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Unit C: The Changing Earth Chapter 1: The Abyss of Time
1.1 The Long Beginning 4 billion years ago the North American continent formed Alberta’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 together What 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 Canada In 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
Earth’s Structure Separated into layers arranged according to their densities Densest material sinks to the centre Least dense material floats on the surface Layers: 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 beneath oceanic ridges and rift valleys) A seismic tool is used to determine the thickness of each of the earth's internal shells.
Structure 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 field Inner core - solid Mantle: 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 rigid The 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
Motion in the Mantle Theories about Earth’s structure developed from indirect evidence (eg. earthquakes, volcanoes) as scientists are unable to make direct observations below the lithosphere Eg. Nuclear decay deep within the core provides much of the heat energy needed to drive the plastic flow of material in the mantle Flow due to convection – hotter material rises to the surface, cools and sinks Pushes 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 year Move apart to create new oceans Slide one over the other – forcing one plate into the mantle to be melted Lava lamp!
Plate Tectonics The process in which crustal plates are driven by convection currents or hot material from within the mantle
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. Formation of the Atlantic Ocean
Paleomagnetism Study of the magnetism of Earth’s rocks Magnetic poles of the Earth have reversed at least 80 times Minerals in the rocks that form the oceanic crust become magnetized and lock into place when the crust hardens as the magma rises Magnetometers 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 ridge Paleomagnetism was one of the strongest pieces of evidence of the theory of plate tectonics
Assignment: Timeline Activity of Significant Events in Earth’s History Questions #1 – 6, page 301 (#1, 2, 5)
1.2 Early Life Sedimentary rocks are formed from compressed layers of pre-existing rock or organic matter Contains 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 ocean Forms a layer of sedimentary rock 11 km thick
Many Precambrian sedimentary rock formations have been found along the Rocky Mountains Evidence of an ancient ocean along the Rocky Mountains 1.5 billion years ago
Life Gets Its Start Older fossils found in other areas of the world show evidence of life dating back to 3.8 billion years ago Previous life may have existed, but there is no fossil evidence So, scientists generally agree that the earliest life forms were single-celled bacteria 3.8 billion years ago
Ancient Earth Hostile location Frequent volcanic eruptions Poisonous gases (methane and hydrogen sulfide) Oceans were hot (>100ºC) Not much oxygen in the atmosphere Life possible under such conditions? Scientists recently discovered … Yes! Extreme bacteria-like organisms (Archaea) that live in extreme heat and live on poisonous gases Eg. Yellowstone National Park hot springs (boiling water) Eg. Deep-sea thermal vents (>150ºC, H 2 S from volcanic vents)
Formation of Oxygen The 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 Alberta Fossil evidence shows stromatolite – layered structure built by cyanobacteria Dying 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 themselves Key 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 forms Banded 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
New Life Emerges “Snowball Earth” – late in the Precambrian Era, the most significant ice age Ice caps covered most of Earth for 10 million years Only small pockets of the oceans did not freeze due to heat from the Earth’s mantle Glaciers 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 forms Fossil imprints shows that multicellular species were living along with the bacteria … the Paleozoic Era had begun
1.3 Strange Rocks Fossils were not, until recent times, believed to be the remains of living organisms Nicolas Steno (17 th century, physician) discovered shark’s teeth looked like “tonguestones” – rocks given this name as they looked like dragon tongues Steno suggested that these rocks were actually remains of once-living shark teeth but how can marine remains be found on land?
Law of Superposition A 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 rock Can be used to determine the relative dating (correct chronological order compared to each other) of rocks in the stratigraphic sequence Exceptions occur when large bodies of magma force hot molten rock into cracks in pre-existing sedimentary rock – an intrusion – which would be younger than surrounding rock What would be the relative ages of each of the minerals in the stratigraphic sequence?
Rocks for Dates Relative dating does not give the absolute age of fossils or events Early 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 planet William Smith (1769 – 1839) examined rock strata all over England as a surveyor for canal projects His observations led to his hypothesis that certain fossils kept reappearing in all locations and that these specific fossils always appeared in the same order If that fossil existed for a specific time, then any rocks containing that fossil must be from the same time period These key fossils which establish a common time for widely dispersed rock layers are called index fossils Smith used these index fossils to make the first geological map of England (1815)
Principle of superposition The principle of fossil succession The most useful index fossil appears for a short time in the geological record, has a wide geographical distribution, and is easily recognizable.
