Geology 105 Midterm #1
Cretaceous Period
- 100 Ma - a big ocean in the middle of N.A.
Earliest life: Cyanobacteria
- 3.5 bya - chemosynthesis, photosynthesis stromatolites
Silurian
- 443-417 mya - crinoids
Earth's internal structure
Compositional layers - crust: basaltic and granitic rocks - mantle: solid to semi-molten silicate compounds - core: iron/nickel (a little sulfur)
Three types of plate boundaries
Divergent (spreading APART), Convergent (coming TOGETHER), Transform (SLIDING past one another)
what period are we in now?
Quaternary - has been going on for the past 2.6 million years, since the onset of a series of glaciation events in North America
How can we determine the age of rocks?
Relative dating, Numerical, or absolute dating,
Three groups of rocks
igneous, sediment, metamorphic
Understanding hazard risks can help people make better decisions - probability
- probability lower magnitude event (smaller in scope/intensity) - greater probability higher magnitude event (larger in scope/intensity) - lower probability
Early geologic thought
Aristotle: suggested that Earth changes at a rate too slow to be observed Pliny the Elder: observed that amber was a fossil Ibn Sina: studied earthquakes, water sources, and how diverse the landscape was Shen Kuo: formulated a theory of geomorphology - that mountains erode and are carried by rivers as silt to the sea James Ussher: became a bishop, an archbishop, and eventually primate of all Ireland, Trinity College, Dublin - using Biblical genealogy and historical records, determined that Creation occurred in 4004 BCE
The layered earth
Behavior of materials - gas, solid, and liquid seem like obvious terms - but considered with respect to time - over geologic time, solids may behave as liquid - ex: glacier is solid ice, yet flows (ultrahigh viscosity liquid) over the course of years
Earth's interior
Four major layers: - crust (4-60 km) ranges in thickness - mantle (2885 km) solid or semi-molten rock - outer core (2270 km) liquid iron and nickel - inner core (1216 km) solid iron and nickel, complete solid TOTAL: 6400 km radius
what epoch are we in now?
Holocene - been going on for the past 12,000 years, since the last glacial maximum in north America; whole or entirely, new - scientists want to call Holocene the anthrocene because the impact of humans on the planet
Late Paleozoic
- 360 Ma - 240 Ma - Pangea: all land mass smashed together as one continent - life: Devonian fishes, amphibians make their move onto dry land, vast forests of wee ferns and mosses, gymnosperms ancestors of trees
Early evolution of earth
- 4.6 billion years ago, our original planet was HOT - heat of formation from gravitational energy - heat from friction of: constant bombardment; aggregating mass of particles and gases - heat from radioactive element decay - early atmosphere = vaporized rock
440 million years ago an extinction event marked the end of the Ordovician period
- 49-60 percent of all marine genera disappear from the fossil record (80 percent of all marine species)
Paleozoic
- 540 Ma - 240 Ma - continents clustered together - early: around S Pole - late: more equatorially
Cambrian
- 541-485 mya: explosion of life - Burgess Shale - 508 million year old mudstone, deposited in a basin next to a coral reef - burgess shale in Canada preserved for 508 million years
Cenozoic era
- 65 ma to now - age of mammals - continents near present position Quaternary Period: northern hemisphere glaciation - ~2 Ma - 12,000 ya
Classifications by sediment size:
- Conglomerate: coarsest, poorly sorted - Sandstone: medium-coarse - Shale: fine particles
Weird and Wonderful Cambrian
- Early Cambrian: critters evolve hard parts - trilobite, brachiopod, cephalopods
More evidence comes in 1950s and 1960s
- Harry Hess taught geology when WW2 was declared - used onboard SONAR equipment to map the ocean floor - global bathymetry map reveals mid ocean ridges - global mid-ocean ridge system are the worlds longest mountain chains - atop these giant mountain chains (ridges) you would expect peaks, but no, they saw rifts and stress fractures - seafloor magnetism - hunting for ww2 submarines with a magnet tow fish, but found out that the rocks on the seafloor were magnetic - seafloor magnetic anomalies - magnetic "stripes"? - normal polarity: white - reverse polarity: red - appear to march outward from mid-oceanic ridges - stripes record paleo-magnetism
Rates of plate motion
- is fast, in the order of a few centimeters per year - movement is rarely smooth or steady instead it is punctuated and punchy - plates can displace several meters during an earthquake
Carboniferous Period
- land clustered into two supercontinents - America is equatorial rainforest climate - carboniferous coal swamp atmosphere RICH in oxygen - horsetail, cycad, bugs love oxygen Time and pressure turns forest into Pennsylvania Coal
