Presentation on theme: "Unit C: The Changing Earth"— Presentation transcript:
1Unit C: The Changing Earth Chapter 1: The Abyss of Time
21.1 The Long Beginning4 billion years ago the North American continent formedAlberta’s oldest rocks are dated 2 billion years old – the Precambrian Shield (the Canadian Shield) formed during the Precambrian Era (4.5 million years ago to 590 million years ago)reddish-coloured granite with multicoloured crystals formed at the collision site of 2 continental plates which welded togetherWhat is left of the original North American continent and makes up more than ½ of Canada’s land mass – most of Ontario, Quebec and northern CanadaIn other parts of Canada, exists deep underground and only is seen as one type of outcrop (a part of a rock formation that appears above the surface of the surrounding land) – mountain faces, canyon walls and cliffs
4Earth’s StructureSeparated into layers arranged according to their densitiesDensest material sinks to the centreLeast dense material floats on the surfaceLayers:Core: Solid inner core (radius 1220 km)Liquid outer core (2260 km thick)Mantle: Mesosphere (2550 km thick)Asthenosphere (approx. 250 km thick, varies)Lithosphere: Oceanic crust (4 – 7 km thick, dense)Continental crust (20 – 70 km thick)Lithosphere (75–125 km including crust,thicker beneath continents, thinner beneathoceanic ridges and rift valleys)A seismic tool is used to determine the thickness of each of the earth's internal shells.
5Structure of the Earth Core: densest layer, made of nickel and iron Outer Core - liquid, spins compared with the rest of the planet which produces Earth’s magnetic fieldInner core - solidMantle: solid layer between the crust and the core, 80% of Earth’s volume, extreme heat and pressure (plastic)Asthenosphere - solid rock but least rigid (soft) and flows easily (most plastic – magma rising in volcanoes). Mesosphere - rest of the mantle, more rigidThe plates that we talk about in plate tectonics are made up of the lithosphere and appear to float on the underlying asthenosphere.Lithosphere - very brittle, easily fractures at low temperature. Note that the lithosphere is comprised of both crust and part of the upper mantle.earth's structure
8Motion in the MantleTheories about Earth’s structure developed from indirect evidence (eg. earthquakes, volcanoes) as scientists are unable to make direct observations below the lithosphereEg. Nuclear decay deep within the core provides much of the heat energy needed to drive the plastic flow of material in the mantleFlow due to convection – hotter material rises to the surface, cools and sinksPushes and pulls on the Earth’s crust which causes it to crack, tear and move the various pieces (crustal plates)Move a few cm per yearMove apart to create new oceansSlide one over the other – forcing one plate into the mantle to be meltedLava lamp!
10Plate TectonicsThe process in which crustal plates are driven by convection currents or hot material from within the mantle
11Formation of the Atlantic Ocean This is an example of a divergent plate boundary (where the plates move away from each other). The Atlantic Ocean was created by this process. The mid-Atlantic Ridge is an area where new sea floor is being created.As the rift valley expands two continental plates have been constructed from the original one. The molten rock continues to push the crust apart creating new crust as it does.As the rift valley expands, water collects forming a sea. The Mid-Atlantic Ridge is now 2,000 metres above the adjacent sea floor, which is at a depth of about 6,000 metres below sea level.The sea floor continues to spread and the plates get bigger and bigger. This process can be seen all over the world and produces about 17 square km of new plate every year.
12Paleomagnetism Study of the magnetism of Earth’s rocks Magnetic poles of the Earth have reversed at least 80 timesMinerals in the rocks that form the oceanic crust become magnetized and lock into place when the crust hardens as the magma risesMagnetometers measure the magnetism of the rocks in the ocean floor and a striped pattern of “normal” and “reversed” magnetism parallel to an ocean ridge is observed – mirror image on each side of the ridgePaleomagnetism was one of the strongest pieces of evidence of the theory of plate tectonics
13Assignment:Timeline Activity of Significant Events in Earth’s HistoryQuestions #1 – 6, page 301(#1, 2, 5)
141.2 Early LifeSedimentary rocks are formed from compressed layers of pre-existing rock or organic matterContains different sediments and fossils preserved in each strata or layer – provides evidence about the type of environment that existed when the rock was formed (as much as 1.5 billion years ago eg. Cameron Falls in SW Albera)In Alberta, geologists suspect the sediment (sand, clay and silt) was deposited at the mouth of rivers flowing into an ancient oceanForms a layer of sedimentary rock 11 km thick
15Many Precambrian sedimentary rock formations have been found along the Rocky Mountains Evidence ofan ancientocean alongthe RockyMountains1.5 billionyears ago
16Life Gets Its StartOlder fossils found in other areas of the world show evidence of life dating back to 3.8 billion years agoPrevious life may have existed, but there is no fossil evidenceSo, scientists generally agree that the earliest life forms were single-celled bacteria 3.8 billion years ago
