this lecture will help you understand:

Copyright © 2009 Benjamin Cummings is an imprint of Pearson

This lecture will help you understand:

• How plate tectonics and the rock cycle shape the Earth

• Geologic hazards

• Mineral resources

• Mining methods and impacts

• Sustainable use of minerals


Central Case: Mining for…cell phones?

• Cell phones and other high-tech products must contain tantalum.

- Coltan: tantalum found with another mineral (columbite)

- In eastern Congo, men dig in streambeds, panning for coltan.

• The Democratic Republic of the Congo has been at war since 1998.

- 5 million people died and millions fled.

- Soldiers seized control of mining operations and forced farmers and others to work, while taking most of the ore.

- The war caused ecological havoc, dead wildlife, and deforestation.

- Profits from coltan sales financed the war.

• Corporations assure consumers they did not use coltan from the Congo.


We use raw materials from the Earth

• We take raw materials from the lithosphere and turn them into products.

- The physical processes in the lithosphere shape Earth’s landforms.

• Geology: the study of Earth’s physical features, processes. and history

- Two processes are fundamentally important: the rock cycle and plate tectonics.


The rock cycle

• Rock cycle: heating, melting, cooling, breaking, and reassembling of rocks and minerals

- Important in the formation and conservation of soil, mineral resources, fossil fuels, and other resources

• Rock: any solid aggregation of minerals

- Affect soils and influence a region’s plant community

• Mineral: any naturally occurring solid element or inorganic compound

- A crystal structure

- A specific chemical composition

- Distinct physical properties


Rock cycle


Igneous rock

• Magma: the molten, liquid state of rock

• Lava: magma released from the lithosphere

• Igneous rock: forms when magma cools

• Two classes, depending on how rock solidifies:

- Intrusive rock: magma that cools slowly below Earth’s surface (i.e., granite)

- Extrusive rock: magma ejected from a volcano (i.e., basalt)


Sedimentary rock

• Sediments: particles of rock are blown by wind or washed away by water

• Sedimentary rock: sediments are pressed together (compaction) or dissolved minerals seep through sediment layers and bind sediment particles (cementation)

• Lithification: formation of rock through the processes of compaction and cementation


Formation of sedimentary rock

• Sedimentary rock is classified by the way it forms.

- Clastic sedimentary rock: forms from physically eroded material (sandstone, shale)

- Chemical sedimentary rock: formed as dissolved minerals precipitate from water or as calcite settles to ocean bottoms (Limestone and rock salt)

• Physical compaction and chemical transformation form:

- Fossils

- Fossil fuels


Metamorphic rock

• Metamorphic rock: great heat or pressure on a rock changes its form

• Deep underground, high temperatures reshape crystals and change a rock’s appearance and physical properties.

• Foliated rock: heat and pressure causes layers (slate)

• Nonfoliated rock: not layered (marble)


Earth consists of layers

• Crust: a thin, brittle, low-density rock

- Covers Earth’s surface

• Mantle: thick layer of denser rock

- Aesthenosphere: the upper mantle containing soft rock, melted in some areas

• Core: dense, consists mostly of iron

• Earth’s heat drives convection currents in the mantle

- Pushes soft rock upward and downward…

- Dragging large plates of lithosphere

• Plate tectonics: the movement of lithospheric plates


Earth’s layers


The Earth has 15 major tectonic plates…

Movement of these plates influences climate and evolution.

…that move 2-15 cm (1-6 in.) per year.


Pangaea: the supercontinent

• At least twice in Earth’s history, all landmasses were joined in one supercontinent.

• Pangaea: the supercontinent that occurred 225 million years ago


There are 3 types of plate boundaries

• Divergent plate boundaries: magma surging upward to the surface pushes them apart, creating new crust as it cools and spreads

• Transform plate boundary: two plates meet, slipping and grinding alongside one another

- Friction spawns earthquakes along slip-strike faults


Tectonic plates can collide• Convergent plate boundaries: when plates collide

• Subduction: one plate of crust slides beneath another

- Magma erupts through the surface in volcanoes, forming volcanic mountain ranges (the Cascades in Washington).

• Two colliding plates of continental crust may lift material from both plates.

- Resulted in the Himalaya and Appalachian mountains


Tectonics creates Earth’s landforms

• The processes of plate tectonics build mountains; shape oceans, islands, and continents; and create earthquakes and volcanoes.

- Topography shapes climate by altering patterns of rainfall, wind, ocean currents, heating, and cooling.

