EOSC 110

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Terms in this set (...)

Define Biosphere
all of the living or once-living material on earth
Define Hydrosphere
the water on or surrounding the surface of the globe, including the water of the oceans, glaciers, and the water in the atmosphere
Define Lithosphere
lithosphere includes the Earth's crust and the uppermost part of the mantle
Define Atmosphere
gases that envelope the earth
Deep Time and an Example
Refers to the entirety of geologic history, an unimaginable length of time that goes far beyond our human scale
Example: India used to be south of Asia, moved up slowly & created the himilayas, caused permanent change in Africa as it moved away from a luscious tropical forest to a dry landscape.
Define Uniformitarianism and provide an example
"The present is the key to the past"--> The theory that all geologic phenomena may be explained as the result of existing forces having operated uniformly from the origin of the earth to the present time.
e.g. Pangea splitting apart (plate tectonics still occuring today) OR weathering and erosion by wind, rain and gravity can wear whole mountain ranges away like to Caledonian mountain range 490 million years ago
The earth's layered structure
The earth is divided into different layers that are distinct in terms of their behavior and composition
The core of the earth:
composition: predominantly iron and nickel
-inner core is solid
-outer core is liquid
The mantle of the earth:
Less dense, Abundant iron & magnesium Silicates, rock type = peridotite, it is solid
Uppermost mantle
Rigid
Asthenosphere
Plastic part of the mantle (below uppermost rigid mantle)
e.g. silly putty example
Lower mantle (mesosphere):
rigid
The crust of the earth:
Least dense, abundant silicates, overall richer in potassium and sodium
The Two Types of crust and their Mnemonics
1) continental crust (FELSIC): "Granite-like" in composition. It is richer in feldspar and silicate minerals. This makes up the continents and is generally thicker.

2) Oceanic crust (MAFIC): "Basaltic in composition. Richer in "ferro-magnesian" minerals. Ocean crust is generally thinner than continental crust.
The lithosphere
The uppermost mantle and
overlying crust are less dense than the underlying layers. Together, they form the rigid lithosphere. The
lithosphere moves over the plastic asthenosphere. Lithosphere ranges in
thickness from ~50km to ~200 km.
Earth classified by chemical composition (layers)
Crust (granite and basaltic rock), mantle (silicate minerals), core (iron and nickel and sulphur).

The asthenosphere is the physical properties definition because it is plastic and is referred to the mantle under chemical composition because it is made of silicate minerals
Earth classified by physical properties (layers)
Lithosphere (rigid), asthenosphere(plastic), mesophere (rigid), outer core (liquid), inner core (rigid)
Anatomy of a plate
Lithosphere= Crust + Upper Mantle
-Plates are fractured blocks of lithosphere "floating"on ductile asthenosphere
-plates' are composed of
lithosphere
-strong, cool composition
-Due to these properties plates are brittle -"fractured"
Plates of the earth
lithosphere is broken into 12 large and several small plates
-plates move on top of the weak asthenosphere
NOTE: Oceanic Crust + Continental Crust can sit on the same lithospheric plate.
e.g. south american plate
Plate tectonics
the study of plate movement and interaction
-the majority of geological activity is at the plate boundaries
Plate tectonics: the development of a theory
Wegener, 1912 "the jigsaw fit"-- the coast of Africa and the coast of South America fit together like two pieces of a puzzle
-fossil, climate, and rock types and styles of deformation match across different continents -like the picture on a jigsaw puzzle
-Mountains like the Appalachians, Mountains of N-England and Scotland, Norway and others are all
composed of rocks of similar age / structure
-Remove North Atlantic and you "reform" the Caledonian Mountain 490 and 390MA
-Fossil distribution: Ancient geographic distribution of Fossils are also good
indicators of connection of landmasses
-Evidence of glaciation: The Dwyka tillite in South Africa. It is of Permian age-- there are glacial striations
-Glacial patterns (permo-carboniferous glaciation) only makes sense when you reconfigure the continents
Summarize what evidence there is for continents once being joined
fossil distributions, continental edges, rock distributions, glaciation
Pangaea:
existed about 225 million years ago
-rifts apart 175 million years ago
-this was not well-respected by the scientific community in 1915
Why was Wegener's hypothesis of pangea rejected?
The MECHANISM :
-continents plow through denser oceanic crust didn't make sense
-Interaction between ocean and continent lead to crumpling mountain ranges (ocean and continental crust can be on same plate or different plates)
-Propelled by: centrifugal force & gravity of sun and moon .... FAR TOO WEAK TO CAUSE THIS!
Vinidcating moving continents: Harry Hess
During WWII -development of sonar to find U boats (submarines): Captain Harry Hess
-Allows for Mapping of the sea floor revealed topographic features of the oceanic crust previously unobservable
-Hess proposed that seafloor was spreading, generated at
the Spreading Centers
represented by the oceanic ridges.
-Continents didn't plough through ocean crust, they ride around on plates as the plates moved relative to each
other.
Sea Floor Spreading and Plate Tectonics (What Hess Discovered)
Last lecture -Hess' new view of the ocean floor:
-Ridges (long volcanic mountain chains)
-Sunken volcanoes
-Volcanic Mountain Chains or ridges
-Deep trenches along margins of some continents
Hess's Mechanism to explain the drifting continents:
-Magma "oozes" up at ridges forming new ocean crust
-Pushes older ocean floor to either side
-Eventually ocean crust descends into the Earth at the ocean trenches
•This Mechanism is called Sea Floor Spreading
•Continents carried as new ocean crust spreads
Wegner's thoery: continental drift is now called:
Plate tectonics
-With this mechanism can interpret the geological activity / features on Earth--> from this idea is where the development of modern plate tectonics theory began
Types of Margins: Passive
Transitions between oceanic and continental crust where there is no
interaction between plates are referred to as Passive Margins.
Passive Margins are typically marked by thick accumulations of sediment. Ocean-continental crust meet eachother but they are on the same plate.
Types of Margins: Active Margins
We refer to the regions where lithospheric plates are interacting with each other as Active Margins
Active Boundaries: Divergent 1) Rift Valley
Plates are spreading apart
-Rift valley: continental crust. Continent undergoes extension, the crust is thinned and a rift valley forms. There is a release of pressure --> Magma and volcanoes. e.g. African Rift Valley
-this same phenomenon happened between S.A. and Africa 100 million years ago
Active Boundaries: Divergent 2) Continued rifting
Continent tears in two. Continent edges are faulted and uplifted. Basalt eruptions from oceanic crust.
Active Boundaries: Divergent 3) Mature Ocean basin with mid-ocean ridge
continental sediments blanket the subsiding margins to form continental shelves. The ocean widens and a mid-oceanic reidge develops as in the Atlantic Ocean.
Active Boundaries: Convergent 1) oceanic and continental
-convergence between oceanic and continental lithosphere
-SUBDUCTION of oceanic plate because of its density
-mountains / trench / volcanoes / earthquakes--> MOST GEOLOGIC ACTIVITY HERE
Seismology and the geometry of subduction zones
Seismic profiles through convergent margins reveal bands of earthquakes-reveal the geometry of subduction zones
Active Boundaries: Convergent 2) Oceanic vs oceanic
-SUBDUCTION, one will subduct below the other. The older one will subduct because it is colder and more dense than the new plate
-Volcanic island arcs / trench / earthquakes
Active Boundaries: Convergent 3) continental vs. continental
Mountains / earthquakes
-This is how the Himilayas were formed
-No subduction, no volcanoes
Active Boundaries: Transform
-Plates are sliding past one another, they go in one direction forever
-Incapable of creating a tsunami
-no mountains, no subduction, no volcanoes
-Often cutting across mid-ocean ridges (spreading centers)
-No material destroyed or created
-Earthquakes
-Classic Example: San Andreas Fault
Rift Valley and Transform boundary
Rift valley will be going in one direction, transform fault will be going in another direction
-Perpendicular to each other
-fracture zones go in the same direction as rift valley
test for Sea Floor Spreading:
Paleomagnetism
-Paleomagnetism: is the study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form
-If sea floor spreading is true how old should the ocean be at the ridges compared to the trenches?
-Close to 200 million years old at the trenches (furthest from the ridge)
How can you date the ocean floor?
-Magentism and the magentosphere
-Magnetic force lines generated by the Dynamo effect in Earth's core
-Lines of magnetic flux near vertical at poles, parallel to ground at the equator
•We have a Northern magnetic pole and a southern magnetic pole
•Compass needle points to the north pole
Earths magnetic field and consistency
Earth's magnetic field NOT constant -it flips
-North and South Pole swap positions
-Last 10 million years -4 or 5
•MAGNETIC REVERSAL -last one 780 000 yrs ago
Paleomagnetism
•This "reversed" or "normal" polarity can be recorded in
rocks -paleomagnetism
•Like recording on magnetic tape.
•Magnetism in rocks measured with a magnetometer
•When pass a magnetometer over mid ocean ridge get "Zebra Skin" Pattern Symmetrical about the ridge
•Patterns compared with those dated on land -allows you to date these reversals on the ocean floor.
•The patterns are consistent -
youngest rocks at the spreading ridges getting SYMMETRICALLY older further away
•This is PROOF that sea floor spreading is occurring
Oldest sea floor?
-only about 280million in Mediterranean
-compare to oldest rocks on continent: 4.031 Billion
GPS Tracking shows absolute movement in three dimensions:
Vancouver Island and Vancouver is moving to the East
What Causes Plate Motion? Still much debated-4 possible mechanisms include: Mantle convenction
•Hot material rising from the core
-mantle boundary rises and
sinks, stirring the mantle-->mantle convection driving plate motion or potentially other way around
What Causes Plate Motion? Still much debated-4 possible mechanisms include: Ridge Push
•Plate moves away from ridge - cools and thickens and subsides (sinks)
•Mantle thickens as cooling converts the asthenosphere into lithospheric mantle -forms a slope down the ridge
-relief of about 80 -100km
What Causes Plate Motion? Still much debated-4 possible mechanisms include: Slab Pull
•Cold dense plate subsides into mantle
•Drags plate behind it -2x more effective than ridge push
•Bigger plates move faster than smaller -more pull
What Causes Plate Motion? Still much debated-4 possible mechanisms include: Trench Suction
•Dipping subducting slab pulls overlying plate towards it
•Continents not moved directly by slab pull (cannot be subducted).
•Probably a minor force -in combination with ridge push may help move continental blocks
What does plate tectonics not explain?
Hawaii-why?
It's in the middle of a plate- the Pacific Plate
Geophysicist John Tuzo Wilson
-"hot spot" hypothesis
Islands form as they move over a fixed "hotspot"
-E.g. HAWAII: The older islands are smaller, more eroded and greener. The newest Island is the largest.
-Hawaii is dead center in the biggest plate, there is no activity boundary. Caused by hot spot/ mantle plume
What causes the hot spot?
•Plume develops at core mantle boundary -heat exchange from core
•Mantle rock become buoyant -rise upward and impacts base of the lithoshere
•At lower pressures melting occurs
-generates magmas
-Plume impacts base of crust
- Plume "punching" out islands as the plate moves 2 -3.9" (5 -10cm) / year
How quickly moving are the plates?
Move as quick as your finger nail growth
When will plate tectonics stop?
When the earth gets too cold
The cave of crystals in mexico
500,000 years to grow to current size
-discovered from mining excursion
-2 men tried to steal some crystals and died
list some common elements with minerals in them
quartz in watch- vibrates 32768 times per second, this is the circuit used to keep time
-gold, gems, sparkly makeup, chalk, phone elements
Definition of a rock
rocks are aggregates of minerals
Refresher on Atomic Structures and Bonding
-Minerals ← Elements ←Atoms ← Protons, Electrons, and Neutrons
-Element: a form of matter that cannot be broken down by heat,
cold, or chemical reaction into a simpler form
-Atom: smallest subdivision of matter that retains the chemical
properties of an element
(consists of protons, neutrons, and electrons)
define a bond
attachments between atoms in crystal structure
concept of an ion
An atom that has a net positive or net negative charge due to a loss or gain of electrons
+= cations, - = anions
e.g. halite (NaCl) forms ionic bonds from Na+1 and Cl-1 attracting eachother
ionic bonds
one ion donates one or more electrons to an ion of opposite charge (the outer shell only)
e.g. NaCl
Covalent bonds
•adjacent ions share one or more electrons
•(makes strong bonds)
•e.g., diamond, DNA
Other types of Bonding (Not covalent or ionic)
•Metallic-a weak covalent bond; occurs in metallic elements, where outer electrons travel freely between adjacent atoms
•Van der Waals -weak bonds between slightly polarized atoms
•Why is bonding important?
Different types of bonds lead to different physical properties
-used to identify minerals, and their properties make minerals useful to society e.g. mica
How do we identify minderals?
Minerals divide into groups with like physical properties, based on their 'anionic groups'
Silicates SiO4 -4
Carbonates CO3- 2
SulfatesSO4-4
Sulfides S-2
Oxides O-2
Note that they all have net negative charges
Silicate Minerals
•Silicates are one third of all known minerals, but make up 90-95% of the crust
•Silica tetrahedron SiO4-4, the basic building block of all silicate minerals
-Silicate minerals are grouped
according to how the tetrahedra
bond together
-Different minerals have different
arrangements of the tetrahedra
Different arrangements of silicate structures??
