DOCSLIB.ORG

Of Reading the Geological Record: Tracking Rocks in Four Dimensions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Of Reading the Geological Record: Tracking Rocks in Four Dimensions EAS 102 / BIO G 170 Lecture 5, Page 1 of 6 The “How To” of Reading the Geological Record: Tracking Rocks in Four Dimensions GEOCHRONOLOGY: TELLING TIME IN HISTORICAL PERIODS Where Are We? Whether the aim is to reconstruct the solar system’s formation (as it was in the last lecture), to chart continental drift in a movie-like series of world maps (as it will be in Lectures 9-12 and 16-18), or to trace the evolution of our own species (as it will be in Lectures 19-26), the technical problem generally comes down to reconstructing the four-dimensional historical trajectories of the rocks, minerals, and other debris that record the story. To accurately map the assembly and breakup Pangaea, for instance, one must be able to track the supercontinent’s constituent terranes by measuring (1) paleolatitude, (2) paleolongitude, and (3) paleoelevation as functions of (4) time. The more fully and accurately a terrane’s or a mineral grain’s four-dimensional trajectory can be reconstructed, the more precisely geological processes’ operation can be studied and the more exactly historical sequences of events can be reconstructed. Labs 3-8 illustrate with some of the original examples how geologists learned how to recognize plate-tectonic processes and reconstruct their operation. The basic concepts in this, the first of four lectures on reading the geological record, are discussed and illustrated in greater detail in Labs 3 and 4. The Discovery of Rocks as Historical Records It seems not to be obvious that rocks are products of everyday processes. Once the connection is made, however, it becomes clear that rocks are historical records. Herodotus (“The Father of History,” 484- c. 425 B.C.) and Leonardo da Vinci (1452-1519), among others, observed fossils in rocks and drew the obvious conclusions: the rocks are ancient sediments, and the Mediterranean Sea must have been higher in the past. More than once when leading Ithaca gradeschoolers on fossil-collecting trips, your professor has watched as the face of a latter-day Herodotus or Leonardo lit up with a corresponding realization: Eureka! Fossils show lake level must have been higher in the past! Among other things, this example shows that measuring geological time in years as well as in historical periods is important to avoid associating many-times-older fossils with a water-filled basin formed only in the last few ka of postglacial time, in the case of Cayuga Lake, or , in the case of the Mediterranean, one that had been as dry as Death Valley for much of the intervening few million years. Importance of the Uniformity Principle — As first discussed in Lecture 1, the discovery of the Earth’s historical record was intimately linked to recognition of the uniformity principle, and so was the realization that recorded events could be put in order on a geological time scale. The uniformity principle’s main implication in this regard is that rocks can be read back as historical records by applying a knowledge of time-invariant rock-forming processes — a knowledge that can be obtained from studying these processes and their products in the present. James Hutton’s phrase “The present is the key to the past” perhaps too concisely sums up the uniformity principle’s implications (or at least too concisely for literal-minded geologists who have mistakenly concluded the implication that processes always have proceeded at more or less the same rate). 1/20/03 EAS 102 / BIO G 170 Lecture 5, Page 2 of 6 Although the uniformity principle is implicit in Herodotus’ and Leonardo’s interpretations of rocks and fossils, many early scientists seemed to expect rocks to be Genesis written in stone. Isaac Newton’s Principia (Mathematical Principles of Natural Philosophy, in Latin; 1687) put the understanding of physical phenomena on a foundation firm enough to give definite, quantitative, testable predictions about the outcome of experiments; but it took another few generations for the understanding to become well and widely enough disseminated among natural philosophers to yield much in the way of applied science, much less technology. During the Enlightenment (c. 1687-1789), natural philosophers began to examine rocks with an eye to explaining them as products of newly understood processes. Ever before them was the prevailing belief that the Earth had been created around 4000 B.C., as many had deduced from chronological information in the Bible1. Sedimentology, marine ecology, and oceanography — the sciences most concerned with those aspects of the “present” most useful as keys to sedimentary rocks— did not develop until the mid- to late 19th Century, by which time “hard-rock” geology was already well advanced. What held up the birth of modern geological science until the end of the 18th Century was precisely what was holding up the Industrial Revolution: chemical knowledge good enough to be put into practice, whether as a key to the past in geology, or as a key to the future