Textbook used: Earth: An Introduction to Physical Geology 12th edition by EDWARD J. TARBUCK, FREDERICK K. LUTGENS

Table of contents

Chapter 1: An Introduction to Geology

1.1 Geology: The Science of Earth

geology: Greek geo (Earth) and logos (discourse). The science that pursues an understanding of planet Earth.

physical geology: examines the materials composing Earth and seeks to understand the processes that operate beneath and upon its surface

historical geology: to understand Earth’s origins and its development through time

physical geology precedes Earth history

Examples of natural hazards: volcano, flood, tsunami, earthquake, landslide

Resources connect people to Earth

1.2 The Development of Geology

catastrophism: believes that Earth’s landscapes were shaped primarily by great catastrophes – sudden, worldwide disasters produced by unknown causes. An attempt to fit the rates of Earth’s processes to prevailing ideas about the age of Earth

uniformitarianism: physical, chemical, and biological processes that operate today have also operated in the geologic past. The forces shaping our planet have been at work for a long time.

  • the present is the key to the past: understand present-day processes in order to understand ancient rocks

Appreciation for the magnitude of geologic time is important because many processes are so gradual that vast spans of time are required before significant changes occur.

Earth is 4.6 billion years old.

1.3 The Nature of Scientific Inquiry

hypothesis: a tentative/untested explanation

theory: well-tested and widely accepted view that the scientific community agrees best explains certain observable facts

scientific method: gather data through observations and formulate scientific hypotheses and theories

1.4 Earth as a System

4 spheres:

hydrosphere: dynamic mass of water continually on the move. Global ocean covers ~71% of Earth’s surface. Freshwater in streams, lakes, glaciers

atmosphere: life-giving gaseous envelope. Energy exchange between atmosphere and Earth’s surface and space produce weather and climate

biosphere: includes all life on Earth

geosphere: solid Earth from surface to the center of the planet, ~6400km deep.

Earth system science: aims to interdisciplinarily study Earth as a system composed of numerous interacting subsystems

system: group of interacting or interdependent parts that form a complex whole

Earth system powered by two energy sources:

  1. Sun drives external processes that occur in atmosphere, hydrosphere, and on the surface. Ex. weather and climate, ocean circulation, erosion
  2. heat from Earth’s interior power internal processes that produce volcanoes, earthquakes, mountains

1.5 Origin and Early Evolution of Earth

nebular theory: proposes that the bodies of our solar system evolved from an enormous rotating cloud called the solar nebula

  1. universe begins
  2. solar system forms
  3. inner planets form
  4. outer planets develop
  5. chemical differentiation and Earth’s layers
  6. atmosphere develops
  7. continents and ocean basins evolve

1.6 Earth’s Internal Structure

crust: Earth’s relatively think, rocky outer skin

  • continental crust: 35km thick, many rock types
  • oceanic crust: 7km thick, composed of dark igneous rock basalt

mantle: contains >82% of Earth’s volume. Extends to 2900km

  • upper mantle: crust-mantle boundary to 660km
    • dominant rock is peridotite
    • crust-mantle boundary to 660km deep
    • lithosphere: (“rock sphere”) consists of entire crust and uppermost mantle
    • asthenosphere: (“weak sphere”) lithosphere can move independently of asthenosphere
    • transition zone: 410km to 660km. Sudden increase in density
  • lower mantle: 660km to 2900km
    • strengthens with depth
    • hot and capable of gradual flow
    • D’’ layer: (“dee double prime”)

core: iron-nickel alloy with minor amounts of oxygen, silicon, sulfur

  • outer core: liquid layer 2250 km thick. Its movement generates Earth’s magnetic field
  • inner core: sphere with 1221km radius. Higher temperature but solid due to pressure

1.7 Rocks and the Rock Cycle

rock cycle: allows us to view many of the interrelationships among different parts of the Earth system

The Basic Cycle

  1. crystallization: magma cools and solidifies. Results in igneous rocks
  2. weathering: atmosphere, hydrosphere, and biosphere slowly disintegrate and decompose rocks. Moved downslope by gravity and transported by erional agents – water, glaciers, wind, waves. Eventually the particles, called sediment, are deposited
  3. lithification: “conversion to rock”. Sediment lithified into sedimentary rock when compacted. Greater pressure/heat results in metamorphic rock
  4. when metamorphic rock subjected to additional pressure/heat, it melts into magma and the cycle repeats

Alternative Paths

  • igneous rocks may remain buried. Eventually they are subjected to pressure/heat from mountain building. They are transformed directly into metamorphic rocks
  • metamorphic and sedimentary rocks and sediment don’t always remain buried. Overlying layers may be stripped away, and exposed material is weathered and turned into new raw materials for sedimentary rocks

