The Solid Earth

Minerals and the Rock Cycle

I. What is a mineral?

A. Definition of a mineral: naturally occurring, inorganic solid consisting of chemical elements in specific proportions, whose atoms are arranged in a systematic internal pattern

B. Definition of a rock: naturally occurring combinations of one or more minerals, with each mineral retaining its own discrete characteristics

All minerals are chemical compounds. Their chemical structures determine their distinctive characteristics.

A. Crystals: when a mineral grows in an unrestricted space, it develops a regular geometric shape, e.g. crystals in a geode.

B. Most minerals do not grow in an open space so they form interlocking masses of mineral grains. BUT they retain their microscopic crystalline form. These determine their physical properties (color, appearance, hardness, how they break, etc.)

C. Which mineral forms? Depends on:

1. Element abundance: what’s available

2. Element interactions: how atoms interact with each other

3. Relative atomic size of element: how things fit together

4. Temperature and pressure at time of formation

5. Other considerations: polymorphism: two minerals have the same chemical formula but different crystalline structures, e.g., graphite, diamonds

Rocks and minerals are products of their environments of formation.

A. The silicates: the building blocks.

1. 90% of continental crust by weight

2. The silicon-oxygen tetrahedron

a. Uses up silicon and oxygen

b. But charge imbalance and problems of relative proportion SO

3. Si tetrahedra combine in various ways and proportions to form the silicates

B. Nonsilicates: 3 different examples (of many!)

1. Carbonates (e.g. calcite), limestone rock, CAVES!

2. Oxides (e.g. hematite), many of our metal ores

3. Sulfides (e.g., pyrite "fool’s gold"), also important metal ores

A. Igneous: molten rock solidifies or crystallizes

B. Sedimentary: formed from weathered pieces of rock or dissolved elements from preexisting rocks

C. Metamorphic: preexisting rocks that have been changed through heat, pressure or circulating fluids

D. The Rock Cycle

What do we have?  Element Abundance in the Earth

The Most Abundant Elements in the Whole Earth Element Prop. of Earth’s Weight (%)	The Most Abundant Elements in the Earth’s Continental Crust Element Prop. of Crust’s Weight (%)
Iron (Fe) 34.8 Oxygen (O) 29.3 Silicon (Si) 14.7 Magnesium (Mg) 11.3 Sulfur (S) 3.3 Nickel (Ni) 2.4 Calcium (Ca) 1.4 Aluminum (Al) 1.2 All other elements 1.6 Total 100.00	Oxygen (O) 45.2 Silicon (Si) 27.2 Aluminum (Al) 8.0 Iron (Fe) 5.8 Calcium (Ca) 5.06 Magnesium (Mg) 2.77 Sodium (Na) 2.32 Potassium (K) 1.68 All other elements 1.97 Total 100.00

 

I. Introduction

A. Major theory of geology: explains mountains, geological phenomena

Geological activity is NOT RANDOM!

B. Layers of the Earth

1. Layers based on physical differences: crust, mantle, core

2. Layers based on different behaviors

a. Lithosphere: rigid, outermost layer, includes crust and upper mantle

1. Continental lithosphere is thicker, less dense, buoyant

2. Oceanic lithosphere is thinner, more dense, sits lower and tends to sink in a collision

b. Asthenosphere: plastic, below lithosphere, rock flows.

II. Major concepts of plate tectonics

A. Lithosphere is composed of 7 major plates and numerous smaller plates

B. Plates move 5-10 cm/yr

C. Large scale geological activity occurs near plate boundaries

D. Interior of plates fairly quiet geologically

III. Plate movements and boundaries

A. Rifting and divergent plate boundaries

1. Plates moving apart

2. Constructive, new lithosphere material created.

B. Subduction and convergent boundaries

1. Plates moving towards each other

2. Destructive, oceanic lithosphere reabsorbed into interior of plate.

C. Transform motion and transform plate boundaries:

1. Plates moving side by side

2. Neither constructive or destructive

IV. Proving plate tectonics

A. Alfred Wegener and continental drift

1. Pangea

2. Continental fit

3. Habitats of living and ancient animals

4. Related rocks

5. Ancient climates -- glaciers, coal deposits

6. Contemporary geologists rejected Wegener’s hypothesis: it did not seem plausible, Wegener figured out what happened with the continents, but not the sea floor.