in chemical manufacturing. Pure chemistry advanced rapidly during the late 18th Century2. Its first industrial success was in dyestuffs manufacture in later 18th Century Edinburgh. Here was the very beginning of the Industrial Revolution. This success was due largely to a close-knit circle of natural philosophers who made it their business to understand the process behind their chemical products. The men applied the same common-sense approach to process-product relations in their shared hobby, geology. Among them was James Hutton, who made his money manufacturing ammonium chloride [NH4Cl] for the dyestuffs industry. Hutton’s Theory of the Earth (1788, 1795) founded modern geology squarely on the uniformity principle. Through him, the uniformity principle has come to be known in geology as the doctrine of uniformitarianism (see Lecture 1). What the Uniformity Principle’s Application Revealed — The first modern geological explorations of the 18th Century were in a sense an extension of geographic explorations. By Hutton’s time, Europeans’ systematic mapping of the globe by latitude and longitude had been under way for three centuries. Australia and Antarctica were still to be discovered when geologists began to take over from miners and sailors in systematically exploring the third spatial dimension, depth. Hutton’s interpretation of rocks in accord with the uniformity principle revealed time to be an unexpectedly, indeterminately vast fourth dimension. Uniformitarian reading of the geological record led Hutton to a further, socially more revolutionary conclusion: as consistent with the notion that nothing supernatural happens, nothing supernatural seems to have happened around 6 ka ago, when Earth was then generally supposed to have been created, or at any other time in a much longer history. 1 Creation is the starting point for the Hebrew calendar, which dates it to 7 September 3760 B.C. on the everyday Gregorian calendar. The Venerable Bede established the convention of numbering years relative to the birth of Christ in his De Temporum Ratione (725; by far the best early medieval computistic work, and the standard work on chronology and the calendar for centuries to come), thus setting the alarm for episode after episode of millennial hysteria. Bede estimated Creation to have taken place on or about 18 March 3952 B.C. For general review, see N. Dershowitz and E.M. Reingold, Calendrical Calculations (Cambridge, 1997). Apparently as unaware of the religious associations as they are of the associated scholarship, some geologists celebrate 23 October as “Bishop Ussher Day” in recognition of the 17th Century protestant archbishop who reckoned Creation to have taken place on or about that date in 4004 B.C. 2 See A. Clough and N.L. Clough, The Chemical Revolution (Batchworth, 1952). 1/20/03 EAS 102 / BIO G 170 Lecture 5, Page 3 of 6 The Geological Time Scale Geological Timekeeping Processes — Any process that generates a time-varying, geologically preserved product is potentially useful in telling geological time. The most useful processes have proved to be (1) sediment accumulation, the usual basis for establishing layers’ relative age within one rock outcrop; (2) evolutionary change in organisms as documented by fossils (change within lineages, including origination and extinction of species), the usual basis for establishing secdimentary rocks’ age relationships between outcrops; (3) radioactive decay, the usual basis for estimating absolute geological age (e.g. ages in years), as will be discussed in the next lecture; (4) sea level change; (5) change in the geomagnetic field’s strength and polarity. In geologically young organic material, (6) chemical decay is sometimes useful. Change in sea water’s 87Sr/86Sr ratio (7) is proving useful in geochronology, though the underlying geochemical processes involved are several and complicated. Deceleration of the Earth’s rotational rate (8) is potentially useful, but hardly ever used. Seasonal growth in organisms (9) can be useful in dating (e.g. tree-ring dating, which in some areas has been carried back a few ka’s), and so can seasonal sedimentation (10) (e.g. annual varves in lake sediments, which have been counted back a few ka’s in some areas, and annual layers in glacial ice, which have been counted back as much as 150 ka in some ice cores). Geological Time Scales — Today’s geological time scale is really several time scales in one. The relative geological time scale is concerned with geochronology, the measurement of time in historical periods (e.g. Enlightenment, Industrial Revolution, Victorian Period, Gilded Age, Cold War Era, Devonian Period). It includes the stratigraphic time scale (the one calibrated in eras, periods, epochs, and other units), the biochronological scale (a collection of many separate scales, each calibrated in the biochrons of variously related species), the geomagnetic time scale (the one calibrated in geomagnetic chrons, periods defined by reversals in the geomagnetic field’s polarity), the sea-level time scale (the one calibrated in cycles of sea-level rise and fall), and various isotopic time scales (e.g.