1.8 The Face of Earth

ocean basins: avg depth of ocean floor is 3.8km. Basaltic rocks of oceanic crust avg 7km thick. Denser than continents

continents: avg elevation 0.8km. Granitic rocks and avg thickness 35km

Major Features of the Ocean Floor

continental margins: portion of seafloor adjacent to major landmasses

  • continental shelf: gently sloping platform along the coasts. An extension of continents
  • continental slope: the real boundary between continents and deep-ocean basins. Steep dropoff from the outer edge of continental shelf to the floor of deep ocean
  • continental rise: more gradual incline, thick wedge of sediment downslope from continental shelf and accumulated on deep ocean floor. Found in regions where trenches do not exist

deep ocean basins: between continental margins and oceanic ridges

  • abyssal plains: flat
  • deep ocean trenches: extremely deep depression, relatively narrow
  • seamounts: submerged volcanic structures

oceanic ridges: most prominent feature of ocean floor. Continuous belt winding more than 70,000km around the globe. Layers of igneous rock

Major Features of the Continents

mountain belts: most prominent continental feature

  • circum-Pacific belt includes western Americas mountains and continues to the western Pacific as volcanic island arcs
  • the other major mountain belt includes the Appalachians in the US and the Alps – older and have more rounded peaks

stable interior: interiors of the continents, cratons, have been stable for the past 600mil years

  • shields: expansive, flat regions composed of deformed igneous and metamorphic rocks
  • stable platforms: highly deformed rocks of the shields are covered by a thin veneer of sedimentary rocks

Chapter 2: Plate Tectonics

2.1 From Continental Drift to Plate Tectonics

Prior to late 1960s most geologists held the view that ocean basins and continents had fixed geographic positions.

Then there was a scientific revolution which proposed continental drift. North American geologists had difficulty accepting continental drift, since much of the supporting evidence was gathered from Africa, South America, and Australia.

2.2 Continental Drift: An Idea Before Its Time

continental drift: Alfred Wegener’s hypothesis

supercontinent (Pangaea): consisted of all Earth’s landmasses

Evidence: Fossils Matching Across the Seas

Identical fossil organisms had been discovered in rocks from both South America and Africa.

Mesosaurus: small aquatic freshwater reptile that suggested that South America and Africa must have been joined

Rafting, trans-oceanic land bridges, and island stepping stones were used to discount the evidence.

glossopteris: seed fern found in Africa, Australia, India, South America. Later found fossils in Antarctica. Wegener concluded that when the land masses were joined, they were closer to the South Pole

Evidence: Rock Types and Geologic Features

Highly deformed igneous rocks in Brazil that closely those in Africa.

Mountain belts that terminate at one coastline and reappear on land across the ocean. Ex. Appalachians from Newfoundland to British Isles.

Evidence: Ancient Climates

Evidence of glaciers in southern landmasses at a time when areas in NA, EU, and Asia were tropical.

Wegener suggested supercontinent Pangaea as an explanation since sourthern continents were joined together near the South Pole.

2.3 The Great Debate

Rejection of the Drift Hypothesis

Main objection to Wegener’s hypothesis: his inability to identify a credible mechanism for continental drift from citing Moon and Sun gravitational forces.

He also incorrectly suggested the larger continents broke through thinner oceanic crust, but there is no evidence of this.

2.4 The Theory of Plate Tectonics

Naval research following WWII found:

  • earthquakes occur at great depths
  • oceanic crust is no older than 180 million years
  • sediment accumulation in deep-ocean basins were thin

These results led to the development of theory of plate tectonics.

Rigid LithoSphere Overlies Weak Asthenosphere

Outer layer lithosphere, oceanic lithosphere is denser than continental lithosphere. Responds to forces by bending or breaking.

Asthenosphere is hotter, weaker, responds to forces by flowing.

These layers can move independently

Earth’s Major Plates

Lithosphere has ~24 segments of irregular size and shape called lithospheric plates. 7 major plates are recognized and account for 94% of Earth’s surface: North American, South American, Pacific, African, Eurasian, Australian-Indian, and Atlantic plates.

Plate Movement

Plates move as rigid units relative to other plates. As plates move, distance between two locations on different plates (ex. NYC and London) gradually changes, whereas distance between places on the same plate remain constant.