B. New evidence from the 1950s to 60s: seafloor spreading

1. Shape of the ocean floor: undersea mountain ranges and deep ocean trenches

2. Earthquake patterns outline the plates and define the top of the subducting slabs

3. Ocean drilling and the age of ocean rocks (youngest rocks are at mid ocean ridges, oldest rocks are adjacent to continents).

4.. Paleomagnetism

a. Magnetic reversals occur regularly in geologic history

b. Paleomagnetism easy to measure in mafic igneous rocks (basalts, sea floor!)

c. Magnetic stripes and patterns show sea floor spreading

d. Plate movement can be measured by magnetic anomalies

e. Plate speeds from 1-10 cm/yr

5. Hot spots and plate motion

a. Hot spot: rising plume of hot material from deep within the mantle. Volcanism occurs above this plume as the hot material melts as it gets near the surface

b. Hot spots don't seem to move much relative to the plates above them

c. They can indicate direction and speed of motion of plates

d. Formation of submarine volcanic chains (seamount chains) show direction and speed of Pacific plate motion

e. Continental hot spots, e.g. Yellowstone National Park

 

C. New evidence from the 1980s: Satellites confirm present day plate movement

D. Plate tectonics combines continental drift and sea floor spreading

V. The Driving Forces of Plate Tectonics: asthenosphere convection currents

I. Introduction

A. Volcanism can be one of the most destructive natural forces

B. Can also be beneficial: atmospheric gases, new land, energy source, information about the Earth

II. The Nature and Origin of Volcanoes

A. Classification of volcanoes

1. Active - volcano that is erupting or has erupted recently

2. Dormant- volcano that has not erupted recently but is considered likely to do so in the future

3. Extinct - no eruptions for a long time, not considered likely to erupt

B. There are different kinds of volcanoes. Why?

1. Composition of lavas varies

2. Along with composition variations, there are some other differences

a. Gas in volcanic magma: causes explosive pressure.

b. Magma viscosity (stiffness)

c. Therefore: stiff, gas-rich lavas are explosive

Why do we get different types of volcanic eruptions?

Answer:  Different types of magma

Composition	Silica Content	Relative temperature of magma	Gas-rich?	Stiff?	Eruptive style
Mafic Basaltic	Low Si	High	No	Not stiff (like honey)	Effusive Flowing
Felsic	High Si	Low	Yes	Stiff (like toothpaste)	Explosive

 

 

III. The Products of Volcanism

A. Lava (magma on the outside of the Earth)

B. Pyroclastics - fragmented volcanic products that are thrown through the air

1. Ash, cinders, volcanic bombs

2. Pyroclastic flows- flowing hot air, ash and volcanic gases - nuee ardente

3. Volcanic mudflows or lahars

C. Secondary volcanic effects

1. Acid precipitation

2. Global climate changes

IV. Eruptive Style and Associated Landforms

A. Eruptive style and volcano shape depend on magma’s characteristics:

1. Effusive eruptions: nonexplosive, lava flows

2. Explosive eruptions: lava explodes

B. Volcanic Landforms

1. Stratovolcanoes (composite cones) cone-shaped volcano

a. Built up by combinations of explosive or effusive eruptions.

b. Tend to be explosive.

c. Mostly occur near subduction zones. Pacific "Ring of Fire."

d. Examples: Mt. St. Helens, Mt. Fuji, W. Pacific Island Arcs, Cascade Range

2. Continental ring calderas: large crater-like depressions

a. Formed when a BIG magma chamber collapses after emptying.

b. VERY, very explosive. Very, very destructive.

c. Can be created by a continental hot spot, a continental rift or (sometimes) a subduction zone.

d. Examples: Yellowstone

3. Shield volcanoes: large, broad, flattish-looking volcanoes

a. Built up by effusive eruptions. Flows, does not explode.

b. Divergent plate boundaries and oceanic hot spots

c. Examples: Hawaii, Iceland

4. Fissure eruptions: no volcano, eruption from a crack

a. Flows, does not explode

b. Divergent boundary, oceanic hot spots

c. Examples: Sea floor spreading, mid ocean ridges

 

V. Coping with Volcanic Hazards

A. Prediction is the best defense

1. Microearthquakes: magma moving around underground

2. Heat flow (ground temperature, temp. of the groundwater)

3. Shape of the ground, esp. bulging of the ground

4. Gas emissions (magma contains dissolved gases)

B. How accurate is volcanic prediction?

I. Introduction

II. The Causes of Earthquakes

A. Introduction

1. How rock deforms: brittlely, elastically, plastically

2. Where it deforms: along faults (cracks in the rock)

3. Cause of earthquakes

a. Sudden release of accumulated strain energy

b. Moves along pre-existing faults (usually), sometimes new faults

4. Earthquake terms: focus, epicenter, foreshocks, aftershocks

5. Earthquakes occur sporadically: accumulation of energy, sudden release (earthquake), rocks lock back in place and resume accumulating energy.