17Ancient Earth Hostile location Life possible under such conditions? Frequent volcanic eruptionsPoisonous gases (methane and hydrogen sulfide)Oceans were hot (>100ºC)Not much oxygen in the atmosphereLife possible under such conditions?Scientists recently discovered … Yes!Extreme bacteria-like organisms (Archaea) that live in extreme heat and live on poisonous gasesEg. Yellowstone National Park hot springs (boiling water)Eg. Deep-sea thermal vents (>150ºC, H2S from volcanic vents)
18Formation of OxygenThe area that drained into the ancient ocean was a large, shallow mud flat where cyanobacteria (microscopic, photosynthetic, single-celled bacteria) lived in the warm, shallow coastal waters of AlbertaFossil evidence shows stromatolite – layered structure built by cyanobacteriaDying cyanobacteria gradually build up layers of calcium carbonate which forms limestone in large mounds (stromatolites up to 1m tall)Examples of trace fossils – remains of evidence left by the organisms not the organisms themselvesKey role in making Earth livable for other organisms - Earth’s first photosynthetic organisms!Main life form on Earth for 2 billion years, long enough to have a major impact on the atmosphere and evolution of future life formsBanded iron (a type of sedimentary rock aged from 1.8 billion to 3.8 billion years) is a key piece of evidence of oxygen in the atmosphere as the red bands in the rock are rust – which requires oxygen to react with iron
19New Life Emerges“Snowball Earth” – late in the Precambrian Era, the most significant ice ageIce caps covered most of Earth for 10 million yearsOnly small pockets of the oceans did not freeze due to heat from the Earth’s mantleGlaciers advanced and retreated – evidence in rocks all over the world (eg. Alberta’s mountains)The stresses on organisms due to massive habitat change from the freeze and thaw is believed to have caused an explosion in species diversity … the first complex life formsFossil imprints shows that multicellular species were living along with the bacteria … the Paleozoic Era had begun
211.3 Strange RocksFossils were not, until recent times, believed to be the remains of living organismsNicolas Steno (17th century, physician) discovered shark’s teeth looked like “tonguestones” – rocks given this nameas they looked like dragon tonguesSteno suggested that these rocks wereactually remains of once-living sharkteeth but how can marine remains befound on land?
23Law of SuperpositionA method geologists use to keep track of the order in which rock layers formed – the higher the strata (layer) in a sequence of rock layers the younger the rockCan be used to determine the relative dating (correct chronological order compared to each other) of rocks in the stratigraphic sequenceExceptions occur when largebodies of magma force hotmolten rock into cracks inpre-existing sedimentary rock– an intrusion – which wouldbe younger than surroundingrockWhat would be the relativeages of each of the minerals inthe stratigraphic sequence?
24Rocks for DatesRelative dating does not give the absolute age of fossils or eventsEarly geologists used fossils and layers to rank strata in chronological order but there was no way to form a unified history of Earth’s crust for entire regions or the planetWilliam Smith (1769 – 1839) examined rock strata all over England as a surveyor for canal projectsHis observations led to his hypothesis that certain fossils kept reappearing in all locations and that these specific fossils always appeared in the same orderIf that fossil existed for a specific time, then any rocks containing that fossil must be from the same time periodThese key fossils which establish a common time for widely dispersed rock layers are called index fossilsSmith used these index fossils to make the first geological map of England (1815)
25Principle of superposition The principle of fossil successionThe most useful index fossil appears for a short time in the geological record, has a wide geographical distribution, and is easily recognizable.
26AssignmentUse the Law of Superposition and Index Fossils to complete the Investigation on Matching Rock Strata from Different Locations, page 311 in the textbook
27Geological Time ScaleIn the 19th century, geologists used index fossils to put together a generalized relative time scale for all of Earth using sequence pieces from all over the world – the Geological Time ScaleThe scale is divided into 4 major eras which are the largest unit of time separated by major geological or environmental changes. Shown by a massive disappearance of fossils and appearance of new fossilsPrecambrianPaleozoicMesozoicCenozoicEach era is divided into periods based on crustal changesSome periods are divided into epochs
29ErasPrecambrian (pre-life) – life begins, simplistic organismsPaleozoic (ancient life) –first fish, land plants, amphibians and reptilesMesozoic (age of reptiles) – first dinosaurs, mammals, birds,Cenezoic (age of mammals) – end of dinosaurs, mammals dominate, humans appearPeriodsEpochs (Cenezoic Era only)
33Assignment: Using a metaphor to represent the geologic time scale – some examples
34A football field and the geologic time scale: How many yard would represent the eras, periods, and epochs?