Most major plate interactinos occur along their boundaries. Three types of boundaries:

  • divergent plate boundaries: 40% of boundaries. Two plates move apart – upwelling and partial melting of hot material from mantle to create new seafloor
  • convergent plate boundaries: 40% of boundaries. Two plates move together. Oceanic lithosphere descends beneath overriding plate, or collision creates a mountain belt
  • transform plate boundaries: 20% of boundaries. Two plates grind past each other without production or destruction of lithosphere

2.5 Divergent Plate Boundaries and Seafloor Spreading

Divergent plate boundaries located along crests of oceanic ridges. As two plates move away from eachother, molten rock from mantle migrates upward to fill the voids (seafloor spreading). Therefore these are constructive plate margins. Also called spreading centers.

Spreading averages 5cm per year.

Ocean Ridges

Divergent plate boundaries are associated with oceanic ridges: elevated areas of seafloor characterized by high heat flow and volcanism.

Continental Rifting

Divergent boundaries can occur within a continent. The broken crust sinks, generating an elongated depression called a continental rift. This can widen to form a narrow sea, and eventually an ocean basin.

Ex. East African Rift

Ex. Red Sea, formed when Arabian Peninsula split from Africa

2.6 Convergent Plate Boundaries and Subduction

convergent boundaries aka subduction zones – lithosphere descends into the mantle

deep-ocean trenches are the surface manisfestation of this

three types of convergent boundaries

Oceanic-Continental Convergence

Buoyant continental block remains floating, while oceanic slab sinks into mantle

Sediment and oceanic crust contains water. When the slab reaches 100km deep, its water causes partial melting in the mantle. The hot material gradually rises and thickens the crust or create volcanic eruptions.

Ex. volcanoes of Andes from subduction of Nazca plate below South America – continental volcanic arcs

Oceanic-Oceanic Convergence

One slab descends beneath the other. Volcanoes grow from ocean floor, can emerge as volcanic island arcs.

Continental-Continental Convergence

Collision occurs and a new mountain belt of deformed sedimentary and metamorphic rock. Ex. Himalayas, Alps, Appalachians, Urals

2.7 Transform Plate Boundaries

Also called transform fault. Plates slide horizontally past eachother. No production/destruction of lithosphere.

Mostly found on ocean floor.

Part of prominent breaks in seafloor called fracture zones.

2.8 How Do Plates and Plate Boundaries Change?

Size and shape of individual plates are constantly changing (ex. African and Antarctic plates mainly bounded by divergent boundaries, so more seafloor lithosphere produced and Pacific plate is being consumed).

Boundaries can also migrate, disappear, and be created.

The Breakup of Pangaea

Breakup created new ocean basin – the Atlantic.

Plate Tectonics in the Future

In 250 million years, Atlantic basin may close and we will have the next supercontinent.

2.9 Testing the Plate Tectonics Model

Evidence: Ocean Drilling

Sediment increases in age with increasing distance from ridge – supports seafloor spreading hypothesis that youngest ocean crust is found at ridge site of seafloor production.

Distribution and thickness of sediment provides additional support for seafloor spreading.

Seafloor no older than 180 million years was found.

Evidence: Mantle Plumes and Hot Spots

Linear chains of volcanic structures. Volcanoes increase in age with increasing distance from Hawaii.

Mantle plume (cylindrical shape upwelling of hot rock) is beneath the island of Hawaii.

Manifests on surface as hot spot, an area of volcanism, heat flow, and crust uplift. As Pacific plate moves over a hot spot, a hot-spot track is built. Hawaiian islands are a result of this.

Main island is newest and on east side, so Pacific plate moving east to create Hawaii.

Evidence: Paleomagnetism

Rocks formed thousands and millions of years ago contain a record of the direction of their magnetic poles at time of formation. This is called paleomagnetism or fossil magnetism.

Apparent Polar Wandering

Studying paleomagnetism in ancient lava flows.

Apparent migration of magnetic poles explained by continental drift.

Magnetic Reversals and Seafloor Spreading

During magnetic reversal, north and south pole reverse.

Establish a magnetic time scale of these reversals. The major division of time is a chron, lasting ~1 million years.

Stripes of normally and reversely magnetized rock across sea floor. Explanation is that magma solidifies along rifts at the crest of ocean ridge and is magnetized locally. Seafloor spreading increases the strip width and new seafloor with opposite polarity solidifies in the middle of the old strip.

2.10 How Is Plate Motion Measured?

Geologic Measurement of Plate Motion

Use drilling + paleomagnetism + seafloor topography to create maps with age of ocean floor.

Measuring Plate Motion from Space

Collect GPS data at numerous sites repeatedly over time.

2.11 What Drives Plate Motions?

Forces That Drive Plate Motion

Convection of mantle.

Subduction of cold, dense slabs of ocean lithosphere drives slab pull. Density causes the ocean lithosphere to be pulled into mantle by gravity. Dominant force.

Ridge push occurs when elevated oceanic ridge causes slabs of lithosphere to slide down the flanks of the ridge.

