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University of Toronto St. George
Earth Sciences
Lisa Tutty

1.1 How does Geology influence where we live? Geologic features and processes constrain where people can live because they determine whether a site is safe from landslides, floods, or other natural hazards. They shape the surface of the planet and produce diversity A) Where is it safe to live? Volcano hazard and help. Other two are hazard Hazard and help Hazard and help talks about how geo influences us. Most of us choose to live in ‘hazard and help?’. Like Alberta there are hazards of living near the rivers, like flooding. Rural area with farms, waters/flooding are good because it brings new nutrients to the area. In the nile, fertility depends on flooding for farms to be furtile. - hazard in the mountains are not good for anyone because it has sediment and deadly to live in -volcano is hazard and help. It can kill people but can help, and be helpful. Living their because it is very fertile. Ash comes out and helps plants grow. - right with hazard with arrows. This is an earthquakes. Earthquakes aren’t helpful because they are devastating. - hazard and help water and river- water is coming down from mountains. It has a water source because there is ice. Glacier is the source of the river. How can you have a glacier there? Elevation. Higher altitude has ice in the summers. If glaciers melt no water source - point: geo infl where we live, where we farm. It is positive and negative B) How foes geo influence our lives Picture Possible test questions!!! On test, if she gave us this picture and said there is a lovely pasture, what is the water source of the pasture? What are the various strengths of the slopes? Hazards?? - water source is glaciers. - Strength- we dont have to know the type of rock. But ithe top forms a solid cliff. Would u be more worried about the cliff or slope? Slope is worrysome because more easily eroded. Material is more likely to come off the hill and slide down. Slope is easy to erode and slide down. - cliffe base looks strong - slope looks hard to climb up you would be sliding. and rocks casafe below because rock is easily eroded. Cliffe is strong - hazard: sheep? worried about rockslide for sheep. Flooding! and earthquakes because new mountains in area so active earthquakes - landslipes, flooding, earthquakes. How do we invest questions? We look for clues. Dont have to know what rock it is In the distance are snow-covered mountains partially covered with clouds. Snow and clouds both indicate the presence of water, an essential ingredient for life. The moun-tains have a major influence on water in this scene. As the snow melts, water flows down-hill toward the lowlands, to the horses and cows. The horses and cows roam on a flat, grassy pasture and avoid slopes that are steep or barren of vegetation. The steepness of slopes reflects the strength of the rocks and soils, and the flat pasture resulted from loose sand and other materials that were laid down during flooding along a des-ert stream. Where is the likely source of the water needed to grow grass in the pasture C) INFL distrubtion of natural resources? This map of North America shows the locations of large currently or recently active copper mines (orange dots) and iron mines (blue dots). What do you notice about the distribution of each type of min COPPER= resrstricted to mountains in west. Magma invaded this part invaded continent and formed copper. Only formed along west so copper forms - Iron mines: common in great lakes and east Canada within Canadian shield. Most rocks here are older than 1 bill. Formed when lots of oxygen in the earth causing iron to go to seas and make iron rich layers. Not in West. - The age of rocks and how the rocks formed are two of many geologic factors that control where mineral resources occur. Lec - the distribution of resources. - certain places you are more likely to find gold then others. This has to do with plate tectonics. -blue dots is iron mines orange is copper mine. Some areas are more prone to one than another. -copper mines land is different because there are more MOUNTAINS. Blue has CANADIAN SHEILD, old flat land. - not randomly distributed Causes sinkholes WHAT TYPE OF EVIDENCE DOES GEO PROVIDE 1.2 HOW DOES GEO EXPLAIN WORLD? A) how continents differ from ocean basins? - darkest blue is deepest seafloor -imp: planet divided into continents and ocean - Surrounding the land is a fringe of seafloor that is not very deep, represented on this map by light blue colors. Fringe called the continental shelf* wider on north than other three sides. - Geologists consider the continent to con-tinue past the