Understanding Geologic Time from the Texas Memorial Museum
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Geologic Time Two Ways to Date Geologic Events Steno's Laws
Frank Press • Raymond Siever • John Grotzinger • Thomas H. Jordan Understanding Earth Fourth Edition Chapter 10: The Rock Record and the Geologic Time Scale Lecture Slides prepared by Peter Copeland • Bill Dupré Copyright © 2004 by W. H. Freeman & Company Geologic Time Two Ways to Date Geologic Events A major difference between geologists and most other 1) relative dating (fossils, structure, cross- scientists is their concept of time. cutting relationships): how old a rock is compared to surrounding rocks A "long" time may not be important unless it is greater than 1 million years 2) absolute dating (isotopic, tree rings, etc.): actual number of years since the rock was formed Steno's Laws Principle of Superposition Nicholas Steno (1669) In a sequence of undisturbed • Principle of Superposition layered rocks, the oldest rocks are • Principle of Original on the bottom. Horizontality These laws apply to both sedimentary and volcanic rocks. Principle of Original Horizontality Layered strata are deposited horizontal or nearly horizontal or nearly parallel to the Earth’s surface. Fig. 10.3 Paleontology • The study of life in the past based on the fossil of plants and animals. Fossil: evidence of past life • Fossils that are preserved in sedimentary rocks are used to determine: 1) relative age 2) the environment of deposition Fig. 10.5 Unconformity A buried surface of erosion Fig. 10.6 Cross-cutting Relationships • Geometry of rocks that allows geologists to place rock unit in relative chronological order. • Used for relative dating. Fig. 10.8 Fig. 10.9 Fig. 10.9 Fig. 10.9 Fig. Story 10.11 Fig. -
Lab 7: Relative Dating and Geological Time
LAB 7: RELATIVE DATING AND GEOLOGICAL TIME Lab Structure Synchronous lab work Yes – virtual office hours available Asynchronous lab work Yes Lab group meeting No Quiz None – Test 2 this week Recommended additional work None Required materials Pencil Learning Objectives After carefully reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to: • Apply basic geological principles to the determination of the relative ages of rocks. • Explain the difference between relative and absolute age-dating techniques. • Summarize the history of the geological time scale and the relationships between eons, eras, periods, and epochs. • Understand the importance and significance of unconformities. • Explain why an understanding of geological time is critical to both geologists and the general public. Key Terms • Eon • Original horizontality • Era • Cross-cutting • Period • Inclusions • Relative dating • Faunal succession • Absolute dating • Unconformity • Isotopic dating • Angular unconformity • Stratigraphy • Disconformity • Strata • Nonconformity • Superposition • Paraconformity Time is the dimension that sets geology apart from most other sciences. Geological time is vast, and Earth has changed enough over that time that some of the rock types that formed in the past could not form Lab 7: Relative Dating and Geological Time | 181 today. Furthermore, as we’ve discussed, even though most geological processes are very, very slow, the vast amount of time that has passed has allowed for the formation of extraordinary geological features, as shown in Figure 7.0.1. Figure 7.0.1: Arizona’s Grand Canyon is an icon for geological time; 1,450 million years are represented by this photo. -
Ice-Core Dating of the Pleistocene/Holocene
[RADIOCARBON, VOL 28, No. 2A, 1986, P 284-291] ICE-CORE DATING OF THE PLEISTOCENE/HOLOCENE BOUNDARY APPLIED TO A CALIBRATION OF THE 14C TIME SCALE CLAUS U HAMMER, HENRIK B CLAUSEN Geophysical Isotope Laboratory, University of Copenhagen and HENRIK TAUBER National Museum, Copenhagen, Denmark ABSTRACT. Seasonal variations in 180 content, in acidity, and in dust content have been used to count annual layers in the Dye 3 deep ice core back to the Late Glacial. In this way the Pleistocene/Holocene boundary has been absolutely dated to 8770 BC with an estimated error limit of ± 150 years. If compared to the conventional 14C age of the same boundary a 0140 14C value of 4C = 53 ± 13%o is obtained. This value suggests that levels during the Late Glacial were not substantially higher than during the Postglacial. INTRODUCTION Ice-core dating is an independent method of absolute dating based on counting of individual annual layers in large ice sheets. The annual layers are marked by seasonal variations in 180, acid fallout, and dust (micro- particle) content (Hammer et al, 1978; Hammer, 1980). Other parameters also vary seasonally over the annual ice layers, but the large number of sam- ples needed for accurate dating limits the possible parameters to the three mentioned above. If accumulation rates on the central parts of polar ice sheets exceed 0.20m of ice per year, seasonal variations in 180 may be discerned back to ca 8000 BP. In deeper strata, ice layer thinning and diffusion of the isotopes tend to obliterate the seasonal 5 pattern.1 Seasonal variations in acid fallout and dust content can be traced further back in time as they are less affected by diffusion in ice. -
The Geologic Time Scale Is the Eon