Assignment Use the Law of Superposition and Index Fossils to complete the Investigation on Matching Rock Strata from Different Locations, page 311 in the textbook
Geological Time Scale In the 19 th 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 Scale The 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 fossils Precambrian Paleozoic Mesozoic Cenozoic Each era is divided into periods based on crustal changes Some periods are divided into epochs
geological time scale
Eras Precambrian (pre-life life begins, simplistic organisms Precambrian (pre-life) – life begins, simplistic organisms Paleozoic (ancient life) – first fish, land plants, amphibians and reptiles Mesozoic (age of reptiles birds, Mesozoic (age of reptiles) – first dinosaurs, mammals, birds, Cenezoic (age of mammals end of dinosaurs, mammals dominate, humans appear Cenezoic (age of mammals) – end of dinosaurs, mammals dominate, humans appearPeriods Epochs (Cenezoic Era only)
Assignment: Using a metaphor to represent the geologic time scale – some examples
A football field and the geologic time scale: How many yard would represent the eras, periods, and epochs?
Assignment Formation of metamorphic and sedimentary rock lab (salt water taffy) Questions #1 – 10, page 313
1.4 Getting a Handle on Time Catastrophic theories dominated geological ideas for over 100 years Violent catastrophes such as earthquakes, volcanic eruptions, enormous floods, meteorite impacts, and upheavals of Earth’s crust to be the main causes of change The processes we see at work in the present seem too weak and slow to be responsible for dramatic change in Earth’s past
Uniformitarianism James 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 of modern geology Used law of superposition and applied it to rock strata Vertical and horizontal layers observed Vertical layers deposited first horizontally but were then tilted Horizontal layers deposited after a period of erosion Top surface of the lower vertical layers is called an unconformity (a surface in a rock sequence that represents a break in the pattern due to erosion or a lack of deposition)
Applying Hutton’s ideas:
Review of Rock Types:
Self-Sustaining System Hutton stated that the geological process of Earth operates as a self-sustained system Heat deep within Earth provides a constant source of energy that creates and destroys material from the crust Started 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 mantle Balanced cycle driven by energy released by nuclear reactions in Earth’s core rock cycle
The Rock Cycle rock cycle
The Rise of Uniformitarianism Hutton’s theories did not catch on until Charles Lyell (1797 – 1875) added more evidence and made the theory easier to understand Lyell argued that processes such as: Erosion Sediment deposition Volcanic action Earthquakes have all operated in the same way and strength throughout Earth’s history
Assignment Read pages 19 & 20 to help answer pages 21 & 22 in the workbook Questions #1 – 4, 6, 8 on page 318
1.5 Pinpointing Time With the rise of uniformitarianism, relative dating was being replaced with the idea of absolute dating Exact age of an object or event (example – your birthdate!) A reliable method to measure the absolute ages of rock or the Earth itself was needed Used the idea of radioactivity (emission of energy from the nuclei of unstable atoms as they change to become more stable atoms) developed by Marie Curie Ernest Rutherford added the concept of radioactive decay and measureable half-lives
Absolute Dating Radioactive isotopes are used to determine exact ages A 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 0 Example carbon-13, carbon-14, carbon-15 are 3 isotopes for C If isotopes are unstable (too few/many neutrons) they naturally break down --- radioactive --- by changing into atoms of other kinds Radioactive isotopes (aka radioisotopes) gain stability when they spontaneously decay into stable, non-radioactive elements Radioisotopes decay at a constant rate in which radiation is given off --- known as radioactive decay.