35AssignmentFormation of metamorphic and sedimentary rock lab (salt water taffy)Questions #1 – 10, page 313
361.4 Getting a Handle on Time Catastrophic theories dominated geological ideas for over 100 yearsViolent catastrophes such as earthquakes, volcanic eruptions, enormous floods, meteorite impacts, and upheavals of Earth’s crust to be the main causes of changeThe processes we see at work in the present seem too weak and slow to be responsible for dramatic change in Earth’s past
37UniformitarianismJames Hutton (1726 – 1797), geologist, believed that you must understand the processes at work in the present to unlock the mysteries of the past (not catastrophist theorist)Start of uniformitarianism and the birth ofmodern geologyUsed law of superposition and applied it torock strataVertical and horizontal layers observedVertical layers deposited first horizontally but werethen tiltedHorizontal layers deposited after a period of erosionTop surface of the lower vertical layers is called anunconformity (a surface in a rock sequence thatrepresents a break in the pattern due to erosion ora lack of deposition)
40Self-Sustaining System Hutton stated that the geological process of Earth operates as a self-sustained systemHeat deep within Earth provides a constant source of energy that creates and destroys material from the crustStarted the modern understanding of how rocks form – the rock cycle:molten magma in mantle → igneous rock on / near surface → surface rock weathered / eroded → sediments → deposited to form sedimentary rock → extreme heat / pressure to form metamorphic rock →all rocks melt and return to mantleBalanced cycle driven by energy released by nuclear reactions in Earth’s corerock cycle
42The Rise of Uniformitarianism Hutton’s theories did not catch on until Charles Lyell (1797 – 1875) added more evidence and made the theory easier to understandLyell argued that processes such as:ErosionSediment depositionVolcanic actionEarthquakeshave all operated in the same way and strengththroughout Earth’s history
43AssignmentRead pages 19 & 20 to help answer pages 21 & 22 in the workbookQuestions #1 – 4, 6, 8 on page 318
441.5 Pinpointing TimeWith the rise of uniformitarianism, relative dating was being replaced with the idea of absolute datingExact age of an object or event (example – your birthdate!)A reliable method to measure the absolute ages of rock or the Earth itself was neededUsed the idea of radioactivity (emission of energy from the nuclei of unstable atoms as they change to become more stable atoms) developed by Marie CurieErnest Rutherford added the concept of radioactive decay and measureable half-lives
45Radioactive isotopes are used to determine exact ages Absolute DatingRadioactive isotopes are used to determine exact agesA chem review of isotopes: yay!Isotopes are elements that have the same atomic number (# p+ and e-) but different atomic masses (n 0 vary). Recall that the mass of an atom is due to the p+ and n 0Example carbon-13 , carbon-14, carbon-15 are 3 isotopes for CIf isotopes are unstable (too few/many neutrons) they naturally break down --- radioactive --- by changing into atoms of other kindsRadioactive isotopes (aka radioisotopes) gain stability when they spontaneously decay into stable, non-radioactive elementsRadioisotopes decay at a constant rate in whichradiation is given off --- known asradioactive decay.
46Radioisotopes can be used to estimate the age of rocks and archeological artifacts. Within a rock sample that we want to determine the absolute age of (or fossil within the rock sample), if we know how much of the radioisotope elements within the rock has decayed, and we know the time period for the half-life, then we can determine the absolute age of the rockWhat is a Half-life?A half-life is the time required for half of an element's atoms (parent material) in a sample to change to the decay product (daughter material)In each half-life only half of the remaining radioactive atoms decay, no matter how large the sample isHalf-lives vary from fractions of seconds to millions of years, giving each radioisotope specific applications in dating
48Lets Review half- life: 1st half life 2nd half life 3rd half life Look at the diagram below which represents the radioactive decay of uranium-238. The shaded area represents the decay product which is lead-206. The half-life of uranuim-238 is 4.5 billion years, since this object has gone through two half-lives it is 9 billion years old.Lets Review half- life:1st half life2nd half life3rd half life4th half life½ parent¼ parent1/8 parent1/16 parent½ daughter¾ daughter7/8 daughter15/16 daughter
49Radioactive Decay Calculations: If we know the ratio of parent to daughter material, we can calculate the number of half-lives elapsedFrom this info, the age of the sample can be calculated from the known length of the half-life of the radioisotopeRemember this chart and draw the graph!# of Half-livesO1234% Parent100502512.56.25% Daughter7587.593.75
50Daughter Isotope (decay product) Examples:Parent IsotopeHalf Life (yrs)Daughter Isotope (decay product)Carbon-145730Nitrogen-14What % of carbon-14 would be left after 3 half-lives?A rock sample weighs 250 g. If it undergoes 2 half-lives of time, what mass of carbon will it contain?
