GEOLOGIC TIME

Reading assignments


Historical Geology

Assertions of Historical Geology

  1. the Earth is extremely old and has a complex history
  2. present day life forms evolved from preexisting species by change over time

GEOLOGIC TIME [Figure 1.2]

 Era              Period                    Epoch
______________________________________________________________

                                          Recent
                Quaternary
                                          Pleistocene
                ----------------------------------------------
 C                                        Pliocene
 E 
 N		                          Miocene
 O
 Z              Tertiary                  Oligocene
 O 
 I                                        Eocene
 C 
                                          Paleocene 
_________________________________________________________________

 M
 E              Cretaceous
 S
 O              Jurassic
 Z
 O              Triassic
 I
 C
_________________________________________________________________

                Permian
 P
 A              Pennsylvanian
 L                            } Carboniferous
 E              Mississippian
 O
 Z              Devonian
 O
 I              Silurian
 C  
                Ordovician
  
                Cambrian

Web Links

Geologic Time


INTERPRETING THE SEDIMENTARY ROCK RECORD

GEOLOGIC TIME

  1. relative ages
    1. A relative dating activity from the UCMP
  2. absolute ages
  3. A paper lab exercise by Frank McKinney for determining ages of rocks and fossils

FUNDAMENTAL PRINCIPLES OF GEOLOGY 

  1. Development of the Geologic Time Scale
  2. Unraveling Geologic Time from Paul Olsen's excellent webpages for his dinosaur class

Birth of Stratigraphy

Nicolaus Steno 1669 (1638-1686)

Geology Becomes a Science

neptunism

catastrophism

uniformitarianism

modern view of uniformitarianism

  1. uniformitarianism - inviolable natural laws
  2. actualism - present laws of science would apply at all times; present day processes are presumed to have acted in the same way, but at varying rates
  3. catastrophic uniformitarianism

STRATIGRAPHY

FOSSILS AND TIME

THE RELATIVE TIME SCALE


Age of the Earth

RADIOMETRIC DATING

  1. Radioactive Decay
  2. radiometric dating
  3. radiometric dating

ABSOLUTE DATING WITH RADIOACTIVITY

  1. Introduction
    1. atom
      1. nucleus
        1. proton
        2. neutron
      2. electron
    2. atomic number
      1. element
    3.  mass number
    4.  isotope
      1. stable
      2. radioactive
    5. Processes
      1. alpha decay
      2. beta decay
      3. electron capture
    6. decay series
      1. Parent element
      2. Intermediates
      3. Stable daughter product
  2. How Radiometric Dating Works, 1
    1. half life
    2. decay constant
    3. mass spectrometer
    4. sources of uncertainty
      1. accuracy
      2. open system
      3. closed system
      4. concordance
      5. instrument error
  3. How Radiometric Dating Works, 2
    1. radiometric decay is independent of external conditions
    2. system must be closed
    3. geometric rates (versus linear rates) [fig 3.6]
      1. each atom has the same probability of decay
      2.  8 = decay constant.
        1. probability of decay
        2. proportion that will decay in a given time.
      3.   -8N  =  number that will decay
      4.   - 8N = dN/dt
        1. this is formula (3.5) on page 57 of Martin
        2. this formula can be integrated using calculus to yield the formula
      5. Nt = Noe-8
        1. this is formula (3.1) on page 55 of Martin, where
        2. Nt = amount of parent after time t has elapsed
        3. No = original amount of parent at time t at the start
        4. e = 2.718, which is the base of natural logarithms [ln] (read page 56 in Martin)
      6.  Solving for t
        1. t = (1/8) ln [No / Nt]
      7. Since, No = Pt + Dt 
        1. where Pt = Nt 
        2. and Dt is the amount of daughter at time t, assuming no original daughter
      8. t = (1/8) ln [Dt / Pt + 1]
        1. this is formula 3.2 on page 56 of Martin.
  4. total time for all the atoms to decay can not be specified
    1. half-life (t1/2): time for half to decay (steps 1-10 on page 57 of Martin)
      1. t1/2 = ln[(1/1) + 1]/8
      2. = ln [2]/8  = 0.693/8
  5. MEASUREMENT of Parent and Daughter Isotopes
    1.  mass specrometer
  6. Error in Radiometric Dating 
    1. closed system (no external loss or gain of P or D) or else error will be introduced
    2. no original daughter or must be corrected for
    3. measurement error 0.2%-2.0%
    4.  probability: precision versus accuracy
  7. Primary Nuclides [table 3.4] 
    1. K/Ar
    2. U/Pb
    3. Rb/Sr
  8. Radiocarbon Dating:  organic matter to 50,000 BP

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