Mantle
- largest layer - solid(ish) - 2,870 km thick (1800 miles) - 500-4000C - density 4.5 g/cm3 - composed of silicate rocks, mineralized with iron and magnesium
Outer core
- liquid - hot: 4500-5500C - 2200 km thick (1300 miles) - density 10.7 g/cm3 - composed of: ~90% iron, ~10% other elements (S,O,Ni)
Transform (SLIDING past one another)
- long divergent boundaries create transform boundaries - creates discontinuity in the mountain range - side to side regime - slide past one another in a strike-slip motion to relieves strain - transforms motion of other plate boundaries - no lithosphere is created or destroyed - hazard risks: earthquakes, rarely volcanism - transform faults are fractures - San Andreas Fault - a rare transform fault on land → has "cut" and offset a river valley
Huttons theory: Uniformitarianism
- means that the Earth is OLD - 4.6 billion years old - geologic time is unimaginably vast - geologic processes operate slowly, over thousands, millions, or even billions of years * write down clicker questions *
Arthur Holmes
- modern geochronology (father of) - pioneered the use of radiometric dating - loved the idea of continental drift (Wegener) - used uranium isotopes to determine that the earth had to be older than 1.6 billion years - Holmes mechanism: earth's mantle is so hot - that is contains convection cells - these convection cells power the movement of the earth's crust
Rheological layering
- non-Newtonian - how density and pressure induces solids to flow like liquid - based on deformation and flow of matter - density - state of matter (solid/liquid) order: lithosphere, asthenosphere, mesosphere, crust, mantle, outer core, inner core (outer to inner)
Family of faults
- normal fault: extension dropped the hanging wall down → hanging wall is dropped down with respect to the footwall - reverse fault: thrust pushed the hanging wall up - strike-slip fault: shear stress tore the fault in a side by side motion (right and left lateral) → no fault scarp, no footwall, no hanging wall 1. identify fault place (draw a line) 2. identify hanging wall and footwall 3. match up layers 4. did the headwall descend? Normal fault ^^^ for normal vs. reverse
Calculate the earth's density
- observation step 1: we can calculate the mass of the earth using planetary physics - mass of earth = 6.055x1027g step 2: we can calculate the volume of the earth because we know its radius (6400 km) (1 km=100,000 cm) v=4/3 x pi x r3 step 3: we can calculate the average density of the earth using the relationship d=m/v D= 6.055g/1.10 cm3 = 5.5g/cm3 Average density - but how can that be, when = continental crust has an average density of 2.7 g/cm3, and oceanic crust has an average density of 3.0 g/cm3? Hypothesis: earth must have layers, with a denser substance inside
Crust
- outer rock layer of Earth - 40 km (25 miles) thick - density 2.8g/cm3 - Mohorovicic discontinuity: separates lighter crustal rocks from more dense mantle
Eight chemical elements make up about 98.5% of all matter in the Earth's crust
- oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium (in order)
Relative dating
- placing rocks in a logical sequence of formations Categorical comparisons and observations Compare younger rocks to older rocks, known layers to unknown layers
Plate tectonics: basic mechanics
- plates are part of the lithosphere - many separate plates, all moving slowly; continents are set within their lithospheric plates - lithosphere: earth's rigid outer shell - contains both crust and shallow mantle; slid, brittle - asthenosphere - partially molten, plastic, denser, beneath the lithosphere hotter and weaker than lithosphere, plastic deformation
Urbanization increases the potential for catastrophe
- poor land-use practices - people live in low-lying or unstable land - the previous, "natural" state of the land may have provided protection that has been removed - enhance the effects of natural hazards turn disasters into catastrophes
Fracking has important consequences
- pressure from fracking can reactivate pre-existing. dormant faults, causing earthquakes - fracking requires millions of gallons of water each year not a big deal in Pennsylvania, but what if water is scarce (i.e., Utah desert)? - Hydraulic fluids from fracking must be pumped back out as wastewater, contaminated with chemicals environmentally hazardous - chemicals in the injected fluids can leach into groundwater - most is stored at the surface in artificial ponds - often, "recycled" - diluted with fresh water and pumped back into the ground to shatter more shale. After several uses, the wastewater must be sent to specialized treatment facilities
Hydraulic fracturing ("fracking")