Exploring Geologic Time Poster Illustrated Teacher's Guide #35-1145 Paper #35-1146 Laminated Background Geologic Time Scale Basics The history of the Earth covers a vast expanse of time, so scientists divide it into smaller sections that are associ- ated with particular events that have occurred in the past.The approximate time range of each time span is shown on the poster.The largest time span of the geologic time scale is the eon. It is an indefinitely long period of time that contains at least two eras. Geologic time is divided into two eons.The more ancient eon is called the Precambrian, and the more recent is the Phanerozoic. Each eon is subdivided into smaller spans called eras.The Precambrian eon is divided from most ancient into the Hadean era, Archean era, and Proterozoic era. See Figure 1. Precambrian Eon Proterozoic Era 2500 - 550 million years ago Archaean Era 3800 - 2500 million years ago Hadean Era 4600 - 3800 million years ago Figure 1. Eras of the Precambrian Eon Single-celled and simple multicelled organisms first developed during the Precambrian eon. There are many fos- sils from this time because the sea-dwelling creatures were trapped in sediments and preserved. The Phanerozoic eon is subdivided into three eras – the Paleozoic era, Mesozoic era, and Cenozoic era. An era is often divided into several smaller time spans called periods. For example, the Paleozoic era is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous,and Permian periods. Paleozoic Era Permian Period 300 - 250 million years ago Carboniferous Period 350 - 300 million years ago Devonian Period 400 - 350 million years ago Silurian Period 450 - 400 million years ago Ordovician Period 500 - 450 million years ago Cambrian Period 550 - 500 million years ago Figure 2. -
“Anthropocene” Epoch: Scientific Decision Or Political Statement?
The “Anthropocene” epoch: Scientific decision or political statement? Stanley C. Finney*, Dept. of Geological Sciences, California Official recognition of the concept would invite State University at Long Beach, Long Beach, California 90277, cross-disciplinary science. And it would encourage a mindset USA; and Lucy E. Edwards**, U.S. Geological Survey, Reston, that will be important not only to fully understand the Virginia 20192, USA transformation now occurring but to take action to control it. … Humans may yet ensure that these early years of the ABSTRACT Anthropocene are a geological glitch and not just a prelude The proposal for the “Anthropocene” epoch as a formal unit of to a far more severe disruption. But the first step is to recognize, the geologic time scale has received extensive attention in scien- as the term Anthropocene invites us to do, that we are tific and public media. However, most articles on the in the driver’s seat. (Nature, 2011, p. 254) Anthropocene misrepresent the nature of the units of the International Chronostratigraphic Chart, which is produced by That editorial, as with most articles on the Anthropocene, did the International Commission on Stratigraphy (ICS) and serves as not consider the mission of the International Commission on the basis for the geologic time scale. The stratigraphic record of Stratigraphy (ICS), nor did it present an understanding of the the Anthropocene is minimal, especially with its recently nature of the units of the International Chronostratigraphic Chart proposed beginning in 1945; it is that of a human lifespan, and on which the units of the geologic time scale are based. -
Scientific Dating of Pleistocene Sites: Guidelines for Best Practice Contents
Consultation Draft Scientific Dating of Pleistocene Sites: Guidelines for Best Practice Contents Foreword............................................................................................................................. 3 PART 1 - OVERVIEW .............................................................................................................. 3 1. Introduction .............................................................................................................. 3 The Quaternary stratigraphical framework ........................................................................ 4 Palaeogeography ........................................................................................................... 6 Fitting the archaeological record into this dynamic landscape .............................................. 6 Shorter-timescale division of the Late Pleistocene .............................................................. 7 2. Scientific Dating methods for the Pleistocene ................................................................. 8 Radiometric methods ..................................................................................................... 8 Trapped Charge Methods................................................................................................ 9 Other scientific dating methods ......................................................................................10 Relative dating methods ................................................................................................10 -
Personal Details: Relative Dating Methods Archaeology; Principles