shoreline and to the outer edge of the continental shelf. - distinction btwn continents/oceans is reflection of diff in geology. Contnents and ocrans differ in thichness or rocks. W.I oceans are diff depths. Each region on land/beneath ocean has own geo history and landscape/rocks have clues to events that affected B) what stories do landscapes tell? -lanscapes has cliffs and slopes of rok with brown, tan, yellow - some large, angular blocks of brownish rock are perched near the edge of a lower cliff. - its hard to predict when the blocks will fall off the lower cliff C) How has global climate changed since the ice ages? - Earth’s climate was slightly cooler than it is today. Cool climates permitted continental ice sheets to extend across most of Canada and into the upper Midwest of the United States. Ice /heets also covered parts of northern Asia and Europe. Today Earth’s climate warmed enough to melt back the ice sheets to where they are today. Our knowledge of the past extent of ice sheets comes from geologists who examine the landscape for appro- priate clues, includ-ing glacial features and deposits that remained after the glaciers retreated. D) evidence that life was different 1 dino. Flowers not abundant and grass not appeared so more trees and busses - dinos during jurasic period 160 mill years ago 2 fossil bones are common in utuah and helps see how long roamed earth, how big. Fossils tell us enviro and record of past geo events 1.2 WHAT IS INSIDE THE EARTH? outermost layer is the crust, which includes continental crust and oceanic crust. Beneath the crust is the mantle, Earth’s most voluminous layer. The molten outer core and the solid inner core are at Earth’s center Continental crust: granite. Thin light gray layer 35-40 km Ocean crust: beneath the deep oceans. Basalt with lava rock. 7km thick very thin Mantle: upper mantle has green mineral oliving. Brought to surface by volcano Lower mantle: minerals at high pressure. Nearly all the material is solid not molten. High temp causes to be part molten while other parts flow bc weak solids Core: iron, nickel. Outer core is molten but inner is solid Based on studies of earthquakes, observations of meteorites, and models for the density of Earth, geoscientists interpret the core to consist of metallic iron and nickel, like that observed in iron-nickel meteorites (◀). The outer core is molten, but the inner core is solid - core comes from metorites. We cant dig to core what we find out about the core is from metiorites - GRANITE=CONTINENTAL CRUST -BASALT= OCEANIC CRUST - crusts are diff under continent/ocean Continental crust= thicker, granite, less dense Oceanic crust= thinner, basalt, rich in mineral, densier - core has solid inner core made of Iron and Nickle - outer core is liquid -diff because of pressure - this is the reason we can have life on earth. When earth began we didn’t have inner and outer crust. 4.56 bill years ago earth did not have a magnetic field. Iron and nickel floated to the centre and became inner core. Basillica floated to centre and became outer crust. -once we formed the core, we had a magnetic field. Only when you have a magnetic field do you have an atmosphere -magnetic field let us have an atmosphere, which gave us oceans. So inner/outer core is imp. - crust has sillica - mantle is PERIDOTITE. Made up of minerals called OLIVINE AND PYROXENE. -in lect 4. -don’t memorize density B) are some layers stronger than others? -aside from layers with diff compositions, earth has layers that are defined by strength/flow - uppermost part of the mantle= strong, attached to crust - crust and mantle for the ridig LITHOSPHERE - mantle below the lito is solid but it can flow under pressure - This part of the mantle, called the asthenosphere, functions as a soft, weak zone over which the lithosphere may move. The word astheno- sphere is from a Greek term for “not strong.” The asthenosphere is approximately 80 to 150 km thick, so it can be as deep as about 250 km. Box: Density ad Isostasy - the relation btwn elevation and crust thickness. Ocran thinker, densier. Continental thinner, less dense is like blocks of diff thickness floating in water - wood floats bc less dense than water. Thick blocks like thick crust rise higher than thinner blocks - earth, crust is supported by mantle that is solid - thickness of crust rising on mantle is called ISOSTASY -explains elevation and ‘mountain bells have thick crustal roots’ - change in crustal thickness occurs at depth and less occurs near the surface. Smaller, individual mountains do not necessarily have thick crustal roots. They can be supported by the strength of the crust, like a small lump of clay riding on one of the wooden blocks. - density: infl regional elevation. Same thickness but wood is denser so it floats lower sinks lower.  