GEOLOGIC PROCESSES The earth is made up of a core, mantle, and crust and is constantly changing as a result of processes taking place on and below its surface. The earth’s interior consists of: – Core: innermost zone with solid inner core and molten outer core that is extremely hot. – Mantle: Thickest zone: a rigid outer part, but underneath is asthenosphere that is melted pliable rock that flows in convection currents – Crust: Outermost zone which underlies the continents and oceans – Lithosphere: combination of crust and outer part of mantle
The Earth’s Crust The Earth’s crust is relatively thin relative to the rest of the planet. 25-70 km thick below the continents around 10 km thick below the oceans. The crust is rich in oxygen and other lighter minerals such as silicon, calcium and aluminum and is less dense than the mantle. The crust rides over the mantle causing the formation of oceans, mountains and volcanoes. Lithosphere Asthenosphere Continental crust The continental crust is made up of igneous, metamorphic, and sedimentary rocks. It is not recycled within the Earth as often as oceanic crust, so some continental rocks are up to 4 billion years old. Oceanic crust More than two thirds of the Earth’s surface is composed of oceanic crust. Oceanic crust is continually formed from mantle material and so is relatively young. Even the oldest parts of the ocean floor are no more than 200 million years old.
The Lithosphere ‣ The lithosphere comprises the crust and the upper most region of the mantle. ‣ The lithosphere carries the outer rock layer of the Earth, which is broken up into seven large, continent-sized tectonic plates and about a dozen smaller plates ‣ The lithosphere overlies the hotter, more fluid lower part of the mantle, the asthenosphere. Continental Crust Oceanic Crust Approx. 70km Asthenosphere Approx. 250km Mantle Lithosphere Mohorovicic discontinuity
GEOLOGIC PROCESSES Huge volumes of heated and molten rack moving around the earth’s interior form massive solid plates that move extremely slowly across the earth’s surface. – Tectonic plates: huge rigid plates that are moved with convection cells or currents by floating on magma or molten rock.
Fig. 15-3, p. 337 Spreading center Ocean trench Plate movement Subduction zone Oceanic crust Continental crust Material cools as it reaches the outer mantle Cold dense material falls back through mantle Hot material rising through the mantle Mantle convection cell Two plates move towards each other. One is subducted back into the mantle on a falling convection current. Mantle Hot outer core Inner core Plate movement Collision between two continents Tectonic plate Oceanic tectonic plate Oceanic crust
Plate tectonics is the theory explaining the movement of the plates and the processes that occur at their boundaries.
Plate Movement Heat from the mantle drives two kinds of asthenospheric movement: convection mantle plumes Plate motion is also partly driven by the weight of cold, dense plates sinking into the mantle at trenches. This heavier, cooler material sinking under the influence of gravity displaces heated material that rises as mantle plumes. IRON-NICKEL CORE New crust created at spreading ridge Mantle plume of hotter material rising from near the core Crust melts as it descends into mantle Crust cools and sinks into mantle under the influence of gravity Heating and cooling causes convection
Fig. 15-4a, p. 338 EURASIAN PLATE NORTH AMERICAN PLATE ANATOLIAN PLATE JUAN DE FUCA PLATE CHINA SUBPLATE CARIBBEAN PLATE PHILIPPINE PLATE ARABIAN PLATE AFRICAN PLATE PACIFIC PLATE SOUTH AMERICAN PLATE NAZCA PLATE INDIA- AUSTRALIAN PLATE SOMALIAN SUBPLATE ANTARCTIC PLATE Divergent plate boundaries Convergent plate boundaries Transform faults Earth’s Major Tectonic Plates
Pacific Plate The Pacific plate is off the coast of California. Lots of volcanoes and earthquakes occur here. “California will fall into the ocean” idea. It is the largest plate and the location of the ring of fire.