Component-I (A) – Personal details: Archaeology; Principles and Methods Relative Dating Methods Prof. P. Bhaskar Reddy Sri Venkateswara University, Tirupati. Prof. K.P. Rao University of Hyderabad, Hyderabad. Prof. K. Rajan Pondicherry University, Pondicherry. Prof. R. N. Singh Banaras Hindu University, Varanasi. 1 Component-I (B) – Description of module: Subject Name Indian Culture Paper Name Archaeology; Principles and Methods Module Name/Title Relative Dating Methods Module Id IC / APM / 17 Pre requisites Objectives Archaeology / Stratigraphy / Dating / Keywords Geochronology E-Text (Quadrant-I) : 1. Introduction In archaeology, the material unearthed in the excavations and archaeological remains surfaced and documented in the explorations are dated by following two methods namely, absolute dating method and relative dating method. In the former method, the artefacts are being preciously dated using various scientific techniques and in a few cases it is dated based on the hidden historical data available with historical documents such as inscriptions, copper plates, seals, coins, inscribed portrait sculptures and monuments. In the latter method, a tentative date is achieved based on archaeological stratigraphy, seriation, palaeography, linguistic style, context, art and architectural features. Though the absolute dates are the most desirable one, the significance of relative dates increases manifold when the absolute dates are not available. Till advent of the scientific techniques, most of the archaeological and historical objects were dated based on relative dating methods. Archaeologists are resorted to the use of relative dating techniques when the absolute dates are not possible or feasible. Estimation of the age was merely a guess work in the initial stage of archaeological investigation particularly in 18th-19th centuries. -
Utah's Geologic Timeline Utah Seed Standard 7.2.6: Make an Argument from Evidence for How the Geologic Time Scale Shows the Ag
Utah’s Geologic Timeline Utah SEEd Standard 7.2.6: Make an argument from evidence for how the geologic time scale shows the age and history of Earth. Emphasize scientific evidence from rock strata, the fossil record, and the principles of relative dating, such as superposition, uniformitarianism, and recognizing unconformities. (ESS1.C) Activity Details: The students begin with a blank calendar and a list of events in the Earth’s, and additionally Utah’s, history. These events span billions of years, but such numbers are too large to visualize and compare. In order to help the mind understand such enormous lengths of time, the year of the event is scaled to what it would Be proportionate to a calendar year (numBers are from The Utah Geological Survey and Kentucky Geological Survey). The students go through the list and fill out their calendar to visualize the geologic timeline of the Earth and Utah, and then answer some analysis questions to help solidify their understanding. Students will need four differently-colored colored pencils or crayons to complete the activity. Background: The following information is taken from The Utah Geological Survey, written by Mark Milligan. It may Be helpful to define some of the terms with the students so they understand where and how ages come from. Geologists generally know the age of a rock By determining the age of the group of rocks, or formation, that it is found in. The age of formations is marked on a geologic calendar known as the geologic time scale. Development of the geologic time scale and dating of formations and rocks relies upon two fundamentally different ways of telling time: relative and absolute. -
Ice-Core Dating and Chemistry by Direct-Current Electrical Conductivity Kenorick Taylor
The University of Maine DigitalCommons@UMaine Earth Science Faculty Scholarship Earth Sciences 1992 Ice-core Dating and Chemistry by Direct-current Electrical Conductivity Kenorick Taylor Richard Alley Joe Fiacco Pieter Grootes Gregg Lamorey See next page for additional authors Follow this and additional works at: https://digitalcommons.library.umaine.edu/ers_facpub Part of the Glaciology Commons, Hydrology Commons, and the Sedimentology Commons Repository Citation Taylor, Kenorick; Alley, Richard; Fiacco, Joe; Grootes, Pieter; Lamorey, Gregg; Mayewski, Paul Andrew; and Spencer, Mary Jo, "Ice- core Dating and Chemistry by Direct-current Electrical Conductivity" (1992). Earth Science Faculty Scholarship. 273. https://digitalcommons.library.umaine.edu/ers_facpub/273 This Article is brought to you for free and open access by DigitalCommons@UMaine. It has been accepted for inclusion in Earth Science Faculty Scholarship by an authorized administrator of DigitalCommons@UMaine. For more information, please contact [email protected]. Authors Kenorick Taylor, Richard Alley, Joe Fiacco, Pieter Grootes, Gregg Lamorey, Paul Andrew Mayewski, and Mary Jo Spencer This article is available at DigitalCommons@UMaine: https://digitalcommons.library.umaine.edu/ers_facpub/273 Journal of Glaciology, Vo!. 38, No. 130, 1992 Ice-core dating and chentistry by direct-current electrical conductivity KENORICK TAYLOR, Water Resources Center, Desert Research Institute, University of Nevada System, Reno, Nevada, U.S.A. RICHARD ALLEY, Earth System Science Genter and Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, U.S.A. JOE FIACCO, Glacier Research Group, Institute of the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire, U.S.A. PIETER GROOTES, Qyaternary Isotope Laboratory, University of Washington, Seatae, Washington, U.S.A. -