Models of Plate–Mantle Convection

What is known:

  • convection in rocky 2900km thick mantle drives plate movement
  • mantle convection and plate tectonics are part of the same system

Models:

Whole-Mantle Convection

Cold oceanic lithosphere sinks to great depths and stirs entire mantle.

Layer Cake Model

Thin dynamic layer in upper mantle and thick slow one below. Driven by subduction of oceanic lithosphere.

Chapter 3: Matter and Minerals

3.1 Minerals: Building Blocks of Rocks

mineral: naturally occurring inorganic solids that possess an orderly crystalline structure and characteristic chemical composition

rock: naturally occuring masses of minerals or mineral-like matter, like glass or organic material

3.2 Atoms: Building Blocks of Minerals

Minerals are composed of atoms elements

atomic number: # of protons in an atom

neutron: weigh the same as proton but no charge

electron: weigh ~2000 times less than protons and neutrons. Negative charge equal in magnitude to proton

principal shell: distinct energy level of electrons

valence electron: electrons in outermost principal shell

  • important for bonding with other atoms
  • elements with similar number of valence electrons behave in similar ways

3.3 Why Atoms Bond

chemical bond: transfer or sharing of valence electrons

octet rule: most stable arrangement for most atoms is 8 electrons in outermost principal shell

ionic bond: positively charged ions bond with negatively charged ions

covalent bond: sharing of electrons between atoms

metallic bond: electrons freely move from one atom to another throughout the entire mass

3.4 How Do Minerals Form?

elements dissolved in solutions of water: precipitation of minerals may be triggered by drop in temperature or evaporation of water

molten rock: free moving atoms form bonds with other atoms as liquid cools, and nucleus of mineral crystal adds more atoms on outer edge growing larger as more atoms enter lower energy state

marine organisms: extract ions from surrounding seawater and secrete skeletal material made of calcium carbonate or silica

3.5 Physical Properties of Minerals

Physical properties occur due to composition and internal crystalline structure of a mineral’s crystal lattice.

luster: ability to reflect light

  • transparent, translucent, opaque describe degree to which a mineral transmits light
  • colour is unreliable due to stains
  • streak: colour of powder generated scraping a mineral against porcelain streak plate

habit: shape a crystal assumes

hardness: resistance to being scratched

tenacity: brittle vs. bend when stressed

cleavage: preferential breakage along planes of weak atomic bonds

density: amount of matter in a givne volume

specific gravity: ratio of mineral’s density to density of water

3.6 Mineral Structures and Compositions

crystal: naturally occurring solids with orderly repeating internal structures

  • all minerals occur in crystal form
  • smallest expression of crystal arrangement is called unit cell

Steno’s Law (Law of Constancy of Interfacial Angles): no matter how big a crystal of a given mineral may be, the angles between its faces will always be the same

polymorph: the same chemical compound can grow into different mineral crystals, with different arrangements of atoms

  • ex. calcite and aragonite are both \(CaCO_3\)

3.7 Mineral Groups

rock-forming mineral: minerals in Earth’s crust

  • only a few dozen out of 4000+ identified minerals

economic mineral: have economic value

silicate: silicon and oxygen are most comcmon elements of Earth’s crust

nonsilicate: make up 8% of crust

3.8 The Silicates

silicon-oxygen tetrahedron: basic building block

polymerization: developing long chains of building blocks when neighboring tetrahedra share their oxygen atoms

3.9 Common Silicate Minerals

Most common mineral class on Earth.

dark (ferromagnesian) silicate): dense, dark, contain iron

light (nonferromagnesian) silicate): less dense, light, no iron

  • ex. Feldspar, quartz, clays

3.10 Important Nonsilicate Minerals

Often economic minerals.

oxides: bonding of metals to oxygen ions

carbonates: \(CO_3\) as critical part of crystal structure

sulfates: \(SO_4\) as critical part of crystal structure

Chapter 4: Magma, Igneous Rocks, and Intrusive Activity

4.1 Magma: Parent Material of Igneous Rock

magma: molten rock below Earth’s surface

  • liquid melt
  • additions of solids (mineral crystals) and gases (volatiles)

lava: molten rock above Earth’s surface

As magma cools, silicate minerals form mobile ions in the melt. They grow with addition of ions to the outer surface. As cooling proceeds, crystallization transforms magma a solid of interlocking crystals, igneous rock.

intrusive igneous rocks: formed by magma cooling below the surface

extrusive igneous rocks: formed by lava cooling above the surface

4.2 Igneous Compositions

Mostly of silicate minerals

granitic (felsic) composition: mostly nonferromagnesian minerals

  • continental crust

basaltic (mafic) composition: mostly ferromagnesian materials

  • darker
  • denser
  • oceanic crust

andesitic (intermediate) composition: in between felsic and mafic

  • continental volcanic arcs

ultramafic: upper mantle

4.3 Igneous Textures: What Can They Tell Us?

Cooling is quick for lava/on the surface. Fast crystallization, small crystals, and fine grained texture.

