2240 Notes

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2240

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Oct 30, 2023

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EARTH SCIENCE 2240F NOTES UNIT ONE CHAPTER ONE- PHILOSOPHY OF GEOLOGY ● Charles Darwin- the father of evolution ○ Used geology to develop his principle ● Nicolaus Steno - the father of stratigraphy ○ Ended up renouncing his life’s work to join the church ○ Collected fossil evidence from the Italian highlands ○ His work was dumped on by scholars such as Issac Newton simply because he wrote in Italian rather than English. ● Thomas Burnet ○ Decided that all uneven features of the world were a cause of Noah’s flood ● Archbishop James Ussher ○ Was tasked with mathematically calculating the age of the earth. ○ Using the Bible he decided that the Earth was created on October 22nd, 4004 BC ● Catastrophism ○ Main belief are: ■ Earth was a record of unique events ■ There is no evolution (biological, geological, or otherwise) ■ No possible way to predict nature ○ Baron Georges Cuvier ■ Published a paper examining stratigraphy and sentiments of the Paris Basin, seeing unusual and repeating layers of fine sentiments and boulders ■ Determined that abnormal layers were due to unpredictable catastrophes ■ Disregarded finding that conflicted with the church and catastrophism. ○ If you were a believer of catastrophism, you would believe that: ■ The earth began as a molten ball ■ While it cooled and solidified, a few seizure-like convulsions whipped up the semi molten peaks and turned them into mountains. ■ Valley were eroded at one during Noah’s Flood ■ Fossils represent previous life forms that were fully erased from Earth by catastrophes ■ There is no biological connection between species. They're all a unique gift from god. ● Uniformitarianism ○ Formerly called gradualism.

○ Introduced in 1795 by James Hutton in his book “Theory of Geology”. He died two years later ○ Hutton theorized that landscapes change over time, not all at once through watching creeks pick up and move sentiment downstream. ○ Charles Lyell drew from Hutton in his book “Principles of Geology” (1830) ■ He threw away the age of the earth decided by Usser and proposed an unlimited geological time. ■ Bishop Cuvier died in 1830, so there was no one eloquent enough to oppose his claims. ■ Lyell changed geology and led the new revolution into Uniformatarianism. Thanks to him many other scholars ditched the Christian ‘earth age’ and were able to further his work. CHAPTER TWO- GEOLOGICAL AGE DATING ● The true age of the Earth is 4.54 billion years. The solar system was created approximately 4.567 billion years ago ● Earth ‘eats up’ and recycles old rocks– not many from the original crust exist anymore. ○ Oldest crustal fragments or earth are both found in Canada, yet none are as old as the original crust. ○ Many recycled rocks make up the grains within sedimentary rocks ● Relative Age Dating ○ Steno proposed three fundamental principles in geology that are the basis for current geological mapping. Also known as Steno’s Laws ■ Principle of Superposition: sedimentary rock layers are deposited onto one another ■ Principle of Original Horizontality: sedimentary rock layers are lain flat and horizontal when deposited ■ Principle of Original Lateral Continuity: sedimentary rock layers are deposited over large areas. ○ Steno’s Laws couldn’t explain igneous intrusions, or the relationship between eroded rock and the strata lain on-top. ○ James Hurron added his own Principle of Cross-Cutting Relationships, which tells us: ■ A fault is younger than the youngest rock it cuts ■ The strata above an unconformity are younger than the strata below ■ Any feature that cross-cuts a rock must be younger than the rock it cuts ○ The final price of Relative Age Dating is the application of Reference Horizons by William Smith. Other principles were able to date rocks relative to each other in a geographic region. But you could not date rocks region to region because there was no effective way to do so.

■ Principle of Faunal Succession: allows geologists to compare fossils found in a layer to one another in order to determine if they were deposited at the same, or similar, time. ● Absolute Age Dating ○ Used for determining age of rocks that aren't sedimentary ○ Henri Becquerel’s discovery of radioactivity has opened up methods for determine the age of radioactive elements ■ As a radioactive atom decays it does so at a consistent rate ■ Determining the ratio of parent atoms (radioactive, decaying atoms) to daughter atoms (mostly-sable products), scientists can easily find the time since decay started in a closed system. ○ In geology and geochemistry, there are a few naturally-occurring radioactive minerals that we look for when trying to find the age of igneous rock. ■ Zircon is a miner that contains Uranium,and by determining the ratio of uranium to lead. ■ UNIT TWO CHAPTER THREE- PLATE TECTONICS ● Continental Drift ○ Formalized by Alfred Wegener in 1912. His indisputable evidence wasP: ■ The jig-saw puzzle-fit of the continents on the globe ■ The correlation of plant and animal fossils across continents. ● Sea-Floor Spreading ○ Interest in world’s oceans piqued geophysical methods were new and starting to be applied in the field ○ A huge volcanic chain was found running up the middle of the Atlantic Ocean. Similar chains were found in other oceans. ○ Magnetic stripes running parallel to these volcanic chains were also found. ○ These symmetrical stripes formed at the same time and were being pushed away from the volcanic chain. These are now called spreading centers for how erupted magma helps push apart the lithosphere. ● Earth’s Magnetic Field ○ Earth can be compared to a bar magnet with two poles (+) and (-)