region of Earth underlain by espe-cially dense crust or mantle is lower in elevation than a region with less dense crust or mantle, even if the two regions have similar thicknesses of crust. - Temperature also controls the thickness of the litho-sphere, and this affects a region’s elevation. If the lithosphere in some region is heated, it expands, becoming less dense, and so the region rises in elevation. Thinner lithosphere also yields higher elevations. 1.3 WHAT PROCESSES AFFECT OUR PLANET? - earth is subject to various forces within earth A) How do forces and processes affect earth? 1 Gravity=air to press down. Weight of air causes atmospheric pressure which is greater at sea level than higher levels - less air on high elevation 2 Water= liquid or frozen transports water and rocks. Downwards movement of ice and water is driven by force of earths gravity 3 Sun and Moon= gravitational pull on eath. Sun is large but less force on earth because farther away than moon 4 e;ectormagnetic energy- visible light, ultraviolet and other enerfy radiated from sun to the earth. Sun provides 99% of eaths energy so drives temp,wind 5 Uneven solar heating: wind and ocean current -diff in air temp causing wind and ocean currents. Blowing wind moves sand and dust making waves on oceans/lakes. Rotation of earth guides wind and ocean and distr thermal energy from one part of earth to another 6 Mass of earth - downward pull of gravity which attracts objects to centre. Gravity makes water, win, ice move down 7. Earths gravity causes the weight of rocks to exert a downwards force on underlying rocks. Rocks push against adjacent rocks causing squessing of rocks from all directons. Increases deeper into the interior bc more rocks lie above. Forces compress rocks from all durections but additional forces arise by processes within earth such as movement of rocks and magma. Forces generated in one area can be transferred to adjacent areas causing sideways pushing or pulling into rocks 8 Radioactive decay- of uranium, pot create heat in crust 9 Temp increases down into earths interior- heat from deeper in earth rises up towards the cooler surface. Some heating is by direct contact btwn hotter rock and cooler rock whereas other transfers of heat occurs via moving material rising molten lava B) How do earths surface and atmosphere interact with solar energy - interactions with solar energy and earth ie wind, clouds, rain, snow - our atmo shields earth from cosmic radiation 1) Atmosphere- includes low percentage of water vapour which evaporates from earths ocrans. Water vapour condenses to produce clouds made of tiny water doplets, ice crystals, tain, hail 2) sun produces energy included UV raditation and visible light. Upper levels of atmo, oxygen absorbs most of the suns UV and prevents from reaching earths surface where it would have determental effect. Suns energy ie light and radiation pass through the atmosphere to warm planet 3) 3)heating of atmo, land, oceans with the change in air pressure is the main cause of winds across the earths surface 4) Water on land or in the oceans can evaporate, becoming water vapor in the atmosphere. Most water vapor comes from evaporation in he oceans, but some also comes from evaporation of lakes, rivers, irrigated fields, and other sites of surface water. Plants take moisture from soils, surface waters, or air, and release water vapor into the atmosphere through the process of evapotranspiratio 5) Much of the Sun’s light that reaches Earth converts into infrared energy, a form of energy related to heat. Some of this energy radiates upward and is trapped by the atmosphere, which warms in a process called the green-house effect. This process regulates global temperatures, which are moderate enough to allow water to exist as liquid water, gaseous water vapor, and solid ice. Water is a key requirement for life. ENERGY AND FORCES - Energy and forces from internal and external -internal energy: within earth and includes heat enerfy trapped when planet formed and heat by radioactive decay. Heat drives melting rocks to make magma external: SUN. Creates thermal energy. Hoter in equatorial areas than polar - Temperature differences help drive wind and ocean currents. Sun-light is also the primary energy source for plants, through the process of photosynthesis. - Early in Earth’s history, meteoroids and other objects left over from the formation of the solar sys-tem bombarded the planet. During the impacts, kinetic energy (energy due to movement of an object) changed into thermal energy, adding a tremendous amount of