Magma cooling is slower, coarse grained texture.

porphyritic texture: has two stage cooling (deep then shallow)

4.4 Naming Igneous Rocks

Classififed based on textures and compositions.

4.5 Origin of Magma

Solid rock melts when:

  • heat added to rock
  • hot rock experiences low pressure (decompression)
  • water is added

4.6 How Magmas Evolve

Bowen’s reaction series: minerals crystallize in a specific order in cooling magma

  • ferromagnesian silicates first, nonferromagnesian silicates last
  • in between, reactions take place resulting in compositional changes to magma

4.7 Partial Melting and Magma Composition

partial melting: rocks do not melt completely due to different melting temperatures

4.8 Intrusive Igneous Activity

plugon: intrusion created when magma intrudes other rocks and crystallizes before reaching the surface

host rock: rock being intruded

Chapter 5: Volcanoes and Volcanic Hazards

5.1 The Nature of Volcanic Eruptions

Lava viscosity

  • more silica = more viscous
  • lower temperature = more viscous

High silica, low temperature = viscous and most explosive

Low silica, high temperature = fluid and least explosive

5.2 Materials Extruded During an Eruption

lava tube: tunnels through which lava flows when surface flow congeals

Volcanoes bring liquid lava, gases, and solid materials to Earth’s surface.

  • gases include water vapor and carbon dioxide
    • when they reach the surface, they rapidly expand leading to explosive eruptions that generate lava fragments called pyroclastic materials (ash, lapilli, blocks/bombs)
  • if bubbles of gas don’t pop before solidification, they are preserved as vesicles

pumice: lightweight, made from frothy silica rich lava

scoria: made from basaltic lava with lots of bubbles

5.3 Anatomy of a Volcano

Conical piles of extruded material that collect around a central vent.

Vent is usually within a summit crater or caldera.

parasitic cone: smaller vents on the flanks of the volcano

fumarole: spot where gas is expelled

5.4 Shield Volcanoes

Many successive lava flows of low viscosity basaltic lava, but lack pyroclastic debris.

Lava tube transport lava far from the main vent resulting in gentle, shield like profiles.

5.5 Cinder Cones

Steep sided structure composed of pyroclastic debris.

Much smaller volcano, form quickly as single eruptive events.

5.6 Composite Volcanoes

Consist of both pyroclastic material and lava flows.

Larger than cinder cones and form from multiple eruptions over millions of years.

Produce silica rich lavas that are more viscous, so material accumulates at a steeper angle.

5.7 Volcanic Hazards

pyroclastic flow (nuée ardente): dense mix of hot gas and pyroclastic fragments

  • greatest volcanic hazard to human life

lahar: volcanic mudflow that occur even when a volcano is not erupting

tsunami: generated by volcanoes at sea level

5.8 Other Volcanic Landforms

fissure eruption: produce low viscosity, silica poor lava from large cracks in the crust

lava dome: thick masses of high viscosity silica rich lava that accumulate in the summit crater or caldera of a composite volcano

  • when the lava dome collapses, creates extensive pyroclastic flow

volcanic neck: lava in throat of volcano that crystallizes to form a plug of solid rock that weathers slowly

  • after pyroclastic debris erodes away, the resistant neck is distinctive

5.9 Plate Tectonics and Volcanic Activity

At convergent plate boundaries, subduction creates magma. Creates a volcanic arc like the Pacific Ring of Fire.

At divergent boundaries, decompression melting generates magma.

At intraplate settings, source of magma is a mantle plume: a column of warm rising solid rock in the mantle.

5.10 Monitoring Volcanic Activity

Volcanoes give off physical signals like shape, earthquakes beneath a volcano, and composition and quantity of gas output.

Chapter 7: Sedimentary Rocks

7.1 An Introduction to sedimentary rocks

Sediments and rock layers they form make a record of past conditions and events at the surface ex. fossils

7.2 Detrital sedimentary rocks

Made of solid particles like quartz and clay.