Isolated silicate structure: single tetrahedron e.g.: Olivine
-single chain structure (chain of tetrahedra) e.g. Proxene group
-double chain structure of teterahedrons e.g. amphibole group
-sheet silicate tetrahedron structure e.g. mica group or clay group
-Framework silicate structure: quartz and feldspar
What are dark silicates called?
ferromagnesian→ high Mg, Fe content E.g., pyroxene & amphibole
What are light colored silicates called?
felsic→ lack Fe E.g., quartz & feldspar
Examples of carbonates
-Calcite: CaCO3
-Dolomite: (Ca,Mg)CO3
Examples of Sulfides
Many ore minerals are sulfides
-Chalcopyrite FeCuS2
-Galena PbS
-Sphalerite ZnS
-Pyrite FeS2
What type of minerals is the ocean plates made up of?
ferromagnesian
What minerals dominate the crust?
•dominated by feldspar, quartz (silicates)
•(note crustal abundances of elements)
-Oxygen (1st) and silicon (2nd) are the most plentiful in the crust, make up 94% of the volume
What minerals dominate the mantle?
•O, Si, Fe (iron), Mgdominate
•Mostly olivine and pyroxene (ferromagnesian silicates)
-known from accidental fragments (xenoliths) found in lava flows
What minerals dominate the core?
•Mostly metallic Fe (iron), Ni (nickel)
•No direct samples
•Educated guess from geophysical evidence (magnetics, gravity, seismology) and meteorites
Identifying Minerals Using Physical Properties: Hardness
Mohs' Hardness Scale
1.Ta l c
2.Gypsum
-Fingernail would fit here
3.Calcite
-Copper Coin would fit here
4.Fluorite
5.Apatite
-Knife Blade, Glass would fit here
6.Feldspar
-Steel File would fit here
7.Quartz
8.Topaz
9.Corundum
10.Diamond
what mineral is the hardest?
diamond
Identifying Minerals Using Physical Properties: External Shape
The shape of minerals is tricky.
Can be formed by one of three properties
a)Crystal habit (Shape of growth)
b)Cleavage (Shape of breakage)
c)Fracture (Shape of breakage)
Crystal Habit
Characteristic external shape-Depends on the atomic structure and bonding e.g. quartz and corudum--hexagonal crystals, pyrite--cubic crystal
Cleavage
the ability to split along one or more planes of weakness. described in terms of: number of planes, angles between the planes, quality or
smoothness of the planes, difficulty or how hard it is to break a mineral along those planes
-strong bonds within laters and weak bonds between layers
-because of weak bonds mica splits easily between "sandwiches"
-there can be one direction of cleavage e.g. mica (like layers of sandwich coming apart)
-there can be two directions of cleavage -- the angle between them is a diagnosticv tool e.g. feldspar
-3 cleavages = rhombohedral cleavage e.g. calcite or cubic cleavage e.g. halite
Fracture
Fractureis the tendency to break along an irregular surface not controlled by cleavage, or in the case of conchoidal fracture, along a curved surface -quartz commonly demonstrates this
Identifying Minerals Using Physical Properties: Streak and lustre
•Streak -Colour of powder
produced when mineral is scratched, Example: mineral
hematite has a red streak
•Lustre -way light interacts
with the surface of a crystal, mineral example: glassy or metallic
Identifying Minerals Using Physical Properties: Other properties
taste, double refraction, specific gravity, reaction with acid, magnetism
Identifying Minerals Using Physical Properties: what is the most unreliable property?
Color! color changes
MINERALS TO BE FAMILIAR WITH: Quartz
1. Quartz: (silicon dioxide -SiO2)
-Hardness 7
-Colour: colourless to variable
-Streak: colourless / white
-Cleavage: none
-Lustre: vitreous (glassy)
-Other features: may form hexagonal crystals and exhibit conchoidal fracture
MINERALS TO BE FAMILIAR WITH: Calcite
(calcium carbonate -Ca(CO3))
-Hardness 3
-Colour: colourless to variable
-Streak: white
-Cleavage: 3, very good-fractures along cleavage into rhombs
-Lustre: vitreous (glassy)
-Other features: reacts vigorously with hydrochloric acid.
Transparent samples demonstrate double refraction.
MINERALS TO BE FAMILIAR WITH: Feldspar
(potassium / sodium -calcium / aluminum silicate)
-Hardness 6
-Colour: very variable
-Streak: white
-Cleavage: 1 very good and 1 good meeting close to 90°
-Lustre: vitreous (glassy) to somewhat dul
MINERALS TO BE FAMILIAR WITH: Biotite
(Potassium iron aluminum silicate hydroxide)
-Hardness 2.5 -3
-Colour: typically brown
-Streak: white
-Cleavage: 1 single very good cleavage -mineral splits into very thin sheets
-Lustre: vitreous (glassy) to somewhat pearly
-Other properties: the thin, flexible cleavage sheets are very
diagnostic
MINERALS TO BE FAMILIAR WITH: Pyrite
(FeS2-Iron Sulfide)
-Hardness 6 -6.4
-Colour: brassy yellow
-Streak: black
-Cleavage: non
-Lustre: metallic
-Other properties: may grow in the form of perfect cubes minerals / feels heavy (high specific gravity).
What is a rock?
a naturally occurring solid aggregate of minerals
What is a mineral?
naturally occurring, solid, inorganic, fixed chemical composition, and ordered atomic structure
Three rock types:
-igenous: derived from melts
-Sedimentary: from weathering or from precipitation
-metamorphic: from preexisting rocks changed by higher pressure and temperature
See notes for rock cycle diagram
:)
Can any rock type turn into another rock type?
YES!
How many mineral species on earth?
4400- this is much higher than the moon or planets like Mercury and Mars
Early solar system (nebula) and minerals present
very limited mineral diversity
-about 4.6 billion years ago
•Material in solar nebula started to clump
•High temperatures and pressures of planet formation
"cook" new minerals.
•60 different minerals make their appearance at this time: around 4.54 billion years ago
why does earth have so many minerals?
Earth went one step further -
probably due to the initiation of plate tectonics sometime between 4 and 3 billion years ago
•New chemical and physical environments -diversity to
more than 1000 types
-earth is the only planet we know of so far with plate tectonics
What was the biggest influence on increase of mineral diversity on earth?
Biggest influence on increase mineral diversity -evolution of life
•First evidence of life about 3.5 billion -first life probably around 4 billion (or even earlier).
•Especially significant when photosynthesis evolves -mineral oxides can form
Minerals and oxidization
•over half today's minerals are oxidized / hydrated
•can only develop on a planet rich in free oxygen
•Earth's atmosphere starts to become oxygenated by about 2.5 billion years ago
•Weathering and the spread of plants about 430 million years ago increase production of clay minerals
Implications for search for life on other worlds
-Clay minerals -need liquid water to form
-Mineral oxides -may indicate photosynthesis
Magma basics
•Molten rock -avery hot (1100 -800°C) viscous liquid
•Found at depth in the Earth
-at the surface, magma is called lava
Chemical / Mineral Composition of magma
-Typical magmas are high in Si and O as well as Al, Ca, Na, Mg, Fe, and K--> form silicate minerals
-magmas cool and crystalize forming igneous rocks
-mafic rocks have more ferromagnesium (dark) silicate minerals than felsic rocks
General mineralogical characteristics of igenous rocks
Felsic magma
Intermediate magma
Mafic Magma


From bottom to top ^^^ there is iscreasing K and Na, Increasing silica, ligher color (most of the time)
From top to bottom there is increasing ferromagnesian minerals (ca, Fe, Mg)--> in maifcs
Three different types of magma and their extrusive and intrusive rock
Mafic: Volcanic (extrusive)= basalt, Plutonic (intrusive)= gabbro
Intermediate: Volcanic (extrusive)= andesite, Plutonic (intrusive)= diorite
Felsic: Volcanic (extrusive)= rhyolite, Plutonic (intrusive)= granite
-intrusive have large crystals
-extrusive have small crystals
Mafic rocks
darker in color
-contain largeley magnesium and iron
Felsic rocks
lighter in colour
-contain largely feldspar and silicate (like quartz)
what determines what minerals can crystallize and what igneous rock will form ?
Chemical composition of magma determines what minerals can crystallize and what igneous rock will form
Bowen's Reaction series
-minerals tend to crystallize in a sequence determined by their melting temperatures
Mafic magmas around 1100 degrees C
Felsic magmas around 800 degrees C
Magma components
-liquid components (the melt)
-solid components (crystallized silica minerals)
-gaseous component (volatiles: these are either dissolved in the melt or exsolved as bubbles)
How do magmas form?
Rock at depth is under pressure, at a temperature below that of melting
-the geothermal gradien temperature increases with depth and pressure
Melting of magma deep within the earth will occur at higher or lower temperatures?
higher
what is the effect of increased pressure with depth on the melting of rocks?
helps prevent melting
To form a melt we need to get _______ to be greater than the geothermal gradient
temperature
Melts can form in three ways:
1) increase temperature
2) move it to lower pressure "decompression melting"
3)Add water/ volatiles (depresses/ reduces the melting point)-- reduces temperature at which rock will melt
Magma generation: The introduction of volatiles (water) at subduction zones
-lowers the melting temperature of overlying mantle material
-causes partial melting in the mantle generating magma with a new composition
Magma generation: Heat is added
e.g. a magma body from a deeper source intrudes crustal rock and the additional heat melts a portion of the rock
-increase temperature by underplating (pooling of magmas at the base of continental crust)
-again partial melting causes generation of new magma
Magma generation: convective upwelling in the asthenosphere
results in decompression melting: thinning of the crust reduces pressure below it in the mantle-- leads to formation of a magma
MAFIC MAGMAS
-mid ocean ridges (divergent plates and hotspots)
-partial melting of mantle Peridotite (ultramafic rock) produces mafic magma
What is an example of mafic magma generation?
HAWAII
Intermediate and felsic magmas
-subduction zones ((convergent margins)
-partial melting of lithosphere generates magma that is richer in silica
differences in composition over time- Magma evolution
1) crystal setting (magmatic differentiation) magma of certain composition can erupt into magma of different composition because of heavier minerals settling to the bottom.
2) assimilation of host rock --> very hot magma may melt some of the country rock and assimilate the newly molten material into the lava
3) magma mixing: 2 different types of magma mixed together--> meet and merge within the crust
intrusive igenous rocks
form from slow cooling of molten rock (magma)
-this occurs deep below the earths surface
-may take 100's-100 000's of years to cool
-slow cooling= large crystal size. Coarse grained
3 key terms associated with intrusive rocks: country rock, contact metamorphism and xenolith
country rock: a rock that was older than and intruded by an igneous body
-contact metamorphism: metamorphism under conditions in which high temperature is the dominant factor
-xenolith: fragment of rock distinct from the igneous rock in which it is enclosed
Diapirs:
rising bodies of magma
Pluton:
large igneous bodies that crystalize at depth within the earths crust
batholoth:
Large (>100 km squared) igneous bodies formed by the coalescence of plutons
Sierra Navada
made up of many stocks or plutons
The cheif
major batholith
Dykes and Sills
thinner sheets of igneous rock
-dykes usually high angeled, cross cut existing strata
ship rock
a feeder dyke
sill
move inbetween strata (unzips) rather than cuts across
how do intrusive bodies get exposed to the surface
by uplift and erosion of both overylying and sorrounding material
volcano definition:
a location where molten rock or pyroclastic material erupt through a vent- often but not always a conical mountain
crater:
a depression overlying a volcanic vent
extrusive igenous rocks
form from fast cooling of :
molten rock (lava) and the earths surface, or fragmentation and fast cooling of molten rock as it explosively erupts forming "pyroclasts"
-fast cooking= small crystal size
example of explosive volcano
mount st helens
example of effusive volcano
kilauea volcano, hawaii
explosive eruptions of volcanoes
high viscosity magmas= high silica content (stong chains of silica tetrahedra)
-magmas that are gas-rich (full of volatiles)
effusive eruptions of volcanoes
-low viscosity magmas= low silica content
-gas poor
-dissolved gases- bubbles escape vessicle- lava fountains may form
which volcanic rock forms during the most explosive eruptions?
rhyolite
eruptive materials:
-lava flows, pillow lavas (formed underwater by crystallizaton of lava through rapid quenching),
- Pyroclastic materials (magma that has been pulverized--reduced to fine particles), gases (water, carbon dioxide, nitorgen etc)
-pyroclasts: "fire pieces"= ash <2mm, lapilli 2-64mm, bombs > 64m, pumice- felsic (floats on water), scoria- mafic (sinks)
-pyroclastic deposits: pyroclastic flows (most dangerous- mixture of gas and pyroclastic debris that is so dense it hugs the ground as it flows rapidly into low areas), pyroclastic fall, splatter, bombs (lava ejected into air and molten blob becomes streamlined during flight)
-gases--> cases acid rain
which type of magma will make the most explosive eruption?
rhyolite with high gas content
Siberian Traps
-form a large region of volcanic rock, known as a large igneous province, in Siberia, Russia. The massive eruptive event which formed the traps, one of the largest known volcanic events of the last 500 million years of Earth's geological history, continued for a million years
-98.5% of the life on the planet was gone, life almost pushed to extinction
Types of volcanoes: Shield volcano
-gentle slopes, basaltic, can be BIG e.g. Muana Loa rises 10km off ocean floor
-since the lava is basaltic it is runny, not very viscous (bc its lacking silicates) and this causes the low profile shape of shield volcanoes--> lava lacking in silicates oozes out of the volcano creating gradual slopes
Another example of a shield volcano: Olympus Mons
On Mars!