heat, some of which remains stored in our planet’s hot interior. -Internal force: all objects have mass that exert gravitational attraction. If mass is large, gravity strong. Gravity pulls objects towards the centre of the earth - gravity is imp moving materials. Causes loose rocks, glaciers drives winds and water. - external pull: sun and moon. Gravity btwn earth and moon maintains orbit around sun. Moons pull is stronger than sun causing rise and fall of ocean tide 1.4 HOW DO ROCKS FORm A) What types of sediments form in familiar surface enviroment Glaciers: rock debris within icy sediment. Mountains: rocks that broke awat with landslides Sand dunes: sand with wind. Sand bc cant pick up larger particles Beaches: broken shells and stones WaterL mud and creatures. Near land as sand from land. Wind delivers sediment from land to sea River: sand, pebbles and cobbles whereas low areas beside channel have silt and clay. What types of rock form in hot or deep enviro? 1) in many volcanoes, magma flows onto the surface, creating lava that flows downhill or piles up around 2) Explosive volcanoes erupt volcanic ash, 3) . Magma that does not erupt may cool and solidify in a magma chamber, forming gran- ite or other rocks at depth. Heat from the magma chamber may bake adjacent rocks, changing them into different kinds of rocks. 4 Deep within Earth where temperatures and pressures are high, forces can squeeze and deform rocks into new arrangements and into new types of rocks. Under such force, solid rocks slowly flow, shear, and bend. Changing a rock by heat, pressure, or deformation is the process of metamorphism 5 Distinctive rocks form when hot waters cool and precipitate minerals. This may occur beneath the surface or on the surface in hot springs CHAPTER 2 2.1 WHAT CAN WE OBSERVE IN LANDSCAPES? What features do landscapes display? - trying to identify distinct parts of the scene and then focusing on one part at a time. After examining the photograph, read the accompanying text.  Color commonly catches our attention. These rocks are various shades of red, tan, and gray. Close examination of these rocks by geologists reveals that the rocks consist of consolidated sand and mud, and therefore are sedimentary rocks hill has different parts. A small knob of light coloured rocks sits on the very top  below the knob is a reddish and tan slop and small reddish cliffe  there is a main light coloured cliffe, upper part is tan and smooth/round  Some parts of the cliff have horizontal lines that can be followed around corners of the cliff. These lines are the outward expression of layers within the rock. We call such layers in sedimentary rocks beds or bedding. These beds originally extended across the area prior to more recent erosion. Lower parts of the cliff have a darker reddish-brown color and display many sharp angles and corners. Some of these corners coincide with vertical cracks, or fractures, that extend back into the rock. The reddish- brown color is a natural stain on the outside of the rocks. Below the cliff is a slope that has pinkish-red areas locally covered by loose pieces of light-colored rock. A reasonable interpretation is that the loose pieces have fallen off the main cliff. When you change the colour it looks different - The uppermost three rock units (numbered 1, 2, and 3) are shaded tan, yellow, and orange. Rocks of the main cliff (4) are shaded light purple. On the lower slope, the reddish rocks are shaded light orange (5), whereas the covering of loose, light-colored rocks is shaded gray (6). -brown lines highlight beds in the rock units - black lines mark fractures cutting the rocks - Simplifying this scene into a few types of features makes it easier to observe, describe, and understand the landscape. In this landscape, we observe only a few beds and rock layers but many fractures. Some layers are more resistant to weathering and form cliffs, whereas less resistant ones form slopes. Weath-ering has rounded off corners on the top of the cliff, removed the reddish-brown stain, and loosened pieces that fell off the cliff, covering a slope of underlying, reddish rocks. Possible test questions!!! On test, if she gave us this picture and said there is a lovely pasture, what is the water source of the pasture? What are the various strengths of the slopes? Hazards?? - water source is glaciers. - Strength- we dont have to know the type of rock. But ithe top forms a solid cliff. Would u be more worried about the cliff or slope? Slope is worrysome because more easily eroded. Material is more likely to come off the hill and slide down. Slope is easy to erode and slide down. - cliffe base looks strong - slope looks hard to climb up you would be sliding. and rocks casafe below because rock is easily eroded. Cliffe is strong - hazard: sheep? worried about rockslide for sheep. Flooding! and earthquakes because new mountains in area so active earthquakes - landslipes, flooding, earthquakes. How do we invest questions? We look for clues. Dont have to know what rock it is C) what are some strategies for observing landscapes? 