1. shale is shattered by pumping fluids (water, chemicals and sand) into the gas-bearing shale unit 2. pressure from the incoming fluid fractures the shale. 3. sand grains (from the pumped fluids) prop the fractures open. 4. natural gas can flow freely and be collected. - lots of naturally gas fro everybody - cleaner-burning, cheap energy
Sedimentary
2) Sedimentary - from sediment (i.e., weathered particles) - sedimentary rocks come from other rocks - rocks exposed at the earth's surface will be weathered - broken down into small pieces or sediment - and then eroded - transported away by wind, water, ice, etc. - deposited somewhere else (carried away) - lithification: process by which sediment is hardened/cemented/chemically altered to form rock - sedimentary rocks form in layers
Metamorphic
3) Metamorphic - changed formed - ex: slate - heat it, twist it, deep inside the Earth - metamorphism can change crystal structure - high heat from earth's interior can cause rock minerals to recrystallize - confining pressure and heat can cause a phase change - rock that were once solid can be slightly liquid Metamorphism needs heat, pressure and time - pressure in all direction from weight of surround material foliation - pressure in one direction from push and pull of tectonic plates deformation
Types of radioactive decay
Alpha emission, Beta Emission, Electron capture
What era are we in now?
Cenozoic - the Cenozoic era has been going on for the past 65.5 million years, since a great extinction event that killed the dinosaurs; new, animal
Layers based on chemical composition (outer to inner)
Crust, Mantle, Outer core, Inner Core
Earthquakes
Earthquake in Ecuador, 7.8M earthquakes, in Quito - aftermath 661 dead, 27,732 injured - roads, bridges permanently destroyed, will cost billions of dollars - largest earthquake to strike Ecuador since 1979 - damage due to earthquakes is often exacerbated by other circumstances - weather → land-sliding - earthquakes don't kill people, building do - where an earthquake strikes, it will strike again - pushing, pulling, sliding of plates causes faulting - faulting: process of fault rupture - similar to sliding one rough board past another, rocks rupture and displaced when stress exceeds strength of rocks - stress: force that results form plate tectonic movements, tensional, compressional, shearing - strain: change in shape or location of the rocks due to the stress - an earthquake is a sudden slip of Earth materials along a fault - what exactly is a fault? Not every crack in the ground is a fault - lithospheric rocks are brittle: fracture and crack under stress - fault scarp: most of a fault is usually buried, part exposed to due vertical displacement - describes a fault's geometry using mining terminology → example: hanging wall, foot wall footwall: the volume of rock geometrically below the fault place (what the miner could walk on) hanging wall: the volume of rock geometrically above the fault place (what the miner could hang his lantern on)
( Igneous)erosion, transportation, sedimentation (Sedimentary) increase pressure and temperature (Metamorphic) melting and magma migration then back to igneous (order can be clockwise and counterclockwise)
FACT
Geologic Time
Geologic time scale - 3 major ERA groups: Paleozoic "ancient life", Mesozoic "middle life", Cenozoic "new life" - Eon, era, period, epoch (longest to shortest)
Igneous rocks you know
Granite - crystalline texture: no pores or open spaces between mineral crystals, easy to keep clean, hard to wear out El Capitan monolith, Yosemite NP - hard, resistant to erosion, makes for great climbing/bouldering
Earth as a system is powered by two forces
Internal processes: powered by the geothermal gradient - drives mountain-building, earthquakes, volcanic eruptions External (surface) processes: powered by the Sun - delivers radiant energy - in the atmosphere: creates weather - in the hydrosphere: powers hydrologic cycle
Layers based on Rheology
Lithosphere - solid, cool, strong outermost layer of Earth - crust embedded on top Oceanic crust vs. continental crust - oceanic crust is.... Denser rides lower atop lithosphere; younger all less than FINISH COPYING , 6-7 km thick - continental crust is... less dense rides high atop lithosphere; older oldest rocks date to 4.4 billion years ago, 35-70 km thick - crustal thickness is not uniform ^^^^^^ Asthenosphere - partially molten, blow lithosphere, semi- solid - hot, very slowly flowing layer of weak rock
ways to categorize: composition
MAFIC rocks: rich in Mg and Fe (low in silica) - gabbro (intrusive) and basalt (extrusive) - dark color, high density - just because a rock is dark, does not always mean it is low in silica INTERMEDIATE (medium silica content) rocks: medium color, medium density FELSIC rocks: rich in silica - lots of orthoclase feldspar and quartz, - light color, light density, - granite (intrusive) and rhyolite (extrusive)
what eon are we in now?