Radioisotopes 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 rock What 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 is Half-lives vary from fractions of seconds to millions of years, giving each radioisotope specific applications in dating
Radioactive ParentHalf-life (in billion years)Stable Daughter Product Uranium Lead 206 Uranium Lead 207 Thorium Lead 208 Rubidium Strontium 87 Potassium 401.3Argon 40 Common Radioactive Isotopes
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. 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. 1 st half life2 nd half life3 rd half life4 th half life ½ parent¼ parent 1/8 parent 1/16 parent ½ daughter¾ daughter 7/8 daughter 15/16 daughter Lets Review half- life:
Radioactive Decay Calculations: If we know the ratio of parent to daughter material, we can calculate the number of half-lives elapsed From this info, the age of the sample can be calculated from the known length of the half-life of the radioisotope Remember this chart and draw the graph! # of Half-lives O 1234 % Parent % Daughter
Examples: 1.What % of carbon-14 would be left after 3 half-lives? 2.A rock sample weighs 250 g. If it undergoes 2 half-lives of time, what mass of carbon will it contain? Parent IsotopeHalf Life (yrs)Daughter Isotope (decay product) Carbon Nitrogen-14
Application of Radiometric Dating World’s oldest rocks – zircons containing uranium found embedded in other rocks Some of the oldest zircons are found in Canada’s Acasta Gneiss Rock Formation in the Northwest Territories – formed 4 billion years ago Dating organic remains is radiocarbon dating – uses carbon-14 When 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 remaining radiosotope dating
Assignment Half Life Lab, pages 17 & 18 in the workbook Calculation questions on pages 15 & 16 in the workbook Pages 21 and 22. Chapter 1 Review: pages
Chapter 2: A Tropical Alberta The Geology of Alberta in the Paleozoic and Mesozoic Eras
2.1 Fossilization The process by which any trace of the existence of ancient life is preserved within rock Process: life → death → burial → preservation → discovery → recovery Fossils often form in two parts: The actual fossil is on one part of the rock The impression is on the other piece of rock Like 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 sediment Can also form in volcanic lava as the lava can flow so quickly that it creates on impression of the object eg. A tree Fossil Formation
Fossilization of Hard and Soft Remains First step is burying of the organism before it completely decomposes Hard parts (shells, teeth) found unchanged in the rock If the original material is replaced by a mineral (eg. Silica) the fossil is then petrified Sometimes, 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 detail Soft tissue (leaves, skin) are fossilized through: The complete replacement of the organic material, leaving behind an impression Preservation as a thin film of carbon
The Burgess Shale A 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 fossils Considered the most important source of Cambrian fossils on Earth so has been declared a World Heritage Site by the United Nations Evidence that 500 million years ago the organisms fossilized in the shale were living in a shallow area close to the shore of a tropical sea
Alberta’s Tropical Sea For millions of years, Alberta was located close to the equator and was repeatedly submerged and lifted above the ocean’s surface For millions of years after the Paleozoic Era, most of Alberta was above the ocean’s surface During 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 Mountains The Burgess Shale contains fossils showing a complete marine ecosystem These 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)
The 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 Earth Previously, 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 explosion Why did this happen? Scientists suggest that the atmospheric oxygen levels reached a high enough concentration to support the metabolic requirements of these animals
Assignment Read page 10 in the workbook Answer the questions on pages 11 and 12 in the workbook
2.2 A Billion-Dollar Reef Alberta’s first oil field (Leduc) discovered in 1947 changed the economy from farm- based to petroleum-based Where 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
Wealth from Ancient Seas Ancient Timeline of the Paleozoic Era: Cambrian Period: life on Earth was aquatic Ordovician Period: life moving onto land then most of Alberta became submerged at the bottom of a tropical sea Next 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 reefs Silurian Period: reefs grew larger, land plants and animals colonized parts of Earth not underwater Devonian 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.
Next 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.
Finding the Wealth In the past, geologists found petroleum by looking for evidence on Earth’s surface Newer methods were used to find the petroleum trap where Leduc #1was located: Drill-core data Seismic data
Finding 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 rocks Environmental conditions Enables drilling into ancient reefs instead of rocks that formed in the deep water away from a reef Years of collecting and analyzing drill-core samples have produced a detailed picture of Alberta’s subsurface rock
Finding Oil Seismic data: Seismology = the study of how waves of energy (seismic waves) move through Earth as a result of explosions or earthquakes Rather than waiting for an earthquake to occur, scientists use: Explosives placed in a hole or Strike 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
Signals 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
Assignment Answer questions #2 and 3 on page 342 of the textbook
What 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 boundaries Earthquakes, or seismic tremors, occur at a rate of several hundred per day around the world In the last 500 years, several million people have been killed by earthquakes around the world especially in third world nations Seismology is a branch of geology that studies earthquakes and other movements in the Earth’s crust
Anatomy 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 epicentre The vibrations caused by seismic waves moving through the ground are strongest at the epicentre Note: seismic waves move through the Earth by passing Ek from one particle to the next (eg. breaking a stick) earthquakes
Where 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 earthquake Most Earthquakes occur at Faults, which are cracks in Earth’s crust where rocks on either side of the crack have moved Most faults occur at Plate Boundaries The properties of an earthquake depend strongly on the type of fault slip, or movement along the fault, that causes the earthquake There 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 direction Strike-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.
