Chapter 1: Introduction to Planet Earth70.8% of Earth is covered by oceanOceans contain 97.2% of surface waterLand 29.2% of Earths surface 4 oceans: Pacific, Atlantic, Indian, and Arctic**Pacific is the larges and deepest**Atlantic is the 2nd largest **Arctic is the smallest, shallowest, and covered with iceThe Antarctic or Southern Ocean connects the Pacific, Atlantic, and Indian oceans at about 50S latitude Average ocean depth is about 12,234 ft Average continental elevation is 2756 ft *The deepest ocean trench is the Mariana Trench at 36,161 ft*The highest continental mountain is Mt. Everest at 29,935 ftFormation of Earth and the Solar SystemNebular Hypothesis: all bodies in the solar system were formed from nebula; Nebula isa cloud of gasses and space dust (mainly hydrogen and helium) *gravity concentrates material at the center of cloud (sun)*protoplanets form from smaller concentrations of matter (eddies)Protoearth-Larger than Earth today-Homogeneous composition-Bombarded by meteoritesThe moon formed from collision with large asteroid -Heat from Solar radiation The initial atmosphere boiled awayIonized particles (solar wind) swept away nebular gasses-Radioactive heat causes spontaneous disintegration of atoms-Heat from contraction (protoplanet shrinks due to gravity)-Protoearth partially melts-Density stratification (layered Earth)Density Stratification: High density=heavy for its sizeEarly Earth experienced gravitational separation *High density materials (iron and nickel) settled in core*Less dense materials formed concentric spheres around coreEarth is layered by chemical composition and physical properties Chemical Composition:Crust-low density, mainly silicate mineralsMantle- mainly iron (Fe) and magnesium (Mg) silicate materialsCore- high density, mainly iron and nickel (Ni)Physical Properties:Lithosphere- cool, rigid, brittle. Surface to about 100 km or 62 milesAsthenosphere- warm, plastic, able to flow. From about 100km-700km or 430 milesContinental vs. Oceanic CrustOceanic has mostly dark colored, igneous Basalt rocks; density: 3.0; and is 5 miles in thicknessContinental has mostly lightly colored, igneous Granite rocks, density: 2.7; and is 22 miles in thicknessIsostatic Adjustment is the vertical movement of Earth’s crust, buoyancy of lithosphereon asthenosphere (less dense continental crust floats higher than denser oceanic crust)Isostatic rebound: rising of crust formerly weighted down by glacier iceOrigin of Earth’s atmospherePartial melting resulted in outgassing about 4 billion years ago-Similar gasses emitted from volcanoes -Mainly water vapor-Carbon dioxide and water-Other gasses such as methane and ammoniaWater vapor released by outgassing, condensed as rain, accumulated in ocean basins.Ocean Salinity: rain dissolves rocks, dissolved compounds (ions) accumulate in ocean basins, oceans salinity based on balance between input and output of ions, ocean salinity nearly constant over past 4 billion yearsLife in oceans: earliest life forms fossilized bacteria in rocks about 3.5 billion years old,marine rocks, proof that life originated in oceans?Evolution of Plants and AnimalsHeterotrophs: earliest life form, require external food supplyAutotrophs: evolved later in life, manufacture their own food supply **First autotrophs most similar to modern anaerobic bacteria. Chemosyn-thesis from chemicals deep at hydrothermal vents. Supports idea of life’s origins on deep ocean floor in absence of light. Complex autotrophs developed chloro-phyll. This allowed the use of sun for photosynthesis and cellular respiration 1) photosynthesis: takes in light energy and produces sugar and oxygen2) respiration: releases light energy and takes in sugar and oxygen Oxygen Crisis- Photosynthetic bacteria release oxygen to atmosphere, about 2 billion years ago sufficient oxygen in atmosphere needed to be oxidized (rust). Ozone (O3) builds up in atmosphere (protects earth from ultraviolet solar radiation)About 1.2 billion years ago most anaerobic bacteria killed off by oxygen rich atmos-phere. Photosynthetic organisms were created.Oxygen makes up about 21% of gasses in modern atmosphereHigh oxygen= biodiversity increasesLow oxygen=extinction rates increase Chapter 2: Plate Tectonics and the Ocean FloorPangea- one large continent existed 200 million years ago and Panthalassa- one large oceanEdward Bullard fit the continents together at 2000 m water depth, he noticed matching sequence of rocks and mountain chains, similar aged, types, and rock struc-tures; there were similar rocks on different continents. Glacial ages and other climate evidence, evidence in glaciation in now tropical regions, direction of glacial flow and rock scouring, plant and animal fossils indicate different climate than today. Also the lo-cation of the north pole changed over timeObjections? Continents cannot possibly plow through ocean basins, tidal gravitational attractions are too smallPlate Tectonics Theory:Lithospheric plates “float” and move around on the asthenosphere, large scale geological features occur and plate boundaries. The two major tectonic forces are:a) slab pullb) slab suction Paleomagnetism is the study of earth’s ancient magnetic field, it interprets where rocks first formed and the magnetic dipMagnetic Polarity ReversalsEarth’s magnetic polarity reverses periodically *records are in ancient rocks Magnetic anomalies-regular pattern of north to south magnetism “stripes” Sea Floor Spreading: Harry Hess 1962 mid ocean ridge site of new ocean crust. Oceanic trench site of crust destruction (subduction)Mid-ocean ridge: spreading centerSubduction zones: oceanic trench site of crust destruction Age of Ocean FloorLate 1960’s deep sea drillingRadiometric dating of ocean rocksSymmetric pattern of age distribution about mid-ocean ridgesOldest ocean floor only 180 million years oldHeat Flow: heat from Earth’s interior released to the surface Very high at mid-ocean ridges and low at subduction zonesEarthquakes As Evidence: Most large earthquakes occur at subduction zones. *Earthquake activity mirrors tectonic plate boundariesTying it all together: the Theory of Plate Tectonics- the ideas of continental drift and seafloor spreading were tied together in the theory of plate tectonics Types of Plate Boundaries1) Divergent: plates move apart; mid ocean ridge; new ocean floor created; shallow earthquakes2) Convergent: plates move toward each other; oceanic crust destroyed;
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