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Plate Tectonics. The Unifying Theory of Geology. The 4 “Big Ideas” in Geology. The Rock Cycle (Friday’s lecture) By the mid-1700s Antiquity of Earth - “Deep Time” (Wednesday’s Lecture) By the early 1800s, millions of years Faunal Succession (Fossil Record – Core 6) By mid-1800s

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plate tectonics

Plate Tectonics

The Unifying Theory

of Geology

the 4 big ideas in geology
The 4 “Big Ideas” in Geology
  • The Rock Cycle (Friday’s lecture)
    • By the mid-1700s
  • Antiquity of Earth - “Deep Time” (Wednesday’s Lecture)
    • By the early 1800s, millions of years
  • Faunal Succession (Fossil Record – Core 6)
    • By mid-1800s
  • Plate Tectonics
    • By late 1960s
the big ideas earth is old and dynamic

The Big Ideas  Earth is Old and Dynamic

Rather than Young and Static

recall the scientific method
Recall: The Scientific Method
  • Observations
  • Hypothesis (a testable explanation)
    • Includes testing by prediction
  • More observations (testing)
  • If ALL observations fit ---> Theory
the ancient greeks
The Ancient Greeks
  • Knew that Earth was round (not discovered by Columbus) by 300 B.C.
  • In fact Eratosthenes (ca. 250 B.C.) measured its circumference

PhotoNot Available

early observations
Early Observations
  • First European explorers started to gather knowledge on world geography
  • Early 1500s: E.g., Magellan & da Gama
early observations7
Early Observations
  • Francis Bacon (1561-1626) first noted how coasts of Africa and South America fit.

Yikes!!!…

bacon!

slide8

Today it’s

known:

Fit best

along their

continental

shelves

the 1800s
The 1800s
  • Better maps available
  • Some people proposed that all continents could fit together
  • In 1872, British Challenger began mapping ocean floor by soundings
  • Similarities in rocks of NW Europe and NE America were discovered
paleontology

Paleontology

The study of fossils

evidence from paleontology

Evidence from Paleontology

Similar fossils in

South America and Africa

paleoclimatology

Paleoclimatology

The study of ancient climates

in south america africa india and australia at same time the northern hemisphere had lush swamps
in South America, Africa, India, and Australia...At same time the Northern Hemisphere had lush swamps...
slide20
Coal
  • Deposits found in Antarctica brrrrr….
  • Coal requires a warm, lush climate ===>
  • What’s Antarctica like today? ===>
paleomagnetism
Paleomagnetism
  • Magnetic minerals in molten rock align with Earth’s magnetic field
paleomagnetism22
Paleomagnetism
  • When igneous rock cools, magnetism is “frozen in”, like little compasses...
polar wandering
Polar Wandering
  • Different continents indicate different position of North Pole - very strange...
  • Only logical explanation is that the CONTINENTS have moved since the rocks were formed
wegener and continental drift
WEGENER and CONTINENTAL DRIFT
  • In the 1910s Alfred Wegener put all these pieces of evidence together and made the hypothesis of CONTINENTAL DRIFT...
  • The Origin of Continents and Oceans (1915)
continental drift
CONTINENTAL DRIFT
  • When Wegener proposed to fit the continental shelves together, rather than the coastlines, we got a better fit for all modern continents...
slide27
All continents have moved to their present positions from one “supercontinent” he called PANGAEA

- 200 Ma

scientific consensus is that earth is about

Scientific Consensus is that Earth is about

4.5 billion years old

(4.5 Ga)

1912 1945
1912 - 1945
  • A few geologists looked for more evidence during this period...
  • Seismologists began studying the deeper layers of the earth and discovered a dense mantleand liquid outer core.
wwii and sonar
WWII and SONAR
  • Sonar, developed to find enemy subs, was used in the decade after WWII to map the deep sea floor...
sonar
SONAR
  • Previously, most geologists thought the sea floor was rather flat and featureless
  • They were wrong...
  • A diverse topography was discovered
topography of the sea floor34
Topography of the Sea Floor
  • Researchers found an undersea mountain range 40,000 miles long.
  • And a trenches seven times deeper than the Grand Canyon.
  • Even more striking were the geophysical findings...
some geophysics

Some Geophysics

Thousands of drilling samples were taken...

geophysics
Geophysics
  • Paleomagnetism in the deep sea floor rocks indicated that many episodes of magnetic reversals had taken place...
these reversals occur in parallel paired bands on opposite sides of a mid ocean ridge
These reversals occur in parallel paired bands on opposite sides of a mid-ocean ridge.

