Chapter 1 Introduction to Planet Earth 70 8 of Earth is covered by ocean Oceans contain 97 2 of surface water Land 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 ice The 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 ft Formation of Earth and the Solar System Nebular Hypothesis all bodies in the solar system were formed from nebula Nebula is a 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 meteorites Heat from Solar radiation The moon formed from collision with large asteroid The initial atmosphere boiled away Ionized 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 size Early Earth experienced gravitational separation High density materials iron and nickel settled in core Less dense materials formed concentric spheres around core Earth is layered by chemical composition and physical properties Chemical Composition Crust low density mainly silicate minerals Mantle mainly iron Fe and magnesium Mg silicate materials Core high density mainly iron and nickel Ni Physical Properties Lithosphere cool rigid brittle Surface to about 100 km or 62 miles Asthenosphere warm plastic able to flow From about 100km 700km or 430 miles Continental vs Oceanic Crust Oceanic has mostly dark colored igneous Basalt rocks density 3 0 and is 5 miles in thickness 22 miles in thickness Continental has mostly lightly colored igneous Granite rocks density 2 7 and is Isostatic Adjustment is the vertical movement of Earth s crust buoyancy of lithosphere on asthenosphere less dense continental crust floats higher than denser oceanic crust Isostatic rebound rising of crust formerly weighted down by glacier ice Origin of Earth s atmosphere Partial 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 ammonia Water 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 years Life 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 Animals Heterotrophs earliest life form require external food supply Autotrophs 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 oxygen 2 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 atmosphere High oxygen biodiversity increases Low oxygen extinction rates increase Chapter 2 Plate Tectonics and the Ocean Floor Pangea one large continent existed 200 million years ago and Panthalassa one large ocean Edward 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 time Objections Continents cannot possibly plow through ocean basins tidal gravitational attractions are too small Plate 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 pull b slab suction Paleomagnetism is the study of earth s ancient magnetic field it interprets where rocks first formed and the magnetic dip Magnetic Polarity Reversals Earth 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 center Subduction zones oceanic trench site of crust destruction Age of Ocean Floor Late 1960 s deep sea drilling Radiometric dating of ocean rocks Symmetric pattern of age distribution about mid ocean ridges Oldest ocean floor only 180 million years old Heat Flow heat from Earth s interior released to the surface Very high at mid ocean ridges and low at subduction zones Earthquakes As Evidence Most large earthquakes occur at subduction zones Earthquake activity mirrors tectonic plate boundaries Tying 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 Boundaries 1 shallow earthquakes earthquakes Divergent plates move apart mid ocean ridge new ocean floor created Convergent plates move toward each other oceanic crust destroyed deep Transform offset perpendicular to mid ocean ridge offsets permit mid ocean ridge to move apart at different rates shallow
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