Load more

Recommended publications
  • Earth Science Power Standards
    Macomb Intermediate School District High School Science Power Standards Document Earth Science The Michigan High School Science Content Expectations establish what every student is expected to know and be able to do by the end of high school. They also outline the parameters for receiving high school credit as dictated by state law. To aid teachers and administrators in meeting these expectations the Macomb ISD has undertaken the task of identifying those content expectations which can be considered power standards. The critical characteristics1 for selecting a power standard are: • Endurance – knowledge and skills of value beyond a single test date. • Leverage - knowledge and skills that will be of value in multiple disciplines. • Readiness - knowledge and skills necessary for the next level of learning. The selection of power standards is not intended to relieve teachers of the responsibility for teaching all content expectations. Rather, it gives the school district a common focus and acts as a safety net of standards that all students must learn prior to leaving their current level. The following document utilizes the unit design including the big ideas and real world contexts, as developed in the science companion documents for the Michigan High School Science Content Expectations. 1 Dr. Douglas Reeves, Center for Performance Assessment Unit 1: Organizing Principles of Earth Science Big Idea Processes, events and features on Earth result from energy transfer and movement of matter through interconnected Earth systems. Contextual Understandings Earth science is an umbrella term for the scientific disciplines of geology, meteorology, climatology, hydrology, oceanography, and astronomy. Earth systems science has given an improved, interdisciplinary perspective to researchers in fields concerned with global change, such as climate change and geologic history.
    [Show full text]
  • Stage 1А–Аdesired Results
    www.nextgenscience.org STAGE 1 – DESIRED RESULTS Unit Title: Earth’s Place in the Universe Grade Level: 6 Length/Timing of Unit: Teacher(s)/Designer(s): Pascack Valley Regional Science Committee Science State standards addressed (verbatim): ​ MS­ESS1­1 . Develop and use a model of the Earth­sun­moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons. [Clarification Statement: Examples of models can be physical, ​ graphical, or conceptual.] MS­ESS1­2. Develop and use a model to describe the role of gravity in the motions within galaxies and the solar system. [Clarification Statement: Emphasis for the model is on gravity as the force that holds together the solar system and Milky Way galaxy and controls orbital motions within them. Examples of models can be physical (such as the analogy of distance along a football field or computer visualizations of elliptical orbits) or conceptual (such as mathematical proportions relative to the size of familiar objects such as students’ school or state).] [Assessment Boundary: Assessment does not include Kepler’s Laws of orbital motion or the apparent retrograde motion of the planets as viewed from Earth.] MS­ESS1­3. Analyze and interpret data to determine scale properties of objects in the solar system. [Clarification ​ Statement: Emphasis is on the analysis of data from Earth­based instruments, space­based telescopes, and spacecraft to determine similarities and differences among solar system objects. Examples of scale properties include the sizes of an object’s layers (such as crust and atmosphere), surface features (such as volcanoes), and orbital radius.
