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Earth SystemsChapter 8
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Earth history
•What’s here now has been here all along•Layers:
▫Core – solid inner, liquid outer▫Mantle – made of magma▫Crust – solid rock
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Theory of Plate Tectonics▫Crust is divided into plates which move slowly,
carried by convection currents in the magma below▫Where plates are in contact:
Divergent plate boundaries – moving apart, magma forces its way up
Convergent plate boundaries – moving together, one plate forced under the other
Transform plate boundaries – one plate moving past another
▫Consequences: Fault zones – pressure between plates
Earthquakes occur when the pressure releases suddenly ‘Ring of Fire’ – areas where volcanoes are common
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The rock cycle
•Igneous rocks – form directly from magma
•Sedimentary rocks – form from sediments compressed and solidified
•Metamorphic rocks – either igneous or sedimentary rocks transformed by heat and pressure
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Soil – 4 Distinct parts
•Minerals – 45% of ‘typical’ soil•Organic matter – about 5%•Water – about 25%•Air – about 25%
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Soil •Slowly renewable – may take from 200-1000
years to form 1 inch•Provides most of the nutrients needed for
plant growth•Also helps purify water•Formation begins when bedrock - the parent
material - is broken down by weathering•Decomposition helps produce new soil –
except in the rainforests, where nutrients in the soil are recycled into living organisms very quickly
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Weathering and erosion• Breaking down of parent material in soil
formation• Physical:
▫Expansion of freezing water▫Biological agents – ex: tree roots
• Chemical:▫CO2 in soil reacts with H2O to form carbonic
acid (H2CO3)▫Air pollution can also cause acid rain
• Erosion – removal of rock or soil▫Wind, water, ice
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Soil properties - horizons• Mature soils have developed over a long time and are
arranged in a series of horizontal layers; composition depends on climate, vegetation, and parent material
• O horizon: organic detritus• A horizon: so-called top soil – organic material and
minerals mixed together• E horizon: a zone of leaching found in acidic soils
only• B horizon: ‘subsoil’ – mainly minerals with very little
organic matter• C horizon: the least weathered; similar to the parent
material
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Soil horizons
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Soil properties - texture
•The percentages by weight of different sized particles of sand, silt, and clay
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Soil properties - texture
•> 2mm = gravel/stone – not actually soil b/c it has no direct value to plants
•0.05 – 2mm = sand (largest soil particles) – can be seen easily with the eye
•0.002-0.05mm = silt (about the size of flour) – barely visible with the eye
•< 0.002mm = clay (has the greatest surface value) – only seen under an electronic microsope
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Soil properties - porosity•How quickly the soil drains water:
▫sand – silt – clay•Best agricultural soils have a mixture to
promote water drainage and retention•Sandy soils can cause problems in areas with
industrial discharge – pollutants move through them quickly and contaminate groundwater
•Many landfills are lined with clay to prevent contaminants from leaching into surrounding soil and groundwater
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Mining
•Some types and rocks and minerals are vital to modern life
•Earth’s chemical composition is variable in different locations of the crust
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Mining…
•Ore – concentrated accumulations of minerals▫Typically contain salt, sand, metals
•Metals – allow electrical and/or heat conduction▫Copper, nickel, aluminum
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Mining – surface mining• Strip mining – removal of strips of soil and rock to
expose ore▫Used when the desired ore is relatively close to the
surface▫Mining spoils or tailings – unwanted material
removed from the surface; usually returned to the hole• Open-pit mining – creation of a large hole
▫Resource is close to surface but extends both horizontally and vertically; copper mines
• Mountain-top removal – just like it sounds• Placer mining – use of river water to separate
heavier items (like gold and diamond prospectors)
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Mining – subsurface
•Used when the resource is more than 100m below Earth’s surface
•Usually a horizontal tunnel dug into a mountainside with vertical shafts
•The deepest mines are 2.2 miles deep•Coal, diamonds, gold
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Mining - Impacts
•Surface▫Air – dust from earth-moving equipment▫Water – contamination of water that
percolates through tailings▫Soil – most soil removed from site▫Biodiversity – habitat alteration and
destruction▫Humans – decline of air and water quality
near mining operation
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Mining – Impacts
•Subsurface:▫Air – emissions from fossil fuels used to
power mining equipment▫Water – acid mine drainage as well as
contamination of water that percolates through tailings
▫Biodiversity – road construction fragments habitats
▫Humans – occupational hazards; possibility of chronic lung diseases
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Mining - Legislation• General Mining Act – 1872
▫Allows individuals and companies to recover ores and fuels from federal lands.
▫Contains very few environmental protection provisions
• Surface Mining Control and Reclamation Act – 1977▫Regulates surface mining of coal as well as the
surface effects of subsurface mining▫Land must be minimally disturbed during the
mining process and reclaimed after mining is completed