1) in entirety it is complex so look at one part at a time. Left compared to centre 2) focus on one geology feature at a time. Concentrate on fractures in the cliffe. Are they steep? Evenly spread out? How do they affect appearance of the cliffe? 3) Colour is imp to rocks. Sediment have range of colours 4) Some rocks are more resistant to erpsopm than ptjer rocks. Cliffes and ledges are hard to erode. Slopes are weaker and wind can blow away 5) Obvious features in many landscapes are layers in the rock. Diff repr thickness of sandstone, whereas slopes and ledges are expression of dozens of layers but layers can be folded 6) Shape of the eroded rocks depends on the hardness of the rock, thickness of the layers, spacing of fractures and other factors. Landscapes will change overtime so shapes seen today will evolve overtime 2.2 HOW DO WE INTERPRET GEOLOGIC CLUES - landscapes and rocks. From character of rock we can tell the age and enviroment in which a rock formed A) How can we infer an enviro which a rock has formed -to infer, compare its characteristics ie size and round less or materials it contains - sedimentaey is smooth and round because they smash into each other and erode overtime ▶ Many river channels contain rounded stones surrounded by a matrix of sand. Does this sediment resemble the rock in the photograph to the left? ◀ Steep mountain fronts typically contain angular rocks of many sizes in a matrix of mud, sand, or small rock fragments. B) How can we envision the slow change of landscapes through time? -Most landscapes evolve so slowly that we rarely notice changes. - to notice changes use ‘Trading location for time’ which uses diff parts of a landscape to repr diff stages in the evolution of the landscape - we mentally arrange the diff parts into a logical progression of how we interpret the landscape we have to change - 3 models 1 2 3 1 is earliest and 3 most recent 1= erosion cuts into rock layers carving a mountain with steep sides and BROAD top. Flat topped mountain is called a MESA 2= with time erosion wears away the edges forming a smaller, steep sided mountain which called BUTTE 3= erosion continues to wear down the terrain leaving low, rounded hills and isolated knobs given enough time, a mesa. Or butte might evolve into such hills and knobs’ C) How do we determine the sequence of past geo events -age of rocks and geo feautes by principles 1 youngest layer on top oldest on bottom 2 geo feature is younger than a rock or feature- fault offsetting layers must be younger than rock layers it crosses and displaces. This fault does not offset land surfaces is younger 3 younger rock can include pieces of older rock 4 a younger magma can bake or otherwise change older rocks that are nearbywhen dark was moleten, heat from magma baked and preexisting rocks caused redish next to granite 2.6 HOW DO GEOLOGISTS REFER TO RATES AND TIME - time is imp. A) how do we refer to rates of geologic events and processes? - calculate rates like speed of car. Yet geo rates are measured using metric units or cm per year not miles per our - geologic processes faster than the runner include motion of energy formed by earthwuakes (5km/sec) or speed of volcano eruption - geo processes slower is the movement of groundwater, motion of continents, uplift and erosion of land B) how do we subdivide geo time? - refer to time spans in millions of years (m.y) or billions (b.y). Time before the present we are using abbreviation MA mega annum for millions of years before present. Ga for bill of years before present 1 C) What are some important times in earths history - 4.56 bill years is in a single calendar year th -Precambrian is first 10 months till November 19 - Palezoic is nov 18 to dec 12 - Mesozoic is dec 12-18 (dinso) -cenozoic is 26 of dec to now 2.7 HOW DO WE INVESTIGATE GEOLOGIC QUESTIONS A) Observations- look, listen smell. We may sense something but want to measure exact value 1- geo take special care to make valid observations and can be used to develop explanations 2- compasses and other instraments provide quantitative info provided they are checked 3- evaluating the validity of observations is critical so repeat measurements to compare values B) How are interpretations different from data -data is not very useful until we analuze them to confirm