51Application of Radiometric Dating World’s oldest rocks – zircons containing uranium found embedded in other rocksSome of the oldest zircons are found in Canada’s Acasta Gneiss Rock Formation in the Northwest Territories – formed 4 billion years agoDating organic remains is radiocarbon dating – uses carbon-14When an animal dies, the carbon-14 clock is set at zero and the age of the remains can be determined by measuring the amount of carbon-14 remainingradiosotope dating
52AssignmentHalf Life Lab, pages 17 & 18 in the workbookCalculation questions on pages 15 & 16 in the workbookPages 21 and 22.Chapter 1 Review: pages
53Chapter 2: A Tropical Alberta The Geology ofAlberta in thePaleozoicandMesozoic Eras
542.1 FossilizationThe process by which any trace of the existence of ancient life is preserved within rockProcess: life → death → burial → preservation→ discovery → recoveryFossils often form in two parts:The actual fossil is on one part of the rockThe impression is on the other piece of rockLike a finger and its fingerprint!Sometimes no remains of an actual organism but only evidence of their presence – trace fossils (eg. Stromatolites from Chapter 1)Fossils most often found in sedimentary rock as remains are usually buried in layers of sedimentCan also form in volcanic lava as the lava can flow so quickly that it creates on impression of the object eg. A treeFossil Formation
55Fossilization of Hard and Soft Remains First step is burying of the organism before it completely decomposesHard parts (shells, teeth) found unchanged in the rockIf the original material is replaced by a mineral (eg. Silica) the fossil is then petrifiedSometimes, with the right conditions and enough time, even hard parts can dissolve leaving a space behind called a mould – can show a great deal of detailSoft tissue (leaves, skin) are fossilized through:The complete replacement of the organic material, leaving behind an impressionPreservation as a thin film of carbon
56The Burgess ShaleA Cambrian-age rock unit found on the side of Mount Wapta (80 km west of Banff) in the Canadian Rockie known for its well-preserved fossilsConsidered the most important source of Cambrian fossils on Earth so has been declared a World Heritage Site by the United NationsEvidence that 500million years ago theorganisms fossilizedin the shale wereliving in a shallowarea close to theshore of a tropicalsea
57Alberta’s Tropical Sea For millions of years, Alberta was located close to the equator and was repeatedly submerged and lifted above the ocean’s surfaceFor millions of years after the Paleozoic Era, most of Alberta was above the ocean’s surfaceDuring the Cambrian Period, life only existed in water (no plants or animals were on land)Previously formed Precambrian rock was eroded and sediments washed downriver to the ocean on Alberta’s shoreline eventually transformed into the sandstones and shales that form the Rocky MountainsThe Burgess Shale contains fossils showing a complete marine ecosystemThese animals were all buried within layers of mud fossilizing the hard body parts and the soft body parts – not normal but because the mud was so fine and avalanched into deep waters with limited oxygen, decay was limited leading to detailed preservation (eg. Gills)
58The Cambrian Explosion Cambrian rocks dating from 545 to 525 million years ago detail all the basic designs / body plans for animals that have ever lived on EarthPreviously, fossils show only soft-bodied organisms (eg. worms) but the Cambrian Period shows a huge variety of animals with hard body parts developed during a short time period (20 million years) – rapid diversification referred to as an explosionWhy did this happen? Scientists suggest that the atmospheric oxygen levels reached a high enough concentration to support the metabolic requirements of these animals
59AssignmentRead page 10 in the workbookAnswer the questions on pages 11 and 12 in the workbook
602.2 A Billion-Dollar ReefAlberta’s first oil field (Leduc) discovered in 1947 changed the economy from farm-based to petroleum-basedWhere did all of Alberta’s petroleum come from? How was it formed? Why in Alberta and not elsewhere?Answers found in the clue’s about Alberta’s ancient past left in the fossil record
61Wealth from Ancient Seas Ancient Timeline of the Paleozoic Era:Cambrian Period: life on Earth was aquaticOrdovician Period: life moving onto land then most of Alberta became submerged at the bottom of a tropical seaNext 200 million years: sea levels rose and fell – while submerged, Alberta was home to sponges that secreted a calcium carbonate skeleton that formed huge underwater reefsSilurian Period: reefs grew larger, land plants and animals colonized parts of Earth not underwaterDevonian Period: maximum reef coverage, microscopic reef organisms (eg. Plankton) living and dying in the reefs covering most of Alberta for millions of years creating a thick layer of organic material. This became a food source for bacteria which removed most of the oxygen and nitrogen leaving behind mostly carbon and hydrogen – main ingredients of petroleum.
62Next 380 million years: layer of organic material exposed to heat and pressure converting it into liquid hydrocarbons. The pressure from sediment layers deposited above that converted into rock forced the liquid into porous rock – fossilized remains of the ancient reefs. The rocks layers above and below the reservoir of petroleum was impermeable shale forming a petroleum trap.