    [Show full text]
  • 6. Relative and Absolute Dating
    6. Relative and Absolute Dating Adapted by Sean W. Lacey & Joyce M. McBeth (2018) University of Saskatchewan from Deline B, Harris R, & Tefend K. (2015) "Laboratory Manual for Introductory Geology". First Edition. Chapter 1 "Relative and Absolute Dating" by Bradley Deline, CC BY-SA 4.0. View Source. 6.1 INTRODUCTION To develop a history of how geologic events have acted on the Earth through time, we need to understand what and when geological processes have occurred through Earth's history. Geologists learn about what processes occur on Earth through studying the rock record and observing geologic processes in modern environments. To understand when these processes have acted during Earth's geologic time, geologists make observations about the relationships of rocks to one another in the rock record, using a process called relative dating. Geologists use this information to construct models for how these relationships developed. For example, if the rock record in an area contains sedimentary rocks that are folded, a model to explain those relationships would start with a region where sediments were deposited, followed by lithification of the sediments to form rock, then the rocks would be subjected to tectonic pressures that folded the rocks. Using relative dating techniques, we know those events occurred in that order, but not when they occurred precisely in time. To add specific dates for the events in the model, geologists can use absolute dating techniques to date the rocks (determine their age). Geologists develop models such as this at locations all across Canada, North America, and around the globe. Each location geologists study may only provide information on Earth history from a short window in time; collectively, however, the information in these models can be used to develop our understanding of processes that have acted on Earth since it first formed.
    [Show full text]
  • Geologic Time Scale Essential Questions: 1
    Geologic Time Scale Essential Questions: 1. How does the relative and absolute age of rocks and the fossil record provide evidence to Earth’s geologic history? 2. How is Earth’s geologic history classified? 3. What are some major events in the Earth’s geologic history? Geologic Time Scale Earth Scientists • Geologist – a scientist who studies the Earth’s crust as well as the processes and history that shaped it • Paleontologist – a scientist that studies fossil remains found on the Earth’s surface in order to study primitive life forms such as: plants, animals, fungi, and bacteria Geologic Time Scale Sedimentary Rock Layers Stratigraphy • A branch of geology dealing with the arrangement of sedimentary rock layers or strata • Geologists assume the newest rock layers are on top of the older ones, unless some type of disturbance occurs. • Called the Law of Superposition © KeslerScience.om Geologic Time Scale Sedimentary Rock Layers Relative Age • The strata of sedimentary rocks is important in determining their relative age. • Relative age determines the “relative” order of past events but not the absolute age. • Like saying you’re relatively younger than your grandfather. Quick Action – Geologic Time Scale Sedimentary Rock Layers Determining Relative Age 1. Which is older sandstone or limestone? 2. Which is older mudstone or siltstone? 3. Which is the youngest rock in this strata? 4. Which is the oldest rock in this strata? Geologic Time Scale Sedimentary Rock Layers Relative Age • Strata is sometimes disturbed. • Here we see a fault (E) and an igneous intrusion (D) • See if you can determine the order of the strata in this diagram.
    [Show full text]
  • Module 22A Geological Laws GEOLOGIC LAWS
    Module 22A Geological Laws GEOLOGIC LAWS Geologic Laws ❑ Superposition ❑ Original Horizontality ❑ Original Continuity ❑ Uniformitarianism ❑ Cross-cutting Relationship ❑ Inclusions ❑ Faunal Succession Missing strata ❑ Unconformity ❑ Correlation Law of Superposition ❑ In an undisturbed rock sequence, the bottom layer of rock is older than the layer above it, or ❑ The younger strata at the top in an undisturbed sequence of sedimentary rocks. Law of Superposition Undisturbed strata Law of Superposition Disturbed strata Law of original horizontality ❑ Sedimentary rocks are laid down in horizontal or nearly horizontal layers, or ❑ Sedimentary strata are laid down nearly horizontally and are essentially paralel to the surface upon which they acummulate Law of Original Continuity ❑ The original continuity of water-laid sedimentary strata is terminated only by pincing out againts the basin of deposition, at the time of their deposition Law of Original Continuity Law of Original Continuity Law of Original Continuity NOTE: This law is considerable oversimplification. The last discoveries indicate that the termination is not necessarily at a basin border. Facies changes may terminated a strata. Uniformitarianism ❑ James Hutton (1726-1797) Scottish geologist developed the laws of geology ❑ Uniformitarianism is a cornerstone of geology ❑ Considered the Father of Modern Geology Uniformitarianism ❑ Uniformitarianism is based on the premise that: ➢ the physical and chemical laws of nature have remained the same through time ➢ present-day processes have operated throughout geologic time ➢ rates and intensities of geologic processes, and their results may have changed with time ❑ To interpret geologic events from evidence preserved in rocks ➢ we must first understand present-day processes and their results Uniformitarianism is a cornerstone of geology Uniformitarianism MODIFIED STATEMENT “The present is the key to the past" • The processes (plate tectonics, mountain building, erosion) we see today are believed to have been occurring since the Earth was formed.
