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Unformatted text preview: Plate Tectonic Theory Plate Tectonic Theory The Earth’s lithosphere is divided into rigid plates of various sizes that move over the asthenosphere. Plates move because of convection cells within the asthenosphere Plate Tectonic Theory Plate Tectonic Theory Convection cells
Heat energy converted to mechanical energy Plate Tectonic Theory Plate Tectonic Theory
Where does the heat come from???
Radioactive Radioactive decay (e.g., uranium) Earth Earth loses 5 million kW every hour (or 44.2 trillion kW per year) enough to keep 50 million light bulbs burning for an hour! Three Three types of plate boundaries:
– Divergent: – Convergent: – Transform: move apart move together move along 1 Divergent: New ocean floor crust created as plates move apart. Mid ocean ridges. Divergent: new ocean floor crust created as plates move apart. Mid ocean ridges. MidMid-Atlantic ridge: Divergent plate boundary Convergent: Crust destroyed as plates move towards one another. Volcanoes, earthquakes & mountains. Iceland: Iceland: rifting at a divergent plate boundary Mountain Ranges Volcanic Mountains: Lauca National Park, Chile Pomerape Parinacota 2 Transform: Plates move past one another in opposite directions. Lithosphere neither created nor destroyed Transform: Orange Orange trees, Imperial Valley, California, 1950 The Rock Cycle
A rock is an aggregate of minerals. rock minerals. There There are three main types of rock:
– igneous - Crystallized from melt – sedimentary - Accumulated rock debris – metamorphic - “Baked” rocks The Rock Cycle The Rock Cycle Any Any rock can be derived from any rock!
Igneous rocks From melt Sedimentary rocks From debris Metamorphic rocks Baked rocks 3 Organic Evolution
Fossils Fossils are the remains of past life
– document changes in life forms over time All All present day organisms have descended from earlier forms
– Natural selection results in the survival of those best suited to their environment (“survival of the fittest”) Cribrohantkenima inflata 35 Ma Geologic Time
Earth Earth is about 4.6 billion years old Oldest Oldest rocks are 4 billion years old Oldest Oldest fossils are 3.7 billion years old Geologic Time
Earth dynamic Earth is dynamic Earth Earth has evolved (changed) throughout history and will continue to evolve
– Climate – Position of continents – Life – Coast lines Acasta Gneisses – Great Slave Lake, Canada 4 Geologic Time
Changes Changes took place over long periods of time. - GEOLOGIC TIME
– millions and billions of years – time is measured
Relative Relative Absolute Absolute (years) Geologic Time
Humans Humans have been around for 3.2 million years (Ma): witnessed 0.07% of Earth history First multiFirst multi-celled organisms emerged 700 million years ago: 15% of Earth history Try Try to imagine 1 million years: 1 million days = ~2740 years! Geologic Time
Collapse Collapse 4.6 billion years into one year:
Jan. 1 – Formation of Earth and Moon Mar. 4 – Oldest known rocks Mar. 27 – Oldest known fossil (anaerobic bacteria) Sept. 2 – Oxygen accumulates in atmosphere Single celled algae appear Sept. 25 – Oldest animal fossil (jellyfish like) Nov. 15 – Hard shelled animals (trilobites) in sea Nov. 15 – Diverse sea life including clams, snails, jawless fish, coral Nov. 26 – First fish with jaws Nov. 27 – First land animals Dec. 5 – Large winged insects, spiders, scorpions Dec. 8 – Widespread extinction of land and sea life Dec. 12 – Age of Reptiles Dec. 15 – Large dinosaurs Dec. 25 – Dinosaurs extinct Dec. 28 – First elephants, horses, deer, bears, ancestors of cats and dogs Dec. 29 – Apes abundant Dec. 30 – 7PM – Early forms of humans 11PM – sabertooth cats, woolly Mammoths, bison, rodents abundant 11:45PM – Many land animals become extinct Dec. 31 – Midnight – humans dominate Earth Geological time: relative younger older Geological time: absolute
Discovered Radioactivity in 1896 Discovered half-life and halfage dating of rocks Absolute Age Dating
Radiometric Radiometric dating
– Uses the fact that some elements (like Uranium) are not stable and decay over time – Decay is constant (p,T) Henri Becquerel (1852(1852-1908) Ernest Rutherford (1871(1871-1937) 5 Absolute Age Dating
Time Uranium U Lead Time Uranium U Lead Half life = half of the radioactive element decayed Absolute Age Dating
Time Uranium U Lead Geologic Time It It takes 4.5 billion years until half the uranium has turned into lead In In all meteorites and moon rocks the ratio of Uranium to Lead is about 1:1, that’s how we know how old our planet is. Uniformitarianism
Principle Principle of Uniformitarianism
– Geologic processes occur today operated similarly in the past
Mudcracks today Mudcracks in the past Why study Geology?
Natural Natural resources
– If it can’t be grown, it has to be mined! Protect Protect our environment Predict, Predict, control, avoid geological hazards Understand Understand our surroundings
– We’re part of it! 6 Why study Geology?
We We depend on Earth for its resources! If If it can’t be grown, it must be mined! Understanding Earth
A Dynamic and Evolving Planet Chapter 1 7 ...
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- Spring '08