GEOLOGIC TIME

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GEOLOGIC TIME
CHAPTER 17
THE GRAND CANYON
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Introduction

• The Grand Canyon - Major John Wesley Powell, in
  1869, led a group of explorers down the Colorado
  River

• Powell returned to map the region.
• Powell was impressed with the geologic strata and
  thus began an investigation that continues today
  into the immense amount of geologic time
  presented in the canyon.
• It is this vastness of geologic time that sets
  geology apart from the other sciences.

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DEEP TIME

•       Time is what sets geology apart from other
  sciences (except Astronomy).  In geology, we are
  talking about deep time  immense spans of time
  that is hard for most people to comprehend. 
  Earth is thought to be 4.6 billion years old
  (based on radiometric dating of meteorites).

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HISTORY OF GEOLOGY AND DISCUSSION OF GEOLOGIC
TIME CONCEPTS

•      There was very little advancement in geology
  until the middle of the eighteenth century.  This
  dark time (prior to mid-1700's) for all
  scientific and original thought was mostly due to
  a strict interpretation of the Book of Genesis in
  the Bible.  Geologic time was considered to be
  but a few thousand years (and some people today
  still adhere to a young Earth based on a literal
  interpretation of the Bible, here is an
  interesting link Radiometric Dating A
  Christian Perspective by Roger C. Wiens -- A
  resource paper of the American Scientific
  Affiliation and the Affiliation of Christian
  Geologists written by a christian who is a
  scientist and gives support for the reality of
  radiometric dating of rocks and the 4.6 billion
  year age for Earth).  Fossils were regarded as
  creatures engulfed by the Biblical Flood, freaks
  of nature, inventions of the devil, or figured
  stones.

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HISTORY OF GEOLOGY (cont.)

•      In 1650, James Ussher (1581-1665),
  Archbishop of Armagh, Ireland, calculated, using
  genealogies described in Genesis, that Earth was
  created on October 23, 4004 B. C.  Thus, Earth is
  only about 6000 years old.  (INTERESTING NOTE 
  Leonardi da Vinci (1452-1519) estimated that it
  took 200,000 years just to deposit the sediments
  in the Po River Valley in Italy.)
• During the late 1700s and into the early 1800s,
  many naturalists believed that Earth history
  consisted of a series of catastrophic upheavals
  that had shaped the geologic features of the
  earth. Those who believed in this concept of
  catastrophic earth history became known as
  CATASTROPHISTS. Baron Georges Cuvier (1769-1832)
  is credited as the first to propose this concept
  to explain the rock record.  Cuvier proposed that
  the physical and biological history of Earth is
  explained by a series of sudden widespread
  catastrophes.  Each catastrophe killed life forms
  in a portion of the area affected, new life forms
  were created (by Divine Power) or migrated in
  from elsewhere. 

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HISTORY OF GEOLOGY (cont.)

•      JAMES HUTTON (1727-1797), a Scottish medical
  doctor (and often referred to as the FATHER OF
  GEOLOGY), proposed a concept in the late 1700s
  now referred to as UNIFORMITARIANISM.  Hutton
  never practiced medicine, but was very interested
  in the processes which formed and shaped the
  earth. By careful observations, he proposed that
  the physical, chemical, and biological laws of
  nature operated the same way in the past as they
  do today thus, the present is the key to the
  past and we can interpret the rock record as
  resulting from the same laws of nature that
  operate today. This is the concept of
  uniformitarianism.

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MODERN GEOLOGIC PHILOSOPHY

•      One of Hutton's greatest contributions to
  geology was his concept of UNIFORMITARIANISM. 
  This concept, meaning "the present is the key to
  the past", states that by studying geologic
  processes in operation today we can safely assume
  that such processes operated in the past and thus
  we can interpret rocks as a response to geologic
  processes.  With modification, this concept is
  still the basis for modern geologic thought.  We
  now realize that, although the processes
  themselves probably have not changed with time,
  the rates of some geologic processes may have
  varied drastically from time to time. However,
  the basics laws of nature are still the same
  today as they were in the past. 

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TWO WAYS TO MEASURE GEOLOGIC TIME

• RELATIVE DATING Placing Earth history events in
  the correct chronologic order.
• ABSOLUTE DATING Determining the real absolute
  age of rocks in years.

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The Geologic Time Scale

• A world-wide relative and absolute time scale of
  Earth's rock record was established by the work
  of many geologists applying the principles of
  geologic age dating to strata of all ages
  throughout the world.

