E N D
1. Plate Tectonics The Unifying Theory
of Geology
2. 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
3. The Big Ideas ? Earth is Old and Dynamic Rather than Young and Static
4. Recall: The Scientific Method Observations
Hypothesis (a testable explanation)
Includes testing by prediction
More observations (testing)
If ALL observations fit ---> Theory
5. 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
6. Early Observations First European explorers started to gather knowledge on world geography
Early 1500s: E.g., Magellan & da Gama
7. Early Observations Francis Bacon (1561-1626) first noted how coasts of Africa and South America fit.
9. 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
11. Paleontology The study of fossils
12. Evidence from Paleontology Similar fossils in
South America and Africa
13. Glossopteris, a seed fern whose seeds are too large to be carried far by wind
14. Mesosaurus, a fresh water reptile that couldn’t swim across the open sea
15. Paleoclimatology
16.
17.
18. in South America, Africa, India, and Australia...At same time the Northern Hemisphere had lush swamps...
20. Coal Deposits found in Antarctica brrrrr….
Coal requires a warm, lush climate ===>
What’s Antarctica like today? ===>
21. Paleomagnetism Magnetic minerals in molten rock align with Earth’s magnetic field
22. Paleomagnetism When igneous rock cools, magnetism is “frozen in”, like little compasses...
23. Polar Wandering = apparent change in position of poles over time
24. 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
25. 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)
26. CONTINENTAL DRIFT When Wegener proposed to fit the continental shelves together, rather than the coastlines, we got a better fit for all modern continents...
27. All continents have moved to their present positions from one “supercontinent” he called PANGAEA
28. Scientific Consensus is that Earth is about 4.5 billion years old
(4.5 Ga)
29. Breakup of Pangaea
30. 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 mantle and liquid outer core.
31. WWII and SONAR Sonar, developed to find enemy subs, was used in the decade after WWII to map the deep sea floor...
32. SONAR Previously, most geologists thought the sea floor was rather flat and featureless
They were wrong...
A diverse topography was discovered
33. Topography of the Sea Floor
34. 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...
35. Some Geophysics Thousands of drilling samples were taken...
36. Geophysics Paleomagnetism in the deep sea floor rocks indicated that many episodes of magnetic reversals had taken place...
37. Radiometric dating showed the rocks get older the farther you get from the ridge. These reversals occur in parallel paired bands on opposite sides of a mid-ocean ridge.
38. 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
39. Earthquakes and Volcanoes Seismology is the study of earthquakes
40. Remember the Tsunami?
41. Earthquakes and Volcanoes Data indicate that earthquakes and volcanoes do not occur at random locations, rather...
42. Earthquakes and volcanoes occur mostly along or near trenches and mid-ocean ridges...
43. E.g., Pacific “Ring of Fire”
44. 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
45. 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
46. 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.
64. MECHANISM Current idea: plates move as a result of mantle convection, driven by earth’s internal heat
65. Consequences of Plate TectonicsEarthquakesVolcanoesMountain Ranges Why it’s a
“Unifying Theory”
66. FIRST, A FEW DEFINITIONS...
67. Types of Plate Boundaries
68. DIVERGENT - pulling apart
Mid-Atlantic Ridge
Great Rift Valley of Africa
69.
Great
Rift Valley
of Africa
70. CONVERGENT - coming together
Japan
Himalaya mountains
71. Himalaya mountains formed when India collided with Asia
72. TRANSFORM - slide past each other
San Andreas Fault
73.
San Andreas Fault
74. Volcanoes Are associated with divergent and convergent plate boundaries ...
Why ?
75. Pacific rim
“Ring of Fire”
Convergent
and
Divergent boundaries
76. Earthquakes Are associated with ALL boundary types ...
Why ?
77. Mountain Building “Tectonics”
79. Appalachians Started forming 400 million years ago (400 Ma)
Cumberland Gap
80. Rockies Started forming 60 Ma
Maroon bells, CO
81. Himalayas Started forming 30 Ma
82. Folded Strata Rockies ?
Appalachians ?
83. MOUNTAIN BUILDING and PLATE TECTONICS
84. CONVERGENT BOUNDARY
85. http://www.pbs.org/wnet/savageearth/animations/rift-subduction.html http://www.cnn.com/2006/WORLD/asiapcf/11/09/new.island.ap/index.html
86. Example: The Andes
87. The Andes
88. Geocycles Rocks, Water, Air
89. GEOCYCLES Recycling of matter at or near earth’s surface
Rock cycle
Lithosphere
Water cycle
Hydrosphere
Weather and Climate
Atmosphere
90. First, the ROCK CYCLE
91. Inner core (solid)
Outer core (liquid)
Mantle (gooey in places)
Crust (solid) 3-40 miles thick 4 concentric layers
92. 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…
What is the Lithosphere and what are the “Plates”?
94. 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
95. 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
96. 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
97. IGNEOUS RXS andABSOLUTE DATING Some igneous rocks can be radiometrically “dated” – i.e., have an ABSOLUTE AGE assigned...
98. On the other hand…SEDIMENTARY ROCKS Are most likely to contain fossils
99. But, SEDIMENTARY ROCKS Can only be “relatively dated”…
100. RELATIVE DATING
101. RELATIVE DATING
102. DEEP TIME Oceans vs. Puddles
103. AIR and WATER
104. 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
105. Mars is too cold...
106. Venus is too hot...
107. Earth is just right...
108. 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
109. Hydrogen Bonding ........O H ........
/ \ /
H H ---- O
| | \
O O H .........
/ \ / \
H H H H .........
| | | |
110. Water... Its heat capacity is higher than similar substances
“A watched pot never boils.”
Moderates Earth’s temperatures
Compare San Francisco and St. Louis
111. 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
112. DISTRIBUTION of EARTH’SWATER and AIR
113. Origin
114. Origin How: Impact of Icy Comets 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)
115. Mt. Erebus, Antarctica
116. 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
117. The Water Cycle How Earth’s water and air interact ...
Natural “recycling” process
118. The Water Cycle
119. ZONES OF CONCENTRATION Of natural waters
120. 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
122. 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
124. 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
125. Structure of the Atmosphere Layers classified by temperature changes ...
126. The Atmosphere All weather occurs in the troposphere = “churning sphere”
127. Convection causes the “churning”
128. Convection in Humid Air
129. Thunderhead
130. Stratosphere The ozone layer is contained in the stratosphere ...
No “churning” because of a temperature inversion, i.e.,
Temperature increases with altitude...
132. 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
134. Coriolis Effect Caused by an unattached atmosphere over a rotating Earth
135. Coriolis Effect
136. Coriolis Effect on Winds
137. Coriolis Effect on Winds
139. 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 ...
140. PREVAILING WINDS
141. 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.
143. 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