old ideas or new interpretations - recent history of volcanoes illustrates diff between data and interpretation C) What is an explanation -several interpretations to make an explanation. Data combine to form possible explanation or hypothsis for how the belt of smooth topography formed LECTURE • Observation • Interpretation vs Data • Explanation/story • Hypothesis – an explanation that is developed to explain observations and that allows testing • Re‐think if necessary; incorporate more data and re‐test Geologist Bob Smith notices drownedrees and higher lake levels on thesouthern side of Yellowstone Lake • This led to the question: What ishappening here? • Bob thought that maybe some areaswere rising or sinking • To test this he surveyed the area • Bob compared the data with older datafrom 1920, the area to the north of thelake had risen • Bob concluded that the rising area northof the lake caused the water to spill overits southern shoreline, drowning trees• Bob considered other data about thearea and concluded that the area wasrising because of a large magmachamber beneath the surface POTENTIAL QUESTION HOW GEO INVESTIGATE GEO QUESTION - this guy investigate geo question. Found there was flooding in yellowstone park. He said why are these trees drowning? - said maybe some areas are rising and others sinking. Tested it. surveyed area and found that area north of the lake is getting higher so water moved to south which is why not many trees in south. -Said why is the area rising? rising because magma was rising and coming closer to surface making area close to surface rise up used steps of scientific method to see what happens 1)observes 2)interpretation (why do i think this is happening) 3)data (this is happening) 4)story 5) hypothesis-test 6)rethink LECTURE 2 OUTLINE Internal zonation of Earth (physical vs compositional) – Theory of...– Evidence for...– 3 types of plate boundaries • Convergent Divergent Transform Measuring plate velocities • Magnetic field • Hot spot tracks • Direct measurement – Why do plates float? – What drives plate tectonics -crust is thin. We cant dig down through the crust - Crust, molten upper mantle, solid lower mantle, liquid outer core and solid inner core EARTHS INNER: systems of zonation - Layers defined by physical properties - Layers defined by physical properties: • lithosphere – solid, rigid • asthenosphere – solid, weak, ductile (flowing) • mesosphere – solid • outer core – liquid • inner core – solid 3 compositional layers 1 crust 2 mantle 3 core IMPORTANT **** In both core is mae of iron and nickel - Phys: core is divided into 2 diff bec of how they behav. -Composition is the mantle with olivine and crust is silica Physical has solid which acts like a solid. Plastic asthen doesnt mean its plastic but acts like playdough. so can be molded. Ridgid lithosphere. - if we look at 2 slices at the top- sometimes they use lithosphere the same as fract. Litho is thicker and includes crust with mantle. - litho works on behaviour and mantle behavs like the ridgid crust. -litho is NOT same as the crust * how do we know the earths interior? We find out from earthquakes EARTHQUAKES - 2 types of earthquake waves 1) P waves- can travel through solids and liquids so it can travel through the liquid core 2) S waves secondary waves- do not travel through liquids. As soon as the get to the boundary to core/mantle it stops. Imp bc tells us the core is liquid and where boundaries are. - we learn about the earth through Seismic waves How do we measure this? Pencil lid and if an earthquake it draws lines more lines bigger the earthquake - to find out about the crust is the trucks. Can't tell us about inside but structure of rocks. Rocks smash into earth and create sesmic waves. When those sesmic wave goes into the crust it reacts with crust. OCEANIC CRUST VS CONTINENTAL CRUST - oceanic is thinner than continental crust - yet oceanic crust is more dense - continental crust is sinking into the stuff underneath - *the crust is not the lithosphere ********* ON TEST - we will come back to this - earth scientists divide the earth into various systems. Now the focus is interdisciplinary so people look at the earth in systems 1) atmosphere (gases and air) 2) hydrosphere ie water 3) biosphere (living and dead) 4) solid earth system (Rocks) HYPOTHESIS - Earth is divided into mechanical layers - outer layer is rigid lithosphere - floats atop plastic asthenosphere - supercontinet called pangea, 200 mill yrs ago broke up -theory that earth was divided into layers so outside is rigid lithosphere is divided into plates; some have continents as “passengers” - Plates are moving apart. The atlantic ocean grows bigger as fast as your