Fig. 17.1, p. 437
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RELATIVE DATING PRINCIPLES

• Relative dating of geologic history refers to
  placing the sequence of Earth history events in
  the proper chronologic order and does not give
  the age of Earth history events in years.
• Absolute dating, on the other hand, refers to
  determining the age of Earth history events in
  years before present. Often this is expressed as
  mya (million years annum) or bya or (billion
  years annum), or more recently Gya (Giga
  billion years annum).

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STENOS PRINCIPLES OF RELATIVE DATING (1669)

• These principles are based on the work of Nicolas
  Steno (1638-1686), a Danish anatomist.  Steno
  worked in Italy and was curious about how
  sediment was deposited and how rocks form.  He
  observed sediment transport and deposition during
  stream flooding near Florence, Italy.  Steno's
  main three principles are listed below
• 1. Principle of Superposition  In a sequence of
  sedimentary strata, the oldest layer is at the
  bottom of the sequence and the strata are
  progressively younger toward the top of the
  sequence.
• 2. Principle of Original Horizontality 
  Sedimentary strata are originally deposited in a
  near horizontal manner.  Therefore, if
  sedimentary strata are found to be in a steeply
  inclined position, some force has altered them
  from their original position.
• 3. Principle of Lateral Continuity  Sedimentary
  strata are originally deposited over a laterally
  extensive area and are continuous until they
  pinch out at the edge of the ancient depositional
  basin (or unless removed by subsequent uplift
  and erosion).

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THE GRAND CANYON

• Horizontally bedded sedimentary strata as seen
  from the North Rim of the Grand Canyon
  illustrating the immensity of geologic time.  It
  took hundreds of millions of years for these
  strata to be deposited as layers of sediment that
  were eventually converted into rock.  The
  geologic history of the Grand Canyon region can
  be read from these sedimentary layers. (photo by
  E.L. Crisp, May 2002)

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THE GRAND CANYON
Kaibab Limestone
Toroweap Formation
Coconino Sandstone
Hermit Shale
Supai Group

• Horizontally bedded sedimentary strata as seen
  from the North Rim of the Grand Canyon
  illustrating the immensity of geologic time.  It
  took hundreds of millions of years for these
  strata to be deposited as layers of sediment that
  were eventually converted into rock.  The
  geologic history of the Grand Canyon region can
  be read from these sedimentary layers. (photo by
  E.L. Crisp, May 2002)

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THE MORRISON FORMATION
Horizontal beds of the Morrison Formation near
Cleveland, Utah.
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THE MORRISON FORMATION(again)

• The Morrison Formation at Dinosaur National
  Monument, Utah. Note that the beds are strongly
  dipping here.

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DEFORMATION OF ONCE HORIZONTAL SEDIMENTARY STRATA
Sidling Hill Syncline on I-68 near Cumberland,
Maryland (Photo by E. L. Crisp, August, 2005)
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PRINCIPLES OF CROSS-CUTTING RELATIONSHIPS AND
UNCONFORMITIES

• James Hutton, of course, recognized that Stenos
  Principles of relative dating are valid and he
  further demonstrated them in his work.  He also
  recognized other principles of relative dating.
• (Principles of Relative Dating, continued)
• 4. Principle of Cross-Cutting Relationships  Any
  geologic event (igneous intrusion, fault, etc.)
  that cuts across or truncates sedimentary strata
  must be younger than the strata affected by the
  event.
• 5. Principle of Unconformities  An unconformity
  is a surface representing a time gap (hiatus) in
  the rock record, due either to erosion or
  nondeposition.  (Hutton realized that rocks did
  not represent continuous deposition in some
  areas.)

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CROSS-CUTTING RELATIONSHIPS
An basalt dike cutting through granite. The
basalt dike is younger than the granite. (Photo
taken on Cadillac Mountain, Bar Harbor, Maine by
E. L. Crisp, August, 2005).
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THE DEVELOPMENT OF AN UNCONFORMITY
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THREE TYPES OF UNCONFORMITIES

• 1.  DISCONFORMITY  The strata are parallel above
  and below unconformable surface.  The
  unconformable surface is an erosional surface and
  can usually be identified by topographic relief
  or pebbles (inclusions) of the older layer
  incorporated into the younger rocks.
• 2.  ANGULAR UNCONFORMITY  The strata below the
  unconformable surface are at some angle to the
  strata above.  The younger strata are essentially
  parallel to the erosional surface, while the
  older strata are inclined to the erosional
  surface.  This type of unconformity implies
  tectonic deformation which folded and/or uplifted
  the older strata, a period of erosion then
  occurred which planed off the surface, followed
  by deposition of  sedimentary rocks roughly
  parallel to the erosional surface.
• 3.  NONCONFORMITY  The rocks below the
  unconformable surface are intrusive igneous or
  high rank metamorphic rocks (usually referred to
  as basement rocks).  The unconformable surface is
  an erosional surface and the younger sedimentary
  rocks above the surface typically have inclusions
  of the igneous or metamorphic rocks. There may be
  considerable topographic relief on the surface,
  but the younger sedimentary layers are not
  intruded by the igneous rocks.