What are shield volcanoes associated with?
•Shield volcanoes are associated with "HotSpots"
•Hot spots-anomalously warm regions of the mantle
•Generate hot, mafic (low silica, low viscosity)
Types of volcanoes: Cinder Cones
-100s of meters high
-built around a volcanic vent or on their own
-mostly composed of basaltic materials
-layers of pyroclastic ejecta (scoria-dark-colored igneous rock with abundant round bubble-like cavities known as vesicles., or bombs)
-mostly mafic
-angle of repose (angle of slopes)= 30-40 degrees
-can develop fairly quickly eg 9 years
-example? Paricutin, Mexico
-Paricutin erupted in a Mexican cornfield in 1943 and buried the village in 9 years.
Types of volcanoes: Composite volcanoes
-Km's accross, several km high
-these are very dangerous volcanoes
-they have interbedded lava flows, pyroclastic flows, lahars, shot through with sills and dykes
-full range of chemical compositions (mafic, intermediate, felsic) and volcanic products including lahars
-local examples: Mt. St. Helens, Mt. Baker, Mt. Garibaldi
Pyroclastic flow:
Hot pyroclastic material flowing donwslope under gravity
ex. Mayon, Phillipines (composite volcano)
-Flows travel 500+km/hr. and can be >500 degrees
Mt St Helens and damage caused
a buldge on the side of the mountain-- pressure continued to build until there was an eruption. led to a landslide.
-explosivity was 8 times all explosive munitions in WW2.
What subduction zone is Mt. St. Helens apart of?
Cascadia subduction zone, part of the pacific ring of fire
Generation of volcanic activity at the surface: 8 steps
Migration of water into mantle above subduction zone, melting in the mantle above the subduction zone, magma rising up through the mantle, underplating, partial melting of the continental crust, generation of intermediate and felsic magmas, migration of magma towards the surface, eruption of viscous magma forming composite volcano
what is not a feature of a cinder cone volcano?
Gentle slopes!
Caldera
large collapse depression (>1km across)
-they form from collapse of overlying landmass into the magma chamber
e.g. yellowstone caldera is 70 km across
super volcanoes
- 100's to 1000's of cubic km of pyroclastic material erupted, highly explosive
Volcanic explosivity index
considers total volume of material erupted explosively
-scale from 1-8 (factor of ten for each unit)
-kilauea Hawaii= VEI 1
Mt St Helens VEI
5
Krakatoa Indonesia and Vesuvius VEI
6
Toba Lake Supervolcano VEI
75,000 years BP, 2800 km cubed

VEI 8
What is weathering?
-Alteration of minerals by atmosphere, water, animal and plant life, temperature fluctuations
-occurs at or near surface
-involves mechanical breakdown (disintegration) and/or chemical breakdown (decomposition)
general definition of weathering:
they physical breakdown and chemical alteration of rock
mechanical weathering:
physical forces break rock into smaller pieces without changing the rock's mineral composition
chemical weathering:
chemical transformation of rock into one or more new compounds
reminder about rocks/ minerals**
rock= aggregate of minerals
minerals= naturally occuring, soild, inorganic, fixed chemical composition, and ordered atomic structure
what happens with weathered material?
weathered material is eroded, transported by water, wind, or gravity and deposited as sediment
-eventually forms sedimentary rocks
-sedimentary rocks are the most commonly seen rocks
-economic commodities through weathering, creates landscape development and landforms
Mechanical (physical) processes of weathering
-physical forces break rock into smaller pieces with no chemical change e.g. frost wedging (9% volume expansion of water into ice)
-common in cool, temperate climates
mechanical processes: Talus deposits
mechanically weathered fragments fall down slope due to gravity-- collect at bottom
mechanical processes : Exfoliation (sheet jointing)
-due to pressure release in intrusive rocks
-removal or overburden (unloading)= decreased confining pressure, it expands and forms cracks
-causes expansion of rocks and sheet jointing
Other mechanical processes:
-root wedging (When roots end up in cracks in rocks, they eventually grow larger and can split the rock apart)
-salt wedging (salt blown into cracks, crystals grow in cracks and break down the rock)
-thermal heating and cooling--> hot days to very cool, temperature causes rock to expand when warm and contract when cool- breaks apart
what can increase mechanical weathing?
presence of water, presence of wildlife, increase the joints and fractures within the rock.. increased surface area= increased weathering
Chemical weathering
chemical transformation of rock into one or more new compounds
-processes that decompose rock by chemically altering the parent material
-chemical weathering was not always present on earth
Chemical weathering 1) oxidation:
affects any material containing iron
Chemical weathering 2) solution/ dissolution
-acid rain= rain water plus carbon dioxide= carbonic acid= hydrogen ion can then interact with other compounds like calcite
-this then breaks down into calcium ion and bicarbonate ion
e.g. limestone cave, complete dissolution= no solids left
-forms caves, caverns, and ground water high in dissolved ions
Chemical weathering 3) hydration
-most common chem weathering processes
-acidic water reacts with rock to form clays
-potassium feldspar + calcium carbonate--> alter it into clay mineral (the clay is a hydrated feldspar)
-a new solid is left after weathering
-left over silica can help form new rocks
summary of chem weathering:
rainwater combined with atmospheric carbon dioxide to form acid
-migration of acidic water over minerals leads to dissoultion and hydration
susceptibility to weathering:
some minerals more susceptible than others
-quartz least susceptible, olivine most susceptible.. why?
-reverse bowen's reaction series
-high pressure and temperature minerals are "out of equalibrium" with surface pressure and temperature conditions
e.g. quartz is closer to surface temp and pressure than olivine (therefore quartz is harder to weather, its not so out of its element)
where will chemical weathering be maximal?
-topical: lots of heat and moisture
what does weathering produce?
Mechanical: smaller fragments of rocks and minerals
Chemical:
1) ions in solution
2) alteration minerals (e.g. clays)
Products of weathering: Clay
Feldspars weathering produces clay
-example clay: Kaolinite-- product of feldspar weathering
-high quality magazine paper, milkshakes, fine porcelain
Product of weathering: clastic (rocks composed of broked pieces of older rocks) sedimentary grains like sand and silt
quartz is most common component.. why? It has the most silica and its the most stable in weathering process
-additionally, quartz is also very hard
products of weathering: solutions, dissolved minerals and ions
-can be precipitated elsewhere
Product of weathering: landscape development
-numerous weathering processes and extensive erosion ("differential weathering") over time produced the grand canyon
example of differential weathering
weak shale (mud rock) overlain by quartz-rich sandstone
-wind carrying sand eroding the structure
Archways as product of differential weathering
arches start as solid sandstone with cracks
-progress to "fins" of sandstone
-weaker rocks weahter faster
-some produce arches, some dont
-all will eventually erode
clastic sediment:
eroded fragments of preexisting rocks
defining clastic sediments: 1) grain size and shape
1) grain size and shape
-large angular grains are called clasts (clasts=big grains)
-grain size/ rounding and transport distance (e.g. clasts don't travel far, as sediment flows further it gets smaller and rounder because of breakage)
-The concept of energy of environments- how "turbid it is"
-"high energy environments"- only coarse heavy material can be deposited- fine material remains in suspension
-low energy environment fine material can settle out
defining clastic sediments: 2) grain sorting exam Q **
sorting refers to the distribution of the grain sizes in sediment or a sedimentary rock
-one way sediment is sorted is by running water
-in general: sediments close to the source: large grains/ angular/ poorly sorted
-sediments far from source: small grains/ rounded/ well sorted
3 Types of rocks:
rocks are aggregates of minerals
-igneous: derived from melts
-sedimentary: from weathering or precipitation--> these are sedimentary archives
-metamorphic: from pre-existing rocks changed by higher pressure and temperature
What can sedimentary rocks be used for?
oil/gas/coal
-building materials (cement, sand)
-placer deposits- heavy minerals concentrated in sediments e.g. gold, diamonds
-fossils: study evolution, time
What is a Sedimentary Rock?
-Sedimentary rocks are products of mechanical and chemical weathering. They form at the surface of the Earth (typically).
-They account for about 5 percent (by volume) of Earth's outer 16 kilometres.
-Contain evidence of past environments--> Provide information about sediment transport, Commonly contain fossils
Forming Sedimentary Rocks: First Method
Weathering
→ Produces fragments
•Transportation
→ Water, wind, ice, gravity
•Deposition
→ Marine, on land
•Compaction and cementation
→ Reduce pore space; cement (quartz, calcite,
hematite) binds grains together (process is called
lithification).....forms DETRITAL (sedimentary rock composed of fragments of preexisting rock) or CLASTIC ROCKS (arrangement of rock fragments bound into a rigid network by cement)
-after deposition there are pore spaces between different materials, then overburden and compaction brings them together, then cementation
Forming Sedimentary Rocks: Second method
-Weathering (chemical)→ ions in solution
•Transportation→ as dissolved ions and ionic groups in water
•Precipitation→ organic and
inorganic...form rocks called
CHEMICAL SEDIMENTARY ROCKS
-organic: calcium carbonate in marine shells
Limestones
-made of calcium carbonate
-can be massive (all in a mass)
-or fossiliferous (showing fossils)
Common Sedimentary rocks:
Two main groups:
1. clastic
2. chemical

Common sed rocks:
Shale; mudstone
Sandstone
Limestone
Rock salt
Coal (organic)--> made of compressed organic material
Clues to environments of deposition
"The present is the key to the
past"
-Observe environments where sediment is deposited today
-Search rocks for clues to their origin
1. grain composition
2. grain size, sorting, and shape
3. sedimentary structures
4. fossils
Sedimentary structures: Bedding
the arrangement of sedimentary rocks into layers
-oldest is on the bottom of the layers
-graded beds: at bottom of bed=big particles, it is higher energy, at top there are smaller particles, lower energy
Sedimentary structures: Cross beds
-form on an angle to bedding
-e.g. wind blows in one direction and builds up the dune into a big layer, then wind changes direction and another layer in opposite direction is created
Sedimentary structures: mud cracks
-mud left out in the sun will crack, mud loses volume as it dries and then it breaks
Sedimentary structures: ripple marks
-indicate currents/ tides, direction of wind
Fossils
-Remains or traces of ancient plants and animals marine e.g.: shells, shark teeth, microfossils non-marine (terrestrial) e.g.: flowering plants, ferns, dinosaurs
Ammonites
-can be quite large e.g. 5 ft across
-old sea creature
trace fossils
-trace/ tracks of a creature
-NOT the original organisms
Limestone
we think about fossil distribution and if the fossils are in their life positions (reef) or broken up (off the reef)
-limestone= very porous, theres oil in it
Metamorphism:
processes of mineralogical and textural change that occur in a rock when it is subjected to pressure, temperature, & fluid conditions different than those when the parent rock formed
-parent rock is the original rock before metamorphism
Metamorphic rocks and the rock cycle:
Pressure and temperature condition above those of sedimentary lithification and below those of melting
-typically between 200-850 degrees C and >300MPa pressure
What forces drive metamorphism? 1) changes in temperatures
Average geothermal gradient: increase of 25 degress celcius/per km depth
(geothermal gradient= the amount of increase in temperature with depth in the earth) This vaires upon tectonic and geologic settings e.g. higher graidents exist close to mid-ocean ridges, lower temp when ocean plate subducts under continental crust
What forces drive metamorphism? 2) changes in pressure
-lithostatic: Equal in all direction, increase in pressure due to depth
-differential: directed stress, which may be compressive or shear (opposite right to left pressure)
what does compressive differential stress produce?
a folitation (parallel Alignment of textural and structural features of a rock)
-need platy minerals to form a foliation (like silica)
Two broad classes of metamorphic rocks: foliated metamorphic rock
has parallel Alignment of textural and structural features of a rock e.g. Schist (metamorphosed mudstone) with strong foliation= differential pressure and platy minerals
Two broad classes of metamorphic rocks: non-foliated metamorphic rock
does not have parallel Alignment of textural and structural features of a rock e.g. marble (metamorphosed limestone) with no foliation= lithostatic pressure (equal pressure in all directions only OR no platy mineral
-pure limestones only consist of carbonates, impure limestones have some clay or mud in them
changes during progressive metamorphism:
-recrystallization (coarsening- they grow)
-formation of new minerals
-foliation (cleavage)
-metamorphic rock is also typically denser
Progressive metamorphism of a shale
shale--> slate: rock takes on platy breaking habit--> phyllite: fine-grained micas forming gives a sheen on folliation planes--> Schist: individual minerals (micas, garnet) recognizable--> Gneiss: medium to coarse grained with alternating layers of mafic and felsic material--> Migmattie (highest grade of metamorphic rock): rock begins to melt in situ (mixed rock) with veins and patches of granitic melt preserved--> felsic layers melt first bc it has lower melting point
-migmatites form where high-grade metamorphic rocks exceed the melthing temperature of the felsic layers but not of the mafic layers
Metamorphic Facies
names areas of Presuure-Temperature "Space"
-some facies are restricted in tectonic setting
if metamorphism occurs at depth why do we see metamorphic rocks at earth's surface?