B. Seismic waves

1. Earthquake energy transmitted in seismic waves

2. Body waves: go all through the Earth

a. P waves: fastest, longitudinal compression

b. S waves: slower, perpendicular shearing waves, can't move through liquid

3. Surface waves: slowest, side-to-side waves, rolling vertical waves, most damaging

C. Measuring earthquakes

1. Modern seismograph

2. The Richter scale

a. Measures seismogram wave amplitude

b. Amplitude scale is logarithmic (each added whole number represents a 10 fold increase in amplitude)

c. Earthquake energy (each added whole number represents a 30 fold increase in energy)

3. Other scales:

a. Mercalli (based on damage and whether people "feel" the quake)

b. Moment Magnitude: based on the amount of movement along a fault during an earthquake (amount of displacement and the total area of displacement)

4. Monitoring seismic waves

D. Epicenters are located based on difference between P and S wave speeds.

E. Most earthquakes, all catastrophic ones occur within 60 km depth- shallow)

F. Tracing earthquake wave motion tells us about the deep structure of the Earth

III. The Effects of Earthquakes

A. Ground movement

B. Landslides - triggers already unstable masses

C. Seiches - the sloshing back and forth of water in a lake or bay

D. Liquefaction- unconsolidated sediment that acts like a liquid

E. Tsunamis - seismic sea waves

1. Waves can be over 100 ft high, travel over 500 mph, can hit land 1000s of km away from quake

2. Caused by sea floor fault movement

3. Tsunamis can take several hours to reach the coast (evacuation possible with warning)

4. Tsunami at sea: wave length of up to 100 miles, wave height less than 3 feet.

5. Tsunamis are small until they reach the shallow water of the coast

F. Fires

V. Coping with the Threat of Earthquakes

A. Short-term earthquake prediction: we can't do it (yet)

B. Determining seismic frequency: how often do earthquakes occur in a given area

1. Historical record too short to be able to calculate regular intervals between episodes of earthquake activity

2.Geological records of earthquake frequency

C. Building in an earthquake zone: ground stability and building design

D. Earthquake prediction: the best defense

1. Long-term prediction from seismic gaps along a fault

2. Short-term prediction methods: microearthquake swarms, bulge in rocks, changes in seismic wave velocity, electrical conductivity, radiowave signals, ground water level changes, animal behavior

E. Can earthquakes be controlled? No.

I. Introduction

A. Shallow-marine sedimentary rocks (and fossils) are found at high elevation in many mountains

B. Mountains have roots.

1. The higher the mountain, the thicker the root

2. Remove some of the weight of the mountain (or glacier or whatever) and the rest of the crust will rise in response: isostatic adjustment

II. Deforming Rocks: where plates interact at boundaries, they are subject to enormous stress (force per unit area)

A. Types of stress

1. Compression

2. Extension (or tension)

3. Shear

B. Types of deformation

1. Elastic: rocks return to original shape when stress removed.

2. Brittle: rocks break. Faults, earthquakes.

3. Plastic (ductile) deformation: rocks bend and keep that shape even when stress removed. Folding. Heat and time increase the possibility of plastic deformation

C. Deformed rocks in the field: all rocks can deform and give us clues to geologic past

III. Folds: plastic deformation

A. Folding can occur on a very mild scale (open folds) or a very complicated scale (recumbent and plunging folds)

B. Plate tectonics and folding: folding is associated with convergence

IV. Faults

A. Introduction: brittle deformation. Rocks at relatively low temperatures

B. Types of faults

1. Strike-slip faulting: shear stress, motion is horizontal. Example: San Andreas fault: a transform fault

2. Dip-slip faults: motion is vertical: normal and reverse (or thrust faults).

Normal: divergence; reverse/thrust: convergence

V. Building Mountains: Types and processes of mountain-building

A. Volcanic mountains: convergence or hot spots, e.g., Cascades, Sierra Nevada, Hawaiian oceanic hotspot, Yellowstone continental hotspot, Mt. St. Helens, Andes, Pacific "Ring of Fire" stratovolcanoes: continental ring calderas.

