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The Geologic Time Scale

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The Geologic Time Scale. Earth's history. Discovering Earth's History. In the 18th and 19th Centuries scientists knew the Earth ... Nicolaus Steno - geologist ... – PowerPoint PPT presentation

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Title: The Geologic Time Scale


1
The Geologic Time Scale
  • Earths history

2
Discovering Earths History
  • In the 18th and 19th Centuries scientists knew
    the Earth had a very long, active history.
  • At the time they had no way of actually dating
    the Earth.
  • A ____________________was developed based only on
    _____________.

3
Discovering Earths History
  • In 1869, ____________________ down the
    _______________through the Grand Canyon he
    realized the history of the Earth is concealed in
    rocks.
  • Rocks record geological events and changing life
    forms of the past.

4
Discovering Earths History
  • We have learned the Earth is much older than
    anyone previously imagined.
  • In the mid-1600s Archbishop James Ussher
    believed the Earth was created in 4004 B.C. His
    theories were widely accepted at the time.
  • In the late 1700s James Hutton created
    the___________________________ the thought that
    the forces and processes we observe today are the
    same that have been at work on the Earth the
    beginning of time.

5
Discovering Earths History
  • Therefore, by studying the processes today, we
    can see what occurred throughout Earths history.

6
Relative Dating
  • Tells the sequence in which events occurred, not
    how long ago they occurred.
  • Nicolaus Steno - geologist
  • 1. _________________________ in an undeformed
    sequence of sedimentary rocks, each bed is older
    than the one above it, and younger than the one
    below it
  • 2.________________________________________
    layers of sediment are typically deposited in a
    horizontal position.
  • If layers are flat, they have not been disturbed,
    if they are bent they have been disturbed by
    tectonic processes.

7
Relative Dating
  • 3.___________________________When a fault cuts
    through, or when magma intrudes other rocks and
    crystallizes, we can assume the fault or
    intrusion is younger than the rocks affected.
  • ____________________ pieces of one rock unit
    that are contained within another.
  • Pg. 339

8
Relative Dating
  • ____________________ represents a long period
    during which deposition stops, erosion removed
    previously formed rocks, and then deposition
    began again.
  • 3 types
  • 1.
  • 2.
  • 3.

9
Relative Dating
  • _________________________ rocks of similar age
    in different regions that must be matched up.
  • Used to develop a geologic timeline of the Earth.

10
Evidence of Past Life
  • ___________________ remains or traces of
    prehistoric life.
  • Found in sedimentary rock
  • The type of fossil that is formed depends on 2
    things
  • 1.
  • 2.

11
Evidence of Past Life
  • __________________________ some remains of
    organisms teeth, bones, and shells hardly
    change over time.
  • ________________________ the remains of
    organisms likely to change over time.
  • Examples petrified rock, casts, molds,
    carbonization, amber

12
Evidence of Past Life
  • ______________________ trace fossils
  • Tracks, burrows, coprolites, and gastroliths.
  • Conditions favoring preservation
  • 1.
  • 2.

13
Evidence of Past Life
  • William Smith, in the late 18th Century stated
  • Fossils are not randomly distributed throughout
    the rock layers
  • ______________________________ fossil organisms
    succeed one another in a definite and
    determinable order. Therefore, any time period
    can be recognized by its fossil content

14
Evidence of Past Life
  • Order of fossils as identified by geologists
    around the world
  • Age of Trilobites
  • Age of Fishes
  • Age of Coal Swamps
  • Age of Reptiles
  • Age of Mammals
  • This same order is found in the fossil record on
    every continent on Earth.

15
Evidence of Past Life
  • __________________ widespread geologically,
    limited to a short time span of geologic time,
    and occur in large numbers.
  • Fossils are also used to interpret and describe
    ancient environments.
  • Ex we know that Kansas used to be covered by a
    shallow sea due to the clam shells found in
    Kansas limestone.
  • Ex they can also tell the relative temperature
    of the environment in which they are found.

16
Dating with Radioactivity
  • Review basic atomic structure
  • Atoms have a nucleus which contains the atoms
    protons and neutrons.
  • ___________can be found orbiting the nucleus
  • In atoms, the number of protons is equal to the
    number of electrons.
  • The ____________________________ is the number of
    protons plus the number of neutrons.
  • The _____________________________ tells the
    number of protons found in the nucleus.

17
Dating with Radioactivity
  • _______________ are atoms of the same element
    having the same number of protons and different
    numbers of neutrons.
  • Usually these isotopes are stable. Some, however
    are not causing the nucleus to spontaneously
    break apart this is called ____________________
    ____________

18
Dating with Radioactivity
  • This decay continues until a stable nucleus or
    isotope is formed.
  • _____________________ the amount of time
    necessary for one-half of the nuclei in a sample
    to decay to its stable isotope.
  • if the half-life of a radioactive isotope is
    known and the parent/daughter ratio can be
    measured, the age of the sample can be calculated.

19
Dating with Radioactivity
  • _________________________ - a way to calculate
    the ages of rocks and minerals that contain
    certain radioactive isotopes.
  • Each radioactive isotope has been decaying at a
    constant rate since the formation of the rocks in
    which it occurs.
  • Five have proven particularly useful in providing
    radiometric dating for ancient rocks
  • Uranium-238, Uranium-235, Thorium-232,
    Rubidium-87, and Potassium-40.

20
Dating with Radioactivity
  • Radiometric dating can only occur for rocks
    contained in a closed system since their
    formation.
  • This is due to the fact that all parent and
    daughter isotopes must be kept within the rock so
    measurement can take place
  • Any loss or addition of parent or daughter
    isotopes will result in a faulty dating

21
Dating with Radioactivity
  • Carbon-14 dating
  • Carbon-14 is continuously produced in the
    atmosphere it is continuously incorporated into
    living organisms.
  • When an organism dies, it no longer takes up
    carbon-14, and it generally decreases as it
    decays.
  • By comparing the amount of carbon-12 to the
    amount of carbon-14, radio-carbon dates can be
    determined.

22
The Geologic Timescale
  • Based on interpretations of the rock record,
    geologists have divided Earths 4.6 billion year
    history into units of time that represent
    specific amounts of time. Taken together, these
    time spans make up the ___________________________
    .

23
The Geologic Time Scale
  • __________- represent the largest amounts of time
    they are further divided into _________, which
    are divided into _______________, which are
    divided into smaller units of time called
    ______________.

24
The Geologic Time Scale
  • ______________________ began 540 million years
    ago
  • Means visible life
  • Rocks of this Eon contain many fossil records
    that document major changes in living organisms
    over time.

25
The Geologic Time Scale
  • Phanerozoic Eon is divided into 3 eras the
    _______________ (ancient life),
    ___________________ (middle life), and the
    _____________ (recent life).
  • The eras were divided according to major
    extinctions that took place at those times.

26
The Geologic Time Scale
  • The eras are divided into periods that represent
    somewhat less profound change in life forms.
  • The Cenozoic is further divided into epochs.

27
The Geologic Time Scale
  • Precambrian Time fewer life forms were present
    on earth during this time. Their fossils are
    difficult to identify and many times the rock and
    fossil record have been disturbed.
  • It represents nearly 88 of Earths history.
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