-isostasy and isostatic uplift--> ex) mountains have deep roots going into mantle and as erosion occurs at the top, these roots rise up closer to the surface
Where does metamorphism occur? 1) Shock metamorphism
-impact craters
-brief but extremely high pressure and temperature
-effects: recrystallization of quartz to high Pressure polymorphs, ejected blobs of moten rock called tektites
Where does metamorphism occur? 2) contact metamorphism
-high temperature is the dominant factor- confining pressure relatively low (non-foloiated)
-adjacent to intrusions in shallow crust (<5km)
-country rock heated by conduction and hydrothermal convection (body of magma intrudes cool country rock)
-often associated with hydorthermal alteration
-results: recrystallization, new minerals, veins form
Where does metamorphism occur? 3) regional metamorphism
-occurs over large areas of the crust due to increased P-T at depths >5km
-effects: recrystallization, new minerals form, metamorphic foliation develops
polymorphs
forms of minerals with same composition but different arrangment of atoms
-stable at different P & T conditions
Four metamorphic settings in a convergent margin:
1) subduction zone (Low T, high P)
2) Plate interior (normal geothermal gradient)
3) Volvano-plutonic complex (new arcs, high P+T)
4) Shallow depths (contact metamorphism- Low P very high T)
Fluid activity and metamorhpism
H2O in pore spaces in rock carries dissolved ions in solution
-fluids increase rates at which new minerals form
Rock veins
typical veins are quartz or calcite; metals are possible as trace (or sometimes highly concentrated) constiuents
Where does metamorphism occur? 4) hydorthermal metamorphism
-transports ions from one mineral to another and increases the rate of metamorphism
-important at midocean ridges
-ocean water seeps into ocean crust- heats up and rises
-returned to ocean via vents e.g. black smokers- rich in metal sulphides
-As water moves through the curst chemically hydrates the rocks (basalts and gabbros).
• Olivine and pyroxene get converted to hydrous minerals like amphiboles.
•Rocks turn a green colour: hence name:Greenstones
•Water released from these at subduction zones promotes melting and magma generation
Chapter 1: What are the various components of the science of geology?
-earth's materials-- e.g. minerals and rocks
-earth's surficial processes-- landscape development
-earth's interior processes-- geological processes like subducting plates
Chapter 1: what three types of science does geology mix?
physics, chemistry, biology
Chapter 1: why are the earth systems important in understanding earth processes?
To understand geology you must understand how the solid earth interacts with water, air, and living organisms- for this reason its important to think of the earth as a system of interacting elements. The earth system is a small part of the larger solar system.
-For example, all of the spheres interact with eachother to produce soil.
Chapter 1: impacts of geology on our lives
-Mining for different resources: e.g. just to make a pencil you need petrolium, brass, clay, graphite etc.
-natural disasters e.g. earthquakes, tsunamis
-volcanic eruptions leading to losses in air traffic, pollution, fossil fuels
Lava fountain:
volcanic phenomenon where lava is forcefully but non-explosively ejected from a crater, vent, or fissure
Volcanic arc
chain of volcanoes formed above a subducting plate, in arc shape
flood basalt
layers of basalt that have built up to great thickness
A'a
a lava flow that solidifies with a spiny, rubbly surface
Pahoehoe
a lava flow characterized by a ropy or billowy surface
Lahar
volcanic mudflow
POST MIDTERM ONE: Age of the Earth: Archbishop James Usher
Archbishop James Usher (1625) works backwards through scripture in the bible: The earth was created on October 23rd, 4004B.C.
Age of the Earth: Uniformitarianists
(c.1830): measure rate of present processes to estimate how long it would take to build up the Earth's crust in its present form--> millions of years
Age of the Earth: Lord Kelvin
(1866) calculated the rate of cooling from a molten body the size of the Earth: 20-40 million years old
-we know now it is 4.5 Billion years old- we had to retrieve this from minerals or Zicron
Oldest material from earth?
around 4.4 Ga (billion years old)
-detrital (redeposited) Zicron (a mineral) in a conglomerate from Australia
-thought that this was origninally in a granite
Oldest rock on earth?
Acasta Gniess from Great Bear Lake region, NWT
-this is the oldest surviving crustal fragment on the planet
-it was metamorphosed 4.031 Ga (Billion years ago)
-high grade metamorphic rock
So just how old is the earth? Planetary accretion
-solar system and earth came about from spinning cloud of interstellar dust and gas--> compressed due to gravity which makes the cloud shrink. Flattens to disk with central bulge. Disk of gas and dust spinning around young sun, dust grains clump into planetesimals, planetesimals collide and collect into planets
Evidence for the age of earth:
Dates from meteroites: around 4.55 billion years
-dates from the moon: 4.53 billion years old
-earth around before the moon (earth around 4.54 G.A ago), earth involved with collision with another planet which then created the moon
-weathering and plate tectonics means that it is more difficult to find older rocks in the earths history
How old will you be after a billion heart beats?
-31.7 years old
Relative age dating
the science of determining the relative order of events without providing a specific age of the features involved
Law of superposition:
in an undeformed sequence of sedimentary rocks, the oldest rocks are at the bottom and youngest at the top
-also applies to lava flows and ash beds
Principle of original horizontality:
layers of sediment are generally deposited in a horizontal position
-if layers are found otherwise, deformation must have occured following deposition
Principle of cross cutting relationships:
if a rock unit (or fault) cuts other layers/units, the rock unit that cuts must be younger, and the layers that are cut must be older
e.g. fault must be the youngest feature because it cross cuts everything
The law of inclusions:
-lumps of country rock in the granite, zenoliths must be older than granite
-rock above erosion surface must be younger than granite itself
Unconformities:
-the contact surfaces between rock types or layer come in two types:
1) parallel contacts are said to be comformable
2) unconformable where contact is not parallel ie: perpendicular
When do unconformities occur?
when a lot of time passes before deposition of the next layer
-unconformities represent a gap in the rock record- a time of erosion not deposition
-unconformities seperate younger rocks from much older rocks
2 types of unconformity:
disconformity (rocks either side of the erosion surface are horizontal) and angular unconformity (rocks below the erosion surface are tilted or folded with respect to the rocks above the erosion surface)
Principle of faunal succession
organisms have evolved through time and certain time periods can be recognized based on their fossil content (fossils correlate across vast areas of rock for particular times in evolution)
Putting the "pages" of Earth's history in the right order: Using relative dating
-determine the geologic history of cold canyon area
1) oldest event= rock just above sea floor
2) rocks deposited ontop
3) a granite intuded
4) rocks titled over and eroded
5) formation of an angular unconformity- reintroduction of water
6) deposit more rocks
7) dyke intrudes
8) further erosion producing erosion surface
9) more rocks deposited--> disconformity
10) gets lifted above sea level, and the river cuts down
What is the possible age of the Tompson Rover Fm.?
Between 78 m.y. and 540 m.y. because river is between the granite and dyke
Absolute age dating: Dendochronology
-yearly growth rings in trees
-use overlapping records of various trees and archaeological findings
-in Northern hemisphere can go back almost 14,000 years
Absolute age dating: Ice cores
ice cores can be used in a similar way to dendochronology
-ice core data take us back 100's of thousands of years
-each fall of snow recording the years like the rings in a tree
Dating with Radioactivity:
provides numeric ages- specifying the actual number of years that have passed since an event occurred (also known as absolute age dating)
-we use decay products of radioactive elements in minerals to get absolute ages
Dating with radioactivity:
some high school chemistry:
-mass number= number of protons and neutrons in an atom
-atomic number= number of protons in an atom
-atomic number "determines" type of element you have
-example: carbon will always have 6 protons
-isotopes are variants of the same parent atom
-differ in number of neutrons
-some isotopes are unstable > decay into stable daughter products--> this is used in radioactive dating
Radioactive isotopes decay in a number of ways:
1) release of an alpha particle--> 2 neutrons and 2 protons
2) release of a beta particle (electron)- neutron converted to a proton
3) electron capture- proton captures an electron and becomes a proton
dating with radioactivity: half life
the time required for half of the radioactive nuclei in a sample to decay
-together with the parent/ daughter ratio, half life (rate of decay) is used to calculate the numeric age of a sample
variation in half lives
-different isotope systems have different half0lives
-some systems better suited for the study of particular materials or particular age ranges
-what would you use to date the worlds oldest rocks? Anyone that can date billions of years
-what would you use to date Mesoamerican artifacts? Carbon 14
What kind of rocks can be dated with radiometric decay?
Igenous: time that the magma crystallized
-metamorphic rocks: time of metamorphism- NOT the age of the parent rock!
geological time scale
formulated over time based on: observations of relative time and measurements of absolute time
arranged into: eons, eras, periods, epochs
-Period nemonic: China Owls Seldom Deceive Clay Pigeons They Just Cant Practice Non-chalence Quietly (Cambrian, Ordovician, Silurian, Devonian, Carboniferous: Mississippian and Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quartenary--> current period
-Eons: Hadean, Archean, Proterozoic, Phanerozoic
-Eras: Precambrian (4.54 billion - 541 million), Paleozoic (541 million - 252 million), Mesozoic (252 - 66 million), Cenozoic (66 - 0 million)
-only had a complex biosphere for a relatively short period of time
-Understanding of the ordering of strata (stratigraphy) & Understanding of
correlation or rocks using fossils (biostratigraphy) By late 1700's / early 1800's ...........
Allows for strata to be place into "geological time periods"
when does oxygen enter earth's system, oldest fossills, first dinosaurs, dinosaurs toat, first humans, ice age ends?
-earth formed 4.54 billion years ago, Jan 1st at midnight
2.5 BYA
-oldest fossils 3.6 by
-first dinosaurs 242 mya
-66 mya dinosaurs toast
-2mya first humans
-10,000 ya ice age ends
Terms to get comfortable with:
-parent isotope, daughter isotope, stable isotope, radioactive decay, half life, eon, era, period, epoch
Stress
Stressis the force (Neutons) applied per unit of area (m2).
Stress is measured as N/m2, also known as Pascals (Pa)
Stress can be compressional, tensional, and shear
Types of Stress: Compression
Forces act towards each other
Types of Stress: Tension
Forces act away from each other
Types of Stress: Shear
Forces are parallel but act on opposite sides of a plane
Stress vs. Strain
The type and extent of strain observed in a material (for this course, rocks and soils) is a
consequence of:
•the type of stress
•How the stress is applied
•temperature
•material properties
Strain (Deformation)
A change in the shape or size of a body because of the application of a stress.
Three kinds of deformation:
1.Elastic
2.Plastic
3.Brittle
Elastic Deformation
Elastic deformation
-Temporary change in shape or size
-Recovers when stress is removed (reversible)
-stores energy
Plastic Deformation
Plastic deformation
-Permanent change in shape or size
-results in folding of rocks
Brittle Deformation
-Brittle deformation
-Loss of cohesion due to stress
-The material fractures, resulting in faults
Plastic Deformation: Folding
-happens at depth, like metamorphic rocks
-Folds can also result from compressional stresses at depth (ductile deformation)
Anticlines
upturned folds, limbs dip away from each other- looks like rainbow, limbs dip away center
Synclines
downturned folds, limbs dip towards each other- the sinking portion, limbs dip towards center
Mapping geological structures: Stike and dip
-strike: is the line parallel to the ground, dip: perpendicular to strike (going downwards to varying degrees)
Mapping geological structures: Geologic map, block diagram, and cross section
-helps us to determine what is happening in the subsurface, if drawing the subsection then you draw the folding @ the contact between different rocks according to the angle. If the "dip"s are facing each other then you have a syncline. If the "dip"s are facing away from each other then you have an anticline
On a geologic map:
-dip symbols will point in opposite directions for an anticline
•dip symbols will point
towards each other to indicate a syncline
-If the dip angles are different, then the fold is not symmetrical (the limbs dip at different angles).
