CEE 1030 1nd Edition Lecture 8: Geologic Time #1Outline of Last Lecture I. Metamorphic rocksa. Agents of metamorphismII. Metamorphic texturesIII. Metamorphic gradeIV. Metamorphic environmentsOutline of Current Lecture I. ReviewII. Geologic Time ScaleIII. Principlesa. Principle of Uniformitarianismb. Principle of Superpositionc. Principle of Original Horizontalityd. Principle of Cross-Cutting Relationshipse. Principle of InclusionsIV. UnconformitiesV. Geological history of a regionCurrent LectureI. Reviewa. Gneiss is characterized by segregation of light and dark-colored minerals into thinlayers or bandsb. Increasing grain size and increasing grade of metamorphism: slate, phyllite, schist, gneissII. Geologic Time Scalea. “Calendar” of Earth’s history, divides geologic history into unitsb. Two ways to date geologic eventsi. Relative dating: determine whether rock is older or younger than surround rockii. Absolute dating: determine actual number of years since rock was formed(determined by radioactive decay)c. Eon: greatest expanse of timei. 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.iv. Hadean (4500-3800 million years ago) Oldest eond. Structure of geologic time scalei. Era: subdivision of eonii. Eras of Phanerozoic eon1. Paleozoic (oldest)2. Mesozoic3. Cenozoic (youngest)iii. Period: subdivision of eraIII. Principlesa. Principle of Uniformitarianismi. James Huttonii. Looking at modern processes allows us to interpret geological past as preserved in the record of rocksiii. Processes that happen today also happened in the pastb. Principle of Superpositioni. Nicolaus Stenoii. In a series of layered rocks, the older rocks are on the bottom (sediment piles up)c. Principle of Original Horizontalityi. Nicolaus Stenoii. Layered strata are deposited in nearly-horizontal positioniii. If rock layer are flat, it means they have not been disturbediv. Applies to both sedimentary and most volcanic rocksv. Like making a PB&J: oldest layer is the plate, you add layers horizontallyd. Principle of Cross-Cutting Relationshipsi. Younger features cut across older featuresii. For example, igneous intrusions and faults cut across established sedimentary layerse. Principle of Inclusionsi. Inclusion: a piece of rock that is enclosed within another rockii. Inclusions are always older than the host rockIV. Unconformitiesa. A break in the rock record produced by erosion and/or deposition of rock unitsb. Three types of unconformityi. Nonconformityii. Angular conformityiii. DisconformityV. Geological history of a regiona. Principle of Lateral Continuityi. Sedimentary rock layers are often laterally continuous over 10s of kmb. Fossils and correlationi. Matching of rocks of similar ages in different regions: correlationii. Correlation relies upon fossilsc. Principle of Fossil Successioni. Different types of fossils always appear and disappear in the same order within the geologic record: time period is recognized by fossilsii. Index fossil: widespread fossil limited to short span of geologic timeiii. Dating rocks can be done by using overlapping fossil
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