Trench Volcanic island arc Craton Lithosphere Subduction zone Lithosphere Asthenosphere Divergent plate boundariesConvergent plate boundariesTransform faults Rising magma The extremely slow movements of these plates cause them to: 1. grind into one another at convergent plate boundaries 2. move apart at divergent plate boundaries 3. slide past at transform plate boundaries. Huge pressures created are released by earthquakes & volcanoes Plate Boundaries
Convergent – the plates push together by internal forces. At most convergent plate boundaries, the oceanic lithosphere is carried downward under the island or continent (subduction zone.) Earthquakes are common here. It also forms an ocean trench or a mountain range.
Convergent Plates: push together – Plate attrition occurs at convergent boundaries marked by deep ocean trenches and subduction zones. The Pacific plate is a convergent plate. Deep sea trench Active volcano Mountain range Continental crust Oceanic crust Mantle Subducting plate Convergent plate boundaryDivergent plate boundary When an oceanic plate collides with a continental plate, it sinks in to the mantle and eventually melts.
Boundaries Divergent – the plates move apart in opposite directions. Creates oceanic ridges
Divergent Plates – The size of the plates is constantly changing, with some expanding and some getting smaller. – These changes occur along plate boundaries, which are marked by well-defined zones of seismic and volcanic activity. – Plate growth occurs at divergent boundaries along sea floor spreading ridges such as the Mid-Atlantic Ridge and the Red Sea. Divergent plate boundary Continental rift zone The changing convection currents inside the Earth can cause new boundaries to form and old ones to disappear. Magma upwellings through fractures cause plates to diverge. Divergent plate boundary
Sea floor Spreading Sea floor spreading occurs as magma wells up from the mantle below, forcing the plates apart. As the new rock cools and solidifies it picks up and preserves the direction of the Earth’s magnetic field. On average the Earth’s magnetic field reverses once every million years. This leaves magnetic bands in the crust. New rock on either side of the ridge has the same magnetic information. This shows clear evidence of sea floor spreading and plates tectonics.
Plate Boundaries The Earth’s major earthquake and volcanic zones occur along plate boundaries. The movements of plates puts crustal rocks under strain. Faults are created where rocks fracture and slip past each other. Earthquakes are caused by the energy released during rapid slippage along faults. New Zealand’s alpine fault is visible from space, marking a transform boundary between the Indo- Australian plate and the Pacific plate.
Continental Boundaries Where continental plates meet, the land may buckle and fold into mountain ranges. The highest mountains on Earth, the Himalayas, were formed in this way as the subcontinent of India collided with continental Asia. Few volcanoes form in these areas because the continental crust is so thick.
Boundaries Transform – plates slide next or past each other in opposite directions along a fracture. California will not fall into the ocean!
Transform Boundaries Plates may slide past each other at transform boundaries Plate size is not affected because there is no construction or destruction of material at these boundaries. However, they are responsible for large earthquakes. Pressure from the plates causes the boundary to lock in position and earthquakes occur when the rock gives way to release the pressure. Faultline movement after an earthquake San Andreas fault Image: NASA Photo: Wiki commons
GEOLOGIC PROCESSES The San Andreas Fault is an example of a transform fault. Figure 15-5
Importance Plate movement adds new land at boundaries, produces mountains, trenches, earthquakes and volcanoes. Important part of recycling earth’s crust, forming mineral deposits
Changing Earth’s surface Internal processes – rely on heat from earth’s interior – tend to build up earth’s surface External processes – rely on energy from sun and earth’s gravity – tend to wear down earth’s surface – Erosion: Wind, water, glaciers, human activities especially deforestation (roots hold soil in place) – Weathering: break down rocks, forms soils Physical – wind, rain, water freezing & expanding Chemical – reactions with water, acids, gases Biological – tree roots, lichen
