Earth SystemsChapter 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