Types of Faults
Earthquakes and Waves Recall that the sudden movement of rocks along a fault causes vibrations that transmit energy through the Earth in the form of waves There 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 moving Transverse waves – particles of matter vibrate perpendicular to the direction of the wave propagation
Waves 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 Earthquake L- 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.
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. P-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. Seismic energy can be transmitted as different waves: P - pressure or primary waves S - shear or swing waves
Measuring Earthquakes Earthquakes are measured at Seismic stations with a device called a seismograph A seismogram is produced and analyzed
Determining the Magnitude of an Earthquake The Richter Scale is used to measure the magnitude of an Earthquake The Richter scale ranks earthquakes based on how much the ground shakes 100 km (60 mi) from the earthquake’s epicentre The scale ranges from 1-9 (open ended) with each point on the scale representing 10X increase in motion over the previous point Earthquakes 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 year Each point represents a 30 X increase in energy over the previous point
Locating 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 stations Seismologists 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
Locations of Recent Earthquakes
Seismic 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 liquids Geologists 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
Properties of Seismic Waves
Tsunamis Second-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 out tsunami tsunamis
Assignment Read page 27 in the workbook Answer questions on pages 28 and 29 in the workbook
2.4 Raising the Rockies The raising of the Rocky Mountains (170 million years ago) and the Alaska Earthquake of 1964 were caused by the same mechanisms – plate tectonics The boundaries of Earth’s tectonic plates can be found by: Plotting the locations of earthquakes – usually occur along the boundaries of crustal plates Plotting volcano locations – also usually occur at the edges of crustal plates
Volcanoes The 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 volcanoes Volcanoes will occur where: Two plates move apart One plate is being pushed under another Volcanism Volcanism at a fault Island Island formation Volcano Brain PopBrain Pop
Evidence of Plate Tectonics Brain Pop! Brain Pop! Paleomagnetism (from Chapter 1) Location of earthquakes Location of volcanoes Pangaea – a single gigantic continent formed from Earth’s land masses at the end of the Paleozoic Era Named by Alfred Wegener (1915) as part of his theory of continental drift (theory that lead to the theory of plate tectonics)
Continental 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 mass Africa, India, Australia and South America joined as a southern land mass Two large land masses continue to move towards each other As 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 beds Plants create an environment for insects and first vertebrates to live on land Early 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
Permian Extinction The fossil record shows evidence of six mass extinctions with the largest occurring 250 million years ago at the end of the Paleozoic Era 90% of ocean species wiped out 70% of land species became extinct Why did this happen?! Don’t know for sure, but scientists are working on some theories.
