geology notes

Jan 2

The universe is everything that's out there, all of space, all of the matter and energy within it.

Solar system anything that revolves around the sun

Geocentric- earth sat at the center of the universe

• Ptolemy proposed equations to predict the movements of the planets

Heliocentric- the sun lay at the center of the universe

• Earth and planets orbited the sun

• The earth and planets orbited the sun

The heliocentric model gained acceptance during the Renaissance 

• The sun lay at the center of the universe

• The earth and planets orbited the sun

Renaissance; a new age of discovery in 1400s Europe

• Copernicus and Galileo's studies led to acceptance that Earth and the planets orbit the sun

• Newton + Kepler- planet motion was explained by the theory of gravity

Stars are immense balls of incandescent gas

• Gravity binds stars together into vast galaxies

• Over 100 billion galaxies exist in the visible universe

The solar system is on an arm of the Milky Way galaxy 

• Our sun is one of 300 billion stars in the Milky Way

We must consider huge expanses of space and time

From the sun to the earth 8 mins for light to travel

Light travels about 6 trillion miles, the nearest star is over 4 light-years away

The Milky Way galaxy is 120,000 light-years across

Edge of the visible universe: >13 billion light-years away

Our sun is a medium-sized star, orbited by 8 planets

• The sun accounts for 99.8% of our solar system mass

• Planet- a planet

  • Is a large solid body orbiting a star (the sun)

  • Has a nearly spherical shape 

  • Has cleared its neighborhood of other objects (by gravity)

• Moon- a solid body locked in orbit around a planet 

• Millions of asteroids and trillions of icy bodies orbit the sun

Two groups of planets occur in the solar system

• Terrestrial planets-small, dense, rocky planets

  • Mercury Venus Earth Mars

• Giant (jovian) planet- large low-density, gas and ice giants

  • Gas giants 

  • Ice giants

The terrestrial planets are the four most interior 

The giant planets occupy the four outermost orbits

All but two planets have moons (Jupiter has 63)

The Astroid belt lies between Mars and Jupiter 

Clouds of icy bodies lie beyond Neptune’s orbit

• Icy fragments pulled into the inner solar system become comets

Theory is an explanation of why something occurred based on the current knowledge

Earth is a planet orbiting a star on the arm of a galaxy

The sun and over 300 billion stars from the Milky Way

Over 100 billion galaxies exist in the visible universe

The Big Bang initiated the expanding universe

• 13.7 billion years ago

• The rapid expansion of a small point

• All mass and energy in a single point

• It exploded ~13.7 ga and has been expanding ever since

The Doppler effect 

Sound waves are stretched out as they move out,

The Doppler effect influences light waves too

Visible light is electromagnetic radiation

• Red light= longer wavelength= lower frequency

• Blue light= shorter wavelength= higher frequency

Moving light waves reveal the Doppler effect 

• Light moving towards an observer compresses (blue)

• Light moving away from an observer expands (Red)

Light from galaxies was observed to be red-shifted

• Edwin Hubble recognized the red shift as a Doppler effect

  • He concluded that galaxies were moving away at great speed

  • No galaxies were found heading toward Earth

• Hubble deduced that the whole world must be expanding 

Hubble’s law 

During the first instant only energy no matter was present

Started as a rapid cascade of events

• Hydrogen atoms within a few seconds

• At 3 min hydrogen atoms fused to form helium atoms

• Light nuclei by Big Bang nucleosynthesis

The universe expanded and cooled

Mass in nebulae was not equally distributed 

An initially more massive region began to pull in gas

• This region gained mass and density

• Mass compacted into a smaller region and began to rotate

• The rotation rate increased, developing a disk-shaped

Fision to break apart atoms

Fusion brings together two small attoms to create larger atoms

The Nebular theory of solar system formation

A third, fourth, or nth generation of nebula forms 4.56 ga

• Hydrogen and helium are left over from the Big Bang

• Heavier elements are produced via;

  • Stellar nucleosynthesis

  • Supernovae

The nebula condenses into a protoplanetary disk

The ball at the center grows dense and hop 

Fusion reactions begin when the sun is born

Dust in the rings condenses into particles

Particles coalesce to form planetesimals

Planetesimals clump into a lumpy protoplanet

The interior heat softens and forms a sphere 

The interior differentiates into 

• A central iron-rich core, and 

• A stony outer shell- a mantle

Terrestrial planets clustered to the center, and lighter gases were pushed further away from the sun, jovian planets are believed to be further from the sun

~4.53 A Mars-sized protoplanet collides with earth

The planet and a part of Earth’s mantle are disintegrated 

The collision debris forms a ring around the earth

The debris coalesces and forms the moon

• The moon has a composition similar to Earth's mantle

The atmosphere develops from volcanic gases

When the earth becomes cool enough;

• Moisture condenses and accumulates

• The oceans come into existence

Land (30%) and water (70%) are the most prominent surface features

Topography (land) defines plains, mountains, and valleys

Bathymetry (sea-floor variations) defines mid-ocean ridges abyssal plains, and deep-ocean trenches 

91.2% of the earth’s mass comprises just four elements

• Iron- 32%

• Oxygen - 30.1%

• Silicon - 15.1%

• Magnesium- 13.9%

The remaining 8.8 of Earth's mass consists of the remaining 88 elements

The first key to understanding Earth's interior; density

• When scientists first determined Earth's mass they realized;

  • Average density of earth>> average density of surface rocks

  • Deduced that metal must be 

Crust, mantel, core.

Earthquakes; seismic energy from fault motion 

• Seismic wave's velocities change with density

• We can determine the depth of seismic velocity changes 

• Hence we can tell where densities change in Earth’s interior

Changes with depth

• Pressure 

  • The weight of overlying rock increases with depth

• Temperature

  • Heat is generated in the earth’s interior 

  • T increases with depth

• Geothermal gradient 

  •  The rate the

The outermost skin of our planet is highly variable 

• Thickest under mountain ranges 

• Thinnest under mid-ocean ridges

Relatively as thick as the membrane of a toy balloon

The Mohorović

There are two kinds of crust continental and oceanic 

The continental crust underlies the continents

Oceanic crust underlies the ocean basins

98.5% of the crust is composed of just eight elements

Oxygen is the most abundant element in the crust

• This reflects the importance of silicate minerals

Lithosphere- asthenosphere

We can also regard layering based on rock strength

Lithosphere the outcomes of the ldeathAsthenosphere upper mantel below the lithosphere

The Mantel is the biggest layer of the earth

The mantel is entirely the ultra-mafic rock peridotite

Convection below

The core Iron-rich sphere with a radius of 3471 km

Seismic waves segregate two radically different parts 

• The outer core is liquid, and the inner core is solid

• Outer core 

• Liquid iron alloy

• 2255 km thick

• Liquid flows

Inner core

• Solid iron-nickel alloy

• Radius if 1220 km

• Greater pressure 

Space visitors would notice Earth’s magnetic felid 

Earth's Magnetic field is like a giant dipole bar magnet

• The field has north and south ends

• The field grows weaker with distance

• The magnetic force is directional

  • It flows from s to n pole along the bar magnet

  • It flows from n to s along field lines outside of the bar

The solar winds distorts the magnetosphere 

Shaped like a teardrop

Deflects most of the solar wind 

The mag

Jan 6

Big bang theory 

Theory is (according to science) backed up by a lot of data and has been put to peer review, scientist were able to replicate the results. 

• Best current explanation for what we have today

• Law explains what will occur

The solar system starts as a nebula, and starts to contract 

The process that creates stars is fusion, the main element is hydrogen, element that leads to t the death of a star, is iron, elements 5-26 can be fused in a star after created by a supernova 

The outermost layer of the earth is the crust,

The outer core is the only fully liquid layer of the earth 

The mantle and parts of the lithosphere are partly liquid 99.9% solid 

Alfred Wegener 

German meteorologist and polar explorer

Wrote the origins of the continents and oceans in 1915 

• He hypothesized a former supercontinent Pangaea

• He suggested that land masses slowly move continental drift

• These were based on strong evidence

  • Fit of the continents

  • Glacial deposits far from polar regions

  • Paleoclimatic belts

  • Distribution of fossils 

  • Matching geologic units

Glacial evidence

Evidence of late paleozoic glaciers found on five continents

Some of this evidence is now far from the poles

These glaciers could not be explained unless the continents had moved

Paleoclimatic evidence 

Placing Pangaea over the late paleozoic South pole 

Wegener predicted rocks deining pangea climate belts

• Tropical coals 

• Tropical reefs subtropical deserts

• Subtropical evaporites 

Antarctica has coal, therefore it had to have moved because coal cannot form in cold climates 

Fossil evidence 

Identical fossils found on widely separated land 

• lystrosaurus - a nonswimming, land-dwelling reptile

• Cynognathus- a nonswimming land-dwelling mammal-like reptile

These organisms could not have crossed an ocean

Pangaea explains the distribution 

Either sea level was so low because it was such a cold climate 

Matching geologic units

Distinctive rock assemblages and mountain belts match across the Atlantic 

Criticisms of Wegener's ideas 

Wegener had multiple lines of strong evidence 

Yet his idea was debated ridiculed and ignored 

• He couldnt explain how or why continents moved

• Wegener died in 1930 on a greenland expedition

• Over the next three decades new research new tech and new evidence from the oceans revived his hypothesis 

Plate tectonics 

The scientific revolution began in 1960 

• Harry hess proposed sea floor spreading 

  • As continents drift apart new oceans floor forms between

  • Continents converge when the ocean floor sinks into the interior 

By 1968 a complete model had been developed 

• Continental drift seafloor spreading and subduction

• Earth's lithosphere is broken

The magnetic field protects the atmosphere from solar winds and solar radiation 

Earths magnetic field 

Flow in the liquid outer core creates the magnetic field 

• It is similar to the field produced by a bar magnet 

• The magnetic pole is tilted ~11.5 degrees from the axis of rotations

• South mag pole is int he northern hemisphere

Magnetic poles 

The magnetic pole intersects earths surface just like geographic pole does 

• Magnetic n pole an dmag s pole both exist

• Magnetic poles are located near gr

The earths magnetic field

Geographic and magnetic poles are not parallel

A compass points to magnetic n not geographic n and mag N is called declination it depends on

• Absolute position of the two poles 

  • Geographic north

  • Mag north

• Longitude

Mag field is weakening, evidence for text plates and moves over times

 Rocks record the mag field 

Earths mag field 

Curved field lines casue a magnetic needle to tilt 

Angle between magnetic field line and surface of the earth is called inclination it depends on latitude 