Radiometric dating showed the rocks get older the farther you get from the ridge.

sea floor spreading
Sea-Floor Spreading
  • In 1962, these data were collected into a theory called SEA-FLOOR SPREADING
    • New crust forms at mid-ocean ridges...
    • Oceanic crust pushes outwards from the ridge and (perhaps) takes the continents along
earthquakes and volcanoes
Earthquakes and Volcanoes
  • Seismology is the study of earthquakes
earthquakes and volcanoes41
Earthquakes and Volcanoes
  • Data indicate that earthquakes and volcanoes do not occur at random locations, rather...
seismology studies
Seismology studies
  • located a zone of weakness where seismic waves travel more slowly
  • It was called the asthenosphere.
  • The rigid lithosphere sits on top of this
finally a unifying theory
Finally, a unifying theory...
  • In 1968, seismologists at Columbia put all the evidence together and came up with the theory of PLATE TECTONICS...
  • This combined the sub-theories of CONTINENTAL DRIFT and SEA-FLOOR SPREADING
plate tectonics46
PLATE TECTONICS

The rigid upper 35 miles or so of the earth (lithosphere) is broken up into a dozen or so plates, which can slide around on the zone of weakness.

mechanism
MECHANISM

Current idea: plates move as a result of mantleconvection, driven by earth’s internal heat

consequences of plate tectonics earthquakes volcanoes mountain ranges

Consequences of Plate TectonicsEarthquakesVolcanoesMountain Ranges

Why it’s a

“Unifying Theory”

slide68
DIVERGENT - pulling apart
    • Mid-Atlantic Ridge
    • Great RiftValley of Africa
slide69
Great

RiftValley

of Africa

slide70
CONVERGENT - coming together
    • Japan
    • Himalaya mountains
volcanoes
Volcanoes
  • Are associated with divergent and convergent plate boundaries ...
  • Why ?
slide75
Pacific rim

“Ring of Fire”

Convergent

and

Divergent boundaries

earthquakes
Earthquakes
  • Are associated with ALL boundary types ...
  • Why ?
mountain building

Mountain Building

“Tectonics”

appalachians
Appalachians

Started forming 400 million years ago (400 Ma)

Cumberland Gap

rockies
Rockies

Started forming 60 Ma

Maroon bells, CO

himalayas
Himalayas

Started forming 30 Ma

folded strata
Folded Strata

Rockies 

Appalachians 

convergent boundary
CONVERGENT BOUNDARY

Complex mountain system develops---> Continent Grows

geocycles

Geocycles

Rocks, Water, Air

geocycles88
GEOCYCLES
  • Recycling of matter at or near earth’s surface
  • Rock cycle
    • Lithosphere
  • Water cycle
    • Hydrosphere
  • Weather and Climate
    • Atmosphere
4 concentric layers
4 concentric layers
  • Inner core (solid)
  • Outer core (liquid)
  • Mantle (gooey in places)
  • Crust (solid) 3-40 miles thick
what is the lithosphere and what are the plates
What is the Lithosphere and what are the “Plates”?
  • The crust, plus the upper 40 miles of the mantle, form the lithosphere, broken into plates which slowly slide around on the zone of weakness…
igneous rxs fire formed
IGNEOUS RXS“Fire-formed”
  • Liquid rock is called magma or lava, depending on amount of dissolved gas
  • INTRUSIVE - cooled under surface
    • Examples: Granite, Gabbro
  • VOLCANIC - cooled at surface
    • Examples: Basalt, Obsidian, Scoria
sedimentary rx settling
SEDIMENTARY RX“Settling”
  • Clastic - formed from pieces “clasts”, which come from the weathering and erosion of other rock.
    • Examples: Shale, Sandstone, Conglomerate
  • Bio-chemical and Organic
    • microskeletons, e.g. in coral reefs:Limestone
    • Salts in stagnant pools, e.g., Halite
    • Organic - decayed remains of plants:coal
metamorphic rx changed form
METAMORPHIC RX“Changed form”
  • Depends on original rock type and amount of heat and pressure
  • Shale ----> Slate or Schist (more heat)
  • Granite or “dirty” sandstone ---> Gneiss
  • Sandstone ----> Quartzite
  • Limestone ----> Marble
igneous rxs and absolute dating
IGNEOUS RXS andABSOLUTE DATING
  • Some igneous rocks can be radiometrically “dated” – i.e., have an ABSOLUTE AGE assigned...
on the other hand sedimentary rocks

On the other hand…SEDIMENTARY ROCKS

Are most likely to contain fossils

but sedimentary rocks

But, SEDIMENTARY ROCKS

Can only be “relatively dated”…

deep time

DEEP TIME

Oceans vs. Puddles

water facts
Water Facts...
  • 70 % of Earth’s surface is covered by H2O
  • 70 % of human body’s weight is H2O
  • Water can exist in 3 states earth’s surface
    • exists only as solid and vapor on Mars
    • only vapor on Venus
more water facts
More Water Facts...
  • Water freezes at 0 degrees Celsius and boils at 100 degrees Celsius
    • This is higher than similar substances because of hydrogen bonding
    • Water is most dense at 4 oC. This explains why ice floats, which prevents lakes from freezing solid in Winter
hydrogen bonding
Hydrogen Bonding

........O H ........

