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The geological time scale

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					     Lecture 14:
     The Dynamic Planet: Geology of the World
                                                                                                                            GEOLOGY (or “Earth Science”)

                                                                                                                                The study of the origin, structure,
                                                                                                                            composition and physical history of Earth,
                                                                                                                            together with the processes which have led
                                                                                                                            to its present state.

                                                                                                                              The science that deals with the dynamics
                                                                                                                            and physical history of Earth, the rocks of
                                                                                                                            which it is composed, and the physical,
                                                                                                                            chemical, and biological changes that it has
                                                                                                                            undergone and is undergoing.
          Geog 1000 Introduction to Physical Geography Fall 2010 : Dr. Hester Jiskoot, University of Lethbridge




                                                                                                                                                              versus
   Fundamental stratigraphic principles                                                                                  Uniformitarianism                             Catastrophism
                                                                                                                             “Present is key to the past”
        1. superposition of layers (strata)                                                                                 Continuing uniformity of existing          Earth created through supernatural
        2. original horizontality                                                                                         processes/physical laws responsible          means and affected by a series of
                                                                                                                         for present & past conditions on earth                catastrophic events

                                                                                                                         Earth is old                                  Earth is young
                                                                                                                         Processes take time to form earth             Catastrophic events form earth

                                                                                                                         James Hutton (1726-97)                    Cuvier (1769-1832)
                                                                                                                         - Father of geology                       Catastrophes are events with natural
                                                                                                                         Earth is in perpetual process of          causes
                                                                                                                         formation & denudation                         Geologists now know that natural
                                                                                                                                                                        catastrophes have had and have
                                                                                                                         Charles Lyell (1797-1875):                     some role in forming the Earth's
                                                                                                                         “Principles of Geology”: evidence from         landforms and rocks/sediments.
                                                                                                                         geologic record for Uniformitarianism
                                                                                                                                                                          Earth formed through gradual
                                                                                                                         Charles Darwin (1809 –1882)                   processes, punctuated by dramatic
                Guiding principle = uniformitarianism                                                                    Biological evolution through natural             events ( volcanic eruptions,
                                                                                                                                                                        earthquakes, floods, landslides)
                                                                                                                         selection




   Pre 2006: Oldest dated rock on earth
         Acasta gneiss found in Northwest Territories, Canada
    Dating methods: radioactive decay of Uranium and Thorium to Lead
                                                                                                                               The geological time scale
                                                                                                                   ars
                                                                                                           o   n ye
                                                                                                     billi
                                                                                                4.28
                                                                                    st ro
                                                                                            ck:                                  Boundaries of eons, eras, periods and epochs
                                                                         w     olde
                                                                    s no
                                                                find
                                               ent
                                           stud ec
                                                                                                                                                             based on
                                     PhD Queb
                              e rsity rthern
                          Univ     No                                                                                              evolvement/extinction of animal life forms
                      Gill e belt,
                 : Mc     n
         (20  08) ensto
                  re                                                                                                                                   &
      nce uq g
  Scie uagitt
     uvv
                                                                                                                                           global climate variations
   N

                                     3.96 billion years
Rock in National Museum for Natural Sciences, Smithsonian institute (Washington, DC)




                                                                                                                                                                                                            1
Eras        Periods
                                                                                                          Eon             Era
                                                                                                 today




                                                          Global climate
                                                         and continental
                                                         plate distribution                                                       New in 2004:
                                                                                             544 M yr
                                                                                                                                  International Cmtee on Stratigraphy
                                                          over geological                                                         http://www.stratigraphy.org

                                                               time                                                               PRECAMBRIAN deleted

                                                                                                                                  PROTEROZOIC
                                                                                                                                  ARCHAEAN           Now EONS
                                                                                             4,500 M yr
                                                                                                                                  HADEAN




             Hadean eon                                    4.5 to 3.8 billion yrs ago
                                                                                                                        Eon     Era
             Solar System was forming (planetisemal hypothesis)                                             today
             Earth starts cooling
             First Rocks form


    Archaean eon                                                3.8 to 2.5 billion yrs ago
    Earth's crust cooled enough          continental plates began to form.
    Oldest fossils date ~ 3.5 billion yrs ago (bacteria microfossils).