Paleomagnetism

Iron minerals archive the magnetic signal at formation 

Hot magma 

• High temp- no magnetization

  • Thermal energy of atoms is bery high

Perpendicular is polar

Parallel to layer formed in, formed close to the equator 

Sea floor bathymetry 

Before ww2 we knew little about the sea floor 

Echo-soundingg allowed rapid seafloor mapping 

Seafloor maps creaated by ships crossing the oceans 

Bathymetric maps are now produced using satellite data 

The ocean floor 

ocean ographers were surprised to discover that 

• A mid ocean mountain range runs through every ocean

• Deep ocean trenches occur near volcanic island chains

• Submarine volcanoes poke up from the ocean floor 

• Huge fracture zones segment the mid ocean ridge

These observations are all explained by plate tectonics 

The ocean floor

Sonar mapping delineated bathymetric features

• Mid ocean ridges 

• Deep ocean trenches 

• Volcanic islands

• Seamoutsn

• Fracture zones

The ocean crust is denser and thinner than the continental crust

By 1950 we had learned much about the oceanic crust 

Oceanic crust is covered by sediment 

• Thicest near the continents 

• Thinnest at the midocean ridge

The oceanic crust consists primarily of basalt 

• Lacks a variety of continental rock types 

• No metamorphic rocks 

• Heat flow is much greater at mid-ocean ridges 

The oceanic crust 

Earthquakes occur in distinct belts in oceanic regions 

The earthquakes were surprising they were limited to -

• Parts of oceanic fracture zones

• Mid oceans ridges ace 

• Deep ocean trenches 

Geologists realized that earthquakes defined zones of movements

Seafloor spreading

Hess called his theory “seafloor spreading:

• Upwelling magma erupts at mid-ocean ridges 

• New crust moves away from ridges gathering sediment

• At trenches, the sea floor sinks back into the mantle 

Instantly provided a mechanism for continental drift

• Continents move apart as seafloor 

Evidence of seafloor spreading 

Magnetism in seafloor varies farther from MOR 

• Stripes of positive and negative magnetic intensity 

• Recorded in seafloor basalts

Plate tectonics

Earths outer shell is broken into rigid plates that move 

Plate motion defines three types of plate boundaries

Spreading of the crust creates a mid-ocean ridge 

Sal

Mantel acts as silly putty or clay

Mantel convection 

Lithosphere is able to flow, what makes up the tectonic plate, in motion over the asthenosphere 

• Lithosphere bends elastically when loaded

Continental , felisc to intermediate crustal rocks - granite

• More buoyant floats higher

Oceanic, mafic crust basalt and gabbro 

• Heavier and more dense, less buoyant, sinks lower

Fragmented into ~12 major tectonic plates

Plates move continuously at a rate of 1-15 cm per year

Plates interact along their boundaries 

Divergent boundary- tectonic plates move apart

• The lithosphere thickens away from the ridge axis

• The new lithosphere created a divergent boundary

• Also called mid-ocean ridge, ridge

• Mid ocean ridge is formed via divergent boundaries  

Early stage, rifting (breaaking apart of land) has progressed to mid ocean ridge formation, before substantial widening of the ocean, forms a long thin ocean basin with young ocean crust 

Example: the red sea

Midstage ocean begins to widen new sea floor 

New crust has a feature of mid-ocean ridges 

Convergent boundary- tectonic platres move together

• The process of plate consumption is called subduction 

• Also called convergent margin, subduction zone (two plates collide one goes under, denser goes under, oceanic goes under)

Transform boundary- tectonic plates slide sideways, can move in same direction, but one moves faster

• Plate materials is neither created nor destroyed 

• Also called transform fault, transform

Asthenosphere like plastic, viscoelastic material, very soft solid  

Lithospehre is hard

Jan 7 

Three types of plate boundaries, divergent convergent and transform 

North east africa the crust is diverging, the Basin and range province is another 

Convection is the process of moving continental crust,

Convergent boundaries

Lithospheric plates move towards one another

One plate sinks back into the mantle 

The subducting plate is always oceanic lithosphere

Continental crust cannot be subducted too buoyant 

Subduction recycles oceanic lithosphere 

• Subduction is balanced by sea floor spreading

• Earth maintains a constant circumference 

Convergent boundaries also called subduction zones

Trench is an underwater valley, mariana trench is the lowest point in crust

Subduction 

Old oceanic lithosphere is more dense than mantle

Subduction is associated with unique feature

• Deep ocean trenches

• Accretionary prisms

• Volcanic arcs

• back -arc basins 

Volcanic arc- a chain of volcanoes on overriding plate 

Plate collisions 

Subduction conusmes ocean basins 

Ocean closure ends in continental collision 

• Subduciton ceases subduction plate detaches sinks

• Continental crust is too buoyant to subduct

• Collision deforms crust

Driving mechanisms

Two forces drive plate motions

• Ridge push- elecated mor pushes lithosphere away

• slab -pull- denser subducting plate is pulled downward

• Convection in the asthenospher speeds or slows motion (underlying cause)

Lithosphere fractures and slides laterally 

• No new plate forms; none consumed

• Many transforms offset spreading ridge segments

• Some transforms cut through continental crust

Characterized by

•  earthquakes 

• Absence of volcanism

Every divergent boundary will have a transfer motion but not ever transform boundary will have a divergent motion

Transform boundaries continental transforms cut across continental crust 

ex ; the san andreas fault california 

Hotspot

Plumes of deep mantle material independent of plates

• Not linked to plate boundaries

• Originates as a deep mantle plume

• Plume partially melts lithosphere; magma rises to surface

We dont know why they happen think its because the earths heat is not uniform, some areas are heated more intensely by the outer core 

Hotspots perforate overriding plates

Volcanoes build above sea level 

Plate motion pulls volcano off plume

• Volcano goes extinct and erodes

• Chain of extinct volcanoes called a hot-spot track

Hot spots reinforce sea floor spreading

Chapter 8

Earth shaking caused by a rapid release of energy

• Energy mover outward as an expanding sphere of waves

• This waveform energy can be measured around the globe 

Earthquakes are common on this planet

• They occur every day

Most earthquakes result form plate boundaries

Most earthquake damage is due to ground shaking

Earthquake also spawn devastating tsunamis

• Dec 16 2004- indian ocean tsunami

• March 11 2011- eastern coast of japan

Seismicity occurs due to

• Sudden motion along a new formed crustal fault

• Sudden slip along an existing fault

• A sudden change in mineral structure

• Movement of magma in volcano 

• Volcanic eruption

• Giant landslides 

• Meteorite impacts

• Nuclear detonations

Fault slip is the most common cause 

1. Hypocenter (foucs) the place were fault slip occurs

   1. Usually occurs on a fault surface

   2. Earthquake waves expand outward from the hypocenter 

2. Epicenter-land surface right above the hypocenter 

   1. Maps often portray the location of epicenters

Faults in the crust

Faults are crustal breaks where movement occurs

• Displacement is a measure of movement 

• Fault trace is the ground surface expression of a fault

On a sloping fault, crustal blocks are classified as

• Footwall

• Hanging wall

The fault type is based on relative block motion

• Normal fault 

  • The hanging wall moves down relative to the footwall

  • Results from extension 

The fault type is based on relative block motion

• Reverse fault

  • The hanging wall moves up relative to the footwall

  • Results from compression

• Thrust fault

  • A special kind of reverse fault

  • The slip of fault surface is much less steep

• Strike slip fault

  • One block slides laterally past the other block

  • There is no vertical motion across 

Displacement the amount of movement across a fault 

• During earthquakes fault blocks move

• Displacement also coalled offset is shown by markers

Displacement is cumulative over time

Faults are found in many places in the crust 

• Active faults ongoing stresses produce motion

• Inactive faults motion occurred in the geologic past

A fault trace shows the fault intersectingnthe ground

Generating earthquake energy 

Tectonic forces add stress (push pull or shear) to rock

• The rock bends slightly without breaking (elastic)

• Continued stress causes cracks to develop and grow

• Eventually cracking progresses to the point of failure

• Stored elastic energy is released at once, creating a fault

Slip on a preexisting fault causes earthquakes

• Faults are weaker than surrounding crust

• Overtime stress builds up leading to slip along the fault

• This behavior is termed stick-slip behavior

Elastic rebound theory

• Rocks bend elasriclaly due to accumulated stresses

Body waves pass through earths interior

• P waves (primary or compressional waves)

  • Waves travel by compressing and expanding material

  • Material moves back and forth parallel to wave direction

  • Pwaves are the fastest

  • They travel through solids liquids and gasses

• S waves (secondary or shear waves)

  • Waves travel by moving material back and forth

  • Material moves perpendicular to wave travel directions

  • S waves are slower than p waves 

  • They travel only though solids never liquids or gasses

• Surface waves-travel along eafrths exterior 

• Surface waves are the slowest and most destructive

  • L waves (love waves

    • S waves that intersect the land surface 

    • Move the ground back and forth

  • R waves (Rayleigh waves

    • P waves that intersect the lands surface

    • Cause the ground to ripple up and sown like water

seismometer - instrument that records ground motion

• A weighted pen on a spring traces movement of the frame

  • A vertical motion records up and downs movement

  • Horizontal motion- records back and foth motion 

• Modern seismometers use a magnet and electric coil

• Record data digitally

• Able to detect ground motion people cannot sense

P wave to s waves to surface waves last

The time difference btween p and s will tell you how far the epicenter was from the graph

P waves always arrive first then s waves 

• P and s wave arrivals are separated in time

• Separation grows with distance from the epicenter

• The time delay is used to establish this distance

Data from three or more station pinpoint the epicenter 

• The distance radius from each station is drawn on a map 

• Circles around three or more stations will intersect at a pont

• The point of intersection is the 

P waves can create s waves 

S waves cannot go through liquid, recreated through p waves 

Jan 8

Review questions

Features of divergent- mid-ocean ridge, 

The process of plates moving sideways

subduction = trench plus volcanoes 

How is a hotspot different from convection in the asthenosphere- hotspots don't need to be on plate boundary, and have material that originates from the core mantel boundary

What causes earthquakes to occur- fault slips main cause, (fault crack in the lithosphere, if it goes through the entire lithosphere becomes a plate boundary) 

Two general types of -  body (P and S waves) and surface (L and R)

Which doesn't X wave move through Y layer- s because it cannot move through a liquid and the outer core is liquid

How many seismometers are needed to pick up the epicenter of an earthquake- 3

Earthquake size is described by two measurements

• Severity of damage (intensity) Mercalli intensity scale

• The amount of ground motion (magnitude)

