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Lecture 8

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Environmental Science
Nick Eyles

EESA06 Planet Earth Dating Planet Earth: Geological Time and Statigraphy Lecture 8 ➢ Statigraphy: geology/science where we place rocks in order; the study of layers  Relative age versus absolute age  One of the first things to do is figure out the relative age (making assumptions comparisons between two different rocks – which is younger/older)  In the past scientists were good with relative age but now with new sciences absolute age is now possible  Absolute age is also important ➢ Final Exam: What's the sequence of events that's recorded in this? ➢ Diagram (Fig 19.2)  Geological history recorded in this complex diagram  The relative order of events  Oldest events are recorded by the lowest rocks  Law of superposition  Younger tops occur on top of older ones ➢ Earth is 4.56 Billion years old  This is an absolute age ➢ 1) Early Ideas on Statigraphy  Mountain inAlaska 2 km high  Layers are called strata  Oldest layers are always at the bottom  Sediments get deposited on top of older sediments  Ancient Greeks recognized fossils embedded in rocks now on tops of mountains  Made the connection that these are marine animals  Puzzled about how they can get trapped in rocks and get elevated above sea-level  Divilium (Bible)  Strict biblical interpretation of Earth's History  Rocks and landscapes result from Noah's flood  Rocks, sediments are all groped together at diluvium (meaning “of a flood”)  Floods are associated with creationism • More than 1 flood recognized (new life created each time so each layer contains diff life forms) • So what we see now is relatively young •  Archbishop Ussher (1581-1656)  Went to the bible and looked at generations  Came up with important number of 4004 BC so earth is about 6000 years old • Based on counting generations in the Bible  This was dominant up until 1830  Niagara falls – great monument for understand the age of our planet earth – they are not static, they are receding,....the falls used to recede a metre a year....carves out softer rock underneath....explains the Niagra gorge, gorge is cut while falls is receding......1830 realized that if you measure the length of the gorge (12 km), you make the assumption that its a meter a year...then thats 12 000 years of earth's history recorded by the gorge and this was a breakthrough in 1830  60% of water from niagra is taken for hydro purposes, but yeah they naturally recede 1 meter  They probably recede cm a year rather than a meter  GeorgiusAgricola (1494-1555)  This is where the practical side of geology comes in  Science of geology evolved out of the need to find resources – mine ores & metals  De Re Metallica (1556) by Georgius Agricola is an important book  He recognized the order of rocks and that rocks are folded and bent  Also that they get older gets upwards?– by reference to the fossils (organisms contained in rocks which evolve through time) – more primitive type of fossils in older rocks  Nicholas Steno, a physician, also spent a lot of time looking at minerals and rocks • Quote = “Mountains can be raised and lowered, land can be conveyed from one place to another” • Great statement about plate tectonics – so some recognition that earth's surface was mobile and had a history  Geology becomes helpful to Industrial Revolution (1790-1820)  Moving stuff out of the ground  Bulk items were moved by canals (water)  Canal-building is important in the development of STATIGRAPHY  Steam-engine =  Discovery of the origin of coal (1830)  Most important rock at the time  Industrial machines needed fuel  Origin: • When they removed coal from Wales they found “Logan trees” in situ in the coals • Named after Sit William Logan, and he had early ideas of geology of Canada • Recognition of trees in coals was a major breakthrough = coals were a product of decay and lithification of peat (marshland and wetland material – vegetation bacteria to break down that material so overtime it is compressed and over millions of years it is turned into coal. • Confirmed by discovery of in situ lithified tree trunks in coal seams • This idea that earth is much older, since coals take extremely long to form • Contributes to the idea of evolution RATHER THAN INSTANT CREATION  William “Strata” Smith  Book published on him by Simon Winchester (the Map that changed the world)  Smith was a mining engineer and canal builder  When you excavate side walls of canal walls you see layers – you can characterize layers by fossils – used to the word index fossils (like a fingerprint)  Recognized that you could correlate rocks that were 200 km away based on their fossil content  So you're starting to order rocks according to relative age  First geological map was produced by Smith – needed to show where Canals and resources were • BUT FIRST geological MAP was actually created by egyptians - 3 500 years old • Tchurin map – on papyrus paper • Very similar to modern maps  SMITH'S GEOLOGICAL MAP of England, 1815 • Shows 2 things • Law of strata superposition • Younger rocks are always on top of older • Law of faunal succession • Fauna organisms and succession of rocks • In younger rocks Fauna evolves and gets younger • Layers • Strike = refers to the edge of layers • Putting some order on geoligcal record  Geological Surveys  People needed to know where minerals and rocks were  1844 – Major milestone in Canadian geology – first mapping was done in Canada  Canadian geological survey was set up in 1844  So this is basically geologicals going out across the continents and beginning to map and observe rocks  SIR WILLIAM LOGAN'S MAP OF UPPER CANADA • What was the point of mapping southern Ontario? Search for Coal! • What's his conclusion? We ain't got no coal! The rocks are too old • So younger rocks have coals! (These are in the states) • So what did this map trigger? • Map gave rise to the “no coal” problem • Upper Canada gets coal from the States but wherelse? • Gave rise to confederation • What has nova scotia got that upper canada needs? • The beginnings of modern day canada (confederation).....creation of economic entity where coal can be brought into Canada • SO THIS TRIGGERED THE BIRTH OF CANADAall because of the lack of coal  “Scottish Englightenment” (1730-1830)  So we see geology becoming a science  Famous people • Jospeh Black contributions to chemistry • James Hutton was a farmer who contributed to geology • Adam Smith was a famous economist = The Wealth of Nations • James Watt = developed steam engine • Walter Scott = famous novelist  What they have in Scotland is something called oil shale • Remember this is a time of increased demand for energy • You can burn oil shale to get the oil out  This is a profound time for rational use of Earth History  James Hutton (1726-97)  Father of modern geology  Why is he well-known?  Hutton's adventures • Skyline of city is dominated by ancient volcanoes • Everyday Hutton would walk up a big hill called “Arthur's Seat” • Even Charles Darwin was taken here to look at the rocks that Hutton had made so famous  Hutton's 2 Major Breakthroughs  Hutton's known for recognizing “unconformities” within layers of rocks • Unconformities are breaks in the rock record • Proposed concept of uniformitarianism = earth has a long history, but we can look at modern day processes to figure out stuff in the past.  First to recognize the igneous origin of granite/rock • Arthur's Seat shows evidence that rocks were molten at one time • This contrasts withAbram Werner's “diluvialism” concept, the idea that everything we see is a product of the flood  Diluvialism was the accepted theory up until this point  Geologists speak of rock “facies” • Facies means “appearance of” • Parody cartoon about Hutton looking at rocks with faces  Hutton's rock – very famous site – spurned appreciation for volcanic activity, etc  Charles Lyell  Famous for writing the first geology textbook  1830 – Principles of Geology  Popularized Hutton's ideas  Rock that interfingers with other rocks so it must have been igneous in origin  So this completely got rid of diluvialism  Hutton's Uinconformity at Siccar Point In Scotland  Famous location  Bottom rocks are turned upside  On the unconformity surface you get younger rocks  John Playfair  Geologist who introduced idea of “Deep Time”  “The mind grows giddy gazing so far back into the abyss of time”  Primary strata = older rocks that are bent  Unconformity = weathered/broken rock that separates two rock masses or strata  Secondary Strata = usually flat  Deep Time ➢ 2)AbsoluteAge (Isotopic Dati
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