Eroded anticlines
oldest rocks exposed at centre
Eroded synclines
youngest rocks exposed at centre
UPRIGHT FOLDS
-upright and symmetrical-axial plane is vertical
-upright and asymmetrical fold -axial plane is inclined
OVERTURNED FOLDS
-axial plane is inclined and
limbs dip in SAME direction (note the geologic map symbols)
RECUMBENT FOLDS
axial plane is horizontal
(or near horizontal)
Increasing degree of deformation means...
greater compressional forces applied
Brittle Deformation
-Movement range can be mm to km
-Usually mm-cm movements are fractures
•m-km are fault
Faults: Normal Faults
-Caused by tension
-Blocks move away
-Hanging wall block (block on top) moves down relative to footwall (block on bottom), footwall block moves up relative to hanging wall
Faults: Reverse Faults
-Caused by compression
-Blocks move towards each other
-Hanging wall block moves upwards relative to footwall
Faults: Thrust Faults
-Similar to Reverse faults,
but with a very low angle.
Large scale thrust faulting can result in overthrusting
(older rocks lying nearly horizontal on top of younger rocks).
Faults: Strike-Slip
-Caused by shear stress, close to 90 degrees
-Motion is lateral (like traffic on a highway)
-The fault itself is vertical (no hanging wall or footwall blocks)
What Types of Strain Are Recorded in Rocks?
-Lower crust and mantle exhibit ductile behavior (anything further than 15km under earth's surface)
-Rock deforms by folding here
Plunging Folds
-folds are not perfectly upright, there are plunging folds with rounded ends. A bunch of layers in earth squished together on an angle
How do mountains affect our lives in BC?
-rain (more rain in the mountains, but Vancouver is in a rainshadow)
-Skiing, Hiking
-Landslides
-Fresh water
-Glaciers
-Tourism
-Mining
-Volcanoes
-Orientation
-Resources (trees, minerals)
Mountains are a balance!
-mountains are created very slowly (sometimes with the exception of volcanoes)
-Forces raising the mountain: (plate tectonics at convergent margins, potentially divergent margins), isostacy (continents floating on mantle, release of glaciers moves them upwards), Volcanoes
Vs
Forces lowering the mountain: Weathering, gravity
-Feedback between: Elevation/uplift And
Weathering/erosion/collapse
Mountains and the rock cycle
All stages of rock cycle operate at the same time Steady-state
process.
-To have mountains
(uplift must be greater than erosion)
What Makes Mountains?
1)Volcanos! (usually convergent margins)
2)Uplift (often convergent margins)
3)Thrust faults/Compression (usually convergent margins)
4)Extension (Divergent Margins)
-Convergent margins make "Orogenic Belts" (mountain belts)--> found mostly at convergent margins
Biggest mountain on earth?
Muana Loa--> can get bigger than Everest bc of support by the water
Mountain Building: Volcanoes
-Pretty simple:
Lava piles up--> forms a mountain
Occurs where volcanoes form:
•Convergent margins
•Hot spots -but only over the ocean (e.g. Yellowstone has hot , spot under it--> when under continent makes things lower)
Mountain Building: Cross-section of Hawaii
-4,169 m from sea level
-9,170 m from sea floor
-compare with Mt.Everest ~8500m
Anywhere with active convergent margin we have ______ mountain range
active
Mountain Building: Uplift
-If continent gets thicker uplift occurs (surprise)
-But, erosion at the top means Rocks from lower in crust move upwards
-Mostly vertical motion
Usually related to compression (convergent margins), can also be "unloading" related to underplating
-Coast Mountains! Here in
BC--> Due to thickening from convergence, old/deep rocks
exposed at surface (Mostly intrusive and metamorphic)
Mountain Building: Thrust faults/Compression
-Large scale compression over a large area
-Low angled faults
-Create thrust faults far inland
e.g.
The Himalayas
The Rocky Mountains
The Andes
Etc
Cordilleran Orogenic Belt
From the Coast Mtns to the Rockies -all of our BC mountains are part of the Cordilleran Orogenic Belt--> but the mountains are very distinct (different formations)
Mountain Building: Extension
Two ways
A) Divergent margins (Continent or Ocean)
-As plates diverge, high heat flow & causes uplift along the margin.
Eg. East African Rift Zone and Mid Atlantic Rift
B) Basin and Range style extension: Western US
-Block faulting, pulled apart and breaks in some places, and then there is an upward push. Visualized: there are hanging walls moving down on either side of a footwall that is moving up, creating a mountain structure. This usually occurs when there is large-scale extension.
-Not well understood
-Extension should thin the crust
Frequency of mountains formed by crustal extension?
On Earth, mountains formed by crustal extension are relatively rare -but exist in western North America!
-Driving East/West means going up and down a lot over mountains
Mass movement
downslope movement of rock and debris under the influence of gravity. Landslide is a general term for mass movement.
Landslides and canada:
a general term for all types of mass movement
-in canada, natural disasters death is highest among landslides
-In canada, what disaster has the biggest potential to kill people? Metiorite> earthqauke> landslide> hurricane
what controls fatal landslides?
slopes and population density
Are landslides important?
-People involved in landslides think so
•Very destructive
Fatal landslides 2002-2008
-many landslides around the himilayas but it depends on populations surrounding the mountains
Haiyuan County, Ningxia, China. 1920 Landslide
•>100,000 people killed
•Earthquake triggered landslides
•240,000 total killed by Earthquake but 100,000 of those were by the landslides
•Huscaran, Peru. 1970 landslide
•>22,000 people killed
•Earthquake triggered large rock slide
•Mass travelled 14 Km at 300 Km/hour
-people here were vulnerable to a landslide--> presence out mountain right by the town
Mt Meager Landslide
Pemberton, B.C. (2010)
~40 million m3--> 0 fatalities
-the reason for the location of pemberton is because it is by a lake (they were lucky they weren't affected by the landslide, not because of good city planning)
•Armero, Columbia. 1985 landslide
•>23,000 people killed (only 31,000) lived in the area
•A volcanic eruption melted a volcano's glaciers caused Lahars
-Volcanic mudslides
-Geologists warned people, but poor distribution
of warnings
-Banner and the mass funeral read: "The volcano didn't kill 22,000 people. The government killed them"
•Vargas, Venezuela. 1999 landslide
•>30,000
•10% of population!
•Much of the town built on Alluvial Fans
•Very rainy month, previous 3 days had 91 cm of rain
Landslide Impacts
Human and Economic impacts of landslides are broadly governed by:
1) Population density (lives and injuries)
2) Cost of infrastructure ($$$)
3) Population preparedness (can effect both)
What are the most important agents of erosion?
-Mass movements and gravity are one of the most important agents of erosion
-As large mountains weaken and are broken the first transport agent is gravity
-Landforms rely on this process
-Creates sediment that is accessible to water and ice
What Are The Relationships Between Surficial Processes?
-Weathering impacts mass movements (gravity) and wind--> impacts on stream processes, glacial processes and landscape development
= landscape development
Mass Movement landforms 1) Fans
A fan shaped landform that occurs at the bottom of a steep valley
-Landslides loose energy as slope flattens out
-Material spreads out on valley floor
-Several varieties:
-Colluvial fan -Just formed by landslides (tend to be quite steep)
-Alluvial fan -Landslides and rivers together (sand and silt)
-Fan Delta -Fan that spreads into a body of water (generally going into a lake)
Mass Movement Landforms: 2) Talus (or Scree) Slope
-An apron of loose rocks covering an area
-Quite dangerous and or difficult to walk on
-looks like a load of gravel on the side of a hill
Classifying landslides and the three rules: 1) type of material
1) Type of material
•Rock
•Soil/Earth--> dirt
•Mud --> dirt with dater
•Debris (mixture of rock, earth, trees, water, and whatever was on the slope)--> could include houses, cars
Classifying landslides and the three rules: 2) type of movement
2) Type of movement
a) Falls-Only Occurs on very steep slopes (usually rock)
-Material detaches because of weakness (fractures etc.)
-Falls due to gravity
-Very fast!
b) Slides-Vary from slow to fast
-Usually soil, rock or debris
-Material moves as a coherent mass along a surface of failure (either curved or straight)
-If surface is curved
i) Rotational slide (Slump)
-Intermediate Speed, usually doesn't travel far
-Usually weak material (sediment)
-Rotation of material on a curved failure plane
-Often characterized by a curved scarp above the slide
-If surface is flat:
ii) Translational slide
-Slow to fast
-Usually strong material moving on flat planes of weakness
-Cohesive motion of material along a flat surface
c) Flows
-Very slow to very fast (mudflows up to 80 km/h!)
-Soil, mud, wet debris, (rock)
-Water is usually very important
-Fluid or plastic flow of material (chaotic)
d) Complex Movements
-Combinations of Mass movements
-Eg. A slide that becomes a flow
Classifying landslides and the three rules: 3) speed
-if you have a slow landslide you call it "creep"
-can also be fast, moderate
The Hydrologic Cycle
-evaportation--> condensation--> precipitation-->runoff in streams, groundwater--> back to ocean water
-all best farm land is in areas where there are rivers
The Rock Cycle
Weathering, erosion and transport of material from the mountains to the ocean -recycling of minerals into new rocks
Why Are Stream Processes Important?
Streams erode, transport, and deposit sediment → form landscapes
Streams do work, depending on:
Discharge Q (cms or m3/s)
Velocity V (m/s)

Q= V x A (area)
How Do Streams Erode?
•Dissolution--> dissolving something
•Hydraulic fracturing--> water causes fractures
•Abrasion--> stream carries rock/ sand causing abrasion, or water can do this by itself
How Do Streams Transport Material?
Streams transport sediment in three ways:
suspended load: material temporarily carried by stream e.g. sand (compare to pulp in orange juice)
bed load: hops and rolls and slides exclusively e.g. gravel
dissolved load: chemical ions carried in solutions
How Do Streams Get Energy?
Streams get energy from slope and discharge- steep at top and flatter near the base
A = "graded" (equilibrium) stream profile + base level
Stream gradient (m/km or ft/mile) varies along profile
-can also occur in v shape in mountains or in a broad flood plain of sediment that surrounds river and is ideal for farming
Excess energy
-downcutting (load is abraiding), channel pattern=straight, v-shaped valley, potholes, high gradient, rapids & falls, young
Balanced energy stream
-lateral erosion
-move back and forth (moves laterally)
-called meandering channels
-flood plains, oxbow lakes, natural levees (an embankment that prevent the overflow of a river), cutbanks (the outside bank of a water channel, which is continually undergoing erosion), point bars (an alluvial deposit that forms by accretion on the inner side of an expanding loop of a river)
-moderate speed, no rapids
-mature, old age
-erosion=deposition (they are balanced), start cutting sideways into the valleywalls but deposits material behind--> eventually this builds flood plains
-levees build up (act as natural dike around river, they are broken when we get a flood)
Features of Balanced
Streams (meandering)
cutbanks (steep) and point bars (smooth) indicate lateral erosion --> steep slopes and smooth slopes
Variations in Stream Velocity
-Note maximum velocity near
outside edge of meanders, in straight stretch maximum velocity in the middle
-In meandering streams,
erosion = deposition
How Do Streams Meander?
Movement of meanders
over time--> meander neck becomes narrower--> neck cut off occurs--> oxbow lake
Deficient energy
tends to deposit, not enough energy to move sediment, channel pattern: braided (looks like braided hair, several small channels), alluvial fans, deltas
-At its base level (e.g. opening into ocean), a stream loses all capacity to carry load
-Creates Deltas (or Fans)
-two ways: the current is slow or the sediment is too high (Can occur in the mountains/ near the ocean)
-commonly low gradient, but landscape varies
Fraser River Delta, BC
-sediments eventually reached Tswassen which used to be an island, eventually it will reach the gulf islands
-one of the best places to grow things
Rejuvinated Stream
downtcutting bc of tectonic uplift, entrenched meanders, terraces, high gradient
Tectonic Influence on Streams
Rejuvenation (due to change in base level) → excess
energy...leads to downcutting,
stream terraces
-can produce meandering in bedrock
-this can happen everywhere!
Where do the products of erosion of the Himalaya end up being deposited?
-sediment carved off of himilayas goes into river systems, goes back into trench and gets recycled
What are glaciers used for?
-water
-tourism
-keep records of the earth
Glaciers defintion
a permanent mass of ice that flows downslope (in moutnains or the continent) under the influence of gravity
Glaciers stats
•Currently cover ~10% Earth's land
•2% of Earth's water
•Advance in periods of
cooler climate
•Four ice advances in last
2 m.y. (5-10°Colder)
-During last Ice Age: 30% land covered, 10% water was ice, sea level dropped 100m
-If all glaciers melted today, sea level would rise 60m!
Requirements to Form a Glacier?
1. Accumulation of snow in winter > melting of snow in
summer (more snow in winter than melting in summer, temperature must be cold enough)
2. Compaction of accumulated snow → ice (it is a metamorphic rock)
3. Ice must flow down slope
Where on Earth today are
these requirements satisfied?
high latitude or high elevation
(e.g., Mt Kilimanjaro, Africa)
how glaciers move:
-rigid zone: 2 grains of ice lock and move together
-plastic zone: upper grain moves somewhat father than lower grain and then considerably farther
when talking about retreating glaciers what are we talking about?
