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Earth
The Dynamic Planet
Earth’s Interior
Courtesy of the USGS
Core
The core is differentiated into an innersolid region and an outer liquid region.
Both regions are composed mostly ofiron and nickel
Inner core is not solidly tied to rest ofEarth, and is free to rotate
Diagram from USGS
Earth’s magnetic field created by electrically conductive fluidflowing past magnetic field, which creates an electric current;current strengthens the magnetic field
Mantle
Mantle is composed mostly of silicon
Thought to exhibit a plastic behavior; solid on short time scales, liquid over long timescales
Diagram from the USGS
Differences in temperature between core and crust cause mantle to convect; this convection drives movement at the surface
Crust
Crust is mostly SiO2
Two types of crust: oceanic and continental crust
Oceanic crust is thinner and denser; darker in color;basaltic (only about 50% silicate)
Continental crust is thicker and less dense; lighter in color;granitic (about 70-80% silicate)
Diagram from USGS
Seismology
Surface waves - Travel along the Earth’s surface, do not penetrate the crust, slowest wave speed
Compressional body waves - particles move in direction of wave velocity, fastest wave speed;called P-waves
Transverse body waves - particles move perpendicular tothe direction of wave velocity, slower than compressional,but faster than surface; also calledshear waves since the particles willexperience a shearing action;called S-waves
Seismology, cont.
S-Wave shadow zone
Use earthquakes to probe theinterior of the Earth
Waves travelling through the Earth are refracted (bent) and reflected depending upon theirproperties and those of the different layers of the Earth
Plate Tectonics
Originally conceived of as continentaldrift by Wegener; he noticed similaritiesin coastlines, fossil record, rock layers,and glacial scarring
Modern satellite technologyallows us to measure the relative movement of the plates
Plate Boundaries
Divergent - Plates move apart from eachother
Convergent - Plates move toward eachother
Transform - Plates move parallel to the boundary in opposite directions
Divergent Plate Boundaries
•Start as rift valleys•Basaltic, high density magma wells up from the mantle-crust interface to replace rock•New crust that forms is thinner and denser; as it cools, it sinks lower than the surrounding continental crust•Ocean water eventually fills in between the two continents
Convergent Plate BoundariesIf oceanic crust collides withcontinental crust, oceanic crust goesunder (subduction zone), melts, andresurfaces as an island arcEx. New Zealand, Aleutian Islands
If two continental plates collide,crustal material “piles up” anda mountain chain is developedEx. Himalayan Mountains
Transform Plate Boundary
Photograph by Robert E. Wallace, USGS
As plates move past one another,friction causes sides to stick together
While sides are stuck, stress buildsbetween the plates
When stress gets high enough, sidesviolently slide past one another
Loma Prieta Earthquake, 1989, Courtesy of the USGS
Rock Types
Constant plate movement drives the rock cycle
Three different types of rock are igneous, metamorphic, andsedimentary
Igneous
Type of igneous rock determined by 1) type of magma from which rock cools and 2) location where rock cools
Volcanic - extrusive; magma cooled at the surface; smaller crystalsPlutonic - intrusive; magma cooled below the surface; larger crystals
Rock formedfrom a moltenstate
SedimentaryFormed from sediment that is cemented together
Photo of Canyonlands National Monument by Pratte
Type of rock depends upon1) size of sediment and 2) origin of sediment
Two TypesClastic - broken rock and mineral that are cemented togetherEx.: sandstone, shale, conglomerate
Chemical - minerals that precipitate out of solution Ex.: limestone, chalk
Metamorphic
Formed from other rocks by changing mineralogy or texture without passing through a moltenstate
Change occurs because of one or more of the followingparameters: 1. pressure - causes rock crystals to change orientation and
structure (Ex. gneiss)2. temperature - induces different chemical bonds without melting
(Ex. hornfels)3. chemically reactive fluid - minerals in the fluid replace minerals
in the rock (Ex. petrified wood) or form new bonds
Rock Cycle
Processes like weathering, erosion, and plate tectonicschange the rock from one form to another
Rock can be transmuted fromany form to any other form’by these processes
Example: An igneous rock that is brought to the Earth’s surface isweathered and eroded. Sediment pile is buried, causing cementationinto a sedimentary rock. Further burial creates pressures strong enough to change chemical bonds, creating a metamorphic rock.
Soil TypesSoil - a mixture of organic andinorganic sediments found on theEarth’s surface; comprised of different layers
O horizon - consists of decomposing organic matter; might be missingA horizon - comprised of a mixture of organic and inorganic matterE horizon - light colored, acidic layer found in evergreen forestsB horizon - brown or red layer enriched in clay, iron, and/or aluminumK horizon - enriched with calcium carbonate; found in arid regionsC horizon - lowest layer comprised almost entirely of inorganic rock sediment
Soil Forming Factors
Different horizonsoccur at differentlocations for many reasons
1. Climate - temperature, precipitation, and wind affect weathering,erosion, vegetation, and decomposition of organic matter
2. Local rock - provides the inorganic material for soil3. Topography - steeper slopes mean more erosion4. Vegetation - holds soil in place; provides the organic material for soil5. Time - more mature soils have had elements working on it longer6. Mankind - our activities affect erosion and soil nutrients
Some factors:
Weathering and Erosion
Weathering - the breaking apart of rocks either physically orchemically
Erosion - the removal of sediment from a location; can occur by water, wind, landslide, etc.; enhanced by mankind’s disturbances
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