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SICCAR POINT, SCOTLAND
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PRINCIPLE OF INCLUSIONS

• 6. The PRINCIPLE OF INCLUSIONS states that
  inclusions of one kind of rock in another are
  always representative of the older rock
  material.  For example, if a granitic magma has
  intruded into a sandstone and chunks of sandstone
  have been incorporated into the rising magma, as
  cooling occurs there will be inclusions of
  sandstone in the granite and the inclusions will
  represent the older rock.

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PRINCIPLE OF INCLUSIONS
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TYPES OF IGNEOUS PLUTONS
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CORRELATION

• Correlation is the matching up of rocks in one
  area to those in another area.
• There are two types of correlation of rock units.
• Physical Correlation correlation of rock units
  based on physical characteristics of the rocks or
  position in a sequence of rocks. Assumes that
  the rock units were once continuous.
• Time-rock Correlation correlation of rock units
  that are time equivalent (rock units in different
  areas that are of the same age).

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PHYSICAL CORRELATION
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CORRELATION USING FOSSILS

• What are fossils?
• Any remains or evidence of activity of a once
  living organism (usually restricted to
  prehistoric time).
• Scientists who study fossils are called
  paleontologists (not archeologists!!!).
• Two major types of fossils Body fossils and
  trace fossils.

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Fossils evidence of past life

• Types of fossils
• Indirect evidence includes Trace Fossils
• Tracks
• Burrows
• Coprolites fossil dung and stomach contents
• Gastroliths stomach stones used to grind food
  by some extinct reptiles

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A dinosaur footprint
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The Formation of Body Fossils

•      The usual prerequisites for fossilization to
  form body fossils is the possession of hard parts
  (bones, teeth, mineralized exoskeleton, etc.) and
  the rapid burial of the hard parts by sediment
  (this reduces the amount of oxygen present to
  very low levels and slows decomposition of the
  hard parts).  Usually soft parts of an organism
  rot rapidly.  Only rarely are soft parts
  preserved (such as skin impressions for
  dinosaurs), but under some conditions they are
  preserved and give paleontologists valuable
  information that is usually not present in the
  rock record.  After burial some sort of
  mineralization typically occurs.  Unaltered
  remains are very rare.

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Altered Remains

• Permineralization Mineral matter from
  percolating ground waters is added to pores and
  cavities in bones, shell, teeth, etc.  In this
  type of preseravation the original material is
  still present with new mineral matter added to
  the void spaces.  Many dinosaur bones are
  preserved by this method.
• Replacement Sometimes original hard parts (bone
  in the case of dinosaurs) is replaced (sometimes
  referred to as petrified, which means turned to
  stone) with new mineral matter of a different
  composition than the original mineral matter
  (often at a molecular level, so the
  microstructure of the original mineral matter is
  preserved).  Silica (as microcrystalline quartz,
  SiO2), iron oxide (hematite, Fe2O3), and calcium
  carbonate (calcite, CaCO3)
• are common replacement minerals (they are
  also common permineralizing agents).  Many
  dinosaur bones are both permineralized and
  partially replaced.
• Recrystallization  The recrystalliztion of
  fossils is another common type of preservation in
  which the original mineral present simply
  recrystallizes (the original crystals grow larger
  and fill most of the void space).  This is more
  common in invertebrate fossils (such as bivalves
  clams, brachiopods, gastropods, etc.) than in
  vertebrate fossils. This form of preservation
  usually destroys or partially obscures the
  original microstructure of the skeletal
  material.  An example would be the
  recrystallization of a clam shell originally
  composed of the mineral aragonite (a metastable
  form of calcium carbonate) to calcite (the more
  stable form of calcium carbonate at low
  temperatures).

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Altered Remains (cont.)