Phanerozoic
Sedimentary rocks are also characterized by...
Porosity - the amount of space between the grains within a rock - low porosity: little space between grains - high porosity: lots of space Permeability - how connected those pore spaces are - fluid flows through rocks that are more permeable
Numerical, or absolute dating
Specify the number of year (+/- error) since an event occurred - for younger events/deposits (<5000 years old): historical record ex: Pliny the Younger describes the eruptions of Vesuvius in 79 AD - anything older FINISH COPYING Relative dating uses principles of logical
Clicker: what direction is the plate currently moving if the red dots are where the most active volcanoes are?
To the left and up - plate tectonics explains everything - distribution of earthquakes, volcanoes, rift zones, mountain chains , hotspots - direction of plate movement: past and future locations - why earth's crust is thicker on continents and thinner on ocean floor - lithosphere is composed of tectonic plates
The geosphere also contains landform-shaping process:
ex: external processes such as landslides, rivers and glaciers, erode and sculpt surface features - internal processes are those that occur beneath earth's surface. Sometimes they lead to the formation of major features at the surface
Principle of superposition
- Nicolas Steno (1638-1686) - Anatomist, Priest - Shark teeth vs. tongue stones - but how did these solid objects (teeth fossils) come to rest inside rocks Steno reasoned that : a solid surface had to exist FIRST - in order to form a deposit, sediment must have a surface to deposit onto KNOWN: sediment deposits in flat layers AND: thus sedimentary rock forms in flat years IT FOLLOWS THAT: in an undeformed stack of layers, the layer on the bottom that was deposited first - younger layers on top - older layers on bottom
1st world vs. 3rd world country: natural disasters
- San Francisco: 7.1 63 deaths, 50 billion in losses greater impact to infrastructure, almost recovered within 5 years, richest country in western hemisphere - Haiti: 7.0 100,00 deaths, 14 billion in losses, less impact to infrastructure, may take 12 plus years to fully recover, poorest country in western hemisphere
First hints from modern mapmaking
- Sir Francis Bacon - Eduard Suess: studied glossopteris fern fossils, found all over southern hemisphere in Permian rocks Gondwanaland and land bridges - sues noted that the seeds were enormous, too large to be carried by wind - suggested that land bridges must have once connected the continents
Inner Core
- Solid - psycho hot: 6000 C - 1278 km thick (800 miles) - density 10.7 g/cm3 - composed of: ~90% iron, ~10% other elements
Natural processes have occurred throughout earth's history
- Uniformitarianism - "the present is the key to the past" the processes that have shaped the Earth are essentially the same as those opting today
Beta Emission
- a beta particle (an electron) is ejected from the nucleus of the atom - neutron decays into one proton and one electron Electron leaves - the mass number remains unchanged - the atomic number is increased by 1 different element - ex: C-14 N-14
Elements bond with each other to form minerals
- a mineral is: solid, inorganic, naturally occurring, regular chemical composition, orderly (crystalline) structure) mineral examples: halite, diamond (carbon), graphite (carbon)... difference is the crystal structure
When does a natural hazard become a natural disaster?
- a natural disaster is a natural hazard that: - occurs over a limited time - occurs in a defined area AND - meets one or more of the following criteria: 1) ten or more people killed 2) 100 or more people affected 3) state of emergency is declared 4) international assistance is requested
What is natural hazard?
- a natural process that is a potential threat to human life or property Ex: earthquakes, tsunamis, volcanic eruptions, flooding, landslides and mass wasting, severe storms (hurricanes,..)
