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Absolute Time Radiometric Dating: the Source of the Dates on the Geologic Time Scale
Absolute Time Radiometric Dating: the source of the dates on the Geologic Time Scale Radiometric Dating • Actually a simple technique. • Only two measurements are needed: • 1. The parent:daughter ratio measured with a mass spectrometer. • 2. The decay constant measured by a scintillometer. Basis of the Technique • Radioactive elements “decay.” Decay occurs as an element changes to another element, e.g. uranium to lead. • The parent element is radioactive, the daughter element is stable. • The decay rate is constant. What is Radioactivity? • Radioactivity occurs when certain elements literally fall apart. • Usually protons and neutrons are emitted by the nucleus. • Sometimes an electron is emitted by the nucleus, which changes a neutron to a proton. • Sometimes an electron is captured. What causes radioactivity? • Carbon-14 is produced by cosmic ray bombardment of Nitrogen-14 in the atmosphere. • All other radioactive elements were produced by supernova explosions before our solar system formed. This is called explosive nucleosynthesis. Common Radioactive Elements, Parents and Daughters • Carbon-14, C14 Nitrogen-14, N14 • Uranium-235, U235 Lead-207, Pb207 • Potassium-40, K40 Argon-40, Ar40 • Uranium-238, U238 Lead-206, Pb206 • Rubidium-87, Rb87 Strontium-87, Sr87 Basis of the Technique • As the parent element decays, its amount decreases while the amount of the daughter element increases. This gives us a ratio of parent:daughter elements. • The decay rate is geometric rather than linear. Unaffected by heat or pressure. Key Term • Half-Life: the amount of time for half the atoms of a radioactive element to decay. Doesn’t matter how many atoms started, half will decay. -
(2016), Volume 4, Issue 2, 77-90
ISSN 2320-5407 International Journal of Advanced Research (2016), Volume 4, Issue 2, 77-90 Journal homepage: http://www.journalijar.com INTERNATIONAL JOURNAL OF ADVANCED RESEARCH RESEARCH ARTICLE LICHENOMETRIC DATING CURVE AS APPLIED TO GLACIER RETREAT STUDIES IN THE HIMALAYAS. Gaurav K. Mishra, Santosh Joshi and Dalip K. Upreti. Lichenology Laboratory, CSIR-National Botanical Research Institute, Rana Pratap Marg, Lucknow- 226001. Manuscript Info Abstract Manuscript History: The study critically favours the importance of lichens in estimating palaeoclimatic events and its use in depicting the future discretion regarding Received: 14 December 2015 Final Accepted: 19 January 2016 glacier retreat. Besides the various lichenometric studies carried out in Indian Published Online: February 2016 Himalayan region, the world-wide classical work of different glaciologist and geologist on different applications of lichenometry is also well focused. Key words: The study also highlights the benefits, restrains, and drawbacks associated Lichens, lichenometry,glacier with the lichenometry. Being a globally accepted biological technique retreat,India. particular emphasis is given on the need of innovative approach in implementation of lichenometry in Indian Himalayan region. *Corresponding Author Gaurav K. Mishra. Copy Right, IJAR, 2016,. All rights reserved. Introduction:- Lichens are slow growing organisms and take several years to get established in nature. Lichens are a unique group of plants, comprising of two micro-organisms, fungus (mycobiont), an organism capable of producing food via photosynthesis and alga (photobiont). These photobionts are predominantly members of the chlorophyta (green algae) or cynophyta (blue-green algae or cynobacteria). The peculiar nature of lichens enables them to colonize variety of substrate like rock, boulders, bark, soil, leaf and man-made buildings. -
Radiocarbon Dating and Its Applications in Quaternary Studies