Classified based on size of grains which indicates energy level of deposition.

shale: made up of small grains of clay

  • fissile due to alignment of clay flakes parallel to bedding

sandstone: sand sized grains

  • sorting: reflection of how abruptly/gradually the sand was deposited
  • rounder grains signify further trnasport

conglomerate, breccia: high proportion of gravel-sized grains

7.3 Chemical sedimentary rocks

Ions dissolved in solution link to form mineral crystals, either inorganically or biochemically.

limestone: most common chemical sedimentary rock

  • shallow warm ocean settings
  • calcium carbonate

dolostone: contains dolomite, a carbonate material with more magnesium

chert: rocks made of microcrystalline silica

  • red: jasper
  • black: flint
  • agate: multicolor

evaporite: minerals precipitate from an ever more concentrated solution of dissolved ions

7.4 Coal: An organic sedimentary rock

Forms from large amounts of plant matter buried in low-oxygen environments like swamps and bogs.

Great compression of peat yields greater grade of coal.

7.5 Turning sediment into sedimentary rock: Diagenesis and lithification

diagenesis: collective term for the chemical, physical, biological changes that occur after sediments are deposited and during and after lithification

  • caused by changes in temperature and pressure

lithification: transformation of sediment into sedimentary rock

  • compaction: reduction in pore space by packing grains tightly
  • cementation: reduction in pore space by adding new mineral material that acts as glue

7.6 Classification of sedimentary rocks

Classified based on detrital, chemical, or organic in nature.

  • detrital subdivided by grain size
  • chemical subdivided by mineral dcomposition
  • also clastic or nonclastic (crystalline) texture

7.7 Sedimentary rocks represent past environments

Continental, marine, and transitional (shoreline) environments have distinctive characteristics that allow geologists to identify sedimentary rocks formed in those environments.

facies: different depositional conditions operating in adjacent areas at the same time

  • ex. beach depositing sand, offshore depositing mud, and beyond that carbonate minerals precipitating

sedimentary structure: patterns that form in sedimentary rock at time of deposition before lithification

  • beds (strata): sheets of sediment deposited in a continuous layer
  • ripple marks
  • graded beds
  • mud cracks

7.8 The carbon cycle and sedimentary rocks

Carbon is a reactive element that is equally at home in rocks, water, air, and living tissue.

Weathering processes and sedimentary rocks relate to the carbon cycle.

Chapter 8: Metamorphism and Metamorphic rocks

8.1 What Is Metamorphism?

Rocks subjected to elevated temperature and pressure can react and change form to produce metamorphic rock

parent rock: the rock it was prior to metamorphism

metamorphic grade: intensity of metamorphosis

  • low grade resembles parent rock
  • high grade destroys textures of parent rock

8.2 What Drives Metamorphism?

Heat, pressure, differential stress, chemically active fluids.

  • heat from intruding magma body provides energy that drives chemical reactions and recrystallization of existing minerals
  • pressure from burial causes compaction into denser configurations
  • differential stress form tectonic forces shorten in the direction of greatest stress and elongate in areas of least stress
  • hot water facilitates chemical reactions and transports dissolved mineral

8.3 Metamorphic textures

foliation: planar arrangement of mineral grains

  • forms perpendicular to direction of maximum differential stress
  • nonfoliated metamorphic rock recrystallize under confining pressure so the mineral grains exhibit random orientation

porphyroblast: large crystals of certain minerals. Larger than other grains in the same rock, and are distributed in the rock

8.4 Common Metamorphic rocks

Foliated: slate, phyllite, schist, gneiss (increasing metamorphic grade)

Nonfoliated: quartzite, marble, hornfels (recrystallization of quartz sandstone, limestone, shale)

8.5 Metamorphic environments

contact metamorphism: heat from magma is dominant variable

hydrothermal metamorphism: hot water rather than conduction as agent of heat transfer

burial metamorphism: under confining pressure, elevated temperature causes metamorphic reactions

  • subduction zone metamorphism is similar but with added differential stress

regional metamorphism: plate collisions

impact metamorphism: faults and meteorite impact

8.6 Metamorphic Zones

Grain size increases with higher levels of metamorphism.

index mineral: act as indicators of the environment and metamorphic grade

8.7 Interpreting Metamorphic environments

blueschist facies metamorphism: subduction zones, pressure

zeolite facies metamorphism: mountain building activity at convergent plate boundaries, temperature and pressure

hornfels facies metamorphism: baked at high temperature but relatively low pressure

Chapter 9: Geologic Time

9.1 Creating a Time Scale: Relative Dating Principles

relative dating: puts events in their proper chronological sequence

numerical dating: pinpoint time in years when an event took place

9.2 Fossils: Evidence of Past Life

For fossil to be preserved, organism must be buried rapidly. Hard parts are most likely preserved

9.3 Correlation of Rock Layers

correlation: matching exposures of rock that are same age but in different places

principle of fossil succession: fossil organisms succeed one another in a definite and determinable order

index fossil: widespread and associated with a relatively narrow time span

9.4 Numerical Dating With Radioactivity

radioactivity: spontaneous breaking apart (decay) of certain unstable atom nuclei

3 types:

  1. emission of an alpha particle from the nucleus
  2. emission of a beta particle (electron) from the nucleus
  3. capture of an electron by the nucleus

An unstable radioactive isotope, the parent, will decday and form daughter products

half life: length of time for one half of the nuclei of a radioactive isotope to decay

9.5 The Geologic Time Scale

Eon > era > period > epoch

9.6 Determining Numerical Dates for Sedimentary Strata

Sedimentary strata are not radiometric datable because they are made up of material from older rocks.