    [Show full text]
  • Igneous Rocks and Relative Time Homework 2: Due Wednesday
    Homework 2: EESC 2200 Due Wednesday The Solid Earth System Igneous Rocks And Relative Time 24 Sep 08 Continental Tectonics Relative Frequency of Rock Types A. Crust B. Surface Magma chemistry Two main classes mafic magmas + rocks ma - fic magnesium + iron (Ferrous) rich ES101--Lect 8 OR: felsic magmas + rocks fel - sic Feldspar and silica rich ES101--Lect 8 felsic ->intermediate-> mafic light dark large ions small ions (K, Na) (Mg, Fe) more Si (>60%) less Si (£ 50%) ES101--Lect 8 felsic ->intermediate-> mafic light dark large cations small cations (K, Na) (Mg, Fe) more Si (>60%) less Si (£ 50%) cooler magmas hotter magmas light minerals dense minerals which more explosive? minerals? ES101--Lect 8 Ultra- Felsic Intermediate Mafic mafic Quartz KSpar PlagSpar Micas Amph. Pyroxene Olivine ES101--Lect 8 Ultra- Felsic Intermediate Mafic mafic Diorite Perid- Granite Gabbro otite Quartz KSpar PlagSpar Micas Amph. Pyroxene Olivine ES101--Lect 8 Granite Diorite Gabbro felsic mafic ES101--Lect 8 Felsic Intermediate Mafic Granite Diorite Gabbro coarse Rhyolite Andesite Basalt fine rock slides ES101--Lect 8 Gabbro (coarse) Basalt (fine) Mafic Igneous Rocks Diorite (coarse) Andesite (fine) Intermediate Igneous Rocks Granite (coarse) Rhyolite (fine) Felsic Igneous Rocks Classifying igneous rocks by composition and texture Ridges: Mantle undergoes decompression melting --->>> Basalts (dry) 1300°C basalt = mantle melt ("blood of the Earth") ES101-Lect9 Mantle Melting Temperature 1100 °C 1300°C All Partial Liq Melting Depth All Solid Lower Pressure!! ES101-Lect9 water --> mantle wedge, --> basalt arc volcanism... ES101-Lect9 H2O -- Lowers Melting Point 800˚C 1100˚C T Depth Wet melting you are here ES101-Lect9 basaltic melts -> andesite melts basaltic andesitic magma magma Olivine Olivine+ Pyroxene cooling + Ca-f'spar ES101-Lect9 Mt.
    [Show full text]
  • North American Stratigraphic Code1
    NORTH AMERICAN STRATIGRAPHIC CODE1 North American Commission on Stratigraphic Nomenclature FOREWORD TO THE REVISED EDITION FOREWORD TO THE 1983 CODE By design, the North American Stratigraphic Code is The 1983 Code of recommended procedures for clas- meant to be an evolving document, one that requires change sifying and naming stratigraphic and related units was pre- as the field of earth science evolves. The revisions to the pared during a four-year period, by and for North American Code that are included in this 2005 edition encompass a earth scientists, under the auspices of the North American broad spectrum of changes, ranging from a complete revision Commission on Stratigraphic Nomenclature. It represents of the section on Biostratigraphic Units (Articles 48 to 54), the thought and work of scores of persons, and thousands of several wording changes to Article 58 and its remarks con- hours of writing and editing. Opportunities to participate in cerning Allostratigraphic Units, updating of Article 4 to in- and review the work have been provided throughout its corporate changes in publishing methods over the last two development, as cited in the Preamble, to a degree unprece- decades, and a variety of minor wording changes to improve dented during preparation of earlier codes. clarity and self-consistency between different sections of the Publication of the International Stratigraphic Guide in Code. In addition, Figures 1, 4, 5, and 6, as well as Tables 1 1976 made evident some insufficiencies of the American and Tables 2 have been modified. Most of the changes Stratigraphic Codes of 1961 and 1970. The Commission adopted in this revision arose from Notes 60, 63, and 64 of considered whether to discard our codes, patch them over, the Commission, all of which were published in the AAPG or rewrite them fully, and chose the last.