Sediments eroded from continents and compressed into sedimentary rock can be later lifted and exposed in mountains Igneous rocks, such as basalt, form a major component of the crust and are essentially unchanged since their formation. The Earth's persistent oceans of liquid water cycle moisture through the atmosphere to the land and back again. Water, as rain, drains to rivers and lakes, which flow back to the ocean eroding the landscape in the process. The Earth’s Crust
The Rock Cycle The interaction of physical and chemical processes that turn 1 type of rock into another The slowest of the earth’s cycles; takes millions of years
Fig. 15-8, p. 343 Erosion Transportation Weathering Deposition Igneous rock Granite, pumice, basalt Sedimentary rock Sandstone, limestone Heat, pressure Cooling Heat, pressure, stress Magma (molten rock) Melting Metamorphic rock Slate, marble, gneiss, quartzite
The Rock Cycle Magma Intrusive igneous rock LAND Metamorphic rock SEA The rock cycle constantly redistributes material within and at the Earth's surface over millions of years by melting, erosion, and metamorphism. It is the slowest of the Earth's cycles and is responsible for concentrating the mineral resources on which humans depend. MANTLE CRUST SURFACE ROCKS FORMED AT THE EARTH'S SURFACE ROCKS FORMED IN THE EARTH'S INTERIOR Extrusive igneous rock cooling and crystallization burial and recrystallization deep burial metamorphic rock deep burial metamorphic rock melting cooling and crystallization uplift and erosion uplift and erosion weathering, exposure, and transport, followed by burial Sedimentary rock burial and recrystallization
The Rock Cycle The Earth's rocks are grouped together according to the way they formed as: igneous metamorphic sedimentary rocks Igneous rocks are created by volcanism and may form above the surface as volcanic rocks or below the surface as plutonic rocks. Heat and pressure within the Earth can transform pre-existing rocks to form metamorphic rocks. When rocks are exposed at the surface, they are subjected to weathering and erosion and form sediments.
Types of Rock The Earth's crust is made up of solid, naturally occurring assemblages of minerals called rocks. The huge diversity of the Earth's rocks has developed over thousands of millions of years through: igneous activity (volcanism) main source of mineral resources metamorphism (changes in form) sedimentation (formation of sediments and sedimentary rocks) Igneous rocks Metamorphic rocks Sedimentary rocks
Types of Rock Igneous rocks solidify from volcanic magma They vary in composition from basalt to granite and in texture from rapidly cooled glasses, such as obsidian, to slowly cooled coarse grains, such as granite. ObsidianMarbleConglomerate SandstoneSchistGranite ‣ Metamorphic rocks result when pre-existing rock is transformed by heat and pressure. Metamorphic rocks are classified by texture and composition. Examples include gneiss, slate, marble and schist. ‣ Sedimentary rocks form when sediments accumulate in different depositional environments and then become compressed into brittle, layered rocks, e.g. shale, sandstone, limestone, and conglomerate.
Igneous Description – forms the bulk of the earth’s crust. It is the main source of many non-fuel mineral resources. Classification – – Intrusive Igneous Rocks – formed from the solidification of magma below ground – Extrusive Igneous Rocks – formed from the solidification of lava above ground Rock Classification
Sedimentary Description – rock formed from sediments. Most form when rocks are weathered and eroded into small pieces, transported, and deposited in a body of surface water.
Clastic – pieces that are cemented together by quartz and calcium carbonate (Calcite). Examples: sandstone (sand stuck together), Conglomerate (rounded & concrete-looking) and Breccia (like conglomerate but w/ angular pieces)
Sedimentary (Continued) Nonclastic – – Chemical Precipitates – limestone precipitates out and oozes to the bottom of the ocean (this is why there is a lot of limestone in S.A.) – Biochemical Sediments – like peat & coal – Petrified wood & opalized wood
Metamorphic Description – when preexisting rock is subjected to high temperatures (which may cause it to partially melt), high pressures, chemically active fluids, or a combination of these Location – deep within the earth
Dynamic Metamorphism – earth movement crushes & breaks rocks along a fault. Rocks may be brittle- (rock and mineral grains are broken and crushed) or it may be ductile- (plastic behavior occurs.) Rocks formed along fault zones are called mylonites.