They can be numerically dated by relatively dating w.r.t. a numerically datable igneous mass.

Chapter 11: Earthquakes and Earthquake Hazards

11.1 What Is an Earthquake?

Suddent movements of large blocks of rock on opposite sides of faults causes most earthquakes.

hypocenter (focus): location where the rock begins to slip

seismic wave: radiate from the hypocenter outward into the surrounding rock

epicenter: point on Earth’s surface directly above the hypocenter

elastic rebound: stress overcomes the frictional resistance keeping a rock from rupturing and slipping, causing the rock to spring back to its original shape

foreshock: smaller earthquakes that precede larger earthquakes

aftershock: smaller earthquakes that occur after larger earthquakes as the crust readjusts to the new conditions

11.2 Faults and Earthquakes

Convergent plate boundaries and associated subduction zones are marked by megathrust faults. These faults are responsible for most of the largest earthquakes in history.

11.3 Seismology: The Study of Earthquake Waves

seismograph: measures seismic waves using inertia, creates a seismogram

body wave: (P and S waves) move through Earth’s interior

  • P waves are the fastest, lowest amplitude
    • push and pull, changing the volume of the rock
    • can travel through fluids
  • S waves intermediate speed and amplitude
    • shaking motion, changing the rock’s shape but not volume
    • cannot travel through fluids

surface wave: only travel along the upper layers of the crust

  • slowest waves, greatest amplitude
  • accounts for most earthquake damage

11.4 Locating the Source of an Earthquake

The distance separating a recording station and an earthquake epicenter can be determined using the difference in arrival times between P and S waves.

3+ seismic stations means triangulation can be used to locate the epicenter.

11.5 Determining the Size of an Earthquake

intensity: measures the amount of ground shaking at a location

magnitude: estimate of the actual amount of energy released during an earthquake

Modified Mercalli Intensity scale: measures intensity at different locations

  • based on verifiable physical evidence and quantifies intensity on a 12 point scale

Richter scale: takes into account both maximum amplitude of seismic waves measured at a given seismograph and distance from the earthquake

  • logarithmic, and each number represents 32 times more energy released

moment magnitude scale: measures total energy released by considering the strength of the faulted rock, amount of slippage, and the fault that slipped

  • modern standard

11.6 Earthquake Destruction

liquefaction: water logged sediment or soil is severely shaken during an earthquake, reducing the strength of the ground so it no longer supports buildings

seiche: sloshing motion of water caused by earthquake waves, dangerous for structures along shorelines and can cause dams to fail

tsunami: large ocean waves formed when water is displaced.

11.7 Where Do Most Earthquakes Occur?

circum-Pacific belt: ring of megathrust faults rimming the Pacific Ocean where most earthquake energy is released

11.8 Can Earthquakes Be Predicted?

precursor: events such as changes in ground elevation or strain levels near a fault that allow shorter range predictions (hours or day)

  • not reliable

seismic gap: portions of faults that have been storing strain for a long time and thus have great potential for experiencing an earthquake

paleoseismology: earthquakes occur on a cyclical basis, so frequency in the past can give insight into the future

  • long range forecast

Chapter 15: Mass Wasting: The Work of Gravity

15.1 The Importance of Mass Wasting

mass wasting: after weathering breaks apart rock, gravity moves the debris downslope

  • rapidly (ie. landslide), or slowly
  • widens stream valleys and helps tear down mountains thrust up by plate tectonics

15.2 Controls and Triggers of Mass Wasting

trigger: an event that initiates a mass wasting process

  • ex. addition of water, oversteepening of slope, removal of vegetation, shaking due to earthquake

angle of repose: critical slope angle at which granular materials can pile which, if exceeded, will spontaneously collpase outward to form a gentler slope

  • between 25 and 40 degrees for most geologic materials

Plant roots form a 3d net that holds soil in place. When plants die from human or natural causes, this structure weakens.

Earthquakes are significant triggers.

