Earth Systems

1. Earth Systems Chapter 8

2. Earth history • What’s here now has been here all along • Layers: • Core – solid inner, liquid outer • Mantle – made of magma • Crust – solid rock

3. 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

6. The rock cycle • Igneous rocks – form directly from magma • Sedimentaryrocks – form from sediments compressed and solidified • Metamorphicrocks – either igneous or sedimentary rocks transformed by heat and pressure

8. Soil – 4 Distinct parts • Minerals – 45% of ‘typical’ soil • Organic matter – about 5% • Water – about 25% • Air – about 25%

9. 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

10. 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

11. 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

12. Soil horizons

13. Soil properties - texture • The percentages by weight of different sized particles of sand, silt, and clay

14. 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

15. 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

16. Mining • Some types and rocks and minerals are vital to modern life • Earth’s chemical composition is variable in different locations of the crust

17. Mining… • Ore – concentrated accumulations of minerals • Typically contain salt, sand, metals • Metals – allow electrical and/or heat conduction • Copper, nickel, aluminum

18. Mining – surface mining • Stripmining – removal of strips of soil and rock to expose ore • Used when the desired ore is relatively close to the surface • Miningspoils 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)

19. 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

20. 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

21. 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

22. 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