Examples: Contact Metamorphism- rock that is next to a body of magma Ex. limestone under heat becomes marble through crystallization Limestone -> marble sandstone -> quartzite shale -> hornfelds (slate)
Metamorphic (Continued) – Regional Metamorphism – during mountain building; great quantities of rock are subject to intense stresses and heat Ex. cont. shelves ram together
Progressive Metamorphism – One form of rock changing into another shale->slate->schist->gneiss coal->graphite granite->gneiss
Minerals Mineral: element or compound occurs naturally Mineral resource: concentration that can be extracted Considered Nonrenewable Essential for modern life Metallic: Aluminum, gold, copper Nonmetallic: sand, gravel, limestone Distribution of mineral resources is uneven 4 strategic metal resources: Manganese, Cobalt, Chromium, and platinum are critical and come from unstable countries in Africa – must stockpile Eventually will run out
Resources Many resources are extracted from the different layers of the Earth and some minerals are mined for their uses economically: Coal, oil, and natural gas are all a mined resource Uranium is mined for nuclear reactions Gold, silver, platinum are precious metals and are used commercially Bauxite is used for aluminum production and are used commercially
Oxygen The most abundant element in Earth’s crust Nitrogen: The most abundant element in Earth’s atmosphere Iron: The most abundant element in the Earth’s core. Core also contain nickel.
Specific Resources & Their Uses Limestone – abundant locally, formed from layers of seashells and organisms under pressure as they were covered; used in sidewalks, fertilizers, plastics, carpets, and more Lead – used in batteries and cars Clay – used to make books, magazines, bricks, and linoleum Gold – besides being used as money and for jewelry, gold is used in medicine (lasers, cauterizing agents) and in electronics (circuits in computers, etc.)
Texas Central – limestone, tin, clay, lead, garnets, freshwater pearls, amethysts, calcium carbonate West – talc, mercury, silver, petroleum, sulfur East – lignite coal, petroleum South – lignite coal, petroleum, uranium, limestone North – helium, uranium, petroleum, bituminous coal
United States Central – diamonds (Arkansas), bituminous coal West – bituminous and subbituminous coal, gold, silver, copper East – anthracite coal, bituminous coal South – some gold (SC), bituminous coal North – bituminous coal, some gold (SD, WI)
ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES The extraction, processing, and use of mineral resources has a large environmental impact. Figure 15-9
Natural Capital Degradation Extracting, Processing, and Using Nonrenewable Mineral and Energy Resources Steps Environmental effects Mining Disturbed land; mining accidents; health hazards, mine waste dumping, oil spills and blowouts; noise; ugliness; heat Exploration, extraction Processing Solid wastes; radioactive material; air, water, and soil pollution; noise; safety and health hazards; ugliness; heat Transportation, purification, manufacturing Use Noise; ugliness; thermal water pollution; pollution of air, water, and soil; solid and radioactive wastes; safety and health hazards; heat Transportation or transmission to individual user, eventual use, and discarding
ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES Minerals are removed through a variety of methods that vary widely in their costs, safety factors, and levels of environmental harm. A variety of methods are used based on mineral depth. – Surface mining: shallow deposits are removed. – Subsurface mining: deep deposits are removed.