Rocks are aggregates of minerals
- a solid, an aggregate of one or more minerals, individual components cohesively brought together by a rock-forming process ex: granite
Understanding hazard risks can help people make better decisions - acceptable risk
- acceptable risk: the amount of risk that an individual or society is willing to take - what is acceptable to you may not be acceptable to your neighbor - frequent problem is a lack of reliable data for either probability or consequences - natural processes can be mapped, monitored, and studied - future activity can be predicted based on patterns: how often they have occurred in the past, where they occur and events that are a precursor a period of activity - natural hazards are predictable to a degree
Radioactive decay curve
- after one half-life, half of the remaining parent atoms have decayed to daughter atoms - Half lives: 1- 50% parent, 50% daughter 2- 25% parent, 75% daughter 3- 12.5% parent, 87.5% daughter 4- 6.25% parent, 93.75% daughter - geologic time clicker - the majority of earth's mass lies below the crust
Devonian
- age of fishes - 419-358 Ma - Dunkleosteus: up to 10 m long and 4 tons (elephants are 2 tons) - ammonite, bryozoan, fan coral Late Devonian - ~380 Ma - amphiabians climb out onto land - Tiktaalik, Ichthyostega
Fossil assemblage
- age ranges of some fossil groups Not everybody gets to be a fossil - conditions favoring preservation: rapid burial, do you have hard parts? #winning - organisms that make for great fossils - trilobites - brachiopods or other shellfish - corals
Alpha emission
- an alpha particle (2 protons and 2 neutrons) is ejected from the atom - atomic number lowered by 2 different element - mass number is reduced by 4
Clicker: why is the inner core solid, But the outer core is liquid?
- because the inner core experiences greater pressure than the outer core
a natural hazard can be powered by:
- can be powered by internal forces (plate tectonics) earthquakes, tsunamis.. - can be powered by energy from the Sun flooding, landslides and mass wasting (when caused by weather-related events), severe storms (hurricanes and tornadoes), weather on the long term = climate global warming - can be powered by gravity (meteorites)
How do we know?
- can we sample the earth's interior? - NO, too hot, pressure is too high - deepest yet drilled - 3.5 km Tau Tona Gold mine, South Africa - at depth, rock face temperature is 60 degrees C (140 degrees F) - average of 5 miners die each year - instead, we must make observation; form a hypothesis
When does a natural hazards becomes a catastrophe?
- catastrophe - massive disaster, usually involving great loss of life and interruption to normal societal function - requires significant amount of money or time to recover
How often to natural processes (hazards) occur?
- clue 1: look at human history ex: Pompeii - clue 2: look at the landscape ex: landslides - clue 3: look at the geologic records ex: eruptions
Understanding hazard risks can help people make better decisions - consequences
- consequences - damages to people and property, cost, etc., location - how many people will be affected? How much will it damage roads and bridges? How much is will damage property?
The Hydrologic cycle
- describes the movement of water between: the atmosphere, oceans evaporation, precipitation: rain, snow, etc., surface runoff Biogeochemical cycles - carbon, nitrogen, phosphorus are transferred through earths systems - related to the other geologic cycles - tectonic cycle: water from volcanic processes
People
- dramatic increased in natural disasters over the last 50 years - averages: 80,00 people die annually, financial losses at 50 billion per year... but why are disasters increasing? - population growth has more than tripled in the past 70 years - increased exposure to hazards - when hazards occur, higher population densities make evacuation .. - increased pollution - reduced availability of food and clean drinking water - greater demand for waste disposal and energy resources
Electron capture
- electron capture: an electron is incorporated into a proton in the nucleus (proton and electron neutron) - the mass number remains unchanged (proton neutron) - the atomic number is decreased by 1 (loss of proton) different element - ex: K-40 Ar-40
Earth materials
- elements (silica), molecules, minerals, rocks, formations (in order) - earth is a self-contained chemistry lab - atoms: made up of protons have mass, a positive charge, number of protons = atomic number ex: the elements oxygen has 8 protons, every atom of oxygen has 8 protons, more protons=heavier elements - proton mass - 1.6726219 x 10 -27 - neutrons also have mass, same as protons, have a neutral charge, atomic isotopes: # of neutrons can vary, even among atoms of the same element, decay of unstable isotopes occurs at a fixed rate MOLECULAR CLOCK ex: helium -4 atom, 2 protons, 2 neutrons helium -3, 2 protons, 1 neutron - electrons have effectively no mass, have a negative charge - ion: neutral atom: number of protons = number of electrons, ...etc.