NOT the ice, but the end of the glacier
Flow of Continental Ice Sheets
move from the center out from the thickest accumulation
What Causes Ice Ages? 1) perturbations of earth's orbit
Milankovitch cycles: change the amount of heat from solar
radiation that any particular part of Earth receives
What Causes Ice Ages? 2) greenhouse effect
Increased CO2 in the atmosphere causes retention of heat, decreased CO2
decreases retention of heat
What Causes Ice Ages? 3) plate tectonics
-Volcanoes
-Rates of plate movement
-Positions of continents
-Continental effects on
ocean circulation--> how the earth migrates heat from the equator to the poles
Evidence of Glaciation
•Glaciers are highly erosive
•Glaciers create distinct (Beautiful) landscapes!
Glacial Erosion
•Erosion
-Glacial polish
-Striations, grooves
-Rock flour- tiny particles change the color (acts differently than clay, was mechanically weathered not chemically)
Erosive glacial features:
1) U-shaped valley
2) Fjord U shaped valley filled with ocean
3) hanging valley: U shaped valley from smaller glacier. high above valley floor.
4) crique: circular features caused by erosion where glacier begins
5) Arete: knife edged ridge, between two cirques
6) Horn: craggy glacial peak, above glaciers
7) tarn- glacial lake, form in cirques or U shaped valleys
Evidence of Glaciation-Deposits
-Glacial sediments:
-Till-poorly sorted, (mix of all grain sizes- can range from clay to bedrock), dumped from end of glacier after being carried
-Outwash-fluvial (stream) deposits, sorted and stratified, by meltwater (Deficient streams)
Glaciation Deposition: Features of deposition 1) Moraine
•Feature formed of Till (mix of sediment types)
•3 types
a) medial moraine: in glacier- caused by glaciers merging
b) end moraine: material dumped where glacier ends, forms when glacier is stationary or retreating
c) lateral moraine: same as end moraine but on the side of a glacier
Glaciation Deposition: Features of deposition 2) Esker
-outwash (sorted)- made of river sediments that are piled high
-deposited by stream flowing under glacier (act like pipes and sediment builds up within them)
Glaciation Deposition: Features of deposition 3) kettle lake
formed by blocks of stagnant ice as glacier retreats
Glaciation Deposition: Features of deposition 4) Kame
river or lake deposits formed on glacier and deposited as glacier retreats (forms on sides)
Glaciation Deposition: Features of deposition 5) drumlin
till- large hill smeared and pushed by glacier
-indicates ice flow direction (same direction as glacier)
Glaciation Deposition: Features of deposition 6) erratic
huge (house sized or larger) rock carried by glacier
How do earthquakes & Tsunamis occur?
-stress builds up at the plate boundary, rupture at boundary, shaking of the earth, sometimes there is movement of sea floor, sometimes you get a tsunami, debris through the Pacific,
Origin of Earthquakes: Japanese folklore
Japanese folklore: a giant catfish living within the Earth. While typically controlled by a god, the catfish gets excitable when the god turns away, it flails and in doing so shakes the Earth.
Origin of Earthquakes: Scandinavia
Scandinavia: god ("Loki") tied to a rock in an underground cave as punishment for killing his brother. When he twisted underground, he made the earth shake.
Origin of Earthquakes: Western North America
•Thunderbird fights a whale/monster that is depriving local tribes of food.
•The ocean rises and falls during the fight
•Eventually the whale is carried over land and is dropped where another fight (and ground shaking) occurs
•Thunderbird wins.
What is an Earthquake?
An earth quake is the sudden release of elastic energy in response to a buildup of stress.
-This energy is released when stress is greater than the strength of the fault
The energy is released as
•Seismic waves
•Displacement along the fault
•Heat and other energy
why study earthquakes?
to help describe, explain, assess, and possibly help determine if an earthqauke is going to happen
Elastic Strain
Elastic materials build up elastic energy when they are strained.
When there is too much strain, the rock will
(1) Deform or flow (plastic deformation)
(2) Break or move along an existing fault ( brittle deformation)
Elastic Rebound Theory
-force applied to the ground (e.g. shear stress), elastic displacement, & subsequent ruptured fault
Elastic & Brittle Dfm. at Plate Boundaries
-A preexisting fault is held stationary (locked) by friction
-The elastic plate on either side of the locked fault are moving slowly relative to each other (~ mms to cms/ yr)
-The blocks are distorted as the (shear) stress builds up
-Earthquake originates at a point (Focus)where the two blocks begin to slide past each other. Most earthquakes are tiny, as is the movement of the blocks on either side of the fault
-hypocenter= under the ground
-Larger earthquakes lead to significant amount of movement along the fault. We describe this movement as the slip: the distance that the blocks have moved past each other.
Type of fault movements:
Dip slip
Strike Slip
Oblique Slip
-not particularly important for earthquakes
Subduction Zones (Convergent Boundaries) and earthquakes
-Subduction interface earthquakes (can be huge-M9.4), thrust faulting, between ocean-ocean and ocean-continent
-Quakes in the subductingor overriding plate
-Benioff Earthquakes—deep in the earth (100s of km), causing little or no damage at the surface
-Locations of earthquakes:
-interface between descending slab and overriding lithosphere (< 50 km depth)
-within overriding plate (<15-20 km depth)
-within descending slab (tension or mineral phase changes) to 670 km depth : WADATI-BENIOFF
South America vs North America and earthquakes
-fast subduction in South America, causing many more earth quakes than in North America (where there is slow subduction)
-the Juan de Fuca plate wants to float because it is a younger plate (not old and super dense), it has a shallow angle and thus subduction here happens slower (in contrast to the Nazka plate thats subducting in South America)
Biggest earth quake in past 100 years?
Chile (1960)> Alaska (1964) > Sumatra (2004)
-these make up HALF of the energy for all of the earthquakes over the past 100 years
-these are all subduction zones
Continent-Continent Collision Zones and earthquakes
Many small to very large (up to ~M 8) thrust faulting earthquakes, but not as large as the largest subductionzone quakes (up to M 9.4)
Can be deeper than most (40 km)
Divergent Boundaries and earthquakes
-Shallow Earthquakes and Normal Faulting
-Small to Moderate Earthquakes
-Examples: East African Rift, Mid Atlantic Ridge
Transform Boundaries and Earthquakes
-Plates move horizontally past each other
Strike-slip parallel to boundary
-Oceanic (majority): Small to moderate shallow earthquakes
-Continental: Shallow (less than 20km), Small to large (up to ~M 8, unlikely to go larger than 7)
e.g. Queen Charlotte Fault, San Andreas Fault (most studied), and North Anatolian Faults (continental transform boundaries)
Intraplate Earthquake
Intraplate Earthquakes not associated with plate boundaries.
-Far from plate margins.
-Rupture due to gradual accumulation of strain --> occur in weak zones within the plate
-New Madrid, USA (1811-1812: 3 quakes, Mw = 7.5 to 8), along the trace of a failed mid-continent rift
-Eastern Canada: several seismic zones,
• Quebec (1925: Mw 6.7)
• old faults, old impact crater
Western Quebec Seismic Zone: June 23, 2010 M5 earthquake• not well understood
-Northern Virginia M5.8 intraplateEQ 2011: Damage to Washington Monument
Seismic waves: Body waves
travel inside materials (the earth), travel in a arc
Seismic waves: Surface waves:
travel along boundaries between materials, travel in an arc
BODY WAVES: P wave (Pressure or Primary wave)
• compression and extension of the solid (or fluid), like a sound wave
• particles move in same direction wave propagates
• fastest type of seismic wave: about 6 km/second in continental crust
-arrive first
BODY WAVES: S wave (Shear or Secondary waves)
• shearing distortion of the solid
• particles move perpendicular to direction wave propagates
• slower than P wave: about 3.5 km/second in continental crust. Cannot pass through fluids!
-second fastest, doesn't pass through the outer core because its liquid
Surface waves
-Require an interface: ground-air, water-air, mantle-liquid outer core
-Slower than body waves
-Rayleigh wave: vertical and horizontal motion parallel to wave travel direction (like an ocean wave)
-Love wave: horizontal movement perpendicular to wave travel direction
-most deadly, slowest waves
Utility of Seismic Waves
•Locate earthquakes and find magnitude
•Provide early warning
-Image the Earth's interior
-Find liquids
Seismographs: the basic idea
-Mass suspended by a spring
-Seismograph moves mass doesn't
-Motion causes pen to move
How far was the earthquake from my seismograph?
Can calculate this by a simple velocity equation
-look at difference between the P and S waves (S-P lag time)
Where was the earthquake?
•Calculate distance "D"to quake at 3 seismographs
•Draw a circle of radius D around each
•Epicenter is where the three circles intersect
-focus: you need three spheres
Local Seismic Networks
-Canadian National Seismograph Network
-GSC operates ~ 30 seismographs in SW BC, larger concentation on Victoria Island and lower mainland
Japan and earthquake detection
-their network is able to function as an early warning system (detection of P waves)--> earthquake warning system!
Parent isotope
the original isotope
Daughter isotope
the new isotope (nuclear change that happen with unstable nuclei of isotopes). Happens through alpha decay, beta decay, and electron capture
stable isotopes
Stable isotopes do not decay into other elements
radioactive decay
the spontaneous nuclear disintegration of certain isotopes
half-life
the time it takes for a given amount of radioactive isotope to be reduced by one-half
Eon
the largest unit of geologic time
Era
major subdivision of the standard geologic time scale e.g. Mesozoic Era
Period
Each era of the standard geologic time scale is subdivided into periods e.g. Cretaceous period
Epoch
each period of the standard time scale is divided into epochs e.g. Pleistocene Epoch of the Quartenary Period
Alpine Glacier
glaciation of a mountainous area
continental glaciation
the covering of a large region of a continent by a sheet of glacial ice
Earthquake Magnitude
Magnitude is a measure of energy released
•Quantitative Scale
•The best known scale is not the best scale... in fact it is obsolete
Richter Scale
The Richter Scale measures amplitude (size of waves on seismograph). Not accurate for large or distant earthquakes
ergo--> No longer in use
Moment Magnitude scale (Mw)
-now used by geologists
-Measures strain energy along rupture surface (energy released)
-Logarithmic (e.g. a 4 earthquake is 10x smaller than a 5)
High magnitude quakes:
Magnitude affects everything about an earthquake
-affect greater areas
-shake longer
-damage more buildings
Earthquake Intensity
•Qualitative (descriptive) Measurement
•It is what we feel in an earthquake
•We use the Modified Mercali Scale
-Ranges from 1 (felt by very few or not at all) to 12 (total destruction)
Modified Mercali Scale
scale of 1-12
ranges from: felt by very few people--> sensation of heavy truck striking a building--> Felt by all. Damage is slight--> Damage is considerable--> Damage is total--> waves seen on the ground surface
Earthquakes Intensity: How people perceive earthquakes depends on several factors
1) Magnitude
2) Distance from epicentre
3) Foundation (ground material)
4) Duration
5) Structural Resistance- in general: brick and concrete=bad, wood steel & reinforced concrete= good (want a building that will sway without cracking, need it to be flexible)
Earthquake Hazards 1) ground shaking/ ground rupture
-ground shakes, scary but not a big deal
-But buildings may fall down
-This is a big deal -responsible for most fatalities
-1556 Shanxi province, China
•Worst recorded EQ (for fatalities)
•Housing was silt caves, most collapsed
•~883 000 people dead
-"Earthquakes don't kill people, buildings kill people."
-Buildings on bedrock or compacted sediments are safer
-Wet, loose sediment and artificial fill have longer and harder shaking
-Can also sever transportation corridors
Earthquake Hazards 2) Liquefaction
-Shaking causes unconsolidated soils to liquefy
-Ground looses cohesion and flows
-we dont generally build on flooding areas (build one ice age upland sediment and bedrock in Vancouver)
Earthquake Hazards: Fire
-Gas and electrical lines severed
-Water lines severed too
-Buildings collapse and burn
-Can make urban areas inaccessible to fire fighters
-Fires after earthquakes are very dangerous
Earthquake Hazards: Tsunami
-must warn people to go to high ground, usually 7 or 8 waves, 20 min apart
-to generate a tsunami: motion of fault block, water column is pushed up, and create massive waves
Earthquake Hazards: Ground failure/ Landslide
-Earthquakes trigger landslides
-Very important in BC because we have lots of mountains, it would be very difficult to get food here in a emergency
Earth's Internal Structure
Main zones within the
Earth:
-Crust- the outer layer of rock that forms a thin skin on Earth's surface
-Mantle- a thick shell of
dense rock that separates the crust above from the core below
-Core-the metallic central zone of the Earth
Direct Evidence of Earth Interior
-we have only dug 12km at Kola Superdeep Borehole
-Deepwater Horizon Drilling Platform
Evidence of earth interior: Kimberlites
-Igneous bodies formed from mantle melts (>150 km deep) that ascend quickly towards Earth's surface and
crystalize.
-Gives us a sample of the
composition of mantle rocks.
-And diamonds!
Evidence of earth interior: Xenoliths
Small fragments of crustal
or mantle rocks that are picked up in an ascending magma - again, evidence for composition, pressures and temperatures at depth within the Earth.