Mercalli intensity scale- amount of shaking damage

• 1=low

• XII = high

• Damage occurs in zones

• Damage diminishes in intensity with distance 

Magnitude- a uniform of size

• The maximum amplitude of ground motion

• Measured by a seismometer at a specific distance

• Several magnitude scales are used

  • Richter scale- useful near the epicenter

  • Moment magnitude scale- most accurate measure

    • Goes from 1 to 10 not linear, logarithmic 

Magnitude scales are logarithmic

How much stronger is a mag 8 earthquake than a mag 5 earthquake= 

Each step is a power of 10

• m6.o is ten times a mag of M5.0

Energy released can be calculated

• M6.o the energy of the Hiroshima atomic bomb, the average hurricane 

• An increase of m1.0 is a 32x increase in energy

Earthquakes are linked to plate tectonic boundaries

Anywhere you see earthquakes there is a deep subduction zone 

Divergent plate boundary- mid-ocean ridges

• Develop two kinds of faulting 

  • Normal faults at the spreading ridge axis 

  • Strike-slip faults along transforms

• Shallow <10km deep

Continental rifts- stretching creates normal faults

• Generate shallow earthquakes similar to MOR

Transforms boundaries

Transform earthquakes occur at shallow crustal levels

Most transforms link segments of mOR

Some however cut through continental crust

• San Andres fault

• L

Large transform earthquakes on continents are usually

San Andreas Fault cuts through western California 

• The Pacific plate shears north of the North American plate

• The San Andreas is a very active strike-slip fault

  • A very dangerous fault hundreds of earthquakes per year

Convergent plate boundaries c

• Shallow both the downgoing and overriding plate

  • Normal faults form as the downgoing slab bends

  • Large trust faults occur at the contact between plates

    • The subducting slab bens the overriding plates downward

    • The overriding slab

The area of the earth's lithosphere subducts is called the Wadadi and Benioff zone

Collision zones - orogenic crustal compression

• Continental lithosphere compresses along thrust faults

• Earthquakes can be very large

• Orogenic uplift creates landslide hazards

Intraplate earthquakes, rare earthquakes, 

Remnant crustal weakness in former fault zones ancient plate boundaries

Ground shaking and displacement 

• Earthquake waves arrive in a distinct sequence

• Different waves cause different motion

Liquefaction- causes solid to lose strength

Tsunamic prediction

Scientific modeling predicts tsunamic behavior

A tsunami warning center tracks pacific quakes

Tsunamic detection is expanding

Can we predict

• Can be predicted in the long term 

• They connot be predicted in the short term

• Hazards can be mapped to assess risk

  • Developing building codes

  • land-use planning, disaster planning

A major earthquake may be preceded by foreshocks

• Smaller tremors indicating cracks in development in rock

• May warn of an impending large earthquake

Aftershocks usually follow a large earthquakes

• May occur for weeks or years

Stress is pushed forward along a fault, 

Tsunamis are generated at subduction zones

Subduction zone slips and causes waves

Chapter 3

Minerals are the building blocks of our planet

• Minerals make up all of the rocks and sediments on the earth

• Understanding earth required understanding minerals

Minerals are important to humans

• Industrial minerals are raw minerals for manufacturing

• Ore minerals sor

Requirements 

• Naturally occurring

  • Humans can recreate natural processes to make minerals 

    • They are called synthetic minerals

• They are formed by geologic processes

  • Freezing from a melt

  • Precipitation (some solid is formed as it evaporates from another, salt from water) from a dissolved state in water 

  • Chemical reactions at high pressures and temperatures

    • Living organisms can create minerals

    • Called biogenic minerals to emphasize this special origin

      • Vertebrate bones (apatite)

• They are solid 

  • A state of matter that can maintain its shape indefinitely

  • Minerals are solid, not liquid or gases

• They have a crystalline structure

  • Atoms in a mineral are arranged in specific orfer

  • This atomic pattern is called a crystal lattice

  • A solid with distorted atoms is called a glass

  • Lacking crystalline structure, glasses are not minerals

• They have a definite chemical composition

  • Everytime you sample this subject, same chemical ratio

  • Minerals can be defined by a chemical formula

    • Simple

      • Ice-h2o

      • calcite- CaCO3

    • Complex

      • Biotite-K(Mg,Fe)3(AISi3O10)(OH)2

    • Trace elements color minerals

• They are mostly inorganic

  • Organic compounds 

    • Contain carbon-hydrogen bons

    • Other elements may be present

    • Common prudcuts of living organisms

  • Most minerals are not organic

A single continuous piece of crystalline solid

Typically bounded by flat surfaces (crystal faces)

Crystal faces grow naturally as the mineral forms

Crystals are sometimes prized minerals specimens

Constancy of interfacial angles

• The same minerals has the smae crystal fases

People consider crystals to be special

• Regular geometric form

• Crystals interact with light to create attractive beauty

Ordered atomic patterns in minerals display symmetry

• Mirror image

• Rotation about an axis

Symmetry characteristic are used to identify minerals

1. Ordered atoms like tiny balls packed tightyly together

2. Held in place by chemical bonds

3. The way atoms are packed defines the crystal structure

The nature of atomic bonds controls characteristics

Diamond and graphite are made entirely of carbon

• Diamond - atoms arranged in tetrahedra, hardest minerals

• Graphite- atoms arranged in sheet; softest mineral

Polymorph- same composition, different structure

New crystals can form in five ways

1. Solidification from a melt

   1. Crystals grow when the melt cools

   2. Liquid freezes to form solid

2. Precipitation from a solution

   1. Seeds form when a solution becomes saturated

3. Solid state diffusion- rearrangement of elements in the solid state

4. Biomineralization

   1. Seashells 

5. Precipitating directly from a gas

What happens gto the pressure as it get deeper in the earth- gets higher

A tiny early crystal acts as a seed for future growth

Atoms migrate to the seed and attach to the outer face

Growth moves faces outward?

Outward crystal growth fills available space

Resulting crystal shape is governed by surrounding 

• Open space- good crystal faces grow

• Confined space- no crystal faces

Mineral growth is often restricted by lack of space

• Anhedral- grown in tight space no crystal faces

  • Much more prevalent

• Euhedral- grown in an open cavity good crystal faces

  • Grow into the open space in a geode

Common properties

• Color 

  • The part of visible light that is not absorbed by a mineral

  • Diagnostic for some minerals

    • Malachite is a distinctive green

  • Some minerals exhibit a broad color range

    • Quartz 

  • Color varieties often reflect trace impurities

• Streak

  • Color of a powder produced by crushing a mineral

  • Obtained by scraping a mineral on unglazed porcelain

    • Streak color is less variable than crystal color

• Luster

  • The way a mineral surface scatters light

  • Two subdivisions

    • Metallic- looks like a metal

    • Non metallic 

      • Silky

      • Glassy

      • Satiny

      • Resinous

      • Pearly

      • Earthy  

• Hardness

  • Scratching resistance of a mineral

  • Derives from the strength of atomic bonds

  • Hardness compared to the Moh scale of hardness

1. Talc, graphite

2. Gypsum - fingernail 2.5

3. Calcite - copper penny 3.5

4. Fluorite

5. Apatite -  glass/steel 5.5

6. Orthoclase - steel file 6.5

7. Quartz

8. Topaz

9. Corundum

10. Diamond 

Higher numbers can scratch lower numbers

• Specific gravity

  • Represents the density of a mineral 

  • Mineral weight over the weight of an equal water volume

  • Specific gravity is heft how heavy it feels

    • Galena 

• Crystal habit

  • A single crystal with well formed faces

  • An aggregate of many well formed crystals

  • Arrgangemt of faces reflects internal atomic structure

  • Records variation in directional growth rates

    • Block or equal

• Special physical properties 

  • Special physical properties

    • Effervescence- reactivity with acid

    • Magnetism- magnetic attraction 

    • Taste

• Fracture 

  • Minerals break in ways that reflect atomic bonding 

  • Fracturing implies equal bond strength in all directions 

    • Example; quartz displays conchoidal fracture 

      • Breaks like glass along smooth 

  • Clevage 

    • Tendency to break along planes of weaker atomic bonds

    • Cleavege produces flat shiny surfaces

    • Described by the number of planes and their angles

    • Sometimes mistaken for crystal habit

      • Cleavage is throughgoing it often forms parallel 

• Mineral classification 

  • Minerals can be separated into a few groups

    • Jj Berzelis a swedish chemist noted similarities

      • Separated by 

        • Principles of anion (negative ion)

        • Anionic group (negative molecule)

  • Most abundant mineral class is the silicate

  • Minerals are classified by their dominant anion

    • Silicates are called the rock-forming minerals

      • SiO44- anionic unit the silicon oxygen tetrahedron

        • Four o atoms are bonded to a central si atom

        • De

      • Divided into several groups

        • Basend on how the silica tetrahedra share atoms

        • The amount of shared oxygen determines the Si;O ratio

    • Oxides  

    • sulflides - metal cations bonded to a sulfide anion

    • Sulfates- metal c

    • Halides 

    • Carbonates 

    • Native metals 

      • Pure masses of a single metal

Gem 

Gems a mineral with special value

• Rare formed by unusual geological processes

Gem- a cut and polished stones created for jewlery

• Precious stones that are rare and sought after

Gems are cut and polished stones used for jewler

Diamonds

Diamonds originate under extremely high pressure

• ~150 km deep in the upper mantle

Review questions

Where geologically do tsunamis take place?