Catastrophism
- enlightenment scientists were puzzled: how could vast Earth features have formed in fewer than 6000 years? - catastrophism: earth's features were formed by sudden and unrelated catastrophes - Georges Cuvier: pre-eminent botanist and expert of the fossil record, established extinction as a fact - outspoken proponent of catastrophism James Hutton: Scotsman, gentleman farmer, erstwhile scientist - observed ripple marks in sandstone - observed horizontal layers of red sandstone above titled layers of greywacke - "the mind seemed to grow giddy by looking so far into the abyss of time"
Earth's core creates a geomagnetic field
- established 3.5 billion years ago as the solid inner core separated from the liquid outer core 1500 C temp difference between outer core and inner core creates convection in liquid outer core Igneous rocks capture earth's magnetism as they crystallize - lava erupts from mid-ocean ridges at over 1000 degrees C - basaltic lava is mafic - iron containing magnetite - Thermoremanent magnetization (TRM) - acquired by an igneous rock as its temp cools below its Curie point - throughout earth' history, that dipole has flipped directions - polarity reversals observed in lavas from terrestrial volcanoes Evidence of seafloor spreading - older magnetic stripes are located farther away from mid-oceanic ridges - newer magnetic stripes are located closer to mid-oceanic ridges - timing and rates of spread can be known
Another relative dating tool: fossils
- evidence of past life environmental indicators: fossils can be used to infer information about past environments - index fossils and fossil assemblages: fossils can be used to give approximate ages of sedimentary rock, if we known when the organism lived - this cast of a camel hoofprint could only occur in Cenozoic-aged rocks (age of mammals)
Ocean-continent convergence
- ex: Cascades
Divergent (spreading APART)
- extensional regime - pulling apart - mid-oceanic ridge (seafloor spreading) → along ridges, mantle material upwells to create undersea volcanoes ( account for most of Earth's volcanism) 80% - rift and rift valleys → ex. Iceland (volcanic island where the mid-Atlantic ridge has grown above sea level), swarms of moderate earthquakes (rarely cause death and destruction - hazard risk: mild(er) earthquakes, mild(er) volcanism and continuous! - constructive margin: this is the place where new crust is made - how they form: centering, doming, rifting, spreading 1. hot upwelling mantle rises 2. transfer of heat via conduction through plastic/elastically deforming asthenosphere 3. heated material expands (extension due to heating) 4. extension stretches brittle lithosphere past its yield point 5. lithosphere breaks - stress relieved 6. creates one or more faults, fractures in the Earth's crust 7. lithosphere above the dome collapses 8. lithosphere lateral to the dome is now free to move, pushed apart from rising magma
Precambrian
- first multicellular organisms evolved during the Edicaran period (635-542 mya) - Dickinsonia, Charniodiscus
The Hydrosphere
- freshwater (groundwater 0.77, glaciers 1.76) 2.56, saline water (oceans and saline groundwater 96.5 and lakes 0.94) - earth's water is stored in "compartments" such as oceans, atmosphere, rivers, streams, etc. - residence time: estimated average time that a drop of water spends in any compartment - only a small amount of water is "active" at any given time
Rocks you know: slate
- heavy, expensive, can last for a hundred years
Ocean-ocean convergence
- huge earthquakes, risk of tsunami, volcanic island chain - ex: the Japan trench - forms deep trenches - friction of descending, denser oceanic plate drags lighter oceanic plate downward (Mariana trench)
Historical geology present a whole different way of looking at science
- in geology - the experiment part is already done 1 - make observation about the end result of the experiment 2 - create hypothesis that finds the best agreement between observations
Enter Alfred Wegener: climatologist
- invented the use of weather balloons to monitor air circulation - fascinated by the poplar climate in Greenland Evidence #1 - Wegener - inspired by a scientific article describing Permian-age fossils of the same species found on both sides of the Atlantic, and Mesosaurus which was a fresh water aquatic reptile - found 4 different groups of fossils - prevailing hypotheses: - rafting: hitched a ride across the ocean - isthmian links - wee little land bridges connecting continents (known: the Bering straight) - island stepping stones: paths across the ocean during times of lower sea level - thought continents were once joined as a supercontinent - Pangaea Evidence #2 - unusual past climate condition - observation: Permian-age glacial deposits in equatorial Africa and the tropics - pointed out - warm, tropical coal swamps in N. hemisphere at that time - Pangaea had moved towards south pole - called it Kontinentalverschiebung continental beyond-boundary shoving (continental drift hypothesis) Evidence #4 Obvious fit between continents Biggest problem - couldn't explain the mechanism behind continental drift - his mechanistic theory: gravitational pull of the sun and moon over time is strong enough to pull the continental around the glove over time
