1. Planet Earth Lecture 6 Evidence for Evolution & its Mechanisms

2. Environmental Change Temporal Patterns Changes over time
Note: amount & speed of change
Spatial Patterns
Changes across the landscape

3. Temporal Scales Longer Term geological scale Short Term
annual to thousands of years

4. Long Time Scales Earth’s Age: 4.5 billion years dinosaurs
250 million years
dinosaurs
65 million years
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5. Long-Term Change
major tectonic plates
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6. Continental Drift Theory
Plate Tectonics &
Continental Drift Theory
German meteorologist, polar explorer, astronomer, and geologist
In 1912 he proposed Continental Drift Theory
Wegner suggested that all the earth’s land has once been joined into a supercontinent called Pangae
Wegener eventually proposed a mechanism for continental drift that focused on his assertion that the rotation of the earth created a centrifugal force towards the equator.  He believed that Pangaea originated near the south pole and that the centrifugal force of the planet caused the protocontinent to break apart and the resultant continents to drift towards the equator.  He called this the "pole-fleeing force".  This idea was quickly rejected by the scientific community primarily because the actual forces generated by the rotation of the earth were calculated to be insufficient to move continents.  Wegener also tried to explain the westward drift of the Americas by invoking the gravitational forces of the sun and the moon, this idea was also quickly rejected.  Wegener's inability to provide an adequate explanation of the forces responsible for continental drift and the prevailing belief that the earth was solid and immovable resulted in the scientific dismissal of his theories
Alfred Wegener
Proposed Theory of Continental Drift (1915)
Failed to provide a mechanism
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7. His ideas were dismissed as crank
Problem– lacked technology that wasn’t available until after WW II
Echosounding, radiocarbon dating, submarines
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8. lithosphere
asthenosphere
mesosphere

9. Lithosphere (hard) Asthenosphere (soft) Mesosphere
Lithosphere includes:
Crust– oceanic (basalt)- heavier and thinner
- continental (granite)- lighter and thicker
Lithosphere and asthenosphere differ both physically and chemically
Asthenosphere (soft)
Mesosphere
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10. Earth formed 4.6 bya granite Mantle- 1000oC mesosphere Solid
~ 2300 km thick
asthenosphere
Soft
~3000 km thick
lithosphere
hard
~100 km thick
granite
2.65 g/cm3
basalt
Crust
floats on top of lithosphere
continental crust (granite)
20 to 70 km thick
oceanic crust (basalt)
~ 8 km thick
mantle-crust mass and is probably composed mainly of silicon, magnesium, and oxygen. It probably also contains some iron, calcium, and aluminum. Scientists make these deductions by assuming the Earth has a similar abundance and proportion of cosmic elements as found in the Sun and primitive meteorites.
Transition region: 7.5% of Earth's mass; depth of kilometers ( miles) The transition region or mesosphere (for middle mantle), sometimes called the fertile layer, contains 11.1% of the mantle-crust mass and is the source of basaltic magmas. It also contains calcium, aluminum, and garnet, which is a complex aluminum-bearing silicate mineral. This layer is dense when cold because of the garnet. It is buoyant when hot because these minerals melt easily to form basalt which can then rise through the upper layers as magma.
Upper mantle: 10.3% of Earth's mass; depth of kilometers ( miles) The upper mantle contains 15.3% of the mantle-crust mass. Fragments have been excavated for our observation by eroded mountain belts and volcanic eruptions. Olivine (Mg,Fe)2SiO4 and pyroxene (Mg,Fe)SiO3 have been the primary minerals found in this way. These and other minerals are refractory and crystalline at high temperatures; therefore, most settle out of rising magma, either forming new crustal material or never leaving the mantle. Part of the upper mantle called the asthenosphere might be partially molten.
Oceanic crust: 0.099% of Earth's mass; depth of 0-10 kilometers (0 - 6 miles) The oceanic crust contains 0.147% of the mantle-crust mass. The majority of the Earth's crust was made through volcanic activity. The oceanic ridge system, a 40,000-kilometer (25,000 mile) network of volcanoes, generates new oceanic crust at the rate of 17 km3 per year, covering the ocean floor with basalt. Hawaii and Iceland are two examples of the accumulation of basalt piles.
Continental crust: 0.374% of Earth's mass; depth of 0-50 kilometers ( miles). The continental crust contains 0.554% of the mantle-crust mass. This is the outer part of the Earth composed essentially of crystalline rocks. These are low-density buoyant minerals dominated mostly by quartz (SiO2) and feldspars (metal-poor silicates). The crust (both oceanic and continental) is the surface of the Earth; as such, it is the coldest part of our planet. Because cold rocks deform slowly, we refer to this rigid outer shell as the lithosphere (the rocky or strong layer).
3 g/cm3
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11. Evidence for Continental Drift: continental shape- jigsaw puzzle
similar geology
volcano and earthquake zone
paleomagnetism
fossil evidence (animal and plant)
Geology: areas of erosion apparently caused by the same glacier in tropical areas now widely separated
Lacked technology
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12. Jigsaw Puzzle
Puzzle noted by Leonardo DaVinci and others
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13. Triassic India conifer trees first dinosaurs, insects 245-208 mya
Pangae formed 650 mya, but separated about 250 mya
conifer trees
first dinosaurs, insects
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15. Jurassic conifer trees dominate, early flowering plants
mya
conifer trees dominate, early flowering plants
dinosaurs dominate, early birds, mammals
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17. Cretaceous first flowering plants dinosaurs extinct at end of era
mya
first flowering plants
dinosaurs extinct at end of era
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19. India collides 10 million years ago
65 mya - present
India collides 10 million years ago
diversification of flowering plants,
mammals, birds, pollinating insects
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20. Age of Mammals
Cronopio dentiacutus