Eg Peridotite (Olivine-rich mantle rock) xenolith in basalt
Evidence of earth interior: Evidence from Waves
Deep interior of the Earth must be studied indirectly
•Direct access only to crustal rocks and small upper mantle fragments
brought up igneous activity
•Can only drill so deep (not to the mantle)
Geophysics
the branch of geology that
studies the interior of the Earth
If the Earth was a uniform solid...
-P wave, S wave, and surface waves would arrive at all stations. We would compute body wave arrival
times at different seismometers
-This would work perfectly
-But the earth isnt a uniform solid
Evidence of earth's interior: Seismic Reflection
Reflection occurs if there is a contrast in seismic wave velocity (due to differet densities). The strength of the reflection depends on the contrast in density--> occurs when you hit a layer (+ difference between 2 layers= greater reflection)
Evidence of earth's interior: Seismic Refraction
Refraction is the bending
of seismic waves as they pass from one material to another with different
seismic wave velocities
Seismic Refraction & Reflection
-seismic waves travel fastest through: Igneous rock bc they are the most dense material--> velocities increase as you go into the core of the earth (more pressure and more density but layers of earth also have an impact)
Effect of material change on paths of refracted and reflected waves
-with no change in properties, there would be no refractions and no relections
-In actuality, velocity gradually increasing with depth due to depth
-curvature (refraction) of the energy--in the outer core there is zero velocity of S waves (S waves can't propagate through liquids)
The Crust of the earth
Seismic waves- indicate crust is thinner and denser beneath the oceans than on the continents
•Different velocities indicate different compositions
•Oceanic crust is mafic,, composed primarily of basalt and gabbro
•Continental crust is felsic, with an average composition similar to granite
Comparisson of oceanic crust and continental crust:
-Oceanic: average thickness 7km, seismic P wave velocity 7km/sec, density 3.0g/ cm cubed, probable composition basalt underlain by gabbro
-continental: crust thickness 30-50km (thickest under mountains), 6km/sec P wave velocity (higher in lower crust), density 2.7g/ cm cubed, probable composition granite, other plutonic rocks, schist, gneiss (with sedimentary rock cover)
The Mantle
The mantle, like the crust, is made of solid rock with only isolated pockets of
magma
•Higher velocities than
crustal rocks indicate denser, ultramafic composition
•Crust and upper mantle together form the lithosphere, the brittle outer shell of the Earth that makes up the tectonic plates
•Beneath the lithosphere, seismic wave speeds abruptly decrease in a plastic low-velocity zone
called the asthenosphere
The Core
P-wave shadow zone (103°-142° from epicenter) explained by refraction of waves encountering core-mantle boundary
-S-wave shadow zone
(≥103°from epicenter) suggests outer core is a
liquid
-Core composition inferred from:
•Calculated density
•Physical and electromagnetic properties
•Composition of meteorites
•iron metal (liquid in outer core and solid in inner core) best fits observed properties
-Core-mantle boundary- great changes in seismic velocity --> density and temperature
What is a magnetic field?
-the field around a magnet: attract or repulse based on the side of the magnet you're on--> earth's magnetic field: protects our atmosphere and blocks cosmic rays
Common detection of a magnetic field
-magnet and compass
Where are the magnetic poles?
-Magnetic North and Magnetic South poles
True north vs magnetic
north?
-Declination: The angle made between lines connecting a point on the Earth's surface to the geographic north and the magnetic north
-Inclination: The angle between the magnetic field's force line and the surface of the Earth
Declination varies with latitude and longitude
-closer to magnetic pole, declination will go to 0
Inclination mostly varies with latitude
-inclination 0 when along equator and 90 degrees when at magentic poles
Actual form of the Magnetic Field
-not perfectly distributed, where on earth would the magnetic field be the strongest? at the poles
Total Magnetic Field Intensity
-at the magnetic poles there are 60,000 Nanoteslas of strength compared to 30,000 at the eqautor
Origin of Magnetic Field in the Outer Core
-Recorded pattern of magnetic field suggests it originates deep inside the Earth.....
BUT
Magnets only function at relatively low temperatures (<770 ̊C)
-Magnetic minerals deep inside the Earth?
NOT a simple answer
The Geodynamo Theory
Convection of electrically
conductive molten iron in the outer core
-Electrical current generates a magnetic field
-For this "core dynamo" to
exist the fluid must be able to convect vigorously enough
-What are the drivers? its the spin that makes a difference--> the planet's spin adds a twist to the convection currents in the molten outer core. Those spirals mean the magnetic fields of the convection currents no longer cancel eachothe rout and we've got a place for our compasses to point to.
Where does the current come from? Geodynamo theory
1)Earth is rotating - liquid metallic outer core is moving and the electrical charges in it are moving too
2)Convection of material between the (hot) lower boundary (inner core
-outer core) and (cooler) upper boundary (core-mantle)
-Moving charges induce a magnetic field
-The magnetic field helps drive movement in the outer core
Is the magnetic field fixed?
-Depends on the "scale of thinking"
-Changes recorded through geological time and observed in the rock record
-Magnetic minerals record the orientation of the magnetic field at their
time of formation
-Older rocks contain magnetic minerals that show significant variations in terms of polarity (which way was north) and orientation
-Palaeomagnetism
Recording variations in the magnetic field
-Normal - the same as today
-Reversed - the opposite direction
-inclination: direction of earth's magnetic field, lava flows can show reverse magnetism
-what drives the variation?
Normal, chaotic (in between switches), reversed--> time period of these reversals (in hundreds of thousands of years and this flip occurs in the span of 1000s of years)
Recording variations in the magnetic field: Polar wander
-Over much shorter timescales we can observe the movement of the Earth's geomagnetic North Pole
-Up to 10s of km per year
-How would this be
recorded in the rock record? igneous rocks!
Polar Wandering
-Igneous (and metamorphic) rocks that contain magnetic minerals (commonly magnetite) record information on where they were formed relative to the magnetic north pole.
-This information is?? magnetic direction and inclination
-Rocks forming today preserve this information and point to the location of the present day pole.
Polar wandering and ancient rocks
Ancient rocks: If we measure the magnetic direction and inclination of the same age rocks in different places we might expect that they would give identical polar positions...which should correspond with the present position.
-BUT THEY DON'T
•Rocks of different ages give different polar positions
•Rocks of the same age but on different continents give different polar positions
•The older the rock the further the calculated polar position is from
the present position
Summary of Earth's interior and magnetism
-Earth's Magnetic field is thought to be generated by convective currents of liquid iron in the outer core.
-Process is chaotic, produces significant variation over time and can be useful for correlating and dating rocks.
-Magnetic signal of material in the subsurface can be remotely detected to make inferences about subsurface structures and rocks.
-Disappearance of the magnetic field would be catastrophic (?!
What does the strength of Gravity depend on?
•Strength of gravity depends on:
•Size of masses involved
•Distance between the masses
•Density of masses involved (inc density and gravity will increase)
Uniform Sphere and force of gravity
Uniform sphere: Same gravitational force at the same distance "r" from center of mass
Depressions & elevations and force of gravity
•Force of Gravity is lower over large depressions (If same material-gravity goes down)
-Force of Gravity is higher over high elevations (If same material)
How does gravity vary over Earth?
-Acceleration due to gravity
9.81 m/s2
-higher gravity at convergent plates, but gravity varies greatly across the globe e.g. high gravity at mid atlantic ridge thats a spreading ridge
Are topography & gravity related?
-No... Why is "somewhat" to "No" the correct answer?
-blocks of same mass and different densities--> will all sink into mantle at same depth
-blocks of same density and different masses--> sink into mantle to different depth "buoyed" up by different amounts of mantle
-this is called isostacy
Why are there no huge gravity anomalies on earth like we see on other planets?
isostacy
-only get gravity anomaly if there hasn't been time to adjust
mountains and isostacy
-Things like mountains come into
isostatic equilibrium through erosion
-This is why deep metamorphic roots of mountains are exposed- the roots of the
mountain RISE as the overlying rock is eroded e.g. local coast mountains
-Implication: Upper mantle
(aesthenosphere) is viscous - i.e. it can flow over periods of about 10 000 yrs. This is why topography DOES NOT
correlate exactly with topography
What areas are not yet in isostatic equilibrium?
-Himalayas - Sill actively rising due to collision of Indian and Eurasia - LOTS of thickened continental crust producing a positive gravity anomaly
-Eventually though asthenosphere will adjust and the area will come into equilibrium (not yet adjusted, they have a high, low and neutral gravity anomaly)
Is gravity higher or lower at Hudson's bay?
-lower-->Negative anomaly here (in part) due to the removal of the ice sheet that covered the area over 10 000 years ago (the continents are still depressed and crustal rebound is occurring)
-the crust is still bouncing back
Gravity and smaller scale structures: applications
-satellites and laser beams used to measure gravity across earth
-weight on spring also measures gravity (over empty hole spring goes up, over dense metallic ore spring goes down- there is a pull)
-oil/gas/mineral exploration, geologic engineering
Solar Nebula Disk Model
Clues from the current state of the solar system:
-planets orbit in same direction (counter clockwise)
-Orbits of planets are approximately in same plane
-The density of the planets decreases away from the sun
-Close in: rocky planets (terrestrial) / Far away: Gassy (Jovian)
Solar Nebula Disk Model A)
5 GA: cloud of dust and gas probably "debris" from
supernova starts to contract and rotate about 4.6GA?
-Prominent elements: hydrogen, helium, oxygen, silicon, carbon
Solar Nebula Disk Model B)
90% of cloud concentrated in the centre, 10% in a surrounding disk - the protoplanetary disk (planetary workshop).
-Temperature in the centre of the cloud starts to increase and glow: the "T-Tauri" phase of the sun
Solar Nebula Disk Model C)
Gravity attracts particles together in the surrounding disk:
accretion, initially it was electrostatic forces (static electricity) not forces causing accretion
Solar Nebula Disk Model D)
Accreted matter starts to form larger bodies: protoplanets (large rock masses - form after about 10million years?)
Solar Nebula Disk Model E)
Pressures / temperatures increase in central portion of cloud: initiates nuclear fusion: our sun in born.
-Stream of radiation from the sun (solar wind) drove enormous quantities of lighter elements outward to outskirts of solar system (only denser
material close to the young sun)
Formation and initial rotation of the protoplanetary disk:
explains why planets (mostly) rotate in same plane and in
same direction
Why the Division of terrestrial (rocky that are close to the sun) and Jovian (high gas that are far from the sun) planets?
•Probably a reflection of where they formed: condensation
hypothesis
•Close to the sun lighter gases "blown away" by active sun
•Condense out beyond the "snow line" to form Jovians
-How do we know this is what happens? We have seen it!
How Did Earth form?
Following Accretion - Earth heats and Differentiates
-Heat from impacts/radioactive decay
-Due to gravity Heavier elements sink to Centre of Planet: The Iron Core, lighter material on the outside
-Earth initially a magma ocean
If earth's core was Silicate, not iron would, would gravity be stronger or weaker?
-weaker less dense
Is the force of gravity higher or lower if you are on a plane in the sky or at sea level? Why?
-lower on plane- further away
Is the force or gravity higher or lower over a metal ore deposit? why?
depends on ore deposit, but generally yes
What is the force of gravity at the center of the earth? why?
0 bc mass is pulling you from all around
Isostatic compensation
Average surface elevation
-ocean: -4.5km
continental +0.5km
IF _____ gravity will _____
if theres a depression, gravity will decline
-if there's a mountain with no roots gravity will increase
-if theres a mountain with roots "downtains" the gravity will stay the same
how to explain hot jupiters?
perhaps these planets formed far away from the sun but migrated closer to the sun over time
BC and Hazards
-BC is a very complex area- there has been tons of subduction over time
•Put together (accreted) over hundreds of millions of years
-Large thrust faults (rocky mountains, boundary between BC and Alberta is the peak of the rocky mountains) Thrust faults have a low angle and cause more displacement than reverse faults--> they can go a very far distance
-volcanoes and glaciers
Paleogeographic Reconstruction Time: Cambiran
-around 500 mya
-Passive continental margin (no active plate tectonics)
•shallow seas (on part of BC)
•equatorial
-early life- trilobites
-much of America also had a shallow sea
Paleogeographic Reconstruction Time: Mississippian
-around 340 mya
-Initiation of subduction along the coast, rocks smered onto the continent causing thrust faults, exotic island arcs, volcanic island arcs
•Active continental margin
•Volcanic island arcs
•Shallow seas
•Tropical
Paleogeographic Reconstruction Time: Permian
-around 280 mya
-subduction is going to East & West in different locations
-Volcanic island arcs
•Uplift of interior and early mountain
building
•Pangea Supercontinent
•Further north
Paleogeographic Reconstruction Time: Late Triassic
-around 200 mya
-Dinosaurs!!
•Eastward subduction
•Accretion of the volcanic island arcs (smeared onto continents)
•Still part of Pangea
-sea covering part of Alberta at this time is the reason for the oil they have (dead sea creatures)
Paleogeographic Reconstruction Time: Late Jurassic
-around 150 mya
-Eastward subduction
•Further accretion of exotic terranes
•Pangea breakup
•Drifting north again
Paleogeographic Reconstruction Time: Early Miocene
-around 23 mya
-Eastward subduction along whole coast line
•Increased inland volcanism
•Cascade arc begins (our volcanic chain)
•World map looks almost the same
as today
Paleogeographic Reconstruction Time: Present
Eastward subduction
•Active Cascade
-Arc Volcanism
•Active transform faults in California
BC Geology - Conclusion
-Complex!