Methods Surface Mining – Description – if resource is <200 ft. from the surface: Machines and explosives are used to break up & remove the topsoil and rocks. This is called the overburden. Remove the resource, reclamation follows – Benefits – cheap, easy, efficient – Costs – tears up the land, byproducts produce an acid that can accumulate in rivers and lakes
Surface Mining Resource that is near the surface can be economically extracted using open cuts in the earth. The alteration of the land and production of acid mine drainage can lead to pollution of waterways and aquifers. Abandoned mines can also leach acid drainage by rainwater. Coal seams exposed Highly erodible highwall remains Land provides economic and technical difficulties
Open-pit Mining Machines dig holes and remove ores, sand, gravel, and stone. Toxic groundwater can accumulate at the bottom. Figure 15-11
Area Strip Mining Earth movers strips away overburden, and giant shovels removes mineral deposit. Often leaves highly erodible hills of rubble called spoil banks. Regrowth of vegetation is slow Figure 15-12
Contour Strip Mining Used on hilly or mountainous terrain. Unless the land is restored, a wall of dirt is left in front of a highly erodible bank called a highwall. Figure 15-13
Mountaintop Removal Machinery & explosives remove the tops of mountains to expose coal. The resulting waste rock and dirt are dumped into the streams and valleys below. Causes extensive environmental damage Figure 15-14
Surface Mining Control & Reclamation Act of 1977 Requires mining companies to reclaim (restore) surface-mined land Most cases only partly successful & take decades Reclamation – Description – returning the rock layer (overburden) and the topsoil to a surface mine, grading, fertilizing and planting it – Benefits – restores land to good condition – Costs – expensive, time-consuming
Methods (Continued) Underground Mining – Description – digging a shaft down to the resource, using machinery (and people) to tear off and remove the resource – Benefits – can get to resources far underground, disturbs less land, creates less waste – Costs – leaves much of the resource in the ground, more expensive, more time-consuming, more dangerous
Two main methods: room and pillar mining long wall mining Room and pillar mining removes blocks of the coal seam while leaving others to act as pillars to keep the roof stable. Long wall mining uses machines that move along the length of the coal face. The removed coal falls onto a conveyor that takes it to the surface. As the machine moves forward the tunnel behind it is allowed to collapse. Photo: Eickhoff Maschinenfabrik and Eisengießereihttp://www.eickhoff-bochum.de/de/ Eickhoff Maschinenfabrik and Eisengießereihttp://www.eickhoff-bochum.de/de/ Underground Mining
Coal Mine Long wall mining Coal crusher Processing plant Silo Ventilation shaft and elevator Coal conveyor Pillars Room and pillar mining
Mining Impacts Scarring / disruption of land Collapse of land above underground mines (subsidence) Pollution – Produces more toxic air emissions than any other industry – Acid mine drainage pollutes water supplies – Processing ore releases mercury & arsenic, cyanide: companies have declared bankruptcy & walked away leaving toxic superfund sites Produced ¾ of all US solid waste: 3 tons of waste is generated to produce 1 gold ring
Nonrenewable Resources Definition – things human use that have a limited supply; they cannot be regrown or replenished by man Depletion time: economically depleted when is costs more to obtain than worth. At that point, 5 choices: – Reduce – Reuse – Recycle – Find a substitute – Do without
Sustainability Definition – prediction of how long specific resources will last; ex. we have a 200 year supply of coal in the U.S. Knowing this helps people make decisions in resource use Problems – these are only predictions; they may not be accurate
Conservation Definition – using less of a resource or reusing a resource, ex. refilling plastic laundry jugs, reusing plastic bags, etc. Part of the solution Problems – this requires a change in our lifestyle and some people will resist. Dealing with Nonrenewable Resources
Recycling Examples – aluminum, glass, tin, steel, plastics, etc. Part of the solution Problems – recycling a resource can costs more than using the raw material; we don’t have the technology to recycle everything, people are resistant, need a market for recycled material
Fig. 15-18, p. 351 Solutions Sustainable Use of Nonrenewable Minerals Do not waste mineral resources. Recycle and reuse 60–80% of mineral resources. Include the harmful environmental costs of mining and processing minerals in the prices of items (full-cost pricing). Reduce subsidies for mining mineral resources. Increase subsidies for recycling, reuse, and finding less environmentally harmful substitutes. Redesign manufacturing processes to use less mineral resources and to produce less pollution and waste. Have the mineral-based wastes of one manufacturing process become the raw materials for other processes. Sell services instead of things. Slow population growth.