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Chapter 14 The History of Life

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Title: Chapter 14 The History of Life


1
Chapter 14 The History of Life
  • 14.1 Fossil Evidence of Change

2
Earths Early History
  • Earth formed 4.6 billion years ago from molten
    material.
  • Cooled for 500 million years and formed a solid
    crust on the surface. Surface is rich in lighter
    elements, as more dense elements were pulled by
    gravity toward Earths center.
  • Atmosphere of Earth consisted of H20, CO2, SO2,
    CO, H2S, HCN, N2 and H2

3
Clues in Rocks
  • A fossil is any preserved evidence of an
    organism.
  • Most organisms decompose before they have a
    chance to become a fossil.
  • Those organisms that are most likely to become
    fossilized are those that are covered quickly by
    sediment (no O2) and have hard parts.
  • Only one in a million organism becomes a fossil.

4
Fossil Formation
5
Fossil Formation
  • Fossils form in sedimentary rocks sediments
    cover the organism.
  • Igneous rocks form from molten rock material
    metamorphic rocks when other rocks are exposed to
    heat and pressure both processes would destroy
    any fossil material in these rock types.

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7
Relative Dating
  • Determine age of fossils by comparing them with
    those in other layers
  • Law of Superposition states that younger rock
    layers are deposited on top of older rock layers
  • Only true of undisturbed rock layers

8
Radiometric Dating
  • Dating method that used the decay of radioactive
    isotopes to measure the age of a rock.
  • Isotope is a form of an element that has the same
    atomic number but a different atomic mass (mass
    number)
  • Half life is the amount of time it takes for ½ of
    the original radioactive isotope to decay or
    change into its decay product

9
Radiometric Dating
  • Commonly used radioactive elements are
    Uranium-238 (U238), Potassium-40 (K40) and
    Carbon-14 (C14)
  • Some radioactive isotopes used for radiometric
    dating are found only is igneous or metamorphic
    rocks (not sedimentary) so isotopes cannot be
    used to date rocks that contain fossils. Relative
    dating of fossils from known igneous or
    metamorphic rocks are used.
  • C14 can be used to date fossils directly if they
    are less than 60,000 years old

10
Radiometric decay Rate of C14 to N14
Half life 5730 years
11
Radiometric decay Rate of U238 to Pb205
Half life 4520 million years (4.510 billion)
12
The Geologic Time Scale
  • Model that expresses the major geological and
    biological events in Earths history.
  • Largest time classification is the eon.
  • Eons are divided into eras
  • Eras are divided into periods
  • Periods are divided into epochs
  • See page 397

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15
Plate Tectonics
  • During the Mesozoic era the location of the
    Earths plates underwent a major shift in
    position and are continuing to move today

16
Chapter 14 The History of Life
  • 14.2 The Origin of Life

17
Origin Early Ideas
  • Spontaneous generation is the idea that life
    arises from nonlife.
  • People believed that it rained frogs, mice
    spontaneous arose out of grain, and from mud came
    insects, fish and worms.

18
Francisco Redi 1668
  • First controlled experiment to disprove
    spontaneous generation in which flies arose out
    of meat.
  • He hypothesized that flies, not meat, gave rise
    to flies

19
Other Scientists
  • Spallanzani
  • Needham
  • Organisms exist in air (microbes)
  • Believed in biogenesis
  • Italian 1700s
  • Life force exists that causes life
  • Believed in Spontaneous Generation
  • English 1700s

20
Louis Pasteur 1850s
  • Experiment showed that sterile broth remained
    free of microorganisms until exposed to air.
  • Flasks still exist today free of microorganisms.
  • Theory of spontaneous generation rejected and
    replaced with theory of biogenesis (life from
    life)

21
Origin Modern Ideas
  • If life can only come from preexisting life
    (theory of biogenesis) then how did the first
    life-form appear?
  • Three ideas
  • Divine creation
  • Extraterrestrial
  • Series of chemical events

22
Origin Modern Ideas
  • Simple organic molecules could have been formed
    from a mixture of gases present in the early
    atmosphere when sparked by lightening.
  • Theory proposed by Oparin and Haldren in 1920s
  • Called the primordial soup. The oceans as a
    soup of chemicals that could have combined to
    form life

23
Origin Modern Ideas
  • Simple organic molecules have been formed in the
    laboratory
  • Experiments of Miller and Urey in 1953.
  • Amino acids, sugars and nucleotides have been
    formed by refining this experiment.

24
Origin Modern Ideas
  • Another ideas is that the organic reactions that
    preceded lifes emergence began at deep-sea vents
    where sulfur forms the base of a unique food
    chain.

25
Origin Modern Ideas
  • In order for life to form from nonlife
    (chemicals) three requirements must be met
  • Making proteins
  • Genetic code
  • Molecules to cells

26
Making Proteins
  • In order for life to exist proteins must be
    formed.
  • Stable proteins can be formed on clay particles

27
Genetic Code
  • A coding system for protein is a requirement for
    life.
  • All living things have DNA and RNA.
  • Since some RNA sequences have changed little over
    time, scientists consider RNA to be the first
    genetic coding system.
  • RNA can also act like an enzyme and could have
    carried out some early life processes
  • Thought that RNA replication took place on a clay
    crystal.

28
Molecule to Cells
  • Cells have a membrane.
  • Scientists have tested ways of enclosing
    molecules in membranes, allowing early metabolic
    and replication pathways to develop.
  • How cells formed has yet to be explained.

29
Cellular Evolution
  • The first cells were prokaryotes similar to
    current day archaebacteria.
  • Today archaebacteria live in extreme environments
    similar to what may have been experienced on
    early Earth.
  • Photosynthesis began by cyanobacteria (not
    archae). Until 1.8 billion years ago no oxygen
    existed in the atmosphere.
  • Fossils of these bacteria have been found and
    dated at 3.5 billion years old.

30
Cellular Evolution
  • Once cyanobacteria produced sufficient oxygen to
    form the ozone layer, conditions were right for
    the evolution of eukaryotic cells.

Ozone layer protects Earth from harmful radiation
31
Cellular Evolution
  • Eukaryotic cells appeared in the fossil record
    about 1.8 billion years ago. (2 billion years
    after archae)
  • The endosymbiont theory suggests that some
    photosynthetic bacteria became engulfed within a
    larger bacteria and became the chloroplast other
    engulfed bacteria became the mitochondria.

32
Endosymbiont Theory
33
Evidence for the Endosymbiont Theory
  • Both mitochondria and chloroplasts contain their
    own circular DNA just like prokaryotes.
  • Both mitochondria and chloroplasts contain
    ribosomes that closely resemble archae ribosomes.
  • Like prokaryotic cells both mitochondria and
    chloroplasts reproduce by fission, independent
    from the rest of the cell.
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