63Finding the WealthIn the past, geologists found petroleum by looking for evidence on Earth’s surfaceNewer methods were used to find the petroleum trap where Leduc #1was located:Drill-coredataSeismic
64Finding Oil Drill-core samples: Drill a well and examine the core sample (a cylindrical sample of subsurface rock)Geologists examine the sample to identify the type of rock below the surface for fossils for information on:Age of the rocksEnvironmental conditionsEnables drilling into ancient reefs instead of rocks that formed in the deep water away from a reefYears of collecting and analyzing drill-core samples have produced a detailed picture of Alberta’s subsurface rock
65Finding Oil Seismic data: Seismology = the study of how waves of energy (seismic waves) move through Earth as a result of explosions or earthquakesRather than waiting for an earthquake to occur, scientists use:Explosives placed in a hole orStrike the ground with a massive plate attached to a truck – vibrating plate uses a force of more than N.Waves travel through the ground and some of the energy reflects off of each boundary between rock layers – recorded by geophones on the surface which convert the waves into electronic signals
66Signals processed by a seismograph which provides an information summary or seismogram Generates possible trap locations but drilling must be done to be sure if oil or gas is present in the traps
67AssignmentAnswer questions #2 and 3on page 342 of the textbook
69What are Earthquakes?Earthquakes are the shaking of the Earth’s surface caused by rapid movement of the Earth’s rocky outer layer.Earthquakes occur when energy stored within the Earth, usually in the form of strain in rocks, suddenly releases.Most earthquakes occur along plate boundariesEarthquakes, or seismic tremors, occur at a rate of several hundred per day around the worldIn the last 500 years, several million people have been killed by earthquakes around the world especially in third world nationsSeismology is a branch of geology that studies earthquakes and other movements in the Earth’s crust
70Anatomy of an Earthquake The point within the Earth along the rupturing geological fault where an earthquake originates is called the focus, or hypocenter.The point on the Earth’s surface directly above the focus is called the epicentreThe vibrations caused by seismic waves moving through the ground are strongest at the epicentreNote: seismic waves move through the Earth by passing Ek from one particle to the next (eg. breaking a stick)earthquakes
71Where do Earthquakes occur? Seismologists examine the parts of an earthquake, such as what happens to the Earth’s surface during an earthquake, how the energy of an earthquake moves from inside the Earth to the surface, how this energy causes damage, and the slip of the fault that causes the earthquakeMost Earthquakes occur at Faults, which are cracks in Earth’s crust where rocks on either side of the crack have movedMost faults occur at Plate BoundariesThe properties of an earthquake depend strongly on the type of fault slip, or movement along the fault, that causes the earthquakeThere are 3 main types of faults; normal, reverse, and strike-slip faults. Normal and Reverse involve the ground on either side moving in a up-down directionStrike-slip faults produce horizontal displacements, or the side by side sliding movement of the fault, such as seen along the San Andreas fault in California. Strike-slip faults are usually found along boundaries between two plates that are sliding past each other.
73There are two main types of waves: Earthquakes and WavesRecall that the sudden movement of rocks along a fault causes vibrations that transmit energy through the Earth in the form of wavesThere are two main types of waves:Longitudinal waves – when particles of matter vibrate parallel to the direction of the wave propagation, or in the same direction in which the wave is movingTransverse waves – particles of matter vibrate perpendicular to the direction of the wave propagation
75Waves that travel in the rocks below the surface of the Earth are called body waves - there are two types of body waves: primary (or P-waves) and secondary (or S-waves)P-waves (primary waves) – Longitudinal wave, also referred to as a compression wave. Responsible for the back and forth motion of an Earthquake. Fastest moving wave.S-waves (secondary waves) – transverse wave, also referred to as a shear wave. Slower moving wave (greater amplitude) and therefore arrives after the primary wave. Responsible for the up and down motion of an EarthquakeL- Waves (long waves) – occur on the Earth’s surface and are both transverse and longitudinal waves. It is the longitudinal L-waves that do the most damage. L-waves are slower moving than the body waves and take the longest to pass over Earth.
78Seismic energy can be transmitted as different waves: P - pressure or primary wavesS - shear or swing wavesP-waves vibrate in the same direction as the wave travels. They are sometimes called primary waves because they travel fast and arrive at the recording station before S-waves. They can be transmitted through both liquids and solids.S-waves, sometimes called shear waves, vibrate perpendicular to the direction of travel. They do not transmit through fluids.Particle movement in P and S-waves.
79Measuring Earthquakes Earthquakes are measured at Seismic stations with a device called a seismographA seismogram is produced and analyzed
80Determining the Magnitude of an Earthquake The Richter Scale is used to measure the magnitude of an EarthquakeThe Richter scale ranks earthquakes based on how much the ground shakes 100 km (60 mi) from the earthquake’s epicentreThe scale ranges from 1-9 (open ended) with each point on the scale representing 10X increase in motion over the previous pointEarthquakes of magnitude 5 are considered moderate, 6 are considered large, 7 are considered major, and quakes of magnitude 8 or larger are considered great. Although there is no upper limit to the Richter scale, earthquakes of magnitude 8 or greater are rare. Worldwide, they occur only about once a yearEach point represents a 30 X increase in energy over the previous point
81Locating the Epicentre of an Earthquake Seismologists can locate the epicenter of an earthquake by triangulation, a method that involves taking measurements from at least three separate seismic stationsSeismologists measure the time it takes seismic waves to reach the recording stations, as well as the magnitude of the waves, and triangulate the measurements to calculate the location of the epicenter
83Seismic Data and the Earth’s Interior Earthquakes provide a rare opportunity for scientists to observe how the Earth’s interior responds when an earthquake wave passes through it.Scientists used waves generated by earthquakes to determine that the outer core of the earth is liquid.Shadows occur on the opposite side of the earth from the earthquake epicenter because the outer core reflects S-waves and bends P-waves.S-waves are reflected because they cannot travel through liquidsGeologists and seismologists determined the size of the outer core by using the 154-degree arc of the S-wave shadow and measurements taken on the surface of the earth.Earth’s Interior and Waves