•Full of "accreted terranes" huge areas of rock formed nearby/far away--> pieces of crust have gotten "stuck" onto NA
•Sea level/shore location changed throughout time
Natural Hazards: Volcanoes
-Cascade chain of volcanoes next
door
•Nearby volcanoes:
-Mt Baker
-Mt Garibaldi
-Mt Cayley
-Mt Meager

-Mt. St. Helens is extremely active compared to the rest

-were far enough away from the volcanoes that we would only need to worry about ash
Natural Hazards: Lahars, pyroclastic flows
-lahar hazard in surrounding valleys--> abbotsford (160,000 people), might have a landslide
-lava and pyroclastic flow hazard- close to Mt.Baker- low risk (uninhabited)
-mainly worried about ash
Natural Hazards: Earthquakes
-where do biggest earth quakes occur? subduction plate boundary
-deep earthquakes not the biggest ones
-seattle earthquake 2001
Natural Hazards: Fatal Landslides
-big ones at Britannia, in the southern half of the province
-tend towards big landslides in the mountains
-Developer wanted to build town of Garabaldi below area where there would be regular rock flow and this was shut down
Why is a paleontologist giving a lecture on alien planets?
As we have seen from an earlier lecture, Paleontology has already gone extra
terrestrial. In 1996 ALH84001,0 hit the headlines
-conatined vessicles with air from mars, fossilized bacteria within meteorite -could these little structures be fossils from Mars?
-possibility that mars developed life before earth, maybe microbes were transported to earth from mars and thats how life began.
-The jury still out on whether these are mars fossils but in searching for life in our solar system it is likely that paleontology is going to be a vital tool in the hunt of the evidence of life outside our planet.
Mars Reconnaissance Orbiter
There is now evidence of water on Mars - even if it is just occasional very salty Brines that seep down the edge of a crater. It is possible that the like may still exist on this planet hidden in the crust
-possible that there is life on mars
At the moment - this planet, earth, is the only one we know of that for sure has a life and a fossil record. Which raises a question - just how likely are we to find life outside of our own solar system - how common is life?
-potential for life? Europa
-This is the question Dr. Frank Drake was asking in the The Drake Equation. What the equation considers are the conditions that need to
be met to give us the number of communicating civilizations in the galaxy? If you Multiply them all together to get your answer (N). R= number of stars in our galaxy. fp= fraction of stars that have planets. ne= number of those planets that might support life. fl=fraction of planets that actually develop life. fi= fraction of planets that actually develop intelligent life. fc= fraction that preveal their presence in space. L= life time that a civilization exists.
-Till recently, R* is the only number we could hazard a reasonable guess at - probably between 100 - 400 billion
Recent developments in the drake equation
Recently though - we have started to get a much better idea about these parts...The number of stars that have planets and the number that exist in the habitable zone.
-This is is research that has been under taken all around the globe including the island of Hawai
Observatories in Hawaii
-Hawaii is one of Earth's window to the rest of the Universe. Mauna Kea on the big island has one of the largest astronomical observatories. The combined light-gathering power of the telescopes here is sixty times greater than that of the Hubble Space Telescope
Mauna Kea
Mauna Kea, "White Mountain" (often snowcapped) is the highest island-mountain in the world - 9,750 meters (32,000 ft) from the ocean floor to an altitude of 4,205 meters (13,796 ft) above sea level. The summit is above 40 percent of the Earth's atmosphere
Mauna Kea Atmosphere
-The atmosphere is extremely dry and stable and distant from city lights.
-A tropical inversion cloud layer isolates the upper atmosphere from the
lower moist maritime air keeping the summit skies clear
-summit isolated from moist maritime air and atmospheric pollutants
-9 optical/ IR telescopes, 3 submillimeter telescopes, 1 radio telescope
The problems of planet hunting: Scale
-The main problem of space is one of scale - consider this analogy using a tennis ball to represent the Earth
-on this scale: moon would be the size of a marble 2.02m (6.6ft) away
-the sun would be 7.3m (24ft) across
-plot sun at 783m away (7 football fields away)
-outermost planet (size of canteloupe) is 26.3 km (15 miles)
-closest star would be 209,000 km (130,000)... travelling from NY to Seattle 54 times
The problems of planet hunting: There is also the problem of glare
-imaging extra-solar planets- lost in the glare of their star
The first alien planet around a sun-like star
6 October 1995, Michel Mayor and Didier Queloz announced the first detection of an exoplanet orbiting sun like star - 51
Pegasi. 50.9 light years away.
-light year: distance it takes light to travel 1 year
-speed of light 299 792 458 meters per second
-distance light travels in 1 year: 9 trillion km (6 trillion miles)
-The planet was discovered using a spectroscope to detect the regular velocity changes in the star's spectral lines. These changes are caused
by the planet's gravitational effects on the star. 51 Pegasi "wobbled, getting faster and then slower.
51 Pegasi b
-Confirmed by multiple observations. Named 51
Pegasi b - first planet
found around a sun-like star. Unofficial name:
Bellerophon for the Greek
hero who tamed pegasu. The cycle of the wobble is just 4 days meaning this planet is very close to its sun. The planet is a massive gas giant - Jupiter sized and is VERY close to its star, less than 5 million
miles (8 million kilometers) from the solar surface (Mercury is about 35
million miles (58 million kilometers) away from the sun). Bellerophon orbits around the sun in 4 Earth days. This planet is fast
... and it's hot. Temperatures on Bellerophon can reach upwards of 3,632°F (2,000°C)
-why is this such an odd location for a jupiter-type planet? gas giants probably form in cold/distant areas of the solar systems, gas giants can migrate after they have formed
Bellerophon is tidally locked to its star (present on face to star at all times)
It is so hot that the clouds on this planet are possibly composed of vaporized iron that may fall as liquid iron rain.
-storms over 1000mph
Temp: 3,632 degrees F or 2,000 degrees C
New tools for the search of exo planets
-March 7, 2009- Cape Canaveral Florida
-Delta II Rocket
-Carrying the Kelper Space Telescope
-Very different to Hubble - a telescope designed to gaze far and wide.
-From the "Pillars of creation" in the Eagle Nebula where new stars are being born to our own back yard - like these impact scars on Jupiter
following the impact with comet Shoemaker
Levvy 9 on May 17 1994 to
the Hubble deep field view which shows some of the farthest away galaxies ever seen, over 3000 in total. -The area of the sky the HDF was taken in makes up less than 1/10th the width of a full Moon, yet it contains over 3,000 galaxies.
-Kepler's mission: to stare like an unblinking eye," not looking for wobbles, looking for "blinks." If a planet transits in front of its star then the light getting to Earth dims just a little. The amount by which the star dims depends on its size and on the size of the planet, among other
factors
-difference were looking for (comparison): Take a major hotel skyscraper - all lights on - lower blind in 1 one window by 10% - this is the range of dimming difference Kepler is hunting for.
-If it's a planet - this dip will repeat, the frequency of the dip will indicate how close to the star the planet orbits
-At Heart of Telescope: 42 CCDs at 2200 x 1024 pixels, total resolution of 95 megapixels
New Earths?
-by June 2010- 15 months after launch
-over 700 new planets found
-extrapolating- number of planets must be in the trillions
Kepler's main mission:
-fnd Earth-like planets - possibility of life. Not to say there are not other life forms on non-Earth like planets but this is the best / only model we have. The factor common to all life on Earth - the need for liquid water.
What is needed for an earth-like planet?
we need to find planets that exist in the habitable or "Goldilocks Zone" of their star - a place where water can exist in all 3 states on a rocky world
-3 forms of water on earth: solid, liquid, gas
Constellation of Cygnus and Kepler 22b.
May 12, 2009. Just a few days after Kepler became operational a possible candidate around a sun-like star in the Constellation of Cygnus. The star would dim every 10 months placing it in the habitable zone (indicating similarity to earth in terms of its distance to its star). It was given the name of Kepler 22b and was found to have a radius 2.4x that of Earth. But what was it composed of? Was it a rocky or a gassy world?
-This is where we turn to the Keck Telescope on Mauna Kea
-The KECK had the first segmented mirror telescope - each 10m / 1 ton segment (36 in total) driven by a motor so can act as a single mirror
-There is a problem though as light passes through air pockets they act like lenses. As a result light rays arrive on Earth at different angles and don't come to a nice clear focal point on mirror producing a fuzzy image
How to compensate for light passing through airpockets? Kepler 22b
First. Build high so there is less
atmosphere to cause the distortion (less twinkling effect)
-Secondly, use Adaptive Optics. A Laser measures atmospheric
turbulence and then the mirror changes shape 2000 times per second to compensate
-Keck used the "wobble method" to measure mass of Kepler 22b. Keck can measure changes in velocity within range of human walking speed. Gassy= less wobble, rocky= more wobble
-What it discovered was a small wobble so not a high density rocky world-- low density gas giant?
Another possibility for Kelper 22b
But there is another possibility though. As the planet is within the habitable zone it is possible that it could be a "water world." -A rocky planet surrounded by a global ocean 1000km deep with no land masses. "
Since discovery of Kelper 22b: many other earth-like candidates found
-The earth similarity index is a measure of how similar a planet is to Earth. The ESI is a function of a planet's radius, density, escape velocity (how fast things can escape from surface of the planet), and surface temperature.
-Earth= 1, Venus= .78
This index is not a PERFECT estimate of how similar any planet would be - consider Venus
Earth=heaven, venus= hell analogy
Although Venus has a ESI of 0.78, if Earth is a heaven then Venus is
Hell. Surface pressure - 91X Earth - equivalent to 1km deep in ocean. Surface temperatures 460°C - hot enough to melt lead. 300km/h Winds laced with droplets of sulfuric acid rush around a planet suffering
a runway greenhouse effect.
Kepler-438b
Given that how about some high ESI exoplanets...
Kepler-438b: rocky (1.2x radius of Earth) 470 light-years from Earth in the constellation Lyra. It is the most Earth-like exoplanet
known to date. Orbits in just 35.2 days so it is close to its star but this star is very different to our own.
-The star is a red dwarf - smaller an cooler than our sun so, although this planet is pretty close, it is within located within the habitable zone, a region where liquid water could exist on the surface of the planet. It has
an ESI of 0.88
Kepler 453b
Another example is Kepler 453b - about 1.6x the size of Earth a "Super Earth." It orbits in the habitable zone of a sun-like star that is around 6 billion year old. This means it could have a biosphere that is even older than our own. Kepler 453 has a ESI of 0.86
How many Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs
in the Milky Way?
-On 4 November 2013, astronomers reported, based on
Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs
in the Milky Way, 11 billion of which may be orbiting Sun-like stars
Recalculating Drake
So now we have some more concrete numbers for the Drake equation in terms of numbers of planets and numbers in the habitable zone
-How about the the fraction of planets that may develop life?
-next generation of space telescopes may help: like the James Webb
-The James Webb telescope will orbit the Earth about 1 million miles away. It needs very cold conditions:-220°C (-370°F) to operate so it is equipped with a Sun shield - the size of a tennis court - to protect it from our sun.
-The James Webb will search in the infrared and may be able to
determine the composition of planetary atmospheres -perhaps like ours which we know has been substantially altered by the presence of a biosphere. "Oragami Telescope" due for launch October 2018.
Hawaii continues the hunt: The Gemini Planet Imager
-Hawaii too will get an upgrade with the Gemini planet hunting infrared telescope.
-it has given us the best image of an exoplanet yet: Beta Pictoris b
We have also seen the tracks of young planets moving in the their protoplanetary disk...
-This is an ALMA image of the disk around the young star TW Hydrae. ALMA obtained its best image of a protoplanetary disk to date, revealing the classic rings and gaps that signify planets are in formation in this system - the Solar Nebular Disk
Model in operation
So what is our current estimate of N?
The fraction planets in Galaxy with communicating civiliations?
-0.00127 (During any 100,000 year period, 127 detectable civilizations will emerge)
-Drake equation estimates around 10,000 civilizations today
Where are these civilizations?
we haven't got there yet!
-Should also consider the Fermi Paradox though...
-The Fermi paradox - There is a high probability of Earth - like planets. So let us assume many of hem develop life and some intelligent life. Some may develop interstellar travel. Even at the slow pace of currently
envisioned interstellar travel, the Milky Way galaxy could be completely traversed in about 1 million years. So shouldn't we have been visited by aliens now? "Where is everybody?" Perhaps we are being avoided.
What is the probability of life?
-high at the microbial level
-This at the moment though - this is where we make our stand - this is the only place we can call home
Carl Sagan
On Feb 14 1990 Carl Sagan got NASA to turn Voyager 1 around and take a final image of Earth - all that could be seen at that distance was a pale blue dot:
"Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident
religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and
father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam."
Carl Sagan
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