15.3 Classification of Mass-Wasting Processes

rock fall: pieces of bedrock detach and fall freely through the air

  • talus slope: apron of angular rock debris accumulating below mountain cliffs caused by repeated rock fall

slide: discrete blocks of rock or unconsolidated material slide downslope on a palnar or curved surface

flow: individual grains or particles move randomly in a slurry, a viscous mixture of water-waturated materials

rock avalanche: move rapidly over distances

  • ride along a layer of compressed air

15.4 Rapid Forms of Mass Wasting

slump: coherent blocks of material move downhill on a spoon-shaped slip surface

rockslide: coherent block of rock slides downhill along a planar surface

debris flow: unconsolidated soil or regolith becomes saturated with water and moves downhill in a slurry, picking up other objects along the way

earthflow: similar to debris flow, but much slower

15.5 Slow Movements

creep: occurs when freezing/wetting causes soil particles to be pushed out away from the slope, ohly to drop down to a lower position following thawing/drying.

solifluction: gradual flow of a saturated surface layer that is underlain by an impermeable zone

  • in arctic regions, the impermeable zone is permafrost

permafrost: permanently frozen ground covering large portions of North America and Siberia

Chapter 16: Running Water

16.1 Earth as a System: The Hydrologic Cycle

hydrologic cycle: undending circulation of water between the hydrosphere, atmosphere, geosphere, and biosphere

When precipitation falls on land it goes through:

  • infiltration: soak into the ground
  • runoff: flows over the surface
  • immediately evaporates

transpiration: infiltrated water is absorbed by plants which release it into the atmosphere

  • evapotranspiration: umbrella term for transfer of water from surface to atmosphere, since both evaporation and transpiration contribute to this

16.2 Running Water

drainage basin (watershed): land area that contributes water to a stream

  • upstream portion is where the stream’s sediment is derived
  • middle section is sediment transport
  • downstream section is sediment deposition

divide: imaginary lines separating drainage basins

headward erosion: lengthening a stream’s course by extending the heads of their valleys upslope

  • a stream erodes most effectively in a headward direction

water gap: steep-walled notch in a ridge through which a stream flows

  • antecedent: stream exists before the ridge or mountain was uplifted and erodes its bed at a pace equal to the rate of uplift
  • superposed: eroded its channel into an existing structure

Chapter 23: Energy and Mineral Resources

23.1 Renewable and Nonrenewable Resources

renewable resource: replenishable over relatively short time spans

nonrenewable resource: form so slowly from a human standpoint that Earth contains fixed supplies

23.2 Energy Resources: Traditional Fossil Fuels

fossil fuel: energy of ancient sunlight captured by photosynthesis is stored in plants and living things which are then buried by sediment

  • coal, oil, natural gas

coal: compressed plant fragments deposited in ancient swamps

oil and natural gas: heated remains of marine plankton

  • leave source rock (shale) and migrate to an oil trap made of other porous rocks (reservoir rock), covered by an impermeable cap rock

oil sands: sedimentary deposits that contain bitumen in their pore spaces

hydraulic fracturing (fracking): method of opening up pore space in otherwise impermeable rocks, permitting natural gas to flow out into wells

23.3 Nuclear Energy

Use controlled nuclear fission chain reaction where heavy uranium atoms are bombarded with neutrons to cause atoms to split. The heat boils water and steam drives turbines.

Uranium-235 must be concentrated

23.4 Renewable Energy

solar energy: can be captured through passive solar design, active solar collectors (to heat liquidsp), and photovoltaic cells

wind energy: windmills and turbines

  • wind speed is an important variable

hydroelectric energy: running water is dammed

geothermal energy: heat in Earth’s subsurface to produce hot water or electricity

  • requres a potent source of heat, large subsurface reservoirs, and a cap of low permeability rock

biomass: animal or plant matter that can be burned directly or converted into a fuel

tidal energy: impounding the waters of the high tide and releasing them at low tide through a dam

23.5 Mineral Resources

ore: metallic mineral resources that can be economically mined

reserve: stockpile of unmined but economically recoverable mineral resources

23.6 Igneous and Metamorphic Processes

  • igneous processes concentrate some elements
  • magmas may give off hot water solutions that penetrate surrounding rock, carrying dissolved metals in them
  • contact and regional metamorphism produce concentrations of minerals where igneous plutons intrude limestone

secondary enrichment: weathering creates ore deposits by concentrating minor amouonts of metals into economically valuable deposits

  • either move unwanted material or wanted material

placer deposit: tough, dense minerals like gold are sorted by water currents and separated from lower density sediments

23.8 Nonmetallic Mineral Resources

nonmetallic resource: Earth material that is not used as fuel or processed for metal

  • many are sediments and sedimentary rock
  • building materials vs. industrial minerals