Planet Earth Lecture 6 Evidence for Evolution & its Mechanisms

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

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

Long Time Scales Earth’s Age: 4.5 billion years dinosaurs 250 million years dinosaurs 65 million years Lecture 5

Long-Term Change major tectonic plates Lecture 5

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 Lecture 5

His ideas were dismissed as crank Problem– lacked technology that wasn’t available until after WW II Echosounding, radiocarbon dating, submarines Lecture 5

lithosphere asthenosphere mesosphere

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 Lecture 5

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 400-650 kilometers (250-406 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 10-400 kilometers (6 - 250 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 (0 - 31 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 Lecture 5

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 Lecture 5

Jigsaw Puzzle Puzzle noted by Leonardo DaVinci and others Lecture 5

Triassic India conifer trees first dinosaurs, insects 245-208 mya Pangae formed 650 mya, but separated about 250 mya conifer trees first dinosaurs, insects Lecture 5

Jurassic conifer trees dominate, early flowering plants 208-145 mya conifer trees dominate, early flowering plants dinosaurs dominate, early birds, mammals Lecture 5

Cretaceous first flowering plants dinosaurs extinct at end of era 145-65 mya first flowering plants dinosaurs extinct at end of era Lecture 5

India collides 10 million years ago 65 mya - present India collides 10 million years ago diversification of flowering plants, mammals, birds, pollinating insects Lecture 5

Age of Mammals Cronopio dentiacutus

Hess- Convection Cell Theory heating heating Heat source Lecture 5

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 Lecture 5

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 Lecture 5

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. Lecture 5

Lecture 5

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. Lecture 5

Fossil Evidence Lecture 5

Fossil Evidence Mesosaurus Lecture 5

volcanoes in a volcanic island arc system Over 100 volcanoes in a volcanic island arc system Meiji (3000 m deep) Big Island Lecture 5

Hawaiian Islands Niihau Kauai Oahu Molokai Lanai Maui Hawaii

Bathymetric Profile of Hawaiian Emperor Chain

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) Lecture 5

Movement of Hawaiian Islands Moves in a northwesterly direction Much of the Hawaiian island arc is underwater and extends toward Midway Lecture 5

Lecture 5

Lecture 5

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 Lecture 5

Fringing Reef- Tahiti Lecture 5

Fringing Reef Shoreline Reef Flat Reef Front Lecture 5

Barrier Reef Profile Lecture 5

Australia- Great Barrier Reef Lecture 5

                                                             Kaneohe Bay Barrier Reef Patch Reef Fringing Reef

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 Lecture 5

Cross Section of an Atoll

Belize- Blue Hole Atoll

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

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