85TsunamisSecond-largest recorded earthquake ever recorded by a seismograph - the Alaska Earthquake of 1964 was caused by the subduction of the Pacific Plate under the North American Plate (Richter magnitude of 9.2)Most of the damage and loss of life was due to a seismic sea wave (tsunami)The strongest earthquake (9.0) since the Alaska Earthquake occurred on December 26, 2004 in the Indian Ocean. A massive tsunami caused the most damage as it hit densely populated areas in South Asia and East Africa ~ people were killed and entire towns were wiped outtsunamitsunamis
86AssignmentRead page 27 in the workbookAnswer questions on pages 28 and 29 in the workbook
872.4 Raising the RockiesThe raising of the Rocky Mountains (170 million years ago) and the Alaska Earthquake of 1964 were caused by the same mechanisms – plate tectonicsThe boundaries of Earth’s tectonic plates can be found by:Plotting the locations of earthquakes – usually occur along the boundaries of crustal platesPlotting volcano locations – also usually occur at the edges of crustal plates
88VolcanoesThe Earth’s crust is made up of many rigid plates that move over the asthenosphere (zone of partially molten rock) which is the source of magma for volcanoesVolcanoes will occur where:Two plates move apartOne plate is being pushed under anotherVolcanism at a faultIsland formationVolcano Brain Pop
89Evidence of Plate Tectonics Brain Pop! Paleomagnetism (from Chapter 1)Location of earthquakesLocation of volcanoesPangaea – a single gigantic continent formed from Earth’s land masses at the end of the Paleozoic EraNamed by Alfred Wegener (1915) as part of his theory of continental drift (theory that lead to the theory of plate tectonics)
90Continental Drift theory History of plate movement:Devonian Period (400 million years ago):Greenland & eastern Canada collide (forms mountain chains) with northern Europe to form a northern land massAfrica, India, Australia and South America joined as a southern land massTwo large land masses continue to move towards each otherAs the land masses move during the next two Periods, fossils show species diversification on both land and sea:More plant life develops – raw material for future coal bedsPlants create an environment for insects and first vertebrates to live on landEarly amphibians and reptiles develop (ancestors of future dinosaurs, birds and mammals)End of the Permian Period, two large land masses (northern and southern) form Pangaea at the same time that the greatest extinction of life takes place
91Permian ExtinctionThe fossil record shows evidence of six mass extinctions with the largest occurring 250 million years ago at the end of the Paleozoic Era90% of ocean species wiped out70% of land species became extinctWhy did this happen?! Don’t know for sure, but scientistsare working on some theories.
92Extinction Theories Widespread glaciation Sea level drops, shallow water around land gone, lower average global temperatureFormation of PangaeaLand masses colliding would reduce shallow seas between them and coastline areas increasing competition in native organismsNot the most likely explanation as Pangaea formed at the beginning of the Permian Period and the extinction occurred at the end of the Period
93Extinction Theories (con’t) Asteroid colliding with EarthSimilar to the aftermath of a nuclear war – massive firestorms, dust in the atmosphere blocking out the sun for monthsMore evidence shows this is the reason for another mass extinction at the end of the Cretaceous PeriodMassive volcanic activityEvidence shows that in Siberia massive lava flows covered 1000s of km to a depth of +3000mDrop in the average global temperature due to ash ejected into the atmosphere blocking sunlight – this effect (though less severe!) is seen with modern volcanic activityeg. Eruption of Mount Pinatubo (Philippines) caused a 0.5ºC drop in world temperature
94The Plates Keep Moving… Mesozoic Era:Triassic Period:North American plate movement causes Alberta to be repeatedly dropped below sea levelThe ocean retreats and forests develop which support the first mammals and later form coal depositsEnd of the Period: the start of the breakup of PangaeaSea levels rise, submerging North America againThis and a possible meteorite collision cause another mass extinction leaving room in the food chain for the dinosaurs to take over – the beginning of the Jurassic PeriodJurassic PeriodNorth American Plate drifts west and collided with arcs of volcanic islands on the Pacific Plate producing the mountain areas of British Columbia and AlbertaThe mountains are the evidence of several processes taking place: raising ocean beds, welding island arcs, flowing magma from volcanic activity
96End of the Mesozoic Era: Cretaceous Period: The weight of the mountains forming caused Earth’s crust to sag and ocean water rushed in creating a network of swamps, seas and forests that was home to many dinosaursWhen another plate collision event occurred, the inland sea was lifted up and drained and the mountains were pushed up even higherFaults moved slabs of rock more that 100 km and in some places stacked older rocks on top of younger rocks – you can see these folded rock layers in the mountains around Jasper and BanffAtlantic Ocean starts to form as the continents move further apart toward their modern positionsEnd of the Cretaceous Period marked by another mass extinctionNearly every land animal with a mass over 25 kg goneIn oceans, extinction of half of the plankton varieties causing the collapse of many oceanic food chains
98Chapter 3: Changing Climates Cenozoic Era on Earth
993.1 The Great CoolingCenozoic Era (65 million years to the present) is the last of the eras. Divided into two periods:Tertiary Period – 65 million years ago to 1.7 mya97% of the eraQuaternary Period – 1.7 mya to the present
100Rising MountainsThe collision of tectonic plates at the beginning of the era produced a rapid period of mountain building (ended about 50 million years ago) giving us the Rocky MountainsThe mountains were round-looking covered by V-shaped valleys cut out by erosionThe continued movement of plates also caused North America to migrate northwards resulting in a cooler climateEventually it got cold enough to form glaciers which would carve out the “rocky” and jagged features of the Rocky Mountains we see today
101Retreating SeaAlberta covered by the Bearspaw Sea until the beginning of the Cenozoic Era when it retreated SW dumping sediment on most of southern AlbertaThis sedimentary formation is rich with dinosaur fossils and other fossilsMore sedimentary rock formed from the run off from the rising Rocky Mountain Range which dumped sediment into the foothills area
102Cenozoic sedimentary rock outcrops are evidence of rivers pouring sediment from the Rocky Mountains.
