Geol113 Final Exam Study Guide

Geol113 Final Exam Study Guide - GEOLOGY 113 Exam 3 Study...

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GEOLOGY 113 Exam 3 Study Guide REVISED 5/13/2015 Deep Earth Time and Geologic Dating Difference between relative and numerical dating Relative dating is based on the sequence of formation (first, second, third...) while numerical dating is based on the actual number of years that have passed since an event occurred. Principles of relative dating in geology Principle of original horizontality -layers of sediment are generally deposited in a horizontal position , P. of superposition -in an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below , P. of lateral continuity -sedimentary rocks originate as continuous layers that extend in all directions until they eventually grade into a different type of sediment or until they thin out at the edge of the basin of deposition , P. of cross-cutting relationships -geologic features that cut across rocks must form after the rocks they cut through , P. of inclusions -the rock mass adjacent to the rock mass containing the inclusions must have been there first in order to provide the rock fragments (inclusion is older) , P. of Fossil (Faunal) Succession - fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content Unconformities -breaks in the rock record and represents a long period during which deposition ceased, erosion removed previously formed rocks, and then deposition resumed; three types: angular unconformity (tilted or folded sedimentary rocks that are overlain by younger, more flat-lying strata), disconformity (gap in the rock record where erosion rather than deposition occurred), nonconformity (younger sedimentary strata overlie older metamorphic or intrusive igneous rocks) Fossils in relative dating –What are fossils? Fossils are the remains or traces of prehistoric life and are important inclusions in sediment and sedimentary rocks. Index fossils? Index fossils are widespread geographically and are limited to a short span of geologic time and helps match rocks of the same age. Fossil assemblages? Fossil assemblages are groups of fossils that are used to establish the age of the bed. Know how to relative date rock layers by applying the Principles of superposition, original horizontality, lateral continuity, inclusions, crosscutting relationships & fossils. Basic principles of radiometric dating – be able to solve problems related to half-lives. First half-life- 50%, second half-life-25%, third half-life-12.5%, fourth half-life-6.25% fifth half-life-3.125% Age of the Earth (4.6 billion years old!!!) What is the Precambrian? The Precambrian is the time period, from ~4600 mya to 542 mya, that comprised of two eons (Archean and Proterozoic) and four eras (Eoarchean, Paleoarchean, Mesoarchaean, and Neoarchean) and represents about 88% of Earth History and is not known in great detail. The Phanerozoic? The Phanerozoic is the time period known as an eon that began about 542 mya and means visible life.
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