21. Hess- Convection Cell Theory
heating
heating
Heat source
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22. Midocean Ridge (Atlantic to Pacific)
New seafloor development at mid ocean ridge
Spreading center
Does this mean that the earth is constantly expanding? No, there are subduction zones
2 football teams: mountain building and trench formation
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23. Earth's Magnetic Field N S Earth has N and S pole
Iron bearing magnetic minerals are found in basaltic magma. As they cool, they align with the earths magnetic field
The rotation of the earth, coupled with liquid iron, produces the earths magnetic field
As the ocean floo rrises from the asthenosphere, its material is magnetized in the current direction
Reverses once every 300,000 to 500,000 years
Effect on animals that use magnetic field to navigate unknown
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24. Mid-Ocean Ridge (Atlantic Ocean)
Molten rock erupts along a mid-ocean ridge, then cools and freezes to become solid rock. The direction of the magnetic field of the Earth at the time the rock cools is "frozen" in place. This happens because magnetic minerals in the molten rock are free to rotate so that they are aligned with the Earth's magnetic field. After the molten rock cools to a solid, these minerals can no longer rotate freely. At irregular intervals, averaging about 200-thousand years, the Earth's magnetic field reverses. The end of a compass needle that today points to the north will instead point to the south after the next reversal. The oceanic plates act as a giant tape recorder, preserving in their magnetic minerals the orientation of the magnetic field present at the time of their creation. Geologists call the current orientation "normal" and the opposite orientation "reversed." - + - + - + + - + - + -
There have been 170 reversal in the last 76 million years. The earth’s present orientation has existed for the past 60,000 years.
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25. Lecture 5

26. Glomar Challenger (1968)- drilling for deep sea sediments
But the purpose of the Glomar Challenger was scientific exploration. One of the most important discoveries was made during Leg 3. The crew drilled 17 holes at 10 different sites along a oceanic ridge between South America and Africa. The core samples retrieved provided definitive proof for continential drift and seafloor renewal at rift zones. This confirmation of Alfred Wegener's theory of continental drift strengthened the proposal of a single, ancient land mass, which is called Pangaea. The samples gave further evidence to support the plate tectonics theory of W. Jason Morgan and Xavier Le Pichon. The theory of these two geologists attempts to explain the formation of mountain ranges, earthquakes, and deep sea trenches.
Another discovery was how youthful the ocean floor is in comparison to Earth's geologic history. After analysis of samples, scientists concluded that the ocean floor is probably no older than 200 million years. This is in comparison with the 4.5 billion years of our Earth. As the seafloor spreads from the rifts, it descends again beneath tectonic plates or is pushed upwards to form mountain ranges.
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27. Fossil Evidence
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28. Fossil Evidence
Mesosaurus
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29. volcanoes in a volcanic island arc system
Over 100
volcanoes in a volcanic island arc system
Meiji
(3000 m deep)
Big Island
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30. Hawaiian Islands
Niihau
Kauai
Oahu
Molokai
Lanai
Maui
Hawaii

31. Bathymetric Profile of Hawaiian Emperor Chain

32. J. Tuzo Wilson (1963), a Canadian geophysicist ,came up the "hotspot" theory.
volcanoes of the Hawaiian chain should get progressively older and become more eroded the farther they travel beyond the hotspot.
Pacific Plate
Kauai
(oldest)
Oahu
Maui
Hawaii
(youngest)
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33. Movement of Hawaiian Islands
Moves in a northwesterly direction
Much of the Hawaiian island arc is
underwater and extends toward Midway
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34. Lecture 5

35. Lecture 5

36. Darwin’s Theory of Coral Atoll Formation: Subsidence Theory
Fringing Reef- boarders coastline closely
Island subsides
Barrier Reef- separated from
land by a lagoon
Atoll- coral ring with central lagoon
lagoon is a shallow area with a sandy floor, patch reefs, and patches of seagrass
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37. Fringing Reef- Tahiti
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38. Fringing Reef
Shoreline
Reef Flat
Reef Front
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39. Barrier Reef Profile
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40. Australia- Great Barrier Reef
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41.                                                             
Kaneohe Bay
Barrier Reef
Patch Reef
Fringing Reef

42. Reef Flat of a barrier reef
Lagoon
Reef Flat of a Barrier Reef
Reef Flat of a barrier reef
Coral Island
(Cay or Motu)
Reef Flat
Reef Front
Open Ocean
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43. Cross Section of an Atoll

44. Belize- Blue Hole
Atoll

45. Midway Atoll
Kure Atoll (28° 25' N - 178° 20' W)
Pearl & Hermes Atoll

46. Questions The Earth is about how old? Plate tectonics describes the:
Evidence for plate tectonics include:
The first Hawaiian Island was formed ____ years ago.