Chapter 13 Mineral and Soil Resources

Objectives of chapter 13 Geologic Processes

Structure of the Earth:

Plate Tectonics: Lithosphere is the crust and solid part of the upper mantle, that portion that lies above the asthenosphere.
Plate tectonic theory explains the movement of the plates and the processes that occur at the plate boundaries. The plates move as solid blocks "floating" on the plastic asthenosphere. Lithospheric plate boundaries: subduction zones with trenches are found at convergent plate boundaries fig. 13.2

The Rock Cycle and Mineral Resources

How are mineral deposits discovered and removed? Use of fossil fuels:

Consider this:

What are Fossil Fuels?

Fossil fuels - term used for oil gas and coal. Produced by the decomposition of deeply buried dead organic matter from plants (coal) and animals under high temperatures and pressures over millions of years.

Provide 90% of energy consumed in world

Oil shale and tar sands relatively untapped fossil fuel

How are crude oil and natural gas formed and how do they accumulate within the Earth?

Accumulation of minute sea creatures
Burial and heat and pressure to transform organic material to oil and gas
Oil and gas traps

anticline- up arching sedimentary strata
fault- a break in the rock along which movement has taken place
salt dome- dome shaped structures composed of salt, less dense than most rocks, traps oil, gas
cap rock- impervious rock that keeps oil from moving through overburden
source rock- the rock from which the oil is believed to have formed
reservoir rock- porous, permeable limestones or sandstones that hold the oil and will release it when pumped

How are crude oil and natural gas extracted?
Wells are drilled in places that are believed to have commercial supplies.

Primary production- pumping from wells under natural pressure. 25% recovery
Secondary recovery- water, steam, chemicals are injected into well to force oil toward wells. Recovery increased to 60%

Oil reserves approximate 1000 billion barrels (bl). Most of it in Middle East.

Natural gas accumulates above oil and is extracted along with oil. Mostly methane CH2 some ethane, propane and butane.

How is oil refined?
Fractional distillation method used in oil refineries. (Fig. from Miller 2000). Crude oil is heated, the various components are driven off at certain temperatures. Products range from gas to asphalt, including plastics and various organic chemicals.

Use of oil shales and tar sands- synfuels - extract hydrocarbons by heating to 500oC yield 14 gal/ton. May be considered when supplies of oil and gas are depleted.


What are the environmental effects of the use of oil and gas?

How is coal formed?

Coal is formed from the partially decomposed remains of vegetation that collected in swamps, bogs and marshes millions of years ago.
Buried under many layers of sedimentary rocks the vegetation compressed into the many forms of coal in use today.
Three forms of coal - lignite, bituminous and anthracite.
Coal classified as a fuel according to its carbon and sulfur content.

How is coal mined?

Strip mining-

Reclamation - process of restoring land, reform surface and replant vegetation. Rarely is it successful.

Underground mining-

How is coal transported and what are the uses and problems associated with coal?

Train is cheapest method to transport coal to power plants near population areas.
Heat energy from burned coal is used to heat water to produce electricity.
Cannot easily be used for trucks, cars etc.
Coal is most abundant and dirtiest fuel.

Several options are being used or developed to clean coal use What is the environmental impact of using mineral resources? Soils

soil - mixture of rock and mineral particles with decaying organic matter, water, air and living organisms. It is produced slowly by rock weathering, deposition of sediments and decay of organisms.

soil profile: fig. 13-14. Fig. 13-15 soil food web

soils with roughly equal mixtures of clay, sand, silt and humus are called loams - the best soil for plant growth
clay soils compact to much, not permeable
sandy soils drain and dry out too much.

Soil Erosion

Desertification Caused by: results in: How can desertification be slowed: Salinization Soil Conservation

To reduce soil erosion and restore fertility.
Conventional-tillage farming leaves fields plowed before winter exposing them to erosion.

Conservation-tillage farming is minimum tillage or no-tillage farming - fields are tilled as little as possible, no overturning.

Terracing: reduces erosion on steep slopes
Contour farming: planting crops in rows across the contour of the land
Strip cropping: alternate crops in strips with other crops, trap soil, reduce runoff, prevents spread of pests and diseases. Use of nitrogenous legumes increase nitrogen to soil
Alley cropping or agroforestry, or intercropping. Several crops planted in strips along with trees or shrubs
Gully reclamation: plant fast growing shrubs, vines to stabilize soil
Windbreaks or shelterbelts: rows of trees are planted to block wind.

How can soil fertility be maintained?

Fertilization by organic or inorganic mineral fertilizers
organic fertilizers: animal manure, green manure (plant derived) and compost. Adds microorganisms, helps retain water, aerates soil.
Inorganic fertilizers: nitrogen, potassium and phosphorus are added to soil as minerals which do not add to the structure or water holding capacity of soil.
Can runoff into streams causing eutrofication of lakes