- These patterns affect weathering and erosion and the ability of plants and animals to inhabit different regions (biomes).

- Helps shape evolution by causing extinctions through limiting suitable habitat


Geologic hazards


Earthquakes result from movement

• Earthquakes: places in the Earth’s crust (faults) where built-up pressure is relieved

- Most earthquakes are not felt, but some do enormous damage.

- Cities built on landfills are very vulnerable.

- To minimize damage: build strong buildings with built-in flexibility


Volcanoes arise from rifts, subduction, or hot spots• Volcano: where molten rock,

hot gas, or ash erupts through Earth’s surface

- Can create a mountain

- Lava can extrude in a rift valley, midocean ridges, or over subduction zones

- Hot spots: plugs of molten rock erupt through the crust

- Create island chains


Effects of volcanoes

• Pyroclastic flow: a fast-moving cloud of toxic gas, ash, and rock

- Mount Vesuvius erupted and buried Pompeii in 79 A.D.

• Ash blocks sunlight.

• Sulfuric emissions cause a haze that cools the atmosphere.

- Cause crop failures


Landslides are a form of mass wasting

• Mass wasting: the downslope movement of soil and rock due to gravity

- Landslide: A severe and often sudden instance of mass wasting, where large amounts of rock or soil collapse and flow downhill

- Occurs naturally, but is also caused by human practices that expose or loosen soil

- Mudslides: heavy rains saturate the soil and cause movement of soil, rock, and water

- Lajars: mudslides caused when volcanic eruptions melt snow and sends volumes of mud downslope


Mass wasting can be devastating

• In 1998, in Nicaragua and Honduras, over 11,000 people died from mudslides.

• In 1985, over 21,000 people died from a lahar that buried the town of Armero, Colombia.


Tsunamis: an immense wave of water

• A tsunami can travel thousands of miles across oceans.

- Triggered by earthquakes, volcanoes, or landslides

- In 2004, 230,000 people were killed in countries around the Indian Ocean from a massive tsunami.

- The U.S. also has had tsunamis.

• To decrease impacts, natural vegetation should be left in place (i.e., mangrove forests).


We can worsen natural hazards

• People face other natural hazards:

- Floods, coastal erosion, wildfire, tornadoes, hurricanes

• We worsen the impacts of natural hazards.

- People live in susceptible areas due to population pressure or choice.

- Use of landscapes increases the frequency or severity of hazards: damming rivers to control floods, suppressing natural fires, clear-cutting forests.

- Climate change will change precipitation, leading to more floods, fire, mudslides, etc.


We can mitigate natural hazards

• Thoroughly understand geology and ecology

• Thoughtful use of technology, engineering, and policy

- Earthquake-resistant buildings

- Early warning systems

- Conserving coastal forests, reefs, marshes

- Better forestry and mining practices

- Zoning regulations and building codes

- Mitigating climate change


Minerals and mining

• Geologic processes and catastrophes influence the distribution of rocks and minerals.

• We depend on a wide variety of minerals for products and technologies.

Minerals are non-renewable, so we need to conserve them and mitigate environmental and social impacts of mining.


We extract minerals from ores

• Metal: an element that is lustrous, opaque, malleable, and can conduct heat and electricity

• Ore: a mineral or grouping of minerals from which we extract metals

• Economically valuable metals include copper, iron, gold, lead, aluminum.

Tantalite ore is mined, processed into tantalum, and used in electronic devices.


We also mine nonmetallic minerals and fuels

• Nonmetallic minerals include sand, gravel, phosphates, limestone, gemstones.

- People in developing countries often suffer war and exploitation because of the developed world’s appetite for minerals.

• Substances are mined for fuel.

- Uranium for nuclear power

- Coal, petroleum, natural gas are not minerals (they consist of organic matter), but they are also mined.


Economically useful mineral resources


A mining method: strip mining• Layers of surface soil and rock are

removed to expose the mineral resource.

• Overburden: overlying soil and rock that is removed by heavy machinery

- After resource extraction, each strip is refilled with the overburden.