○ Currents within Earth’s liquid outer core coming into contact with the solid inner core produce the magnetic field, according the the Dynamo Theory ■ Electric currents generated by enormous ‘dynamos’ are driven by circulating hot currents in the liquid metal outer core and magnetic fields surrounding those electric currents. ■ Earth's flow is not always stable, as liquid outer core currents periodically change orientation. If many dynamos change orientation it can result in the reversal of our magnetic poles. ○ Paleomagnetism is the study of the intensity and orientation of magnetic fields and poles of earth, which have inverted many times throughout history. ○ Magnetic field is anything but stable. Intensity and polarity change chaotically. ○ Magnetite is a common igneous mineral found in many volcanic rocks and is known for its strong magnetism. ■ The crystals, when within a lava, will orient themselves to the earth's magnetic field. Once cooled their position is locked until the rock is melted and recycled. ■ By measuring the orientation of magnetite grains on the ocean floor we have found an intact record of the Earth’s paleomagnetic field and polarity. ● Developing Plate Tectonics ○ After the discovery that continents were moving, interest piqued in Plate Tectonics. Here is what we knew at this time so far: ■ Continents were previously assembled into the supercontinent Pangaea ■ Large volcanic change up middle of oceans are where new oceanic crust is being produced ■ New oceanic crust moves away from spreading centres, forcing continental landmasses to move. ○ Spreading centres are traceable around the world ■ Deep Oceanic trenches because the obvious place where crust was being forced down into the earth, through a process called subduction ■ Subduction Zones were traced around the globe, mirroring areas noted for significant earthquakes ○ Hugo Benioff and Charles Richter worked to develop earthquake monitoring or measuring equipment. ■ Benioff used new equipment to measure seismicity near ocean trenches and found that earthquake foci followed the subducting tectonic plate ■ Three classes of earthquakes were cited with in the Hugo-Benioff Zone : shallow, intermediate, and deep focus earthquakes ■ With modern instruments we can actually track the downward motion of the slab by temperature– the cold oceanic slab stands out through the hot asthenosphere.

● Plate Boundaries ○ Convergent Boundary : tectonic plates are colliding, forcing more dense crust underneath less dense crust, reflects compressional stress of crustal rocks ○ Divergent Boundary : tectonic plates are moving apart with new Basaltic crust morning at mid-ocean ridges, creating extensional stress ○ Transform Boundary: tectonic plates are moving laterally past each other, creating shearing stress. (result of strike-slip faults rather than normal/reverse faults) ● What drives plate motion? Convection within the currents in the asthenosphere ● Mantle Plumes ○ Very hot partially-melted material moves up through the Earth ○ Difference with mantle plumes is plumes produce discrete spots of volcanism, rather than chains of volcanism. ○ Due to decreasing density towards the surface, mantle plumes move upwards as they differentiate– molten rock almost always has a lower density than solid rock ○ There is strong evidence that mantle plumes can interact with and begin rifting of the crust to the surface, leading to the entire separation of continents ● When a hotspot initiates rifting, a characteristic triple-junction with form containing two main branches and one failed branch, known as the aulacogen – which will produce a region of high tectonic/crustal instability ● The convection model of motion within the Earth is not simple, as calls are easily interrupted by subducting slabs and mantle plumes that cut near-vertically through the Earth ○ Two main processes for driving plate motion ■ Slab Push : erupted lavas work to push material away from the speaking centre, forcing the entire tectonic plate away ■ Slab Pull : gravity drags the subducting plate down further into the trench, pulling the length of the tectonic plate behind it. CHAPTER FOUR- EARTHQUAKE BASICS ● Faults and Seismicity ○ Faults are breaks in the rock where it has been broken apart by applied stress ■ Normal faults ■ Reverse faults ■ Strike slip faults ○ We explain earthquakes using the Elastic Rebound Theory, which has four steps ■ a) baseline ■ b) building stress ■ c) rock breaks, fault forms ■ d) new baseline, cycle repeats

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