B. Fault block mountains: normal faults, divergence. e.g., Basin and Range Province

C. Upwarp mountains: caused by broad arching of the crust. e.g., Black Hills, S.D., Adirondacks, So. part of Rocky Mts.

D. Fold and thrust mountains: reverse and thrust faults, convergence, e.g., Alps, Himalayas, Rockies, Appalachians. Continent-continent collision

E. Accretion of displaced terranes

I. Introduction

II. Early History of the Universe

A. The Big Bang: 10-15 billion years ago, a small, infinitely high-energy region exploded outward

1. Accounts for galaxies moving away from us.

2. Before the Big Bang, the universe was small, incredibly dense and hot

3. Big Bang marks the beginning of the Universe (including time!)

4. Matter is moving outward from the site of the BB

5. Future: universe could begin to contract in ~20 billion years

B. Galaxies formed as pockets of gas began to clump together

C. Within these galaxies, smaller pockets of gas began to form into stars and (at least one!) solar systems

III. Geologic Time in Perspective: Geologic Time Table is based on the fossil record!

A. Summary of history of life on Earth: difficulty of fossil preservation: need hard parts!

1. Earth formed 4.6 b.y.a.

2. Oldest rocks 4 b.y.a.

3. First life (bacteria) 3.85 b.y.a.

4. Blue green algae 3.5 b.y.a.

5. "Cambrian Explosion" of life 543 m.y.a.

6. First fish 543 m.y.a.

7. First land plants: 438 m.y.a.; first reptiles 320 m.y.a.

8. Inland sea in the Interior of the U.S. 500-200 m.y.a.

9. Extinction of dinosaurs 65 m.y.a.

10. First humans 4 m.y.a.

11. "Modern" humans 1.6. m.y.a.

12. Last glacial retreat in Ohio: 40,000-10,000 years ago

13. Recorded history begins about 5000 years ago (Chinese)

B. Knowledge of the Earth’s history derived from:

1. Relative dating: comparing 2 or more entities to determine which is older

2. Absolute dating: actual number of years since an event occurred

IV. Determining Relative Age

A. Principles of relative dating

1. Uniformitarianism: same geologic processes throughout time but rate may vary

2. Horizontality and superposition

a. Principle of original horizontality: sed. rock layers are originally deposited horizontally

b. Principle of superposition: younger rock units are deposited on top of older rock units

c. Applies to undisturbed sedimentary rocks and lava flows

3. Cross-cutting relationships provide relative dates for igneous intrusions and faults:

things that "cut" across rock layers must be younger than those layers.

4. Inclusions: fragments of rock that are included in another rock must be older than the "host" rock

5. Fossils and fauna successions

a. Scarcity of fossils: only about 1% of all species are estimated to have been preserved in fossil record!

b. Principle of faunal succession: animals changed in definite order through time.

B. Unconformities

1. Unconformities: "gaps" in rock record.

2. Reasons for unconformities: rock layers removed by erosion, no rock layers deposited

C. Correlation: identifying rock units from geographically distant area that were deposited at the same time

1. Purpose of correlation

2. Methods of correlation: paleontological similarities, mineralogical similarities, key beds

V. Determining Absolute Age

A. Radiometric dating

1. Process of radioactive decay, principle of radiometric dating, principle of half-lives

2. Factors affecting radiometric results

a. Type of rock

1. Useful for igneous rocks

2. Difficult with sedimentary and metamorphic rocks

b. Sample must be very "fresh" to be able to accurately date

c. Age of sample important to what kind of dating method useful

B. Geologic dating is always done by combining relative and absolute dating to determine the complete geologic history of a region

VI. The Geologic Time Scale

A. Introduction

B. Life on Earth

1. Extinction of first life

2. Life of the Precambrian: blue green algae, soft tissue creatures

3. Life of the Phanerozoic Eon: 543 m.y.a., first evidence of hard parts!

a. Paleozoic Era: "ancient life" marine invertebrates, fish, amphibians, insects, land plants

b. Mesozoic Era: reptiles, dinosaurs

c. Cenozoic Era: mammals

d. Early human beings evolved 3.4-3.8 m.y.a. in East Africa

C. The age of the Earth: how do we know what we know?

1. Earth is estimated to be 4.6 billion years old

2. Oldest rocks we have found are 3.96 b.y.a. and they are metamorphosed!

3. Dated moon rocks and meteorites give a consistent 4.5-4.6 b.y.a. age

4. Assumes solar system formed at the same time as the Earth

I. Introduction

A. Natural resource depletion: we are using up resources, exponential growth of world population. Increasing per capita use of natural resources