Extinction Theories Widespread glaciation Sea level drops, shallow water around land gone, lower average global temperature Formation of Pangaea Land masses colliding would reduce shallow seas between them and coastline areas increasing competition in native organisms Not the most likely explanation as Pangaea formed at the beginning of the Permian Period and the extinction occurred at the end of the Period
Extinction Theories (con’t) Asteroid colliding with Earth Similar to the aftermath of a nuclear war – massive firestorms, dust in the atmosphere blocking out the sun for months More evidence shows this is the reason for another mass extinction at the end of the Cretaceous Period Massive volcanic activity Evidence shows that in Siberia massive lava flows covered 1000s of km to a depth of +3000m Drop in the average global temperature due to ash ejected into the atmosphere blocking sunlight – this effect (though less severe!) is seen with modern volcanic activity eg. Eruption of Mount Pinatubo (Philippines) caused a 0.5ºC drop in world temperature
The Plates Keep Moving… Mesozoic Era: Triassic Period: North American plate movement causes Alberta to be repeatedly dropped below sea level The ocean retreats and forests develop which support the first mammals and later form coal deposits End of the Period: the start of the breakup of Pangaea Sea levels rise, submerging North America again This 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 Period Jurassic Period North American Plate drifts west and collided with arcs of volcanic islands on the Pacific Plate producing the mountain areas of British Columbia and Albertaproducing the mountain The mountains are the evidence of several processes taking place: raising ocean beds, welding island arcs, flowing magma from volcanic activity
Break up of PangaeaPangaea The future look of Earth!future
End 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 dinosaurs When another plate collision event occurred, the inland sea was lifted up and drained and the mountains were pushed up even higher Faults 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 Banff Atlantic Ocean starts to form as the continents move further apart toward their modern positions End of the Cretaceous Period marked by another mass extinctionmass extinction Nearly every land animal with a mass over 25 kg gone In oceans, extinction of half of the plankton varieties causing the collapse of many oceanic food chains
Chapter 3: Changing Climates Cenozoic Era on Earth
3.1 The Great Cooling Cenozoic 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 mya 97% of the era Quaternary Period – 1.7 mya to the present
Rising Mountains The 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 Mountains The mountains were round-looking covered by V-shaped valleys cut out by erosion The continued movement of plates also caused North America to migrate northwards resulting in a cooler climate Eventually it got cold enough to form glaciers which would carve out the “rocky” and jagged features of the Rocky Mountains we see today
Retreating Sea Alberta covered by the Bearspaw Sea until the beginning of the Cenozoic Era when it retreated SW dumping sediment on most of southern Alberta This sedimentary formation is rich with dinosaur fossils and other fossils More sedimentary rock formed from the run off from the rising Rocky Mountain Range which dumped sediment into the foothills area
Cenozoic sedimentary rock outcrops are evidence of rivers pouring sediment from the Rocky Mountains.
Not So Tropical The 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 temperatures Drastic change in plant life: Tropical rain forests changed to temperate evergreen forests with rivers, lakes and swamps Animals present included herds of horses, camels, and elephant-like mastodons, crocodiles, rhinoceroses and other, smaller mammals This fossil evidence shows the temperature was cooler but still warmer than it is today
Rise of the Mammals Mammals that survived the Cretaceous Extinction (mainly small rodents) took over the territory left vacant by the extinction of the dinosaurs By 40 mya, many new forms of mammals appear in the fossil record – ancestors of: Modern hooved herbivores Flesh-eating carnivores Large-brained primates
Grasses Take Over Alberta A gradual change from wetlands to woodlands to grasslands occurs as the climate became cooler and drier The dominance of grasses allowed the spread of large herds of grazing species in the late Tertiary Period The resistance of grasses to grazing was a distinct advantage over other plants Other plants grow from the tip which gets eaten by grazers Grasses grow from the base so they can continue to grow after the tips are eaten
Evidence 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 past Absence of tree pollen from current tropical landscapes shows the past climate of these areas must have been too cold for trees to survive
3.2 The Icy Epoch By 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)
Earth’s GlaciersGlaciers During the Pleistocene Epoch, ice sheets reached critical mass as they flowed outward toward the equator Today, the largest glaciers are found in the polar regions – the Greenland and Antarctic continental ice sheets Ice 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
What is an Ice Age?Ice Age Technically, an ice age is a period during which ice sheets cover parts of the Northern and Southern Hemispheres This 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 Europe It is believed that there were four major glaciations during the Pleistocene Epoch
Wisconsin Glaciation Name of the last glaciation ( years ago) as the ice advanced as far south as Wisconsin, USA Largest ice sheet – Laurentide Ice Sheet which fully receded years ago to mark the beginning of the Holocene Epochreceded
Big Kid on the Block During the Pleistocene Epoch, large mammals had the advantage Fossil evidence shows the existence of: Mammoths, modern horses, llamas, reindeer, camels and scavenger dogs Predators such as American lions, short-faced bears, sabre-toothed cats, and birds (8m wingspan) stalked herds of grazing mammals
Glacial Footprints Alberta’s topography was shaped by the Wisconsin Glaciation. As continental ice sheets advance and retreat, they leave behind characteristic landforms such as:landforms 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)
Shaping the Rockies Called the Rocky Mountains due to their jagged shape developed during the Pleistocene Epoch when the mountains were covered with glaciers Still 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 valleys As the glacier flows, it scrapes and gouges the terrain changing the appearance of the mountain At 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!