Eiszeitalter und Gegenwart 57/1–2 2–24 Hannover 2008 Quaternary Science Journal Radiocarbon dating and its applications in Quaternary studies *) IRKA HAJDAS Abstract: This paper gives an overview of the origin of 14C, the global carbon cycle, anthropogenic impacts on the atmospheric 14C content and the background of the radiocarbon dating method. For radiocarbon dating, important aspects are sample preparation and measurement of the 14C content. Recent advances in sample preparation allow better understanding of long-standing problems (e.g., contamination of bones), which helps to improve chronologies. In this review, various preparation techniques applied to typical sample types are described. Calibration of radiocarbon ages is the fi nal step in establishing chronologies. The present tree ring chronology-based calibration curve is being constantly pushed back in time beyond the Holocene and the Late Glacial. A reliable calibration curve covering the last 50,000-55,000 yr is of great importance for both archaeology as well as geosciences. In recent years, numerous studies have focused on the extension of the radiocarbon calibration curve (INTCAL working group) and on the reconstruction of palaeo-reservoir ages for marine records. [Die Radiokohlenstoffmethode und ihre Anwendung in der Quartärforschung] Kurzfassung: Dieser Beitrag gibt einen Überblick über die Herkunft von Radiokohlenstoff, den globalen Kohlenstoffkreislauf, anthropogene Einfl üsse auf das atmosphärische 14C und die Grundlagen der Radio- kohlenstoffmethode. Probenaufbereitung und das Messen der 14C Konzentration sind wichtige Aspekte im Zusammenhang mit der Radiokohlenstoffdatierung. Gegenwärtige Fortschritte in der Probenaufbereitung erlauben ein besseres Verstehen lang bekannter Probleme (z.B. die Kontamination von Knochen) und haben zu verbesserten Chronologien geführt. -
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. -
Forensic Radiocarbon Dating of Human Remains: the Past, the Present, and the Future
AEFS 1.1 (2017) 3–16 Archaeological and Environmental Forensic Science ISSN (print) 2052-3378 https://doi.org.10.1558/aefs.30715 Archaeological and Environmental Forensic Science ISSN (online) 2052-3386 Forensic Radiocarbon Dating of Human Remains: The Past, the Present, and the Future Fiona Brock1 and Gordon T. Cook2 1. Cranfield Forensic Institute, Cranfield University 2. Scottish Universities Environmental Research Centre [email protected] Radiocarbon dating is a valuable tool for the forensic examination of human remains in answering questions as to whether the remains are of forensic or medico-legal interest or archaeological in date. The technique is also potentially capable of providing the year of birth and/or death of an individual. Atmospheric radiocarbon levels are cur- rently enhanced relative to the natural level due to the release of large quantities of radiocarbon (14C) during the atmospheric nuclear weapons testing of the 1950s and 1960s. This spike, or “bomb-pulse,” can, in some instances, provide precision dates to within 1–2 calendar years. However, atmospheric 14C activity has been declining since the end of atmospheric weapons testing in 1963 and is likely to drop below the natural level by the mid-twenty-first century, with implications for the application of radio- carbon dating to forensic specimens. Introduction Radiocarbon dating is most routinely applied to archaeological and environmental studies, but in some instances can be a very powerful tool for forensic specimens. Radiocarbon (14C) is produced naturally in the upper atmosphere by the interaction of cosmic rays on nitrogen-14 (14N). The 14C produced is rapidly oxidised to carbon dioxide, which then either enters the terrestrial biosphere via photosynthesis and proceeds along the food chain via herbivores and omnivores, and subsequently car- nivores, or exchanges into marine reservoirs where it again enters the food chain by photosynthesis. -
Isotopegeochemistry Chapter4
