Lecture-14-F10

Lecture-14-F10 - EAS 111 General Announcements • Schedule...

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Unformatted text preview: EAS 111 General Announcements 10/20/10 • Schedule Reminder Today – Weds 10/20 Geologic Time, Part 1 – Bring your text for lab this week! The week after that (10/25 & 10/27) and beyond – Mon 10/25 – Geologic Time, Part 2 – Weds 10/27 – Review for Lab Exam 2 and Lecture Exam 2 – Monday 11/1 = EXAM 2 – Lab Exams run from Tues 11/2 through Friday 11/5 Earth Science News A New Epoch of Geologic Time? The ANTHROPOCENE • Paul Crutzen, 2002 • Many geoscientists are beginning to add data to support a rapid set of changes, starting around 1780. Earth and Atmospheric Sciences 111 Fall 2010 Geologic Time I -Philosophical Perspectives on Earth History and Science -Relative Dating -Correlation intro -Lecture 14 Philosophical Perspectives • Ways of knowing – epistemology • Types of knowledge – empirical, cultural, indigenous, revealed, etc. • All sciences depend on empirical evidence, data that can be externally verified by your toughest skeptics • Search for naturalistic causes and conclusions for observed phenomena • Everyone should be able to reproduce empirical results and conclusions, even you Observe the orientation of rocks at Siccar Point, Scotland ayers l Red Unconformity Vertical, gray layers 09.00.a1 James Hutton, 1788 • The Present is the key to the Past • very gradual and slow events • very rapid and catastrophic events • everything in between • can processes change? • “We see no vestige of a beginning, no prospect of an end” Some of the Evidence that Earth’s History Some is Not Short is Tree rings 09.09.b Varves Current rates of Current plate motion plate Geologic Time Scale 09.08.a1 Geologic Time: How It Works • Relative Dating – Understand what happened in which order • Correlation – Connect the pieces of the geologic record together to construct a coherent and complete history for all areas of the planet • Absolute Dating – Determine the numerical age of an event or rock using laboratory methods Younger Units Deposited on Older Units Tan sediment deposited Tan over older rock over Red layers deposited Red over tan over Third layer is Third youngest and is on top is 09.01.a 09.01.a In the In view below? below? a) A is the oldest, no question b) B is the oldest, no question c) either A or B could be oldest depending on the Observe these layers. Which is Observe deformation details oldest and which is youngest? oldest d) B is probably oldest, as that’s the simplest solution B A Younger Sediment Younger or Rock Can Contain Pieces of Older Rock Older Determine which rock is Determine younger in each image younger Breccia Gray layers Gray Gray granite granite Conglomerate Dark basalt Dark metamorphic rocks 09.01.a Younger Rock or Younger Feature Can Crosscut an Older Rock or Feature Rock Determine which rock or Determine feature is younger in each image each Red Red layers layers Fractures Limestone Tan Tan dikes dikes Dark dike Dark Dark igneous rock rock 09.01.a Younger Rocks and Features Can Cause Younger Changes Along Contacts with Older Rocks Changes Observe the boundaries between different rock types Gray Gray conglomerate conglomerate Volcanic ash Volcanic and blocks and Dark Dark dike dike Tan sedimentary rock 09.01.a What Does an Unconformity Represent? Limestone folded and Limestone eroded eroded Gray limestone Gray deposited under water water Conglomerate Conglomerate deposited on top of eroded surface forming an unconformity unconformity Unconformity 09.04.a Relative Dating Principles • Superposition – older rocks are on the bottom, younger rocks are deposited on top – only applies for sedimentary and volcanic rocks – watch out for the effects of extreme deformation • Original horizontality – sedimentary rocks are originally horizontal and flat lying • Cross-cutting relationships & inclusions – Any rock body cross-cut by a fault, intrusion or other event must be older – Rocks included as clasts in units above them must be older than the rocks containing them Investigation: What Is the Geologic History of This Place? What is the relative age relationship of the canyon which holds thebserve this area lava flow L? O river N and the and Observe A a.Lava flow the ages ofbecause it partially fills the canyon L is older, determine C D b.Lava flow L is younger, because it partially fills the canyon events. R c.they are exactlyFthe same age R R d.there is no way to tell by relative dating A K B C D F V L N A S L D G As a geologist, you could conclude that Rock D is G younger B than A or C because: 09.15.c1 F a.the principle of superposition C b.the principle of original horizontality G c.the principle of cross-cutting relationships d.Rock D is actually older than A and C EAS 111: Assignments for 10/25/10 • Exploring Geology • Review 9.7, 9.8, 9.4 • Read 9.9, (9.10, 9.11 – lightly, do not memorize this material), 9.12, 9.13 • The basics of correlation of events at remote locations and radiometric and other laboratory dating methods to determine absolute age ...
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This note was uploaded on 01/12/2011 for the course EAS 111 taught by Professor Dr.ericriggs during the Spring '10 term at Purdue.

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