finger nails - in the atlantic ocrans there is a mid atlantic ridge. Here the plates are moving apart and into that space is magma. Magma comes into fill that space, no hole in the earth and when magma comes up forms salt. - at one point na plate and eurasia were attached as land mass but magma broke it and moving them apart forming a new baby ocean. Wider and wider moving continents further apart -oldest crust moves on and new crust is forming in the centre* Baby crust is in the centre and old crust is near land mass -THIS IS CALLED DIVERGENT boundary (plates moving apart) -mid oceanic ridge is the centre THEORY OF PLATE TECTONICS – circa the 1960s Proposes that Earth’s lithosphere is divided into plates (like the shell of a cracked egg) that move relative to one another, and relative to the underlying asthenosphere. As plates move, their interiors remain relatively intact, while their boundaries undergo deformation. -Divergent boundary getting wider. Arrows pointing towards each other. So the pacific ocean is not getting pigger but smaller its dying -some oceans grow some die - arrows grow - earthquakes and volcanos occur at these Boundaries. Find boundaries by mapping earthquakes - in canada we are not near boundary but plate so its calm. Edge of the plate meets with another plate Plate Tectonics • Plate tectonic forces give rise to the formation of the crust , affect continental positions , and produce changes in global topography • The slow inexorable wearing down of the land surface of the Earth would lead to its demise and reduction in height to sea level in less than 20 million years owing to weathering and erosion, if it were not for the return of materials to the continents via plate tectonic forces if we didn't have plate tectonics everything would be flat and there would be no new mountains. All the old mountains would erode. - plate tectonics helps us have water and fight against erosion 3.2 WHY DO SOME CONTINENTS HAVE MATCHING SHAPES Alfred Wegener (1880 –1930) observed the fit of these continents new hypothesis called continental drift.  continetnsts were once joined together but later drifted apart. Hypothesis of continetal drift was an imp historical step that led to current theories that explain distribution of contenents A) were the continets once joined together - southern continents appeared to fit together S America and Afr - fit of the continents and other evidence preserved in rocks and fossils suggests s America, Africa, antartica, Australia and india were once joined but ater drifted - if fit should have similar rocks and geo structures. - Geologists gave the name Gondwana to this hypothetical combination of the southern continents into a single large supercontinent. B) fossils and continental drift - correspondence of fossils and plants and land animals thousands of km apart separated by ocean -dossils of some land animals exist on several continents by wide oceans. Animals lived more than 150 mill years ago and now are extinct. Land animals could not swim across ocean - Gondwana are fossilized leaves of Glossopteris, a seed-bearing plant that was widespread during late Paleozoic time (before 250 Ma). - alternative to the hypothesis of land bridges (discussed in Section 2.8), and it explained why identical plant and animal fossils are found on different continents. The plants and animals were origi- nally on a single huge supercontinent that later split into separate smaller continents. Two continents could share plants and land animals before they split, but not after. - Other fossil data suggest that Antarctica was once farther north, away from the South Pole. Such data include coal beds interpreted to have formed from plants that grew in warm-weather swamps. One explanation is that Antarctica moved to its present polar location after the coal formed more than 150 million years ago. c) How did continental drift explain deposits in unusal places? 1) rounded outcrop in South Africa has a polished and scratched surface that is identical to those observed at the bases of modern glaciers. This observation is surprising because South Africa is cur-rently a fairly warm and dry region without any glaciers. S A similar to artic 2) sedimentary rock above polished with scratches like those near glaciers 3) scratch marks tell direction glaciers move across the land as the gouged the bedrock. Geo interpret scratch marks as glaciers moving across the area 4) glacier movement from scractch marks made it seem that glaciers came from the oceans, something that is not seen today. According to this model, a polar ice cap was centered over South Africa and Antarctica 280 million years ago, and the directions of glacial ice