    [Show full text]
  • How to Get a Date
    How to get a date: establishing chronologies (relative and absolute) change change change change change change Later than last week (relative) March 3, 2010 (absolute) Temporal, or chronological, order • Relative dating – lining things up (before, after) – ‘it is all relative’ • Absolute dating – chronometric dating – actual chronological date assigned – allows measurement of ‘how much’ time has passed between two points Expression of Absolute Dates (culturally specific!) • B.C./A.D. (Before Christ, Anno Domini) • Islamic calendar from A.D. 622 (the Hegira, Mecca to Medina) • B.C.E./C.E. (Before Common Era, Common Era) • B.P. (Before Present) Relative Dating Principle of stratigraphic succession Law of ‘superposition’ (the lower you go, the older you get) Important concepts in geology too Relative Dating Principle of stratigraphic succession Law of ‘superposition’ (the lower you go, the older you get) Typology • Artifact classification into types on the basis of certain similarities… Pots vs. baskets Fine ceramics vs. cooking wares (multiple typologies possible!) • Assumes products of a given place and time have a recognizable style • Styles tend to change through time, but gradually… Unchanging… Constantly changing… Unchanging… Constantly changing… Seriation • Relative dating method involving arranging archaeological materials into a presumed chronological sequence based on cultural and stylistic change • As long as items are gathered from the same cultural tradition, archaeologists assume that stylistic change occurs relatively gradually over time • By tracing similarities and differences in styles and by measuring the relative popularity of these differing styles, one can reconstruct a relative sequence (battleship curve) Seriation ? ? James Deetz seriation studies in New England graveyards Death’s head Cherub Willow and urn ‘battleship curves’ Problems? • Heirlooms • Archaism (‘retro’ looks) (actually a serious issue) Absolute dates Pompeii 24 August A.D.
    [Show full text]
  • Stratigraphic Cross Sections—Why Study Old Rocks?
    From IRIS’ collection: Animations of Geologic Processes www.iris.edu/educate/animations Stratigraphic Cross Sections—Why study old rocks? The earthquake potential of an area can be DEFINITIONS determined by studying the relationships between Stratigraphy— The branch of geology that rock strata, both locally and regionally. Faults and folds studies rock layers (strata) & layering record a probable earthquake history, so by studying (stratification). It is primarily used in the the age of the rocks we can gain an understanding study of sedimentary & layered volcanic about future earthquakes (applying “the past is a key to rocks. the future”). This is done by doing field work, studying drill-hole samples, and interpreting seismic reflection Cross section—A view formed by a plane data. cutting through an object to reveal a profile (a vertical section of the Earth’s crust showing the different horizons or This animation, has both stratification and structure. layers). No strata are overturned, thus the following laws apply: Stratigraphic section—Also called The law of superposition simply states that for non- “stratigraphic cross section”, is a deformed geologic strata, “sedimentary layers are cutaway view, usually with the vertical deposited in a time sequence, with the oldest on the scale exaggerated with relation to the bottom and the youngest on the top”. horizontal scale, that is designed to The principle of original horizontality states that rock show the thicknesses & relationships layers form in the horizontal position, and any between successions of rock types. deviations from this horizontal position are due to Structural geology—Used to uncover the rocks being disturbed later (the exception being information about faults & folds in rocks.