Trench

Slip along a trench causes a tsunami

What is the earthquake scale most commonly used on the news

• Richter scale

Difference 

Mag 9-mag5= mag4, so 1 w/ 4 0s

Min on Earth’s surface must be solid somewhere on Earth's surface 

Nice crystals grow with sufficient space making them euhedral

Luster refers to light reflection, does it look metallic or non-metallic 

Streak it the color of the power when you scratch it on a streak plate

Mineral that can be scratched by fingernail but can scratch glass

Chapter 4

Igneous rock is formed by cooling from a melt

• Magma- melted rock belo

Melted rock can cool above or below ground

• Extrusive igneous rocks- cool quickly at the surface

  • Lava flows- streams or mounts of cooled melt

  • Pryclaisc debris0 coles 

• Intrusive- cools out of sight underground

• Much greater volume than extrusive igneous rocks

• The cooling rate is slower than for extrusives

  • Large-volume magma chambers 

  • Smaller volume tabular

Why does magma form

1. Decrease in pressure (p) - decompression

   1. The base of the crust is hot enough to melt mantel rock

   2.  Ut due to high p the rock doesn't melt

   3. Melting will occur if p is decreased

      1. Occurs in divergent boundaries and midocean ridges

   4. P drops when hot rock is carried to a shallower depth 

      1. Mantel plies

      2. Benieht rifts

      3. Under mid-ocean ridges

2. Addition of volatiles (flux melting)

   1. Volatiles lower the melting T of a hot rock

      1. Salt to water to lower the boiling point

   2. Subduction carries water down to the mantle, melting rock

3. Heat transfer melting

   1. Rising magma carries mantle heat with it 

   2. This raises the t in nearby crustal rock which then melts 

Magmas have three components (solid liquid and gas)

• Solids-solidified mineral crystals are carried in the melt

• Liquids- the melt itself is composed of mobile ions

• Different mixes of elements yield different magmas 

Gas- variables amounts of dissolved gas occur in magmas 

• Dry magma- scarce volatiles

• Wet magma- up to 15% volatiles

  • Water vapors

  • Carbon dioxide 

• There are four magma types based on silica content

  • Felics (Fekdspar and silica) 66-76%

  • Intermediate                         52-66%

  • Mafic (Mg and Fe-rich)         45-52%

  • Ultramafic                             38-45%

Why are there different magma compositions

Magmas vary chemically due to 

The source of the rich dictates the initial magma composition

• Mantel source-ultra maifc and mafic magmas

• Crustal source- mafic intermediate and felsic magmas

Upon melting rocks rarely dissolve completely 

Instead only a portion of the rocks 

• Si-rich minerals melt first 

Assimilation

Magma melts the wall rock it passes through

Blocks of wall rock (xenoliths) fall into the magma 

Assimilation of these rocks alters magma composition

Magma mixing 

Different magmas may blend in a magma chamber 

The result combines the characteristics of the two

Often magma mixing is incomplete, resulting in blobs of one rock type suspended within the other

Magma movement

It is less dense than surrounding rocks

• Magma is more buoyant 

Weight of the overlying rock creates pressure

Speed of magma flow governed by viscosity

• Lower viscosity eases movement

• Lower viscosity is generated by

  • Higher t 

  • Lower SiO content

  • Higher volatile content

Viscosity depends on temperature, volatiles, and silica

• Temperature 

  • Hot = lower viscosity cooler higher viscosity

• Volatile content

  • More volatiles- lower viscosity

  • Less volatiles - high viscosity 

• Silica content

  • Less SiO2 (Mafic) lower viscosity

  • More SiO2 (felsic) higher viscosity

Depth- deeper is hotter; shallower is cooler

• Deep plutons lose heat very slowly take a long time to cool

• Shallow flows lose heat more rapidly; cool rapidly

Changes with cooling

• Fractional crystalization- early crystals settle by gravity

• Melt composition changes as a result

Fractional crystallization- settling early formed crystals

• Felsic magma can evolve from mafic magma

• Modeled by Bowens reactions series 

  • Experimental results of mineral growth in magmas

  • A mineral succession proceeds from cooling

Bowen reaction series

Early crystals settled out removing Fe Mg and Ca

The remaining melt progressively enriched in Si Al and Na

continuous - -plagioclase changed from ca-rich to na-rich

Discontinuous minerals start and stop crystallizing

Olivne 

Pyroxene

Amphibole

Biotite mica

Potassium feldspar

Muscovite mica

Quartz

Two major categories based on cooling locale

Extrusive settings- cool at or near the surface

• Cools rapidly

• Chill too fast to grow big crystals

Intrusive settings cool at depth

• Loose heat slowly

• Crystals often grow large 

xenolith - foreign not from around here 

Tabular intrusions

• Tend to have uniforms thicknesses

• Often can be traced laterally

• Have two major subdivisions

  • Sill-injected parallels to rock layering

    • Balat intrude light sandstones

  • Dike- cuts across layering 

    • Occur in swarms

    • Three dikes radiate away from shiprock

plutons100

Jan 13

Review questions

How does igneous rock form? Magma or lava is cooled forming 

Lava is on the surface magma is below

Inside the earth it would cool slower 

• The deeper in the earth the hotter it is

If a magma cools slowly what hcan you sat about the crystals in that rock,- intrusive rock will have larger grains

Four types of magma

1. Mafic tend to be darker

2. Felsic most viscous, white to pink color 

3. Ultra mafic, tint of green

4. Intermediate

Bowens reaction series- different minerals solidifying at different times, different melting/freezing points of crystals 

What do cleavage means- ways minerals tend to break

What is a dike- when a body of magma cufts across layers

Sil when it is squeezed inbetween layers 

Describing igneous rock

Igneous rock is used extensively as building stone

The size shape and arrangement of the minerals

• Crystalline- interlocking crystals fit like a jigsaw puzzle

  • Interlocking mineral grains from solidifying melt

  • Texture reveals cooling history

    • Fine-grained 

      • Rapid cooling 

      • Crystals do not have time to grow

      • Extrusive

    • Coarse-grained

      • Slow cooling 

      • Crystals have a long tine to grow

      • Intrusive

    • Porphyritic texture- a mixture of coarse and finer crystals 

      • Indicates a two-stage cooling history

        • Initial slow cooling creates large phenocrysts

        • Subsequent eruption cools remaining magma

• Fragmental- pieces of preexisting rocks often shattered 

  • Preexisitign rocks were often shattered by eruption

  • After fragmentation, the pieces fall and are cemented

• Glassy- made of solid glass or glass shards

  • Solid mass of glass or crystals surrounded by glass

  • Fracture conchoidally

  • Result from rapid cooling of lava

Texture directly reflects magma history

Obsidian- felsic volcanic glass

Pumice- frothy felsic rock full of vesicles; it floats

Scoria- glassy vesicular mafic rock

Vesicles means a rock has pores, lava is rich in gas and becomes bubbly cools with bubbles in 

Above rocks would form extrusive rock

Pyroclastic- fragment of violent eruption, gluing together hot fragments

• Tuff volcanic ash that has fallen

• Volcanic Breccia

Igneous activity occurs in four plate tectonics settings

• Volcanic arcs bordering deep ocean trenches

  • Most sub-aerial volcanoes on Earth reside in arcs

  • Mark convergent tectonic plate b boundaries

    • Deep ocean ridges trenches and accretionary prisms

• Isolated hot spots

• Continental rift

• Mid-ocean ridges

Established or newly formed tectonic plate boundaries

Except; hot spots, which are independent of plates

Along ocean ridges, you are getting decompression melting

In what geologic settings did igneous rocks form, hotspot

Normal faults form at divergent boundaries 

Lips- unusually large outpourings of magma

• Mostly mafic, include some felsic examples

• A mantle plume first reaches the base of the lithosphere

• Erupts huge volumes of mafic magma as flood basalts

  • Low viscosity 

  • Can flow tens to hundreds of km

  • Accumulate in thick piles 

Chapter 5

An erupting vent in which molten rock surfaces

A mountain built from magnetic eruptions

Volcanoes are a clear result of tectonic activity

Volcanoes pose several hazards to humans

79 CE mount vesuvius erupted violently

Pyroclastic debris destroyed Pompeii killing 20000

A record of roman life was preserved under ash

Eruptions are unpreductable, dangerous

• Bult large mountains 

• Blow mountains to buts

Eruptions can

• Provide highly productive soils to feed civilizations

• Extinguish a civilization in a matter of minutes

Productios fo volcanic eruptions 

• Lava flows- molten rock that moves over the fround

• Pyfroclastic debris- fragments blown out of a volcano

• Volcanic gases- expelled

Lava can be thin and runny or tick and sticky

Flow style depends on viscosity which depends on

• Composition

  • Higher viscosity with higher Si

• Temperatures 

  • Higher temp lowers viscosity

• Gas content 

• Crystal content

  • The more solids in the magma the slower it is going to move

Mafic lava- very hot, low silica and low viscosity

• Rich in iron magnesium

• Basalt flow is often thin and fluid (

  • They can flow rapidly

  • They can flow for long distances 

    • Most flow measures less than 10 km

    • Long-distance flow is facilitated by lava tubes

Basaltic lava flows

• Pahoehoe- a Hawaiian word for describing basalt with glassy ropy texture

• A’a- is a Hawaiian word describing basalt that solidifies with a jagged sharp angular texture

  • A’a’ forms when hot-flowing  

Columnar joints- solidified flows may contract with vertical fractures

Pillow basalt- round blobs of basalt cooled in water

• Always form underwater, basalt cools instantly forming a pillow

  • The pillow surface is cracked, quenched glass

  • Lava pressure ruptures a pillow to form the next blob

  • The 

• Common along mid-ocean ridges

Andesitic lava flows

Higher SiO2 content makes andesitic lava viscous

• Unlike basalt, they do not flow rapidly

• Instead, they mound around the vent and flow slowly

The crust fractures into rubble called blocky lava

Andesitic lava flows remain close to the vent 

Rhyilitic lava

Rhyolite has the highest SiO2 and the the most viscous lava 

Rhyolitic kava rarely flows

Pyroclastic debris

Pyroclasic flow (nuée ardente)

• Avalanches of hot ash race down 

• Move up to 300 kph and incinerate all in their path 

• Deadly they kill everything quickly 

Volcanic debris flow wetted debris that moves downhill

• Occurs when volcanoes are covered with ice and snow or drenched in abundant rain

Volcanic gas

Up to 9% of magma may be gas

• Water (h20)- the most 

Gases are expelled as magma rises (p drops)

SO2 reacts with water to form aerosol sulfuric acid

Style of gas escapes controls eruptions

Volcanoes have characteristics features

• Magma chamber 

  • Magma chambers are located un the upper crust

    • Usually an open cavity or area of highly fractured rock

    • May contain a large quantity of magma

  • Some magma google s

• Fissures and vents

  • Some magma rises via conduit to the surface 

  • Magma may erupt along a linear tear called a fissure

    • Fissure eruptions may display a curtain of fire

    • Fissures evolve into discrete vents and craters

• Craters

  • A bowl-shaped depression atop a volcano

  • Crates are upt to 500m across and 200 m deep

  • Form as erupted lava piles up around the vent

    • Summit eruptions-located within the summit crater

    • Flank eruption- located along the side of a volcanoes

• Calderas

  • A gigantic volcanic depression

    • Much larger than a crater (one to tens of 

    • Usually exhibit steep sidewalls and flat floors

  • A magma chamber empties and the volcano collapses in

Distinctive profiles

• Shields

  • Broad slightly dome-shaped(inverted shield)