Terminology of Geological Time: Establishment of a Community Standard
Terminology of geological time: Establishment of a community standard Marie-Pierre Aubry1, John A. Van Couvering2, Nicholas Christie-Blick3, Ed Landing4, Brian R. Pratt5, Donald E. Owen6 and Ismael Ferrusquía-Villafranca7 1Department of Earth and Planetary Sciences, Rutgers University, Piscataway NJ 08854, USA; email: [email protected] 2Micropaleontology Press, New York, NY 10001, USA email: [email protected] 3Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades NY 10964, USA email: [email protected] 4New York State Museum, Madison Avenue, Albany NY 12230, USA email: [email protected] 5Department of Geological Sciences, University of Saskatchewan, Saskatoon SK7N 5E2, Canada; email: [email protected] 6Department of Earth and Space Sciences, Lamar University, Beaumont TX 77710 USA email: [email protected] 7Universidad Nacional Autónomo de México, Instituto de Geologia, México DF email: [email protected] ABSTRACT: It has been recommended that geological time be described in a single set of terms and according to metric or SI (“Système International d’Unités”) standards, to ensure “worldwide unification of measurement”. While any effort to improve communication in sci- entific research and writing is to be encouraged, we are also concerned that fundamental differences between date and duration, in the way that our profession expresses geological time, would be lost in such an oversimplified terminology. In addition, no precise value for ‘year’ in the SI base unit of second has been accepted by the international bodies. Under any circumstances, however, it remains the fact that geologi- cal dates – as points in time – are not relevant to the SI. -
Relative Dating Unit B
Geologic Time Part I: Relative Dating Unit B Unit A James Hutton conceived of the Principle of Uniformitarianism at Sicar Point, Scotland in 1785. Think about how much time would pass to create the rock record shown above. What sequence of events would occur to produce the above record? Unit B Unit A 1. Deposition of sediment comprising Unit A (Sedimentation rates in the deep ocean range from .0005 - .001 mm per year). How long would it take to accumulate 200 meters of sediment?) 2. burial compaction & lithification of Unit A, 3. deformation (folding) of Unit A, 4. uplift and erosion of Unit A, 5. Deposition of sediment (Unit B), 6. burial compaction & lithification of Unit B, 7. deformation (folding) of Unit B, 8. uplift and erosion of Unit B. These geologic events require millions of years of time! Principle of Original Horizontality: Layered sedimentary rock is typically deposited horizontally, but can be deformed by tectonic processes. Can you think of a depositional environment where sedimentary layers are not deposited horizontally? Geologists use sedimentary structures to determine whether sedimentary layers or beds are right-side up, vertical or overturned. The Principle of Uniformitarianism states that the “present is the key to the past.” Those processes operating at the earth’s surface today are inferred to have operated in the past, such as the mudcracks forming in a playa lake today. Note the blowing sand in the background will fill in the cracks. The mudcracks shown above formed over 1.1 billion years ago in a dry lake basin are now found in Glacier National Park, Montana. -
Dating Techniques.Pdf
Dating Techniques Dating techniques in the Quaternary time range fall into three broad categories: • Methods that provide age estimates. • Methods that establish age-equivalence. • Relative age methods. 1 Dating Techniques Age Estimates: Radiometric dating techniques Are methods based in the radioactive properties of certain unstable chemical elements, from which atomic particles are emitted in order to achieve a more stable atomic form. 2 Dating Techniques Age Estimates: Radiometric dating techniques Application of the principle of radioactivity to geological dating requires that certain fundamental conditions be met. If an event is associated with the incorporation of a radioactive nuclide, then providing: (a) that none of the daughter nuclides are present in the initial stages and, (b) that none of the daughter nuclides are added to or lost from the materials to be dated, then the estimates of the age of that event can be obtained if the ration between parent and daughter nuclides can be established, and if the decay rate is known. 3 Dating Techniques Age Estimates: Radiometric dating techniques - Uranium-series dating 238Uranium, 235Uranium and 232Thorium all decay to stable lead isotopes through complex decay series of intermediate nuclides with widely differing half- lives. 4 Dating Techniques Age Estimates: Radiometric dating techniques - Uranium-series dating • Bone • Speleothems • Lacustrine deposits • Peat • Coral 5 Dating Techniques Age Estimates: Radiometric dating techniques - Thermoluminescence (TL) Electrons can be freed by heating and emit a characteristic emission of light which is proportional to the number of electrons trapped within the crystal lattice. Termed thermoluminescence. 6 Dating Techniques Age Estimates: Radiometric dating techniques - Thermoluminescence (TL) Applications: • archeological sample, especially pottery.