CEE 1030 1nd Edition Lecture 8 Geologic Time 1 Outline of Last Lecture I Metamorphic rocks a Agents of metamorphism II Metamorphic textures III Metamorphic grade IV Metamorphic environments Outline of Current Lecture I Review II Geologic Time Scale III Principles a Principle of Uniformitarianism b Principle of Superposition c Principle of Original Horizontality d Principle of Cross Cutting Relationships e Principle of Inclusions IV Unconformities V Geological history of a region Current Lecture I II Review a Gneiss is characterized by segregation of light and dark colored minerals into thin layers or bands b Increasing grain size and increasing grade of metamorphism slate phyllite schist gneiss Geologic Time Scale a Calendar of Earth s history divides geologic history into units b Two ways to date geologic events i Relative dating determine whether rock is older or younger than surround rock ii Absolute dating determine actual number of years since rock was formed determined by radioactive decay c Eon greatest expanse of time i Phanerozoic visible life most recent eon 540 million years ago ii Proterozoic 2500 540 million years ago iii Archaen 3800 2500 million years ago These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV V iv Hadean 4500 3800 million years ago Oldest eon d Structure of geologic time scale i Era subdivision of eon ii Eras of Phanerozoic eon 1 Paleozoic oldest 2 Mesozoic 3 Cenozoic youngest iii Period subdivision of era Principles a Principle of Uniformitarianism i James Hutton ii Looking at modern processes allows us to interpret geological past as preserved in the record of rocks iii Processes that happen today also happened in the past b Principle of Superposition i Nicolaus Steno ii In a series of layered rocks the older rocks are on the bottom sediment piles up c Principle of Original Horizontality i Nicolaus Steno ii Layered strata are deposited in nearly horizontal position iii If rock layer are flat it means they have not been disturbed iv Applies to both sedimentary and most volcanic rocks v Like making a PB J oldest layer is the plate you add layers horizontally d Principle of Cross Cutting Relationships i Younger features cut across older features ii For example igneous intrusions and faults cut across established sedimentary layers e Principle of Inclusions i Inclusion a piece of rock that is enclosed within another rock ii Inclusions are always older than the host rock Unconformities a A break in the rock record produced by erosion and or deposition of rock units b Three types of unconformity i Nonconformity ii Angular conformity iii Disconformity Geological history of a region a Principle of Lateral Continuity i Sedimentary rock layers are often laterally continuous over 10s of km b Fossils and correlation i Matching of rocks of similar ages in different regions correlation ii Correlation relies upon fossils c Principle of Fossil Succession i Different types of fossils always appear and disappear in the same order within the geologic record time period is recognized by fossils ii Index fossil widespread fossil limited to short span of geologic time iii Dating rocks can be done by using overlapping fossil ranges
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