/ \ /

H H ---- O

| | \

O O H .........

/ \ / \

H H H H .........

| | | |

water
Water...
  • Its heat capacity is higher than similar substances
    • “A watched pot never boils.”
  • Moderates Earth’s temperatures
    • Compare San Francisco and St. Louis
slide110
AIR
  • Main gases in present atmosphere: Nitrogen (78%), Oxygen (21%), and Argon (0.9%), variable amounts of water vapor
  • Average sea level atmospheric pressure is 14.7 pounds per square inch and decreases with altitude
origin113
Origin
  • How: Impact of IcyComets and Degassing of volatiles ... bottle
  • Earth’s atmosphere was forming 4.4 to 4.0 Ga
  • It then (probably) consisted mainly of water vapor, carbon dioxide, ammonia, methane (Some controversy)
brief history
Brief History
  • Icy Comet impacts ---> add H2O to atmosphere and down to about 70km
  • Earth cools ---> Water condenses
  • Lots of rain; Volcanoes add CO2
  • Most of CO2 dissolved in oceans
  • Photosynthesizing organisms evolve
    • CO2 + H2O ------> C6H12O6 + O2
the water cycle

The Water Cycle

How Earth’s water and air interact ...

Natural “recycling” process

zones of concentration

ZONES OF CONCENTRATION

Of natural waters

zones of concentration119
ZONES OF CONCENTRATION
  • Marine (saltwater)- The oceans contain over 97 % of earth’s water -- salt water
  • Brackish (mixture of salt and fresh):
  • Found in estuaries, where fresh and salt water meet
    • Important to aquatic life
    • 3rd most productive ecosystem
    • Example: Chesapeake Bay
fresh water
Fresh Water
  • Less than 3 % of earth’s water is fresh
  • Glaciers contain over 75 % of Earth’s fresh water, but this source is not usable by biota
fresh water123
Fresh Water
  • Lakes and rivers contain less than 1 %
  • Groundwater (including soil moisture) accounts for the remaining 24 %
  • If all Earth’s water fit in a gallon jug, there would be one tablespoon of available fresh water
structure of the atmosphere

Structure of the Atmosphere

Layers classified by temperature changes ...

the atmosphere

The Atmosphere

All weather occurs in the troposphere = “churning sphere”

convection causes the churning
Convection causes the “churning”

Temperature

decreases

with altitude

stratosphere
Stratosphere
  • The ozone layer is contained in the stratosphere...
  • No “churning” because of a temperatureinversion, i.e.,
  • Temperature increases with altitude...
slide130

A

l

t

i

t

u

d

e

Stratosphere --->

Troposphere --->

Temperature

the ozone layer
The Ozone Layer
  • Ozone, O3 , is an air pollutant in the troposphere, but in the stratosphere protects from UV radiation :
  • O3 + UV --------> O2 + O
  • Chlorine radicals (like from CFCs) interfere with this process:
  • Cl + O --------> ClO
slide132

WEATHER and CLIMATE

- Atmosphere Geocycles

coriolis effect

Coriolis Effect

Caused by an unattached atmosphere over a rotating Earth

slide137

ACTUAL

NON-ROTATING

prevailing winds
PREVAILING WINDS
  • The direction the winds blow most of the time ...
  • Changes temporarily due to weather systems ...
  • In the middle latitudes (30o- 60o), the prevailing winds are from the west.
  • These affect climate as we shall see in a moment ...
ocean currents
OCEAN CURRENTS
  • (Surface) currents caused by prevailing winds and Coriolis Effect ...
  • They play a major role in redistributing earth’s heat ...
  • They are called warm or cold, compared with other water at that latitude ...
    • Example: The Gulf Stream is a warm current.
effects on climate
Effects on Climate
  • Many factors affect climate
  • Prevailing winds and ocean currents are only two of these
  • Example: Why is the weather in Paris more pleasant than in Quebec City ?
  • Gulf Stream + Prevailing westerlies
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