GEO 102 Lecture 12Outline of Last Lecture I. Geologic TimeOutline of Current Lecture II. Types of unconformitiesIII.CorrelationIV.Absolute DatingV.Half-lifeCurrent LectureBasic Principles of Rock Formation-Cross-cutting relationships: If one rock formation intrudes or bisects another, the rock being cross-cut must be older-Also inclusionsBasic Principles of Rock Formation-Unconformities-Non-deposition-ErosionAs opposed to a conformable transitionTypes of Unconformities-Angular unconformity-Rocks were tiled prior to later sedimentation-disconformity-Erosional surface between 2 parallel layers of rock-nonconformityThese 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.-Sedimentary rocks in contact with non-sedimentary rocks Most of these are based on simple fundamental logic – it almost seems unnecessary to define them.-The Really Big Picture-How do we take the previous interpretation of a single outcrop and extrapolate global time?-Correlation-Linking outcrops of the same rock over wide areas-Even globallyCorrelation-Linking time-equal rocks-Presently many different depositional environments form simultaneously.-Later they will be preserved incompletely as a wide range of rocksHow do you link the outcrops?-Rock types-Geochemistry-Fossils-Fossil succession-Fossils change in an orderly way through time-Index fossils-Extinction and evolution-Absolute datingAbsolute dating-Relative dating has been around centuries, and, but absolute estimates of the age of theEarth varied.-The goal was a fixed and absolute age-Radioactivity can act as a clock Decay and Half-life-Unstable nuclei eject particles predictably in order to achieve equilibrium-alpha particles ()-2 protons and 2 neutrons-beta particles ()-Electron from nucleus-Electron capture-Forms a neutron after fusing with a protonHalf-Life-For any given atom, it can not be predicted when decay will occur-However, a POPULATION of atoms will decay like clockwork-the time it takes for half of the population to decay = one half-lifeWhat do we date?-Only some elements have radioactive isotopes-Only some isotopes have half-lives that are useful-Only some minerals contain these few isotopes-Only some rocks contain pristine minerals-There must be no non-radioactive alteration of parent or daughter-Closed
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