17, 1994 (4:30am)
© A.K. Morris 2009
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y So what is actually moving the plates?
y No one knows for sure. A few plausible explanations:
y Convection Model
y Ridge‐Push, Slab‐Pull Model
y Plate‐Driven Plate Tectonics Model
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Gravity is the important force
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Combination of forces
Fig. 3.22
Fig. 3.21
Trench suction
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Fig. 3.13
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“I am Archean from
the Planet Cratons”
Pangaea
(from Wagener)
≈ 250 mya
• Reeeeally old Earth Crust
(>2.5 bya)
• Pieces all over the world
• Implies there may have been one originally
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Fig. 3.15
250 mya
150 mya
2,500 mya
540 mya
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100 mya
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40 mya
today
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Fig. 3.17
Fig. 3.18
• Super Sci-Fi Science – proposed
in 1996
by UNC Prof John Rodgers
• Bordering on Sci-Fi –
proposed in 1990 based on
paleomagnetic and geochemical data
• 3,000 mya supercontinent cycle
• worked only with craton fragments
• 1,100–1,000 mya came together
• 850–800 mya broke up
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Fig. 3.19.a-c
• Genesis and elimination of oceans
• Oceans form by a rifting of a continent
• Ocean destroyed by subduction zone
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Fig. 3.19.d
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200 m.y. the vast Pacific will close
Fig. 3.19.d-g
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