movement were those shown by the blue arrows. OLD AND NEW IDEAS ABOUT CONTINENTAL DRIFT -theory of continental drift recievd mix vviews. Explained the similarities of rocks, fossils and geo structures on atlantic and Indian ocran - N hemisphere was more skeptical - weakness is that he could not explain how or why continents moved. - believed that continents plowed through or over oceanic crust but continental crist does not survive forces to move mass across such a distance while pushing aside oceanic crust - surfaced with the availability of new information about the topography, age, and magnetism of the seafloor. The magnetic data had largely been acquired in the search for enemy submarines during World War II. These data showed, for the first time, that the ocean floor ( ▼) had long submarine mountain -examined the new data on ocean depths, and also new data on magnetism of the seafloor. Hess and Dietz both proposed that oceanic crust was spreading apart at underwater mountain belts, carrying the continents apart. This process of seafloor spreading rekin- dled interest in Alfred Wegener’s idea of continental drift. Wegener’s hypothesis morphed into the theory of plate tectonics, which is described later in this chapter. LECTURE 3.2 Evidence for plate tectonics continents were connected - matching coastlines - similar rocks, glacial features “cross” oceans - same fossils (ex, Glossopteris, Mesosaurus) Notes-* know alred Wegener=a metorologist. Noticed that the rocks on either side of the atlantic ocean and fossils were the same but were from animals that couldnt swim across the ocean also found glacial evidence from ice sheets and coastlines matched up. Looked like sa would fit into africa. -SA and Afr were joined together ** -laughed at bc ppl didnt think continents moved. 1) bc he was a metorologist 2) no mechanism to explain how it could have happened. -he said maybe tidal force caused it or continents plowed through earth crust 3.3 TEXTBOOK WHERE DO EARTHQUAKES AND VOLCANOES OCCUR - volcanoes and earthquakes are not random but but show association with mountain belts and other features of earth processes A) where do earthquakes occur? - earthquakes are not distributed uniformly but in belts ie west coast of north and S America - Most occur along midocean ridges. Where the ridges curve or zigzag so do earthquakes - are sparse in some interiors but lots in others ie middle east, china -large areas of sea floor have few ie abyssal plains. Volcanoes active islands like hawii have earthquakes - some continental edges have earthquakes but other edges have few. Earthquakes are common along the west coasts of S America and N America and these edges also have narrow continental shelve. Few earthquakes along e coast of Americas where continental shelves are wide - ocean trenches have many and some of the biggest ie Indian ocean and japan earthquake * lecture=earthquakes happen at boundaries of plates B) which areas have volcanoes? - v like earthqu are widespread but occur in belts ie w of N and S America -some volcanoes occur in centres of oceans such as volcanoes near Iceland. Iceland is large volcanic island along mid ocean ridge in centre of N atlantic ocean -v occurs along w of Pacific through N Australia, Philiphines and Japan -volcanoes occur beneath oceans but map only shows largest submarine volcanic mountains. Volcanoes are widespread among mid ocean ridges but do not form mountains -some form in middle of continets ie china - Lecture - earthquales occur mostly in shallow surface. *THEY only occur on SUBDUCTION ZONES - volcanos ring of fire is the pacific ocean it is a dying ocean. Many volcanoes around dying ocean of pacidic ocean - mountain belts are also occurring along pacific dying ocean, mountains happen at edges of plates - pacific ocean - more evidence? The age of the ocean floor is young as are ocean sediments- newest crust is in the centre 3.4 WHAT CAUSES TECTONIC ACTIVITY TO OCCUR IN BELTS? A) what do earthq and v activity tell us about lithosphere? -yellow earthquakes happens when plates spread apart - organge volcanoes when come together -Earthquakes, volcanoes, and other processes that deform the crust and mantle are called tectonic activity, or simply tectonics. The belts of yellow and orange on the map are areas of active tectonics. The regions between the belts are relatively stable. -earths strong outer layer, the litopsphere is broken into a dozen or so fairly rigid pieces, called tectonic plates. This map shows names and boundaries of he larger plates. -Some earthquakes occur in the middle of plates, indicating that the situation is more complicated t
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