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