Most common minerals: silicates
- quartz: harder than glass, difficult to break, varieties used in jewelry (i.e., amethyst) - Mohs' hardness scale - potassium feldspar, plagioclase feldspar: as hard as glass, difficult to break - calcite: softer, weaker than silicates, dissolves very slowly under acidic conditions, seashells, limestone and marble
Half-life: parent and daughter
- radioactive half-life: period of time over which the number of radioactive nuclei (parent material) decreases by one-half through decay into the daughter product. - half-life is a well-defined average
Absolute dating: using radioactive decay
- radioactivity emitted when an unstable nucleus falls apart - occurs on a regular basis, like a clock (an atomic clock!) - because this reaction is atomic, your population sample is astronomical in size - unstable isotopes decay according to the following chemical reaction: time parent element daughter element + energy - if you lose or add protons you become a different element - change in neutrons different mass
Earthquake is Haiti 2010: a human-caused catastrophe?
- recognized as an environmental catastrophe waiting to happen - four hurricanes and tropical storms hit before the earthquake - deforestation - 85 percent of people in the capital lived in slums - reason was clear: heavy human footprint - earthquake killed a quarter million people - two million homeless with poor sanitation
Understanding hazard risks can help people make better decisions - risk
- risk - (probability of event) x (consequences)
The Geosphere: Earth's surface
- rocks and minerals - landforms ex: Tetons, badlands, dinosaur national monument
Principle of original horizontality
- sediment from a fluid, such as water, deposits in flat layers as it drops out of suspension, due to gravity lithification of sediments forms flat layers of sedimentary rock - Jurassic-age sequence in Utah - carboniferous sandstone and shale in Utah - But sometimes we find sedimentary rock layers that AREN'T flat KNOWN: sedimentary frocks deposit in flat layers
Principle of lateral continuity
- sedimentary rocks deposit in flat layers.. that extend across the horizontal plane until their sediment runs out - layer ends by thinning at margin of sedimentary basic, lateral continuity allows us to infer that the layers were originally continuous across the canyon, layer ends by grading into a different kind of sediment (grand canyon example) - sedimentary rocks deposit in flat layers.. that extend across the horizontal plane until their sediment runs out - layer ends by thinning at margin of sedimentary basic, lateral continuity allows us to infer that the layers were originally continuous across the canyon, layer ends by grading into a different kind of sediment (grand canyon example)
Earthquakes provided an unprecedented peek inside
- seismic waves travel through earth's interior - rheological properties of the mantle diffract the paths of seismic waves, making them curve - shear waves cannot travel through the liquid outer core
Mancos Shale (Crescent Junction, Utah)
- shale is dark gray = soft, easy to erode (gentle slopes) - shale is made form smaller grain sizes (think mud), tightly packed low porosity - sandstone - more resistant to erosion (steeper slopes) - sandstone is made from coarser grain sizes (sand) more porous
Death and Damage causes by natural hazards
- some hazards are exacerbated by human influence - ex: earthquakes due to fracking - some hazards are beyond human influence - expansive soils causes over 15 billion in property damage every year
Linkages exist between natural hazards
- some natural hazards could possibly (but not always) causes others ex: hurricanes, flooding, flooding, landslides, earthquakes tsunamis, landslides, volcanic eruption, climate change, hurricanes - some hazards can be linked to earth materials certain rock types are prone to landslides, sinkholes, etc.
Major plates of the world: features to note
- some plates contain a mix of continental crust AND oceanic crust - some plates contain entirely oceanic crust Recall: continental crust has LOWER density, oceanic crust has HIGHER density
Why study natural hazards?