    [Show full text]
  • Lithostratigraphic Unit
    E. F. McBride Geo. 420K Spring, 1999 NOTES ON STRATIGRAPHY FOR GEO420K TYPES OF STRATIGRAPHY Lithostratigraphy - Lithostratigraphic unit [Group, Formation, Member] - Lithodemic unit (intrusives, etc.) Pedostratigraphy - Pedostratigraphic unit Biostratigraphy - Zones Chronostratigraphy - Chronostratigraphic units [Period, Epoch, Age] Geochronostratigraphy - Geochronostratigraphic unit [System, Series, Stage] Magnetostratigraphy - Reversals, chrons Chemostratigraphy - Isotope zones Sequence Stratigraphy - Allostratigraphic units [Unconformity-bounded units] IMPORTANT SURFACES & TIME IMPLICATIONS 1) FAULTS, FRACTURES 2) UNCONFORMITIES = Buried erosion surfaces Physical erosion Biological erosion Chemical erosion Hiatus = amount of time record missing Diastem = small amount of rock missing Paraconformity " " " " Non-conformity: sedimentary rocks on top of igneous or metamorphics Disconformity: sediments conformable with sediments Angular unconformity: angular discordance 3) BEDDING Problem: how much time is represented by each bedding plane? FACIES Definitions: 1) Aspects of a rock that characterize it (minerals, fossils, color, etc). 2) Mappable, areally restricted part of a lithostratigraphic body that differs from its coeval equivalents. 3) A distinctive rock type that is characteristic of a particular environment: black shale facies, bioherm facies, channel facies, turbidite facies. 4) A body of rock distinguished on the basis of its fossil content: Ophiomorpha facies, Exogyra texana facies. BIOSTRATIGRAPHY PROCEDURE: plot range of every
    [Show full text]
  • Paleoanthropological Methods: Dating Fossils "Archaeologists Will Date Any Old Thing" (Jim Moore, UCSD)
    Paleoanthropological methods: Dating fossils "Archaeologists will date any old thing" (Jim Moore, UCSD) Taphonomy: study of processes of fossilization (literally, "laws of burial"; study of diagenetic processes acting on a dead animal's remains). Diagenesis: sum of the physical, chemical, and biological changes affecting a fossil-bearing sediment; for sedimentary deposits, includes the length of time over which fossils were deposited (single catastrophe or slow accumulation?). mya: Million years ago (my, million years); kya/ky: thousand years I: Why it matters Morris (1985: 220-221) talks about methods used to date fossils. He claims that "... fossils are not dated by the rocks in which they are found; rather, the rocks are 'dated' and correlated by the fossils found in them. ... rocks are 'dated' on the basis of the stage of evolution of their fossils." (p. 220); he argues that this makes dating follow from a belief in evolution rather than the other way round, and so we should reject estimates of an ancient earth (as well as evolution) as based on circular logic. He supports his statements with 3 lengthy quotations from other authors; here's one (Morris, 1985: 220): "The only chronometric scale applicable in geologic history for the stratigraphic classification of rocks and for dating geologic events exactly is furnished by the fossils. Owing to the irreversibility of evolution, they offer an unambiguous time-scale for relative age determinations and for world- wide correlations of rocks" (O. H. Schindewolf, Am. Journal of Science, Vol. 225, June 1957, p. 394). The other two were written in 1952 and 1961.
    [Show full text]
  • Rocks and Geology in the San Francisco Bay Region
    Rocks and Geology in the San Francisco Bay Region ������� ����� ��������� �������� ���� ������ ��� ��������� �������� ��������� �������� ������ ������ ������ ����� ����� ������ ����������� ����� ����������� ����� ��������� ������������ ���� ���� ������� ���� ������ ���� ������� �������� ������ ��� ����� �� ����� ������ ��� ����� ������ Bulletin 2195 U.S. Department of the Interior U.S. Geological Survey This page intentionally left blank Rocks and Geology in the San Francisco Bay Region By Philip Stoffer Bulletin 2195 U.S. Department of the Interior U.S. Geological Survey 1 U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. U.S. Geological Survey, Reston, Virginia: 2002 Electronic copies of this publication are available online at http://geopubs.wr.usgs.gov/bulletin/b2195/ Additional USGS publications can be found online at http://geology.usgs.gov/products.html For more information about the USGS and its products: Telephone: 1-888-ASK-USGS (1–888–275–8747) World Wide Web: http://www.usgs.gov/ Published in the Western Region, Menlo Park, California Manuscript approved for publication, September 30, 2002 Text and illustrations edited by James W. Hendley II Production and design by Susan Mayfield III Contents Introduction..............................................................................................................................................................
    [Show full text]