B. Global uneven use of natural resources: U.S. 6% of world population, uses 30% of natural resources

C. Global uneven distribution of natural resources: Japan vs. the U.S.

D. Reserves and resources. Reserves are identified resources.

E. Renewable vs. nonrenewable resources: can it be replenished over a relatively short time?

II. Fossil Fuels

A. Petroleum: hydrocarbons, oil and gas

1. Composition: marine microorganisms: limestone

2. The origin of petroleum: scarcity of oil -forming conditions

3. Oil shale and oil sand

4. Depletion of petroleum reserves: 35-50 years

B. Coal and peat: semi-decayed swamp vegetation

1. Description

2. Origin: decomposition of tropical and semi-tropical vegetation

3. Progression: swamp vegetation, peat, brown coal, coal

4. Problems with coal: pollution, acid rain, global warming

Why do we have oil and gas reserves and coal deposits in North America??

C. Depletion of Fossil fuels

D. Fossil fuels and the environment

1. Acid rain

2. Global warming

3. Ozone Depletion

4. Marine oil spills

III. Alternative Energy Resources

A. Nuclear power

1. Nuclear fusion (like the Sun, hydrogen into helium)

2. Nuclear fission (nuclear power, nuclear weapons, "splitting" the atom)

B. Geothermal energy

C. Hydroelectric power

D. Tidal power

E. Wave energy

F. Solar energy

G. Wind power

H. Biomass

I. Hydrogen fuel cells

IV. Mineral Resources

A. Metals: metals are present in almost all rocks but they are too "diluted" to be useful. We need to find places where the metals have been concentrated.

1. Some categories: oxides, sulfides, native elements

2. Processes that concentrate metals

a. Metamorphic processes: e.g., hydrothermal processes: metal-rich hot water. sea floor spreading, subduction zones.

b. Igneous processes: gravity settling, filter pressing

c. Sedimentary processes: e.g., placer deposits in the bends of rivers

d. Secondary enrichment processes: weathering, e.g. bauxite

3. Environmental problems caused by metal refining.  groundwater pollution.

B. Nonmetals: at least as important economically as metals!

1.Nonmetal building material: limestone, gypsum, sand, gravel, clay minerals, various stones

2. Nonmetals for agriculture and industry

I. Introduction

A. Weathering-the process by which atmospheric agents at or near the Earth’s surface cause rocks and minerals to break down

B. Erosion-the process by which moving water, wind, ice or gravity picks up pieces of rock and deposits them elsewhere.

C. Sediment-loose, fragmented surface material (raw material for sedimentary rocks)

D. Benefit of weathering: produces soils

E. Downside of weathering: destroys manufactured structures

II. Weathering Processes

A. Introduction

1. Mechanical weathering-breaks a rock or mineral into smaller pieces but does not change chemical composition

2. Chemical weathering-changes chemical composition of rock or mineral

B. Mechanical weathering: some examples

1. Frost wedging-water in cracks, freezes and expands, breaks rock

2. Mechanical exfoliation- rock expands upward after erosion removes top

3. Other: growth of plant roots, animal activities, abrasion (scratching)

C. Chemical weathering- WATER, WATER, WATER!

1. Dissolution (dissolving) water, carbonic acid removes and carries away. caves

2. Hydrolysis of potassium feldspar into clay, silicic acid, potassium ions

III. Soils and soil formation

A. Soil composition

1. Disintegrated and decomposed rock

2. Humus: decayed remains of animal and plant life (organic matter)

3. 50% is pore space where air and water can circulate

B. Factors that influence chemical weathering and soil formation

1. Climate factors (water and temperature) affect rate of chem. reactions and growth of vegetation. warm humid climate, thickest soil

2. Living organisms: more vegetation, more chem. weathering, thickest soil

3. Time: soil can take 100-100,000 yrs to develop

4. Mineral composition of parent rock

5. Topography: flat terrain produces thicker soil

C. Soil erosion

1. Water and wind carry soil away

2. Soil erosion becomes a problem when more soil is being removed than is being formed (or replenished)

3. One third of farmland is losing more topsoil than is being replenished

4. Consequences: lower productivity, poor crop quality, reduced ag income

5. Deposition of polluted soil in streams, rivers, reservoirs can also be a problem