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
- Chapter 2: Plate Tectonics
- Chapter 3: Matter and Minerals
- Chapter 4: Magma, Igneous Rocks, and Intrusive Activity
- Chapter 5: Volcanoes and Volcanic Hazards
- Chapter 7: Sedimentary Rocks
- Chapter 8: Metamorphism and Metamorphic rocks
- Chapter 9: Geologic Time
- Chapter 11: Earthquakes and Earthquake Hazards
- Chapter 15: Mass Wasting: The Work of Gravity
- Chapter 16: Running Water
- Chapter 23: Energy and Mineral Resources
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
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:
- Sun drives external processes that occur in atmosphere, hydrosphere, and on the surface. Ex. weather and climate, ocean circulation, erosion
- 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
- universe begins
- solar system forms
- inner planets form
- outer planets develop
- chemical differentiation and Earth’s layers
- atmosphere develops
- 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
- crystallization: magma cools and solidifies. Results in igneous rocks
- 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
- lithification: “conversion to rock”. Sediment lithified into sedimentary rock when compacted. Greater pressure/heat results in metamorphic rock
- when metamorphic rock subjected to additional pressure/heat, it melts into magma and the cycle repeats
- 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
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.
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.
Divergent plate boundaries are associated with oceanic ridges: elevated areas of seafloor characterized by high heat flow and volcanism.
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
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
One slab descends beneath the other. Volcanoes grow from ocean floor, can emerge as volcanic island arcs.
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.
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
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.
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
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: as critical part of crystal structure
sulfates: as critical part of crystal structure
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
- 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
5.1 The Nature of Volcanic Eruptions
- 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.
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.
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
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
- emission of an alpha particle from the nucleus
- emission of a beta particle (electron) from the nucleus
- 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.
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
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
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
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
23.7 Mineral Resources Related to Surface Processes
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