Isotope Geochemistry W. M. White Chapter 4 GEOCHRONOLOGY III: OTHER DATING METHODS 4.1 COSMOGENIC NUCLIDES 4.1.1 Cosmic Rays in the Atmosphere As the name implies, cosmogenic nuclides are produced by cosmic rays colliding with atoms in the atmosphere and the surface of the solid Earth. Nuclides so created may be stable or radioactive. Radio- active cosmogenic nuclides, like the U decay series nuclides, have half-lives sufficiently short that they would not exist in the Earth if they were not continually produced. Assuming that the production rate is constant through time, then the abundance of a cosmogenic nuclide in a reservoir isolated from cos- mic ray production is simply given by: −λt N = N0e 4.1 Hence if we know N0 and measure N, we can calculate t. Table 4.1 lists the radioactive cosmogenic nu- clides of principal interest. As we shall, cosmic ray interactions can also produce rare stable nuclides, and their abundance can also be used to measure geologic time. A number of different nuclear reactions create cosmogenic nuclides. “Cosmic rays” are high-energy (several GeV up to 1019 eV!) atomic nuclei, mainly of H and He (because these constitute most of the matter in the universe), but nuclei of all the elements have been recognized. To put these kinds of ener- gies in perspective, the previous gen- eration of accelerators for physics ex- Table 4.1. Data on Cosmogenic Nuclides periments, such as the Cornell Elec- -1 tron Storage Ring produce energies in Nuclide Half-life, years Decay constant, yr the 10’s of GeV (1010 eV); while 14C 5730 1.209x 10-4 CERN’s Large Hadron Collider, 3H 12.33 5.62 x 10-2 mankind’s most powerful accelerator, 10Be 1.500 × 106 4.62 x 10-7 located on the Franco-Swiss border 26Al 7.16 × 105 9.68x 10-5 near Geneva produces energies of 36Cl 3.08 × 105 2.25x 10-6 ~10 TeV range (1013 eV). -
A Review of Lichenometric Dating of Glacial Moraines in Alaska a Review of Lichenometric Dating of Glacial Moraines in Alaska
A REVIEW OF LICHENOMETRIC DATING OF GLACIAL MORAINES IN ALASKA A REVIEW OF LICHENOMETRIC DATING OF GLACIAL MORAINES IN ALASKA BY GREGORY C. WILES1, DAVID J. BARCLAY2 AND NICOLÁS E.YOUNG3 1Department of Geology, The College of Wooster, Wooster, USA 2Geology Department, State University of New York at Cortland, Cortland, USA 3Department of Geology, University at Buffalo, Buffalo, NY, USA Wiles, G.C., Barclay, D.J. and Young, N.E., 2010: A review of li- scarred trees provide high precision records span- chenometric dating of glacial moraines in Alaska. Geogr. Ann., 92 ning the past 2000 years (Barclay et al. 2009). A (1): 101–109. However, many other glacier forefields in Alaska ABSTRACT. In Alaska, lichenometry continues to be are beyond the latitudinal or altitudinal tree line in an important technique for dating late Holocene locations where tree-ring based dating methods moraines. Research completed during the 1970s cannot be applied. through the early 1990s developed lichen dating Lichenometry is a key method for dating curves for five regions in the Arctic and subarctic Alaskan Holocene glacier histories beyond the tree mountain ranges beyond altitudinal and latitudinal treelines. Although these dating curves are still in line. Some of the earliest well-replicated glacier use across Alaska, little progress has been made in histories in Alaska were based on lichen dates of the past decade in updating or extending them or in moraines (Denton and Karlén 1973a, b, 1977; developing new curves. Comparison of results from Calkin and Ellis 1980, 1984; Ellis and Calkin 1984) recent moraine-dating studies based on these five and the method continues to be applied today (e.g. -
Paleomagnetism and U-Pb Geochronology of the Late Cretaceous Chisulryoung Volcanic Formation, Korea
Jeong et al. Earth, Planets and Space (2015) 67:66 DOI 10.1186/s40623-015-0242-y FULL PAPER Open Access Paleomagnetism and U-Pb geochronology of the late Cretaceous Chisulryoung Volcanic Formation, Korea: tectonic evolution of the Korean Peninsula Doohee Jeong1, Yongjae Yu1*, Seong-Jae Doh2, Dongwoo Suk3 and Jeongmin Kim4 Abstract Late Cretaceous Chisulryoung Volcanic Formation (CVF) in southeastern Korea contains four ash-flow ignimbrite units (A1, A2, A3, and A4) and three intervening volcano-sedimentary layers (S1, S2, and S3). Reliable U-Pb ages obtained for zircons from the base and top of the CVF were 72.8 ± 1.7 Ma and 67.7 ± 2.1 Ma, respectively. Paleomagnetic analysis on pyroclastic units yielded mean magnetic directions and virtual geomagnetic poles (VGPs) as D/I = 19.1°/49.2° (α95 =4.2°,k = 76.5) and VGP = 73.1°N/232.1°E (A95 =3.7°,N =3)forA1,D/I = 24.9°/52.9° (α95 =5.9°,k =61.7)and VGP = 69.4°N/217.3°E (A95 =5.6°,N=11) for A3, and D/I = 10.9°/50.1° (α95 =5.6°,k = 38.6) and VGP = 79.8°N/ 242.4°E (A95 =5.0°,N = 18) for A4. Our best estimates of the paleopoles for A1, A3, and A4 are in remarkable agreement with the reference apparent polar wander path of China in late Cretaceous to early Paleogene, confirming that Korea has been rigidly attached to China (by implication to Eurasia) at least since the Cretaceous. The compiled paleomagnetic data of the Korean Peninsula suggest that the mode of clockwise rotations weakened since the mid-Jurassic. -
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 -
Bicentennial Review
Journal of the Geological Society, London, Vol. 164, 2007, pp. 1073–1092. Printed in Great Britain. Bicentennial Review Quaternary science 2007: a 50-year retrospective MIKE WALKER1 & JOHN LOWE2 1Department of Archaeology & Anthropology, University of Wales, Lampeter SA48 7ED, UK 2Department of Geography, Royal Holloway, University of London, Egham TW20 0EX, UK Abstract: This paper reviews 50 years of progress in understanding the recent history of the Earth as contained within the stratigraphical record of the Quaternary. It describes some of the major technological and methodological advances that have occurred in Quaternary geochronology; examines the impressive range of palaeoenvironmental evidence that has been assembled from terrestrial, marine and cryospheric archives; assesses the progress that has been made towards an understanding of Quaternary climatic variability; discusses the development of numerical modelling as a basis for explaining and predicting climatic and environmental change; and outlines the present status of the Quaternary in relation to the geological time scale. The review concludes with a consideration of the global Quaternary community and the challenge for the future. In 1957 one of the most influential figures in twentieth century available ‘laboratory’ for researching Earth-system processes. Quaternary science, Richard Foster Flint, published his seminal Moreover, although unlocking the Quaternary geological record text Glacial and Pleistocene Geology. In the Preface to this rests firmly on the use of modern analogues, the uniformitarian work, he made reference to the great changes in ‘our under- approach can be inverted so that ‘the past can provide the key to standing of Pleistocene events that had occurred over the the future’. -
2. Geomagnetism and Paleomagnetism
2-1 2. GEOMAGNETISM AND PALEOMAGNETISM 1 https://physicalgeology.pressbooks.com/chapter/4-3-geological-renaissance-of-the-mid-20th-century/ 2 2-2 ELECTRIC q Q FIELD q -Q 3 MAGNETIC DIPOLE Although magnetic fields have a similar form to electric fields, they differ because there are no single magnetic "charges," known as magnetic poles. Hence the fundamental entity is the magnetic dipole arising from an electric current I circulating in a conducting loop, such as a wire, with area A . The field is described as resulting from a magnetic dipole characterized by a dipole moment m Magnetic dipoles can arise from electric currents - which are moving electric charges - on scales ranging from wire loops to the hot fluid moving in the core that generates the earth’s magnetic field. They also arise at the atomic level, where they are intrinsic properties of charged particles like protons and electrons. As a result, rocks can be magnetized, much like familiar bar magnets. Although the magnetism of a bar magnet arises from the electrons within it, it can be viewed as a magnetic dipole, with north and south magnetic poles at opposite ends. 4 2-3 MAGNETIC FIELD 5 We visualize the magnetic field of a dipole in terms of magnetic field lines pointing outward from the north pole of a bar magnet and in toward the south. The lines point in the direction another bar magnet, such as a compass needle, would point. At any point, the north pole of the compass needle would point along the DIPOLE field line, toward the south pole MAGNETIC of the bar magnet.