103Not So TropicalThe cooling trend that was one of the factors that led to the Cretaceous Extinction continued into the Cenozoic Era causing a significant drop in average global temperaturesDrastic change in plant life: Tropical rain forests changed to temperate evergreen forests with rivers, lakes and swampsAnimals present included herds of horses, camels, and elephant-like mastodons, crocodiles, rhinoceroses and other, smaller mammalsThis fossil evidence shows the temperature was cooler but still warmer than it is today
104Rise of the MammalsMammals that survived the Cretaceous Extinction (mainly small rodents) took over the territory left vacant by the extinction of the dinosaursBy 40 mya, many new formsof mammals appear in thefossil record – ancestors of:Modern hooved herbivoresFlesh-eating carnivoresLarge-brained primates
105Grasses Take Over Alberta A gradual change from wetlands to woodlands to grasslands occurs as the climate became cooler and drierThe dominance of grasses allowed the spread of large herds of grazing species in the late Tertiary PeriodThe resistance of grasses to grazing was a distinct advantage over other plantsOther plants grow from the tip which gets eaten by grazersGrasses grow from the base so they can continue to grow after the tips are eaten
106Evidence for a Cooling Trend Tertiary Period saw an overall cooling trend as show by evidence in sedimentary rocks:Presence of tropical plant and animal life in current-day polar regions show these places must have been a lot warmer in the pastAbsence of tree pollen from current tropical landscapes shows the past climate of these areas must have been too cold for trees to survive
1083.2 The Icy EpochBy the end of the Tertiary Period the climate was so cold that snow began to accumulate year after year in polar regions (1.7 million years ago to years ago)The weight of these layers of snow caused lower layers to become compacted into ice, the beginning of the formation of glaciers (large rivers of ice that form on land and move under the influence of gravity)
109Earth’s GlaciersDuring the Pleistocene Epoch, ice sheets reached critical mass as they flowed outward toward the equatorToday, the largest glaciers are found in the polar regions – the Greenland and Antarctic continental ice sheetsIce accumulates at their centres to depths of over 2 km and then flows outwards to the sea where chunks break off and float away as icebergs (calving)Mountain glaciers are remnants of larger glaciers left over from the Pleistocene Epoch
110What is an Ice Age?Technically, an ice age is a period during which ice sheets cover parts of the Northern and Southern HemispheresThis means Earth is in an ice age right now!! (ice sheets in Antarctic and Greenland)A Glaciation is a period during which polar ice sheets advance to cover large regions of North America and northern EuropeIt is believed that there were four major glaciations during the Pleistocene Epoch
111Wisconsin GlaciationName of the last glaciation ( years ago) as the ice advanced as far south as Wisconsin, USALargest ice sheet – Laurentide Ice Sheet which fully receded years ago to mark the beginning of the Holocene Epoch
112Big Kid on the BlockDuring the Pleistocene Epoch, large mammals had the advantageFossil evidence shows the existence of:Mammoths, modern horses, llamas, reindeer, camels and scavenger dogsPredators such as Americanlions, short-faced bears,sabre-toothed cats, andbirds (8m wingspan)stalked herds ofgrazing mammals
113Glacial FootprintsAlberta’s topography was shaped by the Wisconsin Glaciation. As continental ice sheets advance and retreat, they leave behind characteristic landforms such as:Drumlins (teardrop-shaped hills)Sand dunes (glacial lake sediment)Glacial till (rocks and debris left as the glacier retreats)Moraines (ridge of earth, stones, etc. carried and deposited along the edges of the glacier)Cirques (circular valley with precipitous walls)Kettles (lakes that form in depressions)
116Shaping the RockiesCalled the Rocky Mountains due to their jagged shape developed during the Pleistocene Epoch when the mountains were covered with glaciersStill areas of glaciers today (winter snowfall exceeds summer melting)Gravity causes the accumulating snow to compact to become ice which then flows down the mountain and into valleysAs the glacier flows, it scrapes and gouges the terrain changing the appearance of the mountainAt lower elevations, the leading edge of the glacier melts in summer heat and the meltwater runs into streams and on to rivers – most tap water is glacier meltwater!
117AssignmentIn your workbook, read and complete the questions on pages
1183.3 Explaining/Predicting Climate Change Weather: the state of the atmosphere in terms of variables such as temperature, cloud cover, precipitation and humidity for a particular place at a particular timeClimate: the average of daily and seasonal weather events that occur in a region over a long period of timeJust as it is difficult to predict the weather, predicting changes in Earth’s climate is even more challenging!