• Used for coal, sand, gravel, and oil sands

• Destroys natural communities over large areas, triggers erosion

- Acid drainage: sulfuric acid forms and flows into waterways


A mining method: subsurface mining• Accessing deep concentrations of

a mineral through tunnels and shafts

- The deepest mines extend 4 km (2.5 mi)

• Used for zinc, lead, nickel, tin, gold, copper, diamonds, phosphate, salt, coal

• The most dangerous form of mining

- Injury and death from dynamite blasts and collapsed tunnels

- Toxic fumes and coal dust can be fatal

- Acid drainage and polluted groundwater


A mining method: open pit mining• Used with widespread, evenly

distributed minerals

- Terraced so men and machines can move

• Used for copper, iron, gold, diamonds, coal, clay

• Quarries: open pits for clay, gravel, sand, stone (limestone, granite, marble, slate)

• Huge amounts of waste rock are removed to obtain small amounts of minerals.

- Habitat loss, aesthetic degradation, acid drainage, fill with toxic water

One Utah mine is 4 km (2.5 mi) across and 1.2 km (0.75 mi) deep.


A mining method: placer mining

• Using running water, miners sift through material in modern or ancient riverbeds.

- Congo’s coltan miners, California’s gold rush of 1849

• Used for gold, gems

• Debris is washed into streams, making them uninhabitable for fish and other life.

• Disturbs stream banks, causes erosion, and harms riparian plant communities


A mining method: mountaintop removal

• Entire mountaintops are blasted off and the waste is dumped into valleys.

• Mainly for coal in the Appalachian Mountains

• Economically efficient

- In 2002, President Bush loosened regulations, allowing dumping of waste into valleys and streams.

• Deforestation, degrades and destroys vast areas, pollutes waterways, erosion, mudslides, flash floods

An area the size of Delaware has already been removed.


Mountaintop removal is socially devastating

• Mine blasting cracks foundations and walls.

• Floods and rock slides affect properties.

• Overloaded coal trucks speed down rural roads.

• Coal dust causes illness.

• Local politicians do not help.

• High efficiency mining reduces the need for workers.


A mining method: undersea mining

• Minerals are extracted from the ocean floor using large hydraulic dredges.

• Used for sulfur, phosphorite, calcium carbonate (for cement), silica (insulation and glass), copper, zinc, silver, gold

• Manganese nodules: small, ball-shaped ores scattered across the ocean floor

- Mining them is currently uneconomical.


Restoration of mined sites

• In some countries (i.e., U.S. and Canada), companies must “reclaim” (restore) vegetation on mined sites after mining.

- Other nations (i.e., Congo) have no regulations.

• The U.S. 1977 Surface Mining Control and Reclamation Act mandates that companies:

- Must post bonds before mining to ensure restoration

- Remove structures, replace overburden, and replant vegetation when mining is complete


Restored sites can still have problems

• Complex communities are simplified.

- Forests, wetlands, etc., are replaced by grasses.

• Essential symbioses are eliminated and often not restored.


The General Mining Act of 1872• Government policy plays a role in mining through this

controversial law.

- It encourages mining on federal lands by letting any U.S. citizen stake a claim on any public land for a few dollars per acre.

- The public gets no compensation for any minerals found.

- Once a person owns the land, that land can be developed for any reason, having nothing to do with mining.

• Supporters of the Act say it encourages a domestic industry that is risky and provides essential products.

• Critics say it virtually gives the land for free to private interests.

- So far, efforts to amend the Act have failed in Congress.


Minerals must be processed to be useful

• Alloy: a substance formed by mixing, melting, and fusing minerals (i.e., steel = iron + carbon)

• Smelting: removes metal from ore using heat and chemicals

- Melting and reprocessing the metal produces the strength, malleability, or other characteristics desired.

• Processing minerals impacts the environment.

- Water and energy intensive

- Toxic air pollution

- Tailings: heavy metals and chemicals in the ore left after the metal has been extracted


Minerals are non-renewable and scarce• Once we have mined all known reserves, minerals will be

gone.

- i.e., Indium, used in LCD screens, might only last 32 more years

• Reserve estimates, however, are uncertain.

- New discoveries, technologies, consumption patterns, and recycling will affect mineral supplies.


We can use minerals sustainably• Challenges facing us regarding

minerals

- Finite supply and environmental damage

• The solutions? Recycling

- i.e., 72% of our lead comes from recycled materials

- Steel, iron, platinum, etc., for auto parts

- Gold, nickel, germanium, tin, and chromium

- 50% of aluminum is recycled

- Affected by recycling efforts and facilities


Conclusion

• Plate tectonics and the rock cycle shape Earth’s terrain and form the foundations for biotic patterns.

• Geologic processes can threaten our lives and property.

• We mine mineral resources by various methods.

• We need to minimize the environmental and social impacts of mining.

- Maximize recycling and sustainable use of minerals

this lecture will help you understand:

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