• Carbonization Sometimes soft parts and/or hard
  parts of the body of an organism are compressed
  by burial before decomposition is complete such
  that the volatile substances (such as oxygen,
  nitrogen, carbon dioxide, water, etc.) are
  squeezed out leaving behind a film of fairly pure
  carbon.  This is particulary common in the
  preservation plant fossils (such as ferns and
  leaves Look at the fossil leaves and insects
  from the Green River Formation of Utah that are
  present in the Geology Lab at WVUP, these are
  preserved by carbonization) and some
  invertebrates, but also occurs sometimes for
  vertebrates (for example, fifty million year old
  fossil fish of the Eocene Green River Formation
  of Wyoming, Colorado, and Utah).
• Molds and Casts Sometimes the hard parts (bone
  or other material) (and sometimes even soft
  tissue) of organisms are buried by sediment and
  even may remain until the sediment is lithified
  (by compaction and cementation), but are later
  dissolved by acidic ground waters percolating
  through the pores of the rock (or decomposed by
  other processes).  This will leave an impression
  of the external morphology of the original
  material that was buried.  This is called an
  external mold.  If later the mold is filled in
  with mineral matter or sediment, a cast is formed
  which mimics the external morphology of the
  original material.  Sometimes internal cavities
  of skeletons (from both invertebrates and
  vertebrates) may be filled with sediment or
  mineral matter resulting in a mold of the
  internal morphology of the cavity that was
  filled, this is called an internal mold. Internal
  molds are quite common for some invertebrates
  (such as for clams and gastropods).

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Natural casts of shelled invertebrates
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PRINCIPLE OF FOSSIL SUCCESSION

• Although rocks may be correlated based on
  physical correlation and superposition, this can
  only be done in a limited area where beds can be
  traced from one area to another. Also if we are
  correlating over a large area (from region to
  region, or continent to continent), it is
  unlikely that we can use physical correlation
  because rock types will change.
• To correlate over large regions and to correlate
  age-equivalent strata, geologists must use
  fossils. The use of fossils to correlate
  sedimentary strata is based on the work of
  William Smith (1812), the first to accurately
  state and use the Principle of Fossil Succession.
• The Principle of Fossil Succession states the
  assemblages of fossils succeed themselves in a
  definite and determinable order and the age of
  sedimentary strata can be determined by their
  contained fossils.
• To use the Principle of Fossil Succession,
  geologists and paleontologists use Index Fossils
  (Guide Fossils).

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PRINCIPLE OF FOSSIL SUCCESSION

• The Principle of Fossil Succession is based on
  the following
• Life has varied through time. Of course this
  implies that evolutionary change has occurred
  over time.
• Because biologic diversity has varied over time,
  fossil assemblages are different in successivly
  younger strata.
• The relative ages of fossil assemblages can be
  determined by superposition.

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PRINCIPLE OF FOSSIL SUCCESSION
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INDEX FOSSILS

• Index fossils are used to correlate
  age-equivalent strata via the Principle of Fossil
  Succession.
• Index fossils have the following characteristics
• Short geologic time range.
• Wide geographic distribution
• Abundant
• Easily recognizable

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CONCURRENT RANGE ZONES
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CORRELATION OF SUBSURFACE STRATA
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ABSOLUTE DATING

• RADIOMETRIC DATING
• TREE-RING DATING

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MODEL OF THE ATOM
Electron Orbits
Protons Red. Positive Charge.
Neutrons Green. Neutral Charge.
Nucleus
Electrons Tan. Negative Charge.
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Radioactivity and radiometric dating

• Carbon-14 dating
• Half-life of only 5730 years
• Used to date very recent events
• Carbon-14 produced in upper atmosphere
• Incorporated into carbon dioxide
• Absorbed by living matter
• Useful tool for anthropologists, archeologists,
  historians, and geologists who study very recent
  Earth history

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Fig. 9-26b, p. 288
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The Geologic Time Scale
Figure 11.16
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Geologic time scale

• Divides geologic history into units
• Originally created using relative dates
• Subdivisions
• Eon
• Greatest expanse of time
• Four eons
• Phanerozoic ("visible life") the most recent
  eon
• Proterozoic

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Geologic time scale

• Subdivisions
• Eon
• Four eons
• Archean
• Hadean the oldest eon
• Era
• Subdivision of an eon

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Geologic time scale

• Subdivisions
• Era
• Eras of the Phanerozoic eon
• Cenozoic ("recent life")
• Mesozoic ("middle life")
• Paleozoic ("ancient life")
• Eras are subdivided into periods
• Periods are subdivided into epochs

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The Geologic Time Scale

• A world-wide relative and absolute time scale of
  Earth's rock record was established by the work
  of many geologists applying the principles of
  geologic age dating to strata of all ages
  throughout the world.

Fig. 17.1, p. 437
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END