119Holocene Epoch (current Epoch) Began years ago with the great melt that followed the last glaciationPeople were in North America (oldest archaeological evidence of humans in North America are stone tools dating from years ago)Laurentide Ice Sheet receded:an ice-free corridor opened upallowing the early northern residentsa passage southProduced a lot of water which filledglacial lakes such asLake Edmonton (150 km long)
120Changing Climate During the Holocene A repeating pattern exists of a warming trend following a glaciation – Alberta should experience the next glaciation within the next yearsThis pattern has repeated all the way back to Snowball Earth in the Precambrian Era as shown by the global climate record
121Average Global Temperature Evidence from rock strata shows that Earth has mostly been warmer than todayIn warmer times, unlikely that the continental ice sheets stayed frozenBut the hot climate was broken up by several long cold periods lasting millions of years – Earth is experiencing one of these major cold periods now
122Climate ModelsSupercomputers are used to create mathematical models that attempt to describe Earth’s climateStudying links between the amount of solar radiation reaching the planet and each layer of Earth: atmosphere, lithosphere and hydrosphereNumerous links and intricate interactions have, so far, stumped the supercomputers from coming up with accurate models
123Possible Causes of Glaciation Periods Most likely a combination of the following effects:Continents moving north (plate tectonics)Ocean as a heat pumpVolcanic activityWobbly EarthVariation in the Sun’s Energy OutputEnhanced Greenhouse Effect
124Continents Moving North The timing of long periods of repeated glaciations seems to be randomCould be due to the random nature of plate tectonicsWhen Earth’s tectonic plates are near the poles glaciations can occurContinental ice sheets must form on land so as snow and ice accumulate, the white ice sheet reflects most of the solar energy hitting it back into spaceOverall cooling effect on the planet making it easier for more ice to form
125Ocean as a Heat PumpEarth’s oceans have giant convection currents that act as a global conveyor:Circulates warm water away from the tropicsRecirculates cold water of the polar regions
126Ocean as a Heat Pump Heats some areas and cools others: Heat from the tropics is brought up to the north Atlantic and released to Europe by winds (why Europe is warmer than Canada!)In Antarctica, a circling oceancurrent prevents warm tropicalwaters from enteringThis could explain thePleistocene Epoch cold periodas Australia separated fromAntarctica allowing the circlingcurrent and the Antarctic IceSheet to form
127Old volcanic activity may have contributed to long-term climate change Volcanoes were a major reason for the extinction of many species in the Permian Period, but they can also add to short-term fluctuations in climateEg. Temporary cooling effectcaused by the 1991eruption of MountPinatubo (Philippines)
128Wobbly EarthRepeated glaciations appear to match changes in Earth’s orbit around the Sun and Earth’s rotation on its axisThe Milankovitch Theory states that Earth’s orbit varies in 3 ways:The shape of the orbit (eccentricity)The tilt of the axis of rotationThe wobble of the axis of rotationAll of these affect the amount of solar radiation reaching Earth’s polar regionsNot believed to be the cause of the cold periods but instead control the timing of the glaciations
129Sunlight Variation The sun doesn’t always shine so bright! The changes in the intensity of solar radiation appear to follow a regular pattern determined by the frequency of sunspotsMore sunspots: additional energy released by the Sun but minor impact on climate change (0.1 to 0.2% increase only)Less sunspots: Maunder Minimum (1645 – 1715)corresponds with an unusual cold period in the Little Ice Age in EuropeMore recent theories relate the changes in the north Atlantic Ocean’s circulation current, not sunspots
130Greenhouse EffectIn Earth’s atmosphere, gases such as carbon dioxide and methane trap heat near Earth’s surface – natural insulating effect (it’s a good thing!)CO2 levels can fluctuate greatly due to:Natural events – volcanic activity or weathering of carbonate rocksCorrelates with changes in the average global temperature over the last yearsCO2 changes with other factors (Milankovitch Cycles, global ocean circulation) may have increased the effect on the atmosphere’s temperature
131Enhanced Greenhouse Effect Not so natural changes to CO2 levels also occur:Exponential increase since the Industrial RevolutionLargest human-caused source of CO2 is the burning of fossil fuelsScientists believe this increase is enhancing Earth’s natural greenhouse effect leading to significant increases in the average global temperature during the last centuryIn Alberta, we contribute more than the global/person average share of emissions (fossil fuel energy sources, low efficiency)
133How Nature Records Climate Change Two key methods are used by scientists to track Earth’s average temperature:Ice-core dataDeep-ocean sediment dataOther methods are used to provide further information:Geological evidence (eg. volcanic activity)Archaeological evidence (human populations)Fossil evidence (flora, fauna and environment)
135Can the warming cause cooling? Current models of climate change predict that global warming could end up causing a drastic cooling!As the Earth warms:Mountain glaciers and continental ice sheets meltRelease fresh water into the North Atlantic OceanIf enough fresh water is released (if the temperature gets high enough), it will slow down warming tropical currents resulting in less heat being pumped to the poles from the tropicsRapid cooling effect allows ice sheets to advance in the north and it gets even colder!!
136Assignment Textbook page 387 complete the chart in question #12 Chapter 3 ReviewGeology Unit ReviewGeomorphology applet, fill in #1 on page 395