Download Chapter 8 - Earth Systems

Earth Systems
Chapter 8
Earth history
• What’s here now has been here all along
• Layers:
▫ Core – solid inner, liquid outer
▫ Mantle – made of magma
▫ Crust – solid rock
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
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
Soil – 4 Distinct parts
•
•
•
•
Minerals – 45% of ‘typical’ soil
Organic matter – about 5%
Water – about 25%
Air – about 25%
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
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
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
Soil horizons
Soil properties - texture
• The percentages by weight of different sized
particles of sand, silt, and clay
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
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
Mining
• Some types and rocks and minerals are vital to
modern life
• Earth’s chemical composition is variable in
different locations of the crust
Mining…
• Ore – concentrated accumulations of minerals
▫ Typically contain salt, sand, metals
• Metals – allow electrical and/or heat
conduction
▫ Copper, nickel, aluminum
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)
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
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
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
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