Assignment In your workbook, read and complete the questions on pages
3.3 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 time Climate: the average of daily and seasonal weather events that occur in a region over a long period of time Just as it is difficult to predict the weather, predicting changes in Earth’s climate is even more challenging!
Holocene Epoch (current Epoch) Began years ago with the great melt that followed the last glaciation People 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 up allowing the early northern residents a passage south Produced a lot of water which filled glacial lakes such as Lake Edmonton (150 km long)
Changing Climate During the Holocene A repeating pattern exists of a warming trend following a glaciation – Alberta should experience the next glaciation within the next years This pattern has repeated all the way back to Snowball Earth in the Precambrian Era as shown by the global climate record
Average Global Temperature Evidence from rock strata shows that Earth has mostly been warmer than today In warmer times, unlikely that the continental ice sheets stayed frozen But 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
Climate Models Supercomputers are used to create mathematical models that attempt to describe Earth’s climate Studying links between the amount of solar radiation reaching the planet and each layer of Earth: atmosphere, lithosphere and hydrosphere Numerous links and intricate interactions have, so far, stumped the supercomputers from coming up with accurate models
Possible Causes of Glaciation Periods Most likely a combination of the following effects: Continents moving north (plate tectonics) Ocean as a heat pump Volcanic activity Wobbly Earth Variation in the Sun’s Energy Output Enhanced Greenhouse Effect
Continents Moving North The timing of long periods of repeated glaciations seems to be random Could be due to the random nature of plate tectonics When Earth’s tectonic plates are near the poles glaciations can occur Continental 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 space Overall cooling effect on the planet making it easier for more ice to form
Ocean as a Heat Pump Earth’s oceans have giant convection currents that act as a global conveyor: Circulates warm water away from the tropics Recirculates cold water of the polar regions
Ocean 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 ocean current prevents warm tropical waters from entering This could explain the Pleistocene Epoch cold period as Australia separated from Antarctica allowing the circling current and the Antarctic Ice Sheet to form
Volcanic Activity Old 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 climate Eg. Temporary cooling effect caused by the 1991 eruption of Mount Pinatubo (Philippines)
Wobbly Earth Repeated glaciations appear to match changes in Earth’s orbit around the Sun and Earth’s rotation on its axis The Milankovitch Theory states that Earth’s orbit varies in 3 ways: The shape of the orbit (eccentricity) The tilt of the axis of rotation The wobble of the axis of rotation All of these affect the amount of solar radiation reaching Earth’s polar regions Not believed to be the cause of the cold periods but instead control the timing of the glaciations
Sunlight 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 sunspots More 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 Europe More recent theories relate the changes in the north Atlantic Ocean’s circulation current, not sunspots
Greenhouse Effect In Earth’s atmosphere, gases such as carbon dioxide and methane trap heat near Earth’s surface – natural insulating effect (it’s a good thing!) CO 2 levels can fluctuate greatly due to: Natural events – volcanic activity or weathering of carbonate rocks Correlates with changes in the average global temperature over the last years CO 2 changes with other factors (Milankovitch Cycles, global ocean circulation) may have increased the effect on the atmosphere’s temperature
Enhanced Greenhouse Effect Not so natural changes to CO 2 levels also occur: Exponential increase since the Industrial Revolution Largest human-caused source of CO 2 is the burning of fossil fuels Scientists believe this increase is enhancing Earth’s natural greenhouse effect leading to significant increases in the average global temperature during the last century In Alberta, we contribute more than the global/person average share of emissions (fossil fuel energy sources, low efficiency)
How Nature Records Climate Change Two key methods are used by scientists to track Earth’s average temperature: Ice-core data Deep-ocean sediment data Other methods are used to provide further information: Geological evidence (eg. volcanic activity) Archaeological evidence (human populations) Fossil evidence (flora, fauna and environment)
Can 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 melt Release fresh water into the North Atlantic Ocean If 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 tropics Rapid cooling effect allows ice sheets to advance in the north and it gets even colder!!
Assignment Textbook page 387 complete the chart in question #12 Chapter 3 Review Geology Unit Review Geomorphology applet, fill in #1 on page 395