- they will always occur - effects may become more severe - to become a more scientifically literate individual - can help to save lives
Convergent (coming TOGETHER)
- two types: continental-continental, oceanic-oceanic (when density is unequal → subduction) denser plate goes underneath - when density is roughly equal → collision (continental-continental) - compressional regime - plates are being pushed together - hazard risk: powerful earthquakes, explosive volcanoes, tsunamis - destructive margin: crust is destroyed and re-assimilated into the asthenosphere - subduction - loads of energy stored and released, highest magnitude earthquakes, continental volcanic arcs form - subduction creates locked faults - locked fault: a fault that is not slipping because frictional resistance on the fault is greater than the shear stress across the fault - locked faults store strain for extended periods of time - eventually, shear stress will overcome and energy will be released in the form of an earthquake Earthquakes localize on a specific plane - Wadati-Benioff Zone → plot where the earthquakes occur - x-axis: map-distance from entrance to subduction zone - y-axis: depth below earth's surface → and you can trace the angle of subduction
Over time, folded layers erode to create an angular unconformity
- unconformity: a plane of mission depositional history - Siccar point, Scotland - Huttons unconformity - Devonian sandstone (370 million years old), Silurian mudstone (435 million years old) Put the layers of the famous grand canyon in order oldest to youngest: 1,2,4,3
65 million years ago an extinction event marks the end of the cretaceous period
- up to 75 percent of all plant and animal species disappear from the fossil record
252 million years ago an extinction event marks the end of the Permian period
- up to 96 percent of all marine species and up to 70 percent of all terrestrial vertebrates disappear from the fossil record. THE GREAT DYING Mesozoic Era - 248-65 ma - age of reptiles - at first, dry climate, courtesy of Pangaea
More evidence of plate motion - Hotspots
- volcanic chains NOT at a plate boundary - active volcanoes lead in a line of extinct volcanoes - ex: Hawaiian island, Yellowstone caldera - hot spot tracks are due to mantle plumes - hotspots leave snail-trails
Convection
- wax next to a heat source gets hot - temp rises, wax become less dense - rises through liquid - as wax moves away from the heat source it cools, temp decreases, wax becomes more dense - sinks through liquid - makes a convection cell - motion generates a current ex: a lava lamp - driven by intense heat from earth's interior
Material stress
- yield stress: the point beyond which deformation occurs - elastic deformation: recoverable - object returns to original shape (ex: a hair tie) rocks at earths surface (low temp, low pressure) - ductile deformation: permanent - stress applied over long time or at high temps, deforms (ex: gum) rocks in upper mantle - brittle deformation: permanent - stress applied very quickly to shatter of break object, breaks (ex: a cracker) rocks in the asthenosphere: allows earth to flatten slightly due to rotational forces (oblate spheroid); allows continents to float on top
Principle of cross-cutting relationships
- younger features cut across older features 1st: horizontal sedimentary strata deposited 2nd: igneous dike intrusion
Clicker: why is it so shallow?
-ex. Mariana arc, Kuril arc, Peru trench - subduction angle is controlled by 1. buoyancy of the descending slab - younger oceanic lithosphere is hotter and less dense (more buoyant) - older oceanic lithosphere is colder and more dense (less buoyant) 2. force (or resistance) by the asthenosphere - asthenosphere current and density - resisting descent of incoming plate? → shallow subduction angle
Place tectonic theory summary
1. lithosphere is broken into pieces → tectonic plates 2. Plates move relative to one another
Igneous
1) Igneous - (of fire): formed by crystallization of magma or lava ways to categorize: texture - extrusive igneous: crystallized quickly on earth's surface from cooled lava - formed from volcanism volcanic, smaller/fewer noticeable crystals in rocks ex: basalt, obsidian (forms as one big crystal; no visible crystals), pumice, scoria (made out of rock crystals) - intrusive igneous: crystallized slowly beneath earth's surface from magma - coarse grained, porphyritic (long time to cool, extremely coarse) - intrusive - formed at depth plutonic - more and bigger crystals in rock
Suggests a logical order:
1st: sediment was deposited in flat layers lithified into flat rocks 2nd: these flat rock layers were altered by crustal deformation