                                                                                                    544 million yrs


   Proterozoic eon                                    2.5 billion to 544 million yrs ago
   First stable continents
   First abundant fossils of living organisms (bacteria, archaeans, eukaryotic cells)
   First evidence of oxygen build-up in the atmosphere                                              4,500 million yrs




       Paleozoic Era                                   544 to 245 million yrs
       Two of the most important events in the history of animal life:
       1)     Multi-celled animals underwent a dramatic "explosion" in diversity
       2)     the largest mass extinction in history wiped out approximately 90% of
              all marine animal species
       Seas       Limestone/coal


   Mesozoic era                                                245 to 65 million yrs
                                                                                                                                      Albertosaur
   Culmination of world fauna (except for insects): very different from previous eras.
   First fossils of modern mammal and bird groups
   Dinosaurs (+ ammonites, etc) evolve and become extinct
        Lush terrestrial vegetation

                                                                                                   Cretaceous Rocks
            Cenozoic era                             65 million yrs to the present
                                                                                                    146 to 65 My BP
            Evolvement to modern times
            >2.7 M yr Cyclic Ice Ages




                                                                                                                                                                        2
         ERA                              PERIOD
               Holocene
                                           Quaternary               K/T boundary: marker of one of the extinction events
                                                                      ASTEROID IMPACT                   Chicxulub crater at the bottom of Gulf of Mexico

                                                                                                                                                  Tertiary
                                           Tertiary
                                                                                                                                                               Mass extinction
                                                                      iridium-rich layer
                                                  K/T boundary
                                                                                                                                                  Cretaceous




                                                                                                                              World-wide thin layer of same sediment:
                                                                                                                              Upper "Fireball layer" ~ 3mm thick.
                                                                                                                              Lower "Ejecta layer“ ~ 2cm thick.
                                                                                                                              Layers mostly clay, with soot in upper parts.



                                                                 See a video on http://videos.howstuffworks.com/science-channel/29285-100-greatest-discoveries-chicxulub-crater-video.htm




                                                                                 Earth diameter = 12750 km                    known by the ancient Greeks
               RECAP 1:
                                                                                       20th   century: planet earth is made up of 3 main layers:
               What are the main stratigraphic principles?                                            crust, mantle, and core

               What are the geological time periods based on?

               What are the main eras?

               In which era did the dinosaurs live?

               Why does the science of geology evolve so fast?




    Excellent website on geological time:
http://www.ucmp.berkeley.edu/exhibit/geology.html




                                                                                                                                                           Moho discontinuity
Think of an egg



                                                                                                                                                                 Magnetic field &
                                                                                                                                                                Magnetic reversals




                                                                                       How do we know?                            Seismic waves




                                                                                                                                                                                            3
         MAGNETOSPHERE
                                                             THE EARTH’S CRUST




      Northern lights / aurora borealis




ISOSTACY & ISOSTATIC REBOUND              ISOSTACY & ISOSTATIC REBOUND




                                                 3.0 g/cm3




                                           THE PEOPLE BEHIND PLATE TECTONICS
       Tectonic plates (~14)              1596       Abraham Ortelius, map maker: “Americas torn away from
                                                     Europe and Africa by earthquakes & floods"
                                          1858       Antonio Snider-Pellegrini made ‘before’ and ‘after’ maps




                                          1912-15 Alfred Wegener develops theory of continental drift
                                                  “understanding of how the Earth works requires input and
                                                  knowledge from all the earth sciences.”
                                          1970s Theory of plate tectonics




                                                                                                                4
      Assumed convection cells in the mantle.
         Below ~ 700 km, the descending slab softens,                                                  Break-up
              becomes liquid, and loses its form.
                                                                                                          of
                                                                                                       Pangaea




                                                                                               Distribution of continental
                                                                                                  plates and orogens
                                                                                              important for world climate




How do we know how to fit the jig-saw?                             Directions & rates of plate movement
        Dated rocks/rocktypes/fossils - spatial distribution
             Dated shorelines and marine deposits




                                                                  Plate tectonics animations
                                                                             http://www.ucmp.berkeley.edu/geology/anim1.htm
                                                                                          http://www.scotese.com/sfsanim.htm




Plate convergence/divergence/faulting                                    Seafloor surface map
                 Divergent plates
                                              Convergent plates




  Transform boundary:
  transverse movement
  along a fault




                                                                                                    Mid-Atlantic ridge




                                                                                                                               5
 Magnetic time record     CRUSTAL FORMATION                                   Orogenesis related to plate convergence:
                                                                                    TECTONIC MOVEMENT
                                                                                                                1) Oceanic plate
                                                                                                                subducted under
                                                                                                                continental plate




                                                                                                               2) Continental plate
                                                                                                                subducted under
                                                                                                                continental plate




                                                                                                               3) Oceanic plate
                                                                                                               subducted under
                                                                                                                oceanic plate




                                                                                  Reading for Friday
RECAP 2:

What is the earth’s inner/outer core composed of and why is this important?

What types of plate boundaries are there?

Why is plate tectonics important (what other processes does it influence?)
                                                                                  Chapter 8 p. 273-280
What is Pangaea and why did it break up?




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