  • Constructed by lateral flow of low-viscosity basaltic lava

  • Have a low slope and cover large geographic areas

  • Mauna Loa in Hawaii is a perfect example

• Scoria cones 

  • Conical piles of tephra; the smallest type of volcanoes

  • Built of ejected lapilli and blocks piled up at the event

  • Often symmetrical with a deep summit crater 

  • Typically from a single eruption events

• Stratovolcanoes

  •  Large cone-shaped volcanoes with steeper slopes

  • Formed from a mixture of lava and ash

  • Made of alternating layers of lava, tephra, and debris

  • Examples include Mount Fuji mount Rainer Mount Vesuvius 

Andesitic is an intermediate lava synonym 

Eruptive style

Effusive - produces lava flows (mafic)

• Lava flows stream away from vents

• Lava lakes can form near or inside the vent

• Can produce huge lava

Explosive eruptions- blows up (felsic, intermediate)

• High gas pressure is from more viscous Si02-rich magma

• Create pyroclastic flows and cover the land with tephra

Eruptive style is related to volcano-type 

• Effusive eruptions form shield volcanoes 

• Small pyroclastic eruptions form scoria cones 

• Alternating effusive and pyroclastic eruptions result in stratovolcanoes

• Large explosive eruptions create calderas 

Recurrence interval

Warning signs indicate that an eruption is imminent

• Earthquake activity- magma seismicity

• Heat flow- magma causes volcanoes to heat up

• Changes in shape magma causes expansion

• Emission increases- changes in gas mix and volume

These signs cannot predict exact time of eruption 

Volcanic activity evident on the moons and planets 

• Lunar maria  are regions of floor basalts

• Olympus mons- extinct martian shields volcanoes

• The jovian moons 

Jan 14

Composition what a rock is made of 

Textures 

Sedimentary rocks form layers like the pages of a book

• The layers record a history of ancient environments

• Layers occur only in the upper part of the crust

Sedimentary rocks cover the underlying basement rock

• Clastic- loose rock fragments (clasts) cemented together

  • Detrital (or clastic) sedimentary rock consists of 

    • Detritus (loose clasts)

      • Mineral grains 

      • Rock Fragments

    • Cementing material

  • How they are formed

    • Weathering- generation of detritus via rock disintegration

      • Initial breakdown of one rock into finer fragments

    • Erosion- removal of sediment grains from parent rock

      • A process that removed the rock from the parent rock

    • Transportation- dispersal by gravity, wind water, and ice 

      • The continued motion of that grain/ how it was transported to the deposit point  

    • Deposition- setting out of the transporting fluid 

    • Lithification- Transformation into solid rock

      • Compassion- burial adds pressure to sediment 

        • Squeezes out air and water

        • Compresses sediment grains 

      • Cementation- minerals grow in pore spaces

        • Often quartz or calcite

        • Precipitate from groundwater

        • Glue sediments together

  • Classified based on texture and composition

    • Clast (grain) size- the diameter of the fragments or grains

      • Range from very coarse to very fine

      • Boulder cobble, pebble, sand, silt, and clay

        • Gravel- coarse-grained sediment (boulder, cobble, pebble)

        • Mud- fine-grained (silt and clay) 

    • Clast composition- the mineral makeup of sediments

      • May be individual minerals or rock fragments

      • Composition yields clues about the original source rock 

    • Angularity and sphericity

      • Angularity- the degree of edge or corner smoothness

      • Sphericity- the degree to which a clast nears a sphere

        • Fresh detritus is usually angular and non-spherical

        • Grain roundness and sphericity increase with transport

          • Well-rounded- long transport distances

          • Angular- negligible transport

    • Sorting- the uniformity of grain size

      • Well-sorted- all clasts have nearly the same grain size

      • Poorly sorted- all clasts show a wide variety of grain size 

    • Character of cement 

  • Types of sedimentary rocks

    • Coarse clastics- gravel-sized clasts

      • Breccia- angular rock fragments

        • Angularity indicates the absence of rounding by transport

        • Deposited relatively close to clast source

      • Conglomerate- rounded rock clasts

        • Clasts rounded as flowing water wears off corners and edges

        • Deposited farther from the source then breccia

      • Arkoze- sand and gravel with abundant feldspar

        • Commonly deposited in alluvial fans (buildup of sediment at the bottom of a valley)

        • Feldspar indicates short transport

      • Sandstone- clastic rock made of sand-sized particles

        • Common in beach and dune settings

        • Quartz is by far the most common mineral in sandstones 

  • Fine clastics are deposited in quiet water settings

    • Floodplains, lagoons, mudflats, deltas, deep-water basins

  • Silt, when lithified becomes siltstone

  • Mud, when lithified, becomes mudstone or shale

• Biochemical (bioclastic)- cemented shell of organisms

  • Sediment derived from the shells of living organisms

    • Hard mineral skeletons accumulate after death

    • Different sedimentary rocks are made from these materials

      • Calcite and aragonite- limestone

      • Silica- chert

        • Chert is made of cryptocrystalline quartz

          • Silica skeletons are some marine plankton

          • After burial, silica in the bottom sediments dissolves

          • Silica in pore fluids solidifies into a gel

          • The silica gel precipitates chert as nodules or beds

  • Limestone- sedimentary rocks made of CaCO3 

    • Fossiliferous limestone- contains visible fossil shells

    • Micrite- fine carbonate mud

    • Chalk- made up of plankton shells

• Organic- Carbon-rich remains of once-living organisms

  • Made of organic carbon, the soft tissues of living things

    • Coal- altered remains of fossil vegetation

      • Black, combustible sedimentary rock

      • Over 50-90% carbon

      • The fuels industry since the Industrial Revolution began

• Chemicals- Minerals that crystallize directly from water, evaporation of water

  • Comprised of minerals precipitated from water solution

    • Have a crystalline (interlocking) texture

      • Initial crystal growth in solution

      • Recrystallization during burial

  • Several classes

    • Evaporites- rock from the sea or lake water

      • Evaporation triggers the deposition of chemical precipitates

      • Thick deposits require large volumes of water

      • Evaporite minerals include Halite (rock salt) and gypsum

    • Travertine- calcium carbonate precipitated from groundwater where it reaches the surface

      • CO2 expelled into the air causes CaCO3 to precipitate

        • Thermal (hot) springs

        • Caves- speleothems

          • Stalactites

          • Stalagmites

    • Dolostone- limestone altered by Mg-Rich fluids

      • CaCO3 altered to dolomite CaMg(CO3)2 by Mg2 rich water

    • Replacement chert- nonbiogenic 

      • Cryptocrystalline silica gradually replaced calcite, long after limestone was deposited

      • Many colors and varieties

        • Flint- colored black or gray from organic matter

        • Agate- Precipitates in concentric rings

        • Petrified wood- wood grain preserved by silica

Physical and chemical weathering provide the raw material for all sedimentary rocks

Physical, chemical, and biological changes to sediment

• Lithification is one aspect of diagenesis (compaction and sedimentation of grains)

As sediments as buried, pressure and temperature rise

• Temps between burial and metamorphism (~300 Celsius)

• Interactions with hot groundwater-chemical reactions

• Cements may precipitate or dissolve 

• At higher pressure + temperature, metamorphism begins 

Sedimentary Structures

Features imparted to sediments at or near deposition

• Bed- a layer of sedimentary rock with similar grain size, mineralogy, and features throughout

Provide strong evidence about conditions at deposition

Bedding and stratification

Why does bedding form?

• Bedding (individual layers of sedimentary rock)  reflects changing conditions during deposition

  • Climate 

  • Water depth 

  • Current velocity

  • Sediment source

  • Sediment supply

Current Deposition

Water or wind flowing over sediment creates bedforms

Bedform character is tied to flow velocity and grain size

Ripple marks- cm-scale ridges and troughs

• Develop perpendicular to flow

• Ripple marks are frequently preserved in sandy sediments

• Found on modern beaches

• Found on bedding surfaces of ancient sedimentary rocks 

Cross beds- created by ripple and dune migration

• Sediment moves up the gentle side of a ripple or dune

• Sediment piles up and then slips down the steep face

  • The slip face continually moves down the current

  • Added sediment forms sloping cross beds

Turbidity- currents and grades beds

• Sediment moves on a slope as a pulse of turbid water

• As the pulse wanes, water loses velocity and grains settle

• Coarsest materials settle first, medium next, then fines

• Can be caused by landslides hurricanes earthquakes 

Terrestrial Environments- deposited above sea level

• Glacial environments- due to the movement of ice

  • Ice carries and dumps every grain size

  • Creates glacial till; poorly sorted gravel sand silt and clay

• Mountain stream environments

  • Fast-flowing water carries large clasts during floods 

  • During low flow, these cobbles and boulders are immobile

  • The coarse conglomerate is characteristic of this setting

• Alluvial Fan- sediment that piles up at a mountain wedge

  • The rapid drop in stream velocity creates a cone-shaped wedge

  • Sediments become conglomerate and arkose

• Sand-dune environment- windblown well-sortered sand

  • Dunes move according to the prevailing winds

  • Results in uniform sandstone with gigantic cross bands

• River environments- channelized sediment transport

  • Sand and gravel fill concave-up channels

  • Fine sand, silt, and clay are deposited on nearby floodplains

• Lake- large ponded bodies of water 

  • Gravels and sands trapped near shore

  • Well-sorted muds deposited in deeper water

• Delta- sediment piles up where a river enters a lake

• Often topset, forest, bottomset (gilbert-type) geometry.

Marine Delta environments- deposited at sea level

• Delta- sediment accumulated where a river enters the sea

  • Sediment carried by the river is dumped when velocity drops

  • Deltas grow overtime, building out into the basin

  • Much more complicated than simple lake deltas

  • Many sub-environments present

• Coastal beach sands- sand is moved along the coastline

  • Sediments are constantly being processed by wave action

  • A common result of well rounded medium sand 

  • Beach ripples often preserved in sedimentary rocks

• Shallow-marine clastic deposits- finer sands, slits, muds

  • Fine sediments deposited offshore where energy is low

  • Finer silts and muds turn into siltstones and mudstone

  • Usually supports and active biotic community

• Shallow water carbonate environments

  • Most sediments are carbonates- shells of living organisms

  • Warm, clear, marine water, relatively free of clastic sediments

  • Protected lagoons accumulate mud

  • Wave-tossed reeds are 

  • Sources of limestones

• Deep marine deposits- fine settles out far from land

  • Skeletons of planktonic organisms make chalk or chert

  • Fine silt and clay lithifies into shale?

Sedimentary Basins

Sediments vary in thickness across earths surface

• Thin to absent where nonsedimentary rocks outcrop

• Thicken to 10-20+ km in sedimentary basins

Subsidence- sinking of the land during sedimentation

Basins are special places that accumulate sediment

Transgression (sea level rise)- Regression (sea level fall)

Sea level changes

• Sedimentary deposition is strongly linked to sea level

• Changes in sea level are commonplace geologically

  • Sea level rises and falls up to hundreds of meters

    • Changes in climate, tectonic processes

  • Depositional belts shift landward or seaward in response

  • Layers of strata record deepening or shallowing upward

Sea level changes

• Transgression- flooding due to sea level rise

  • Sediment belts shift landward; strata “deepen” upward

• Regression- exposure due to sea level  fall

  • Depositional belts shift seaward; strata “shallow upward”

  • Regression tied to erosion is less likely to be preserved

• Sea level rise and fall create a predictable pattern

Jan 15

Review

Igneous rock forms

How does an igneous rock form

Cooled magma or lava 

Cool slow large crystals cool fast small to no crystals

What is a sedimentary rock and how is it formed

Sedimentary rocks are mostly made of sediment or clasts

Weathering 

Erosion is the main way transport

The main modes of erosion are water and wind, ice seeping into cracks and expanding, gravity 

Lithification is the rock-forming process, compaction, and cementation

Types of sedimentary rock

Organic- coal, made in swamps and lakes, peat, lignite, anthracite  

Bioclastic

Clastic

Chemical- chemical reaction, evaporation of water or liquid

The more round the farther the sediment has traveled

Finer sediment can only settle in commer waters

The texture of sedimentary rocks- the size of the grains, the shape of the grains, 

Chapter 7

Metamorphic rock- solid state alteration of a protolith (first rock) 

• meta=change

• morphe= form

Protoltih are preexisting rocks

Metamorphism can alter any protolith

Protoliths undergo slow solid-state changes in

• Texture- change in size or arrangement (foliation)  

• Mineralogy

Metamorphic changes are due to variations in

• Temperature

• Pressure 

• Tectonic stresses

• Amount of reactive water

Red shale- quartz clay and iron oxide

Gneiss(nice)- quartz, feldspar, biotite, and garnet

Unique texture- intergrown and interlocking grains

Fossil to calcite

Metamorphism often creates foliation (layering)

• Texture defined by 

  • Alignment of platy minerals

  • Creation of alternating light and dark bands

Recrystallization- minerals change size and shape

Mineral identity doesn’t change

• Example; limestone to marble 

Neocrystallization- new minerals form from old

• Initial minerals become unstable and change to new minerals

  • Original protolith minerals are digested in reactions

  • Elements restructure to form a new mineral

Shale to garnet mica schist

Phase change- new minerals form with 

• The same chemical formula

• Different crystal structure

  • Andalusite to kyanite

Plastic deformation- mineral grains soften and deform

• Requires elevated temperature and pressure

• Rock is squeezed or sheared

• Minerals change shape without breaking like plastic 

The agents of metamorphism are 

• Heat (t)

• Pressure (p)

• Compression and shear

• Hot fluids

Not all agents are 

One cause of metamorphism is heat

• Between 250 and 850 Celsius 

• Between diagenesis and melting (up to 1200 Celsius)

  • First to melt the last to crystalize, felsic is first to melt

Heat energy breaks and reforms atomic bonds

• Solid state diffusion

P increases with depth in the crust

• Metamorphism occurs within 2-12 kbar range

An increase in P packs atoms more tightly together

• Creates denser minerals

• Involves phase changes or neo-crystallization

The formation and stability of many minerals depend on both P and T

Compression- stress greater in one orientation

Different from pressure which is equal in all directions

Compression is a common result of tectonic forces

Pressure is forces from all direction 

Shear- moves one part of a material sideways

• Causes material to be smeared out 

• Like sliding out a deck of cards

Compression and shear applied together causes the mineral grain to change shape

• Euquant is roughly equal in all dimensions

• Inequant- dimensions not the same

  • A platy pancake like one dimension shorter

  • Elongate cigars shaped one dimension longer

The preferred orientation of inequant minerals is a common feature of metamorphic rock

Compression and shear combined with elevated 1 and p  ca

Hot water with dissolved ions and volatile 

Hydrothermal fluids facilitate metamorphism

• Accelerate chemical reactions

• Alter rocks by adding or subtracting elements

Hydrothermal alteration is called metasomatism

Two major subdivisions- foliated and non-foliated 

• Foliation parallel surfaces or layers in metamorphic rocks (layering)

• Alignment of inequant grains or compositional banding

• Classified by composition, grain size, and foliation type

Slate- fine-grained, low-grade metamorphic shale

• Has a distinct foliation called slaty cleavage

  • Develops by parallel alignment of platy clay minerals

  • Slaty cleavage develops perpendicular to compression

  • Slate breaks along foliation creating sheets used for roofing 

Phyllite- fine-grained mica-rich rock

• Formed metamorphism of slate

• Clay minerals neo-crystallize into tiny micas

• Has a silky sheen called phyllitic luster

• Phyllite is between slate and schist 

Schist- fine to coarse rock with larger micas

• Forms at a higher temperature than phyllite

• Has a distinct foliation from large micas called schistosity

• Shist has abundant large micas- biotite and muscovite 

Gneiss- distinct compositional bands often contorted

• Light bands of felsic minerals (quartz and feldspar)

• Dark bands of mafic minerals (biotite or amphibole)

Metaconglomerate- metamorphosed conglomerate

• Pebbles and cobbles are flattened by

  • Pressure solution

  • Plastic deformation

• Foliation is defined by the flattened clasts

Gneissic bending develops in several ways

• Original layering in the protolith

• Extensive high t shearing

• Metamorphic differentiation; mineral segregation

Compositional banding- solid-state differentiation

Chemical reactions segregate light and dark layers

Mignatite is a partially melted gneiss

It has features of igneous and metamorphic rocks

Mineralogy controls behavior

• Light colored (felsic) minerals melt at lower t

• Dark colored (mafic) minerals melt at higher t

The felsic bands melt and recrystallize in the gneiss

Two major subdivisions of metamorphic rocks

• Nonfoliated- no planar fabric evident

  • Minerals recrystallized without compression or shear

  • Comprised of equant minerals only

  • Classified by mineral composition

• Absence of foliation is possible for several reasons

  • Rock not subjected to differential stress

  • Dominance of equant minerals

  • Absence of

Quartzite- almost pure quartz in composition

• Forms by alteration of quartz sandstone

• Sand grains in the protolith recrystallize and fuse

• Quartz is hard glassy and resistant

• Breaks into conchoidal

Marble- coarsely crystalline calcite or dolomite

• forms from limestone protolith

• Extensive recrystallization completely changes the rock

• Original textures and fossils in the parent or obliterated

• Exhibits a variety of colors

• Marble may have color banding

Different minerals are stable as t and P changes

Metamorphic grade is a measure of intensity\

• Low grade- weaker metamorphism

• High grade- intense metamorphism

The metamorphic grade determines mineral assemblages

As the grade increases, new and larger minerals form

Increasing metamorphism of shale protolith

• Low grade- shale protolith

  • Clays recrystallized into large aligned clays to yield state

• Intermediate grade

• High grade

Index minerals indicate a specific p and t range 

Metamorphic zones are defined by index minerals 

Index minerals maps

Minerals assemblages from a specific protolith at specific p and t conditions 

Create predictably similar rocks

Name for a dominant mineral

Types of metamorphism are

• Thermal metamorphism

  • Due to heat from magma invading the host rock

  • Creates zoned bands for alterations in host rock

    • Called a contact aureole

    • The aureole surrounds the plutonic intrusion

      • Zoned from high (near pluton)to low grade (far)

• Burial m

  • As sediments are buried in the sedimentary basin

• Dynamic

  • Breakage of rock by shearing at the fault zone

  • Fault location determines the type of alteration

    • Shallow crust- upper 10 to 15 km

• Dynamothermal

  • Metamorphosis where mountains are,

  • Tectonic collisions deform huge mobile belts

• Hydrothermal 

  • Most common near divergent boundaries

  • Alteration by hot chemically aggressive water

• Subduction 

  • Subduction creates the unique blueschist facies

• Shock

  • Impacts generate compressional shock waves

    • Involves extremely high pressure

Exhumation

This is due to uplift collapse and erosion

Large regions of ancient high-grade ricks called shields- are exposed in continental interiros 

Shields are eroded remnants of orogenic belts

Jan 16

Review 

Processes for metamorphic 

Temp

Pressure

Hot watery fluids/hydrothermal

Shearing forces

Compression

Categories of metamorphic rock

Foliated and non-foliated 

Protolith- the preexisting rock

Marbles protolith is limestone

Index minerals tell about the p and t range and the conditions of the environment

Neomorphism- new crystals in the rock/ new minerals

Recrystallization- change the size and shape of the rock

Limestone to calcite crystals

Fase change typically becomes more dense

Ga- giga annum or billions of years

Mars-sized protoplanet 

The ocean crust is around 180-200 million years old

Chapter 11

Earth is a complex system undergoing constant change

Geologic materials record conditions and changes

• Earth consists of physical chemical and biological 

• Continents grow migrate rift and erode

• Oceans basins form grow and close

• Species emerge flourish and become extinct

Hadean eon

Eon is the longest periods 

Then eras

Epoch

Hadean- hell-like

Earth formed 4.57ga based on radiometric analysis of planetesimal-fragment meteorite

Differentiated into core and mantle by 4.5 ga

Much of the surface remained a magma ocean until

Collison with a mars sized object (thea) 4.4 to 4.5 ga

• Ejected large amounts of earth mantel and crust into nearby space

• Much of the ejected material caught in the orbit and coalesced quickly to form earth moon

• Moons orbit initially much closer than today 

Earths hadean atmosphere was different from ours

• Probable formed by outgassing from mantel during differentiation and subsequent volcanism 

• Colliding comets may have contributed some gases

• Humans anad most modern life forms could not have survived in earths eaflu atmospher

• The early atmosphere was denser than ours

• Contained water vapor h2o nitrogen n2 methane ch4 ammonia nh3 hydrogen h2 carnon dioxide co2 and sulfur dioxide so2

Outgoing search for older rocks

• The oldest geologic material found is zircon 4.4 ga

• The oldest crustal rock found is 4.03 ga

• The oldest sedimentary rock found is 3.85 ga

Why are there no rocks older than 4.03ga

• Massive bombardment of earth and its moon by meteorites 

Archean eon

archean= beginning 

From 3.85 to 2.5 ga

Based on the first abundance of crustal rocks 

Early plate tectonics

• Early crystal was probably made up of mafic igneous rocks formed as island arcs and hot spot volcanoes

• Partial melting of basaltic crust created felsic rocks 

• Small blocks of buoyant crust were created

• Rifting let to flood basalts

• Erosion produced

Protocontinents were formed by collisions of buoyant blocks

• Volcanic arc hotspots and sedimentary debris were sutured together

First life (3.8)

• Around 3.2 ga - oldest undisputed fossils

• Shapes in rocks indicate organisms as old as 3.4 to 3.5 ga 

• Possibility as old as 3.8

• Photosynthesis occurring by late archean

Origins remain uncertain

• Probably from deep dark submarine hot water vents or black smokers

• Thermophilic (heat-loving) bacteria or archaea existed in extreme conditions

Archean strata contain stromatolites

• First large fossil structures- layered mounds of sediments 

• Still exists growing today near Australia

• Alternating layers of cyanobacteria 

• 3.2 ga

Proterozoic

proterozoic= early life 

Around 2.5 ga to 542 ma 

Several rounds of supercontinent assembly and rifting

90% of continental crust is formed by middle proterozoic

Continental collisions form proterozoic supercontinents

• Rodinia formed 1 ga 

• Rodinia rifted apart 700ma

• Pannotia formed 600 ma

• Precursors to present-day continents can be identified

Atmospheric oxygen rose dramatically after the appearance of photosynthetic organisms ~2.4 ga

• Great oxygenation event 

• 2.4-1.8 ga banded iron formations (BIF)

Life forms evolved slowly

• Eukaryotes bacteria with nuclei evolved 2.7 to 2.1 ga

• Multicellular life forms appeared by 750 ma

• Large life forms leaving obviously recognizable fossils evolved ~620 ma

• Ediacaran 

Proterozoic snowball earth

Major climate shifts in late continents, ocean surfaces frozen

Glaciers covered continents ocean surfaces frozen

Many life forms probably became extinct 

Phanerozoic eons

Phanerozoic = early life 

From 542 ma to present

Defined by widespread diverse life forms 

• Carbonate shell's skeletal materials enhance the  preservation

Divided into three eras

• Paleozoic era

Vast shallow epicontinental seas and platform deposits 

Early paleozoic rifting of pannotia

• New ocean basins

• The Siberian craton 

Worldwide sea levels rose and fell several times during the Paleozoic

Transgression widespread sea-level

Regression of widespread fall in sea level

Taconic orogeny created pre-Appalachians 

Biological diversification of life shortly after 542 ma

• Cambrian explosion- rapid diversification of life forms 

Middle paleozoic 

• Silurian greenhouse 

  • Sea levels rose climate warmed continents flooded

  • Vast reef complexes in shallow epicontinental seas

  • New marine species evolved in the early Silurian

  • Acadian orogeny uplifts early Appalachians mountains

Around 420 ma life emerges from the sea and adapts to living and reproducing on land

First amphibians in late Devonian 

Late paleozoic era

Global cooling and regressing seas initially

Epicontinental seas replaced with coastal swamps 

• Formation of thick coal beds in sub-tropic

Continental collisions led to the formation of Pangea

• alleghanian orogen- led to the final collision of Appalachian Uplift

Pangea collisions caused vast continental deformation

• Eastern North America collided with North Africa

• Rocks across North American continent were impacted

Plant cover and forest continued to evolve and expand 

• Gymnosperms, cycads widespread in the Permian period 

Reptiles first appeared

• Hard-shelled eggs allowed reproduction on land

Large mass extinction event at end of Permian period

• 95% of marine species disappeared

• Possibly related to intense volcanism

  • Changed atmosphere and oceans 

• Mesozoic era

Pangea breaks up; modem features begin to appear 

Late Triassic Pangea rifting of Pangea formed deep basins

• Vast salt deposits formed from the evaporation of inland seas

• Thick sediments filled the basins

Jusaristc period

• Continued rifting opens proto-Atlantic ocean

• The west coast of North America becomes a convergent margin

The mesozoic era the age of the dinosaurs and reptiles 

Triassic

• The rapid evolution of species after Permian extinction

• Swimming reptiles evolved 

• New types of corals evolved

• First turtles and flying reptiles appear

Late Triassic and Jurassic evolution

• Sauropod dinosaurs weighing up to 100 tons

• Stegaosausrus 

Late meso

The breakup of Pangea continued

• South Atlantic ocean opened 

Sea levels rose dramatically 

Plutons form Serran Arc in western North America

• Eroded and uplifted as the Sierra Nevada today

Servier orogeny produced Canadian Rockies

Laramide orogeny formed the Rocky mountains

Plate tectonics actively increased in the cretaceous 

Sea-floor spreading occurred at a rate over x3 of today

• Seafloor rose at buoyant new oceanic crust displaced ocean water

• Vast eruptions of submarine basalts formed plateaus

• Atmospheric co2 rose

Sea level rise and increased CO2 lead to warming climate

Modern fish appeared and became dominant

• Shorter jaws rounded scale syme

The K-t boundary event

Widespread extinction occurred at the end of the cretaceous period, disappearances include

• All dinosaurs 

• 75% of plant species

• 90% of plankton

The Chicxulub crater is 65 ma 100 km wide x 16 cm deep

Sediments around the world dated at 65 ma show

• A lawyer of clay between layers of plankton skeletons 

• The clay contains iridium abundant only in meteorites

• Shock quarts formed only under tremendous pressure

• Small glass spherules formed from instantly melted magma thrown into the air

• Ash from burned plants and wood

Impart would have generated 2km high tsunami

• Cenozoic era  

The final breakup of Pangea

• Australia rifted from Antarctica

• green land rifted from North American

Continental collision

Western North America began evolving to see what we see today

• Subduction changed to transform activity between 25 and 40 ma, eventually forming the San Andreas fault

• The interior western

There was a cooling climate throughout the Cenozoic 

Ice sheets increased during the Cenozoic 

• Glaciers formed and how remained in antarctica beginning ~34 ma

• Pleistocene ice age began 2.5 ma. Ice advanced and retreated >20 times 

The Pleistocene ice ages 

• Sea levels dropped exposing the sea floor of the Bering Strait between Alaska and Russia 

• Humans may have migrated along the coastline from Asia 

Recovery after the K-T impact led to new species

Dinosaurs are extinct but early bird descendants radiated

ape-like primates diversified in Miocene ~20 ma

The human genus of primates (Homo) 2.4 ma

• Earliest known use of tools; homo erectus 1.6 ma

• Homo sapiens diverged from homo neanderthalensis about 500 ka

• Modern homo sapiens appeared about 200 ka 

Jan 21

The difference between era eon and epoch

• Increments of time

What ws the hadean eon like

• Molten surface, no livable surface in general

What happened during the hadean eon

The core and mante were distinguished 

The moon was created

First atmosphere

Next eon after hadean

Archean where the earliest life was evident 

Early life came from black smokers

Early plate tectonics started to form

How did life change at the end of the archean

• Photosynthetic organisms 

Evidence of early oxygenation in proterozoic

• Iron banding 

Three eras in in phanerozoic

• Paleozoic mesozoic cenozoic

When life came from the oceans

• 420 ma

Orogeny- mountain building events

Taconic

Acadian

Alleganian 

Event that differentiates the palozoic era?

• Permian mass extinction

Cenozoic is the age of mammals

Mezozoic is the age of reptiles 

Chapter 10

Geologic time 

Earth has a history that is billions of years old

Discovering this was a major step in human history

It changes our perception of time and the universe

Deep time0 the immense span of geologic times

The concept is so vast it is difficult for people to grasp

• We think of time in terms of our lives

Human history is minuscule against geologic time

James hutton’s principle of uniformitarianism

• The present is the key to the past

  • Processes seen today are the same as those of the past

  • Geologic change is slow; large changes require a long time

  • Therefore there must have been a long time before humans

Geologic history happens very slowly

There are two ways of dating geological materials

• Relative ages- based upon order of formation

  • Qualitative method developed hundreds of years agpo

  • Permit determination of older vs younger relationships

• Numerical ages- actual number of years since an events

  • Quantitative method developed recently

Sir charles lyell wrote the principles of geology in 11830-33

• Laid out a set of principles for deciphering earths history

• Used to estabilish relative ages of earth materials

• The principles of uniformitarianism

  • Processes observed today were the same in the past

  • Mudctack inold sediments

Principle of original horizontality

• Sediments settle out of a fluid by gravity

• This causes sediments to accumulate horizontally

• Sediment accumulation is not favored on a slope

• Hence tilted sedimentary rocks must be deformed

Principle of superposiition

• In an undeformed sequence of layered rocks 

  • Each bed is older than the one above and younger than the one below 

• Younger strata are on top, older strata on the bottom

Strata means layer

Principle of lateral continuity

• Layers will extend horizontal in sheets but they wont abrupt end

• Strata often forms laterally extensive horizontal sheets

• Subsequent erosion dissects once-continuous layers

• Flat-lying rock layers are unlikely to have been disturbed 

Principle of cross cuting relations

• So any feature, whether it be a fault or igneous intrusion That cuts across layers of rock. Has to be younger.Then the material it's cutting across

• Yonder features truncate (cut across) older features

• Faults dikes erosion etc must be younger than the material that is faulted intruded or eroded

• A volcano cannot intrude rockets that arent there

The principle of baked contacts

• An igneous intrusion cooks the invaded country rock

• The baked rock must have been there first (its older)

Pluton is hot rock in the earth

Principle of inclusions- a rock fragment within another

Inclusions are always older than the enclosing material

• weather ing rubble must have come from older rokc

• Fragments (xenoliths) are older than igneous intrusion

Law of cross cuting, inclusions cut contact override the law of superposition

If something is included in a layer it is older than the layer that it is in

Physical principles allow us to sort out relative age

This si possible even in complex situations

Consider this block of geologic history we see;

• Folded sediment 

• Intrusions

• Granite 

• Basalt 

• A fault xenoliths 

• Inclusions

• Baked contact

Easily deciphered 

Whatever is fully surrounded by something else must be older. Than that layer that it is in because you cannot have solid rock underneath the ground already formed already formed

Geologic history 

A sequence of horizontal strata accumulates 

The principle of fossil succession

Fossils are often preserved in sedimentary rocks

Fossils are time markers useful for age-dating 

• Fossils speak of past depositional environments 

• Specific fossils are only found within a limited time range

Fossil range- the first and last appearance

• Each fossil ahs a unique range

• Range overlap narrows time

Index fossils are diagnostic of a particular geologic time

Fossils correlate strata;

• Logically

• Regionally

• Globally

Best index fossil is one that is short lived

Unconformites

An unconformity is a time gapn in the rock record from 

• Erosion 

• Nondeposition

Disconformity- parallel strata  bounding nondeposition

• Due to an interruption in sediment

  • Pause in deposition

  • Sea levels falls then rises

  • Erosion

• Often hard to recognize

Angular 

An angular unconformity represents a huge gap in time

• Horizontal marine sediments deformed by orogenesis 

• Mountains eroded completely away

• Renewed marine invasion

• New sediments

Huttons unvonformity, siccar point scotland

• A common destination of geologist

Nonconformity- igneous/metamorphic rock that comes into contact with sedimentary rocks

• Igneous rocks or metamorphic rocks were exposed by erosion

• Sediment was deposited on this eroded surface 

No baked contact/metamorphis that means there is a nonconformity

Correlating formations

Earths history is recorded in sedimentary strata

The grand canyon has thick layers of strata and numerous gaps

• Formations can be correlated over long distances

A stratigraphic column describes the sequence of strata 

• Formations can be traced over long distances

• Contacts define boundaries between formations or beds

• Several formation may be com,nbined as a group 

Lithologic correlation is regional

• Sequence is the relative order in which the rock occurs

• Marker beds have unique characteristics to aid correlation

Fossil correlation is based on fossils within the rocks

• Applicable to much broader areas

The geologic columb

A composit stratigraphic colum can be cinsturcted 

The composite colum is divided into time blocks

This is the geologic time scale of earths calendar

• Eons the largest subdivision of time (hundreds to thousands of ma)

• Eras subdivisions of eons (65 to hundreds ma)

• Periosn

• epochs

Tiem-scale subdivisions are variously named

• The nature of life “zoic” means life

• Characteristic of the time period

• A specific locality 

Numerical age

Numerical age gives age of rocks in years

Based on radioactive decay of atoms in minerals

• Radioactive decay proceeds at a known fixed rate

• Radioactive elements act as internal clocks

Numerical age study is also called geochronology

Radioactive decay

Isotopes- elements that have varying numbers of neutrons

Isotopes have similar but different mass numbers

• Stable- isotopes that never change

• Radioactive- isotopes that spontaneously decay

Radioactive decay progress along a decay chain

• Decay creates a new unstable elements that also decay

• Decay proceeds to a stable element endpoint

Parent isotope- is the unstable atom

Daughter- the stable product of that decay

Half-life- time for half of the unstqable nuclei to decay

• Half life s a characteristic of each isotope 

• After one t½ one half of the original parent remains

• After three t⅓ one eight of the original parent remains

As the parent disappears the daughter grows in

The age of a minerals can be determined by;

• Measuring the ratio of parent to daughter isotopes

• Calculating the amount of time by using the know t ½

Different radioactive isotopes

How is isotopic date obtained

• Collect unweathered rocks with appropriate minerals

• Crush and separate desired minerals

• Extract parent and daughter isotopes

• Analyze

Isotopic dating gives the time a mineral cooled below its closure temperature

• Cooling of magma or lava to solid cool igneous rock 

• Metamorphic rock temperatures drop below closure temp

Sedimentary rocks cannot be directly dated

Sedimentary rocks are hard to date

• Too many pieces from smaller rocks

• Not resetting the rocks clocks

Other numerical ages 

Numerical ages are possible without isotopes

• Growth rings- annual layers from trees or shells

• Rhythmic layering- annual layers in sediments or ice

Geochronology is less useful for sedimentary deposits

Sediment ages can be bracketed by numerical ages

• Date adjacent igneous and mgamorphic rock

The age of the earth

Before radiometric dating age estimates varied widely

• Lord kelvin estimated earths cooling at 20 ma

• Uniformitarianism and evolution indicated an earth much older than ~100 ma

• Radioactivity discover in 1896 by henri becquerel 

  • Led to isotopic dating beginning in 1950s

The oldest rocks on earths surface date to 4.03 fa

Jan 22

Review questions

Difference between relative and numerical

• Relative is a comparative 

• Numerical is exact

Law of horizontallity

• Everything is layed down horizontally at the surface

Law of lateral continuity

• If you see an abrupt end to a layer of rock (doesnt lay out) it mean something had cut that layers

• All layers naturally come to a thinning 

Law of superposition

• Oldest rock is at the bottom of the sequence 

• Only on sequence that is undeformed 

  • Sometimes overridden, crosscutting

Law of cross cutting 

• Any geologic feature that cuts across layers is going to be younger than surrounding rock

Law of baked contact 

• Igneous intrusions heat up surrounding rocks (metamorphoes surrounding rocks)

• Is younger than surrounding rocks

Law of inclusions 

• Inclusions are older than surrounding rock

Absolute dating 

Half life is the time it takes for the material to decay

16 atoms, on half life half of them are decayed, 8, after another 4, than 2, than 1

What causes plates to move?

Mantle convection

What is the earliest undisputed life on earth?

3.2 ga

How did the biosphere change our atmosphere? How long ago was that?

Photosynthesis changed the atmosphere, late archean time period, causing oxygen to build up, evident in BIF or the great oxygenation event 

Why cant we date sedimentary rocks

• Made up of different fragments from different ages 

• The fragments are too small

What does unsorted mean for sedimentary rocks 

Grains are different sizes

What makes the magnetic field on earth?

The outer core 

Chapter 19

Why does the earth constantly change?

• A plastic asthenosphere permits tectonic plate motion

• A star is close enough to warm earth and its atmosphere 

• Liquid water is possible thus weathering and erosion

• Biotic evolution continually modifies the biosphere

Life on earth is due to interactions among the;

• Lithosphere

• Atmosphere

• Hydrosphere

• biosphere

The “earth system” is composed of these physical components 

The earth system

The interlinkage of the physical and biological

Global changes transform or modify both realms

• There are many ways to describe changes 

  • Gradual change- evolution

  • Catastrophic change- fast change in climate or change in climate due to eruption

  • Unidirectional changes- differentiation of the earhts layers

    • Atmosphere and oceans

      • Volcanic gases created an early atmoshpehre

      • Liquid water condensed to form oceans

      • Photosynthetic organisms appeared

    • Evolution of life

  • Cyclic change- e.g. seasons from year to year

    • The supercontinent cycle

      • Plate tectonics drives continental movement

      • Ocean basins open and close

      • Continental landmasses collide and rift apart

      • Super continents (like pangea) have formed several times

    • Sea level has risen and fallen many times over earth's history

      • +/- meters during the phanerozoic eon

      • Transgression shorelines move landawrd

      • Regression shorelines more seaward

      • Sedimentary rocks preserve evidence of sealevel change

    • Rock cycllce

      • Igeous 

      • Sedimentary

      • Metamorphic 

    • Chemical fluxes between living and non-livinng

      • Involve storage and transfer between resevoris 

        • Nonliving resovious 

          • Atmosphere

          • Lithosphere

          • Hydrosphere

        • Living reservoirs

          • All linging organisms

            • Microbes

            • Plants 

            • Animals

      • hydro cycle 

        • A biogeochemical cycle that regulates climate

          • Volcanic co2 adds carbon to the atmosphere

          • Atmospheric co2 id removed in several ways

            • It dissolves in water as carbonic acid and bicarbonate

            • Photosynthesis removes CO2

            • Weathering 

      • Carbon cycle

        • Carbon may be stored for long periods of time

          • Limestones

          • Fossil fuels

          • Organic shales

          • Methane hydrates

        • Carbon is returned to the atmosphere

          • Biotic respiration creates CO2 from organic matter

          • Rapid oxidation of organic matter creates CO2

Methods of study

Paleoclimates 

Computer simulations

H2O, CO2 and CH4 in earth’s atmosphere absorbs longwave energy from the earth and reradiate it warming the lower atmosphere

• This is called the green house effect

Paleoclimate- past climates are interpreted by datable earth material that are climate sensitive 

• Stratigraphic records- sequences of rock strata

  • Depositional environments are often climate sensitive

    • Glacial till- cold and continental 

    • Coral reefs- tropical marine 

Paleoclimatic evidence

• Paleontological- faunal assemblages

  • Assemblage changes record shifts

    • Pollen in pond sediments 

      • Spruce (colder) vs hemlock (warmer)

      • Trees (colder, drier) vs grasses (warmer, wetter) 

Oxygen Isotope Analysis

Isotope is a different type of the same element

Use different things like ice cores and marine sediment

Ice cores record condiciosn of the past atmosphere

Heavier isotopes means cooler climate, vs lighter isotopes mean warmer climate

There have been at least five major icehouse (ice age) periods in earths history 

Complex interactions across the earths system

• Plate tectonics modifies the position of continents

• Uplift of land surfaces influences atmospheric circulation

• Formation of coal and oil reomoves carbon from atmosphere

• Evolution of life affected composition 

Ice forms first on land

Ice reflects the light, cools the planet

Natural short term climate

Warmer or colder climates could last thousands of years

The past million years = dramatic flux of climate

Shorter term climate changes may last decades to centuries

The last 15000 years (holocene)

• Warming led to deglaciation temperature still fluctuate

• Several cold periods have punctuated this interglacial

  • Little ice age

Short-term climate changes regulated by several factors

• Fluctuations in solar radiation and cosmic rays due to milankovitch cycles

• Changes in earths orbit and tilt

  • The less tilt means the less variation of the seasons

  • Tilt affects the intensity

  • Northern hemisphere affects the worlds climate 

  • Precession eaths axis pointed towards sun when closest to sun more drastic seasons

• Changes in ocean current

• Changes in surface albedo

• Abrupt changes in concentrations of greenhouse gasses

Catastrophic extinction

Mass extictions events; the stratigraphic record contains evidence of dramatic decreases in biodiversity 

Catastrophic changes

Millions of years needed for biodiversity

Major extinctions

Prehistoric humans were having a small impact

Today humans are a huge force of planetary change

• Exponential population growth aided by advancements in

  • industry , agriculture, tectology, and medicine 

  • Fueled by suitable

Recent global wariming human greenhouse gas additions alter climate

• CO2 in the atmosphere has steadily climbed since the industrial revolution

  • Ice core data show atmospheric co2 in 1750 was ~280 ppm

  • In 1958 CO2 was 315~ ppm in 2010 CO2 was ~390 ppm

Many scientist think that global warming could lead to:

• Interruption of the oceanic heat conveyor system

• Polar ice meltwater is fresh water

  • Would dilute surface ocean water near the poles

  • This fresh water wont sink and move southward 

  • Thermohaline circulation would stop preventing warm water from flowing northward

Our future on earth requires sustainable growth 

• Prosperity based on balancing societal and human needs

• Erosion will resphae the landscape 

• Seas will invade or expose land

Homo sapiens may no longer be present

• A new species of hominids might have evolved by then

In about 5 billion years the sun will run out of fuel and become a red giant 

• Earth will dry out

• It will become vaporized 

Oldest to youngest

1. Appelacians 

2. Rocky

3. Himilayans