Geology
-Layering determined by the differences in both chemical composition and physical properties
-On basis of chemical composition: earth has three layers:
core (dense inner sphere)
Radius 3500 km, 95% iron+ 5% nickel
Inner core (solid) we know it’s solid because both p-waves and s-waves pass through it
Outer core (liquid) we know it’s liquid because p-waves pass through it but s-waves cannot
Mantle (less dense) 2900 km made of rock-peridotite
Lower mantle 2400 km (solid)(bottom)
Asthenosphere 400 km (weak/plastic)
Lithosphere solid (100-150 km) (top) plate tectonics occur here
crust (light and very thin outer skin of earth)
Less than 30 km made of rocks
Oceanic crust (8-10 km) gassalt 200 million years old, under ocean, thinner than continental crust
Continental crust (35 km) granite 20 billion yrs (under land) thicker then oceanic crust
-On basis of physical properties:Lithosphere: rigid outer layer that includes crust and upper mantle, has flexibility. Asthenosphere: weak rocks, able to slowly flow in response to uneven distribution of heat within earth. Principal division of earth’s surface: continents and ocean basinP-waves: are able to travel faster than other seismic waves and are the first signal from an earthquake to reach the seismograph. Can be transmitted through gas, liquid, or solid. s-waves:shear wave that causes particles to move back and forth perpendicular to the direction the wave is moving. Can only travel through solids and move at slower velocity than p-waves surface waves: when body waves reach the ground surface of earth these waves generate. And is confined to to the material along earth’s surface Faults: any fracture in the crust that shows offset between rocks on either side Vertical Faults (dip/slip fault) 1. Normal fault:vertical motion due to tension stress, Hanging wall moves down relative to footwall
2. Reverse Fault: Vertical motion due to compressional stress, Hanging wall moves up relative to footwall 3. Thrust Fault: Low angle reverse fault,Typically larger than a reverse fault with greater displacement Strike-slip faults (transform faults):Horizontal motion due to shear stress, Types include: right/left lateral strike-slip fault, San Andreas fault is a right lateral strike-slip fault Bowen’s reaction series: Explains why certain types of minerals tend to be found together and others are almost never associated with one another. Bowens idealized progression of minerals produced by cooling basaltic magma that undergoes fractional crystallization. Most abundant volcanic gases: 1. water vapor (75-90%) 2. carbon dioxide (5-15%) 3. sulfur dioxide Guyot: submerged, flat-topped seamounts Atoll: ring-shaped structures that extend from slightly above sea level to depths of several thousand meters. Ocean ridges (mid ocean ridge): is the longest topographic feature on Earth, wrapping around the world through all major ocean basins. form due to seafloor spreading: as plates of oceanic lithosphere move apart, the warm mantle beneath rises and undergoes decompression melting. Seamounts: (submarine volcanoes) if they emerge at the ocean’s surface, we call them volcanic islands.Deep-ocean trench: are long, narrow creases in the seafloor that are the deepest parts of the ocean floor.Deep-ocean basin:between the continental margin and the oceanic ridge. (seamount and abyssal plain) makes up half of the ocean floors. -types of marine sediments 1. Lithogenous Sediment: the sources of lithogenous sediments are the rocks of the earth’s crust.2. Biogenous Sediment: comprises the insoluble remains of organisms, for example, bones and teeth of animals and the protective shells of animals and coverings of plants that are deposited on the ocean bottom.Calcium carbonate (CaC03) and silica (Si02) are the most common chemical compounds found in this type of sediment. 3.Hydrogenous Sediment: The word ‘hydrogenous’ means derived from water. This type of sediment results from the chemical reaction occurring within the seawater. Manganese deposits, phosphorite, and glauconite are minerals that form by chemical precipitation from water. However, the rate of accumulation of this sediment is rather very slow.4.Cosmogenous Sediment:derived from meteoric dust falling from the outer space. Magnetic spherules rich in iron and ranging in size from 10 to 640 micrometers are typical particles of cosmic origin present in marine sediments. These sediments are less important than the inorganic precipitates. Continental margins: active or passive according to the presence or absence, of plate tectonic activity. Shelf: The gently sloping region of the continental margin that extends seaward from the shoreline to the continental shelf break.Slope: The steeply sloping region of the continental margin that extends from the continental shelf break downward to the ocean basin.Rise: The gently sloping, smooth-surfaced, thick accumulation of sediment at the base of certain continental slopes.Abyss: An abyssal plain is an underwater plain on the deep ocean floor usually found at depths between 3,000 metres (9,800 ft) and 6,000 metres (20,000 ft). cover more than 50% of the earth’s surface.Water on Earth: Depth avg=3800m,deepest 11000m,Mean temp= 3.9 degrees Celsius Composition of Seawater Seawater consists of 3.5% dissolved saltsSalinity: total amount of solid materials dissolved in water. Typically expressed in parts per thousands. Average salinity is 35%. Major constituents are sodium and chlorideProcesses that affect seawater salinity include Decreases salinity (adds water) precipitation, icebergs melt